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Description of the critical data compilation and tables
CHAPTER 8
DESCRIPTION
OF THE CRITICAL
COMPILATION
DATA
AND TABLES
8.1. Scope The tables in this critical compilation present the available quantitative Knight shift data as accurately as possible. A high degree of Knight shift data evaluation was attained both by experts at the Alloy Data Center performing critical reviews, as well as via direct communications with several of the authors of the original source documents, who on the one hand helped review the final tables and on the other hand assisted in arriving at “best values” for several cases where discrepancies or uncertainties could be resolved. The literature sources include both published and unpublished data that have become available to us in Technical Reports, theses, and private communications. The literature search was done by scanning “Current Contents” and by using various abstracting journals and services. Defense Documentation Center automated bibliographic searches were performed to obtain the report literature. In addition, various journals were scam-red directly and secondary referencing (relevant references given in papers dealing with NMR) was used extensively for locating source papers. The search is thought to be approximately 97-98% complete for the published literature through 1972 and somewhat less comprehensive for unpublished documents and for articles published through 1975. Using this file of data, as arranged in an automated reference system described in NBS Technical Note No. 4154,(~*‘)we have compared the available literature for each metal, and each alloy system separately. This compilation has been prepared over a period of several years. As a result evaluations for different metals or alloys have different cut-off dates for the literature search, since our policy has been to make as much accurate data available as possible, rather than adhering to a straightforward cut-off date for the whole compilation. Thus, some recent papers may not be cited under each of the alloys they deal with. A list of pertinent papers that have been added to our files by end 1975, since each writeup has been completed, is given at the end of the data compilation, under “Addenda”. These addenda at times give quantitative updates or added descriptions to the metal and alloy evaluations as well. The data that in our judgment are the more accurate ones are tabulated, followed by discussions of the evaluations as well as additional tables and figures. Throughout this compilation we have used the definition of the Knight shift described in the earlier chapters. Interpretations of the NMR results in terms of theoretical knowledge of the materials, or in terms of the constitution of the samples (phase diagram information) or magnetic origins, etc., as discussed in these chapters, are noted in the evaluations. These interpretations as well as other related NMR data are not evaluated to the same degree as the Knight shift. No attempt has been made to prepare complete bibliographies for the other NMR properties. They are listed in the sense of “additional information”, rather than added critical evaluations, although these numbers have been screened to some degree by us and both the critically evaluated Knight shifts as well as the other NMR data have undergone valuable reviewing prior to publication, by several authors in the field of NMR. Additionally, when discrepancies were encountered which could not be resolved from the source papers, the authors of these reports were usually contacted directly to obtain needed information. Further details relating to the degree of coverage and evaluation are discussed in the next section. In order for the NMR results to be related to the other properties of the material, and in order to interpret the NMR data and arrive at the best X-values, it is often necessary to have a knowledge of several of the other physical properties of the materials. To present the NMR data to its best utility, several other available properties have been listed. Similarly, where the NMR data enhance the 109
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Metallic Shifts in NMR
understanding of some of the other properties of the materials, such interconnections are often noted in the evaluations. For certain materials very little information is available and no Knight shift data are reported. For some of these materials, related information has been included, although our files are not complete for such other subjects. This is in an attempt to give the reader some information to help locate literature pertinent to NMR research. Examples of related information are FNR hyperfme fields, NQR, and perturbed angular correlation data. Also, in a few selected cases, where the materials may have some more practical applications (either experimentally, theoretically, or technologically), hyperfme fields determined by the Mossbauer effect are noted. It should always be kept in mind; however, that these related data are not evaluated. Most of the evaluations, especially for those systems where ample NMR data are available, do not include non-NMR data. The size of the present compilation at this time prohibits more comprehensive inclusion of these topics. For clarity of presentation, topics discussed in the more lengthy descriptions of the evaluations are noted as marginal notes, whenever they do not bear on the room temperature Y values. These marginal notes also bring to the reader’s attention any non-NMR techniques discussed in the paragraphs, or any conclusions about other properties of the materials from the NMR experiments. Finally, this compilation encompasses in its scope all metallic materials. This includes liquid ammonia solutions of the alkali metals, hydrides, superconductors, and materials with semiconductorto-metal transitions. For some nonmetallic elemental substances data are given, so that a comparison can be made when these substances are alloyed with metals. In addition, a substantial number of compounds have been included that show relatively large NMR shifts, of the order of Xvalues, which are likely to be due to magnetic origins (e.g., AlaC00~). These shifts are not Knight shifts in the ordinary sense, since these materials are not metallic. Only those cases that have come to our attention are listed and the literature search for this type of compound is not complete. These compounds have been included in this compilation as examples of large shifts due to mechanisms described in sections 2.10 and 3.4. Semiconductors are generally excluded from this compilation. In the literature, the NMR shifts in semiconductors are often called Knight shifts. These shifts are due to the conduction electrons in impurity bands, outside of any chemical shifts, and are thus very sensitive to the purity, or the amount of doping of the material. However, a few systems showing semiconducting properties have been given in this compilation as examples. The Knight shift in semiconductors gives information concerning the type of interactions of the charge carriers with the nuclei of their constituent elements. Again, completeness is not attempted as semiconductors fall outside the scope of completeness of this data compilation.
8.2. Organization and Degree of Evaluation of the Data In this compilation the elemental metals are treated first, in order to give a fully evaluated basis set of Yvalues from which variations upon alloying can be presented. In order for the metals to be properly understood in terms of the NMR research, some nuclear and solid state properties are tabulated. These will now be discussed in the order in which they appear. The extent of their evaluations, or literature sources, will be indicated. 8.2.1. Metals (a) NMR Properties Knight shifts: This compilation presents a complete and m-depth evaluation of all reported Knight shifts. The data are made as self-consistent as possible and whenever enough information is available, the data have been adjusted to the use of the Ydetinitions given in previous chapters. Unfortunately the majority of the literature reviewed in our evaluations lack adequate descriptions of the criteria used in X deductions (e.g., centroid of a resonance versus derivative zero, etc.) or descriptions of sample preparation and characterization, so that comparison between disagreeing data and adjustment to a uniform .X definition was often not possible. In several cases authors have been contacted in order to be able to tabulate more accurate data. Mostly, for metals with little available data, the numerical values are presented as reported. The reliability of these data will be evident from the discussion of the data, or the
Description of the Critical Data Compilation and Tables
111
source, which may be no more than an abstract. It is not possible for us to estimate reasonable errors for these data SOthat such values are often accompanied by the note N.E.(no errorsgiven). Errorsare denoted in this compilation by the numbers in brackets immediately following the numerical value, and signify the uncertainty of the digit(s) immediately preceding the bracket, i.e. .$ = 0.20(2)$% stands for $= (0.20 + 0.02)%. This notation is used for all parameters given in this compilation. When stating errors separately for X, this is denoting by AX= f . . . %, which should not be confused with an alternate method of denoting the error in percent of the absolute Xvalue. Since% itself is expressed in percent, this notation is confusing, and therefore not used in this compilation. When errors are given in the literature they may be representative of the root mean square deviation of the scatter of the values obtained from several runs, using the same equipment, the same sample, and the same conditions. This is a calculable number, and when presented in the source papers has usually been included in this compilation along with the reported values. Because these numbers represent precision rather than total error due to various experimental conditions, we have given estimated errors whenever the reported error seemed unreasonably small in view of the description of the experiment. However, at times insufficient information has been given to estimate a reasonable error. In the discussions the sources of the errors or reasons for their choice, if different from the author’s, is included in the discussion. Whenever an average of two or more reported Xvalues was thought to give the most probable X value, the error was chosen so as to include all these numbers plus a possible error connected with each value, as was deemed necessary for individual cases. In evaluating the X values for the elemental metals, the best room temperature value was first determined, when available. Once this point was determined the variation with temperature or pressure was evaluated. As there is an error associated with the absolute value of the$(300”K), the error of the X(2’) variation was added onto the room temperature error. Thus, the tabulated metal .X-valuesand their errors are in terms of absolute values. Often the variation of Xhas been determined more accurately. Such higher precision determinations are represented in our tables by giving separately values for (qTi) -L%!(Ti))/(Tj - Ti) with the error associated with that measurement. Pressure dependences have been treated in a similar way. Instrumentation is not described explicitly in the evaluation discussions, except for those cases where this may be a cause of discrepancy of the data. As a result, the notation N.I. (no instrumentation description given) is only used occasionally in this compilation. Similarly, sample analysis is not described unless pertinent to the evaluation. The notation N.A. is used to indicate that sample analysis was not discussed in the reference. However, since NMR itself can be a probe of the sample quality, often the experimental results themselves could be used as indicator for certain aspects of sample quality in the data evaluations. Several paragraphs in the previous chapters, especially Chapters 6 and 7, discuss this topic. A common adjustment made in this compilation is that of chemical shifts. Whenever values for chemical shifts have come to our attention they are mentioned in the text, or in a few cases tables are given. Adjustments of svalues for chemical shifts have been made when possible; these corrections are noted in the discussions. The notation of AX= . . . % is used to indicate the value of the adjustment. Again, these corrections are given in terms of additions or subtractions to the XvaIues, and not in terms of a percentage of the original Xvalue. As Y has not been convincingly proven to be dependent on isotopes (except possibly for Rb, and Sb in GaSb, see section 2.9), no effort is made in this compilation to identify specific isotopes for theX measurements, except in those cases where a deliberate attempt has been made to determine the presence of such an effect. Unless special experimental efforts are made, the accuracy of Knight shift measurements is lower than any anticipated isotope effect. For other NMR parameters that do depend on isotopes, such as relaxation times, the isotope is indicated. Often data have been published in the form of graphs. Such graphs have generally not been reproduced, but rather, short tables with values read from the graphs have been prepared. Figures including private communications, unpublished data, or graphs drawn for this compilation are included, however, as they are not readily available in the published literature. At times, numerical data are difficult to obtain from graphs. Such cases are noted, and often cause representation of errors larger than those of the actual measurements. Obtaining s(T) data from Y vs. x graphs is an example of complications encountered in X deductions from graphical representations: if x(T) is not known,NT) cannot be deduced. TIT: Although no attempt has been made to completely evaluate TIT, or to give a complete set of
112
Metallic Shifts in A4MR
literature references, we have given these data some consideration so that the listed value, or range of values, are reasonably accurate. Quantitative knowledge of Tt T is important as this NMR parameter is connected to the Knight shift by the Korringa relation and thus can give insight into the Knight shift behavior (see section 2.8). In order not to expand our scope of Knight shift evaluations into a project of unmanageable scope, we have used some of the TIT values given by Drain(*.‘) for pure metals. These values have been reconsidered, often in view of more recent results. Employing our newly evaluated sand y values and our reconsidered T1 T values, we have recalculated the Korringa product. The results are similar to the numbers given by Drain for the metals listed in his review, and are summarized in Table 2.4. Tz, e2qQ/h: Values for the parameters have been included only when they were mentioned in readily available literature. However, no attempt has been made for completeness, nor have they been evaluated. Methods for obtaining T2 values experimentally are discussed in a comprehensive review by Weisman et a1.;(8.3) Chapter 6 of the present review discusses methods of obtaining quadrupole coupling constants, e2qQ/h, from experimental NMR spectra. An earlier review on quadrupole effects is given by Cohen and Reif,cs4) and pure NQR is treated by Das and Hahn. (8*5) Earlier tables of numerical values for quadrupole coupling constants include those by Lucken(8*6) and by Segel and Barnes,(‘*‘) although these deal to a large extent with nonmetallic materials. Line width: The line width values are approximate. They are not evaluated and a detailed literature search has not been made for this quantity. Our listings are not complete, nor are they deduced in a uniform fashion from the spectra. Nm: For elemental metals we have attempted to note reports of pure NQR, and some unevaluated results have been included in some cases. A review on this subject has been written by Das and H&.(8.5)
FNR: All metals and alloys for which FNR reports are available are included. Numerical Herr values as obtained by FNR, using the relation I&-(FNR) = v(FNR)/(y/2 7~ ) , are noted when readily available. These values are generally not critically evaluated (also see under Heff, next paragraph), but when possible they have been made consistent with our preferred y/271values. For metals or alloys for which a large number of FNR reports are available, short summarizing tables have been prepared giving only a small fraction of the total data and a limited bibliography. Additional references can be obtained from compilations and bibliographies such as given in references 8.8 through 8.15. Some more recent references are available in the NBS Alloy Data Center files. H ,_ft: Heff values resulting from NMR, ferromagnetic resonance (FNR), and at times perturbed angular correlation (PAC), have been noted, although full coverage or evaluation of these parameters has not been attained. The listed Heff values have been adjusted to our preferred y values when possible. Those determined by%(T) vs. x(T) plots (see discussion in section 3.4.1) have been presented in units of kilogauss (kc) for each aligned Bohr magneton @n, or spin l/2) rather than for each aligned spin (spin 1). Those cases for which adjustments to these units were made are so noted. Heff values as determined by other methods such as FNR are given in units of kG. For the important metals such as Fe, Co and Ni care has been taken in presenting accurate Heff values, although the bibliographies are by no means complete (see FNR paragraph, above). PAC, Nuclear specific heat, Miissbauer effect: Unevaluated hyperfme fields obtained by these methods have occasionally been included when such information was readily available in our files. No attempt has been made to give details, or completeness in these areas, although increased coverage of these topics has been given for relatively important materials, when essentially no other NMR data were available. For any of these types of experiments other compilations and bibliographies are available. References 8.8 through 8.15 include numerical Heff values obtained with these techniques (see especially the review article by Lounasmaa in reference 8.10 for nuclear specific heat values and also see reference 8.16 which deals with PAC only). Other NMR parameters: Some other parameters derived from NMR measurements and discussed in the previous chapters are at times noted, when they have been given in the literature (e.g. t, or jsr values). No attempt has been made here to extract such parameters from existing data, nor have the numerical values been evaluated. EPR: When EPR has been reported for a metal; this is often noted in a paragraph of the evaluation text. Completeness on EPR bibliographies has not been attempted, however. The availability of EPR reports is mentioned since these may be of interest in NMR research, mostly in connection with obtaining Pauli susceptibilities (see section 2.3). Some reviews dealing with EPR for both metals and
Description of the ch’tical Data Compilation and Tables
113
semiconductors are given in the articles by Low,(~*’‘1 Ludwig and Woodbury,(8*‘8) and Yafet.(8*’ 9, Electron-nuclear and other double resonances are at times also brought to the attention of the reader when these reports were encountered in our files. Again for these topics our bibliographies are not intended to be complete, but rather representative. The conference series “Colloque Ampt%e”(8*20) covers the topics of NMR, EPR as well as ENDOR and other double resonances. Additional references are available from reference 8.15 and the Alloy Data Center files. (b) Properties of the Nucleus Nuclear properties themselves do not vary when the environment is varied. Their values are listed with each metal for convenience, but not repeated under the alloys. n, y/2n, Z, Q: The magnetic moments, ZL,not corrected for core diamagnetism, and the magnetogyric ratios, y, derived therefrom (more commonly referred to as gyromagnetic ratios), the nuclear spins, and electric quadrupole moments have been taken from Fuller and Cohen,(8.2*) unless otherwise stated. Only those isotopes of possible interest in NMR research are given. Since $values are derived from shifts of y’ (or r_l’)as seen in the metal with respect to our preferred y, or n reference values for the nucleus, and since these magnitudes are often in the range of uncertainty of the absolute 7 (or cc)values, some 7 values were reevaluated. Thus the present set of 7 values represents a listing of fully evaluated numbers, for use in NMR. Those cases for which reevaluation was indicated are described in the discussions of the Knight shift evaluations for elemental metals. Table 2a lists our preferred r/2n values in the format of the periodic tables. Table 2b lists these values by increasing ~/2rr value. This is a format often convenient in resonance identification in a spectrum or in search of a suitable reference for Smeasurements. In this compilation we have employed the value for the nuclear magneton, /.IN= 5.05050 x 1o-24 erg/C, used by Fuller and Cohen(8.2 ‘) in order to retain consistency with their listed nuclear moments. This same listing gives for the proton, corrected for the diamagnetism of water, ZJ= 2.79278 &v, and a conversion factor to y of y/2n = 0.762273(~#, giving y/2n = 4.25772 kHz/G for the proton. The choice of these quantities affects the factor converting ccto y/2n for any nucleus in the last significant figure. For example, 1965 internationally accepted values give y/2n = 0.7622750 and a set of values proposed later gives y/2n = 0.762269(n/Z). A consistent set of fundamental constants adopted internationally by CODATA ( see CODATA Bulletin 11, Dec. 1973) lists &,, = 5.050824(20) x 1O-24 erg/G and for the proton (corrected for the diamagnetism of water), /.l= 2.7928456(11) BN and y/27r = 4.25771 l(12) kHz/G, resulting in a conversion of y/2n = 0.7622530 These 1973 values became available too late to incorporate in the present compilation. Numerically, X measurements made directly between a metal and a salt for a particular nuclear species are not affected by the choice of these constants. However, when X is measured with respect to an intermediate chemical, such as described under Nb metal in Chapter 9, then the choice of the above values can make a significant difference in the numerical results. This is so because (a) the unit of ~1,c(N, is different in different listings, thus changing the value of Z.L, and (b) the ratio for conversion, r/(‘Ln~), is different. For example, if the 1973 set of constants are used, then all the 7 values given under the metals in Chapter 9, which were derived from Fuller and Cohen’&‘** ‘) ZJvalues, will be smaller according to the new r/(%m) ratio. Xmeasurements involving the use of y or n values often fail to state the numerical VdUeS of c(N, p or 7, or the ‘Y//Jratio employed. It is not possible to critically compare and evaluate numerical results, or to adjust to new standards of fundamental constants, unless the physical constants used in the original data reductions are specifically stated. Other fundamental constants listed in this compilation do not affect the critically evaluated Knight shift data, however, and those listed are taken from the 1973 CODATA list of fundamental constants. A correction for the diamagnetism of water has been included for the nuclear moment of the proton and the deuteron (i.e., the chemical shift correction). No further core diamagnetism exists for the proton or the deuteron. For all other isotopes, no core diamagnetism corrections have been made. It is very nearly the same for a given isotope in any environment. Furthermore, the corrections are a result of calculations for the atomic states, which are the same for a given nucleus in any solid, and thus cancel out in shift measurements. As relative shifts are usually measured in NMR, it is often useful to employ a reference 7 value of figh precision SOthat data can be compared, although the absolute accuracy may be lower. For this reason Cc values from which the listed y values were obtained were not always taken from the rounded values given by Fuller and Cohen,(8*2’1 but rather from their other tables, mostly Table E, giving p values
114
Metallic Shifts in NMR
determined by NMR, or from double or triple resonances. In the cases of NMR determinations the reference salt used for the /L measurements could be stated. The method of measuring fi has also been indicated for each listed /J value. The standard isotope notation, giving the isotope value to the upper left of the chemical symbol or nuclear property symbol, is adhered to in this manuscript (e.g. 27Al). Abundance: The % abundance or half-life of the isotopes were taken directly from Holden and Walker.(8*22) In our listings we have given the stable (or near-stable) isotopes of non-zero spin. Those radioactive isotopes that are of possible interest in NMR have also been listed, and are indicated with an asterisk to the upper right of the chemical symbol (e.g. 2 3OPti*). Abundances are included in Tables 2a and 2b. (c) Solid State Properties All listed solid state properties have been taken from existing compilations and have not been evaluated anew. For a few indicated systems, new data have been taken directly from recent publications when these new data have come to our attention, and included when the existing compilations gave no data. No specific searches have been done for these properties. All data not referenced specifically were taken from the the following sources: Ckystal structures: All data were taken from Pearson (8*23) unless otherwise noted. For details of notation see below under Alloys: “Crystal Structures, Point Symmetries and Metallurgical Information”. Melting points and other phase transition temperatures: Melting points (abbreviated m.p.) and other phase transition temperatures were taken from Hultgren et a1,(8*24) or from Pearson(8.23) when not available from Hultgren et aL(8.24) (Pearson’s thermodynamic data are mostly unevaluated.) Superconducting transition temperatures: For the superconducting elemental metals the superconducting transition temperatures, T,, are listed as given by Roberts. (8.2 ‘) The lowest temperature at which superconductivity tests show other metals to be normal are noted when given by Roberts. Magnetic transition temperatures: For the rare earths Gschneidner(8.26) has supplied the data; Conn~lly(~*~~) was consulted for other metals with a few noted exceptions. The paramagnetic Pauli susceptibilities: @’ values have been derived directly from electronic specific heat coefficients, ycp, listed by Hultgren (8.241 using the relation, xFp = 3(/+/7~k)~7c~, which is rigorously true only for the case of free electrons (see section 2.3). In addition, for several cases, xp values are noted using an alternate estimate simply to give an idea of the range of values one may obtain using different estimates. Section 2.3 discusses the shortcomings of the various methods of estimating xp. For the alkalis, Bi and Sb, the alternate xp values are derived using xexp listed in the Landolt-Bornstein Tables.(8.2 ‘) For other metals Busch and Yuan(8*29) gave xex n values. These were then used to compute xp = 3/2 [xexp - x~~~~], employing x~~~e values given by Hurd and Coodin.(8.30) Later experimental values may give some improvement, and at times alternate estimates of x~~~e may result in better xp values. Our listed xr, values thus represent a set deduced in a somewhat uniform fashion, rather than the best value for each individual case, since even “best estimates” may not be accurate. For liquid metals a more recent survey by Dupree and Seymour(8.31) is available, and it appears(a.3i9 8.321 t h at use of the Hurd and Coodin(s*30) x~~~ values generally leads to lower apparent electronic susceptibilities for liquid metals, than are suggested by Dupree and Seymour.(8.3 ‘) Li and Na metals are two exceptions for which direct measurements of x,, have been made in the solid state, using EPR and a more indirect method was used for Be metal (see section 2.3). The numerical values are listed under the metals. Compressibilities: Compressibility data were taken from Gschneidner,(8.33) and are representative room temperature values. A later extensive listing of compressibilities by Simmons is also available,(8.34) but as these data are unevaluated they are not used in our listing. References: The references have been generated by computerized techniques using our automated NMR files described in reference 8.1. For each metal or alloy system all papers indexed under Knight shift are listed, whether they are discussed in the text or not. In addition, a list of “Related References” is given which lists those papers dealing with other topics discussed in the evaluations. These “Related References” are used in our evaluation process and do not represent a listing of all papers in our files on
Description of the Oitical Data Compilation and Tables
115
the related subjects. NBS Special Publication 324 (‘J ‘) of the Ahoy Data Center can be consulted for additional references for properties other than K All the authors, full titles, and citations are given, together with a few descriptive words for subtopics such as “single crystal” work, or sample also studied in the “superconducting state”. For those papers noted as “Theory” or “Review” this signifies that the paper gives only theory or review for this metal. Papers including any experimental data (Knight shift or other) for a material are considered as experimental so that some papers may not be denoted as theory or review because the property Knight shift (or other) is indexed as experimental, although the paper may give a theory or a review as well.
8.2.2. Alloys
(a) Solid State Properties All alloys are listed in alphabetical order, following the elemental metals. Phase diagrams are presented with the element of first alphabetic occurrence on the left-hand side. Compounds are written in alphabetic order, e.g. GaVs, rather than VsGa, to conform with the phase diagram, with a few exceptions, such as the oxides and phosphides, where the second element is clearly a non-metallic constituent. The alloys have been written in the following sequence: for an ahoy A-B, first the A resonance (denoted by underlining the A, A--B) is treated. The tables of preferred data, a description of the evaluation, and the figures are given. Then the B resonance, A-B, is treated in the same sequence. When only few data are available, only a brief comment, or only a table or a figure is presented. Phase diagrams: The phase diagrams for nearly all binary systems were taken from the series of Hansen,(8*3s) Elliott,(8*36) Shunk,(8.37) and unpublished addenda. Where other data have been included, reference to such material is given in the text. Crystal structures, point symmetries, and metallurgical information: Pearson(8.23) has been used throughout for this information, and his classification and designation system for the structures has been adopted. A section of the description of this system, given by Pearson!8*23) reads as follows: “The structures are primarily classified according to the fourteen Bravais lattices and then the number of atoms in the conventional crystallographic unit cell for the standard space group and setting. Secondary classification within these groups follows the numerical order of the 230 space groups, and finally, if necessary, within any space group structures follow the alphabetical order of their names. This classification is in some ways similar to that adopted by the ASTM* for naming or describing alloy phases. But whereas the ASTM uses a single arbitrary capital letter to characterize each of the fourteen Bravais lattices, we have chosen to use two characters and thus retain the crystallographic letters P, C, F, I, and R for primitive, one-face-centred, all-face-centred, body-centred and rhombohedral lattices respectively, combining with these the small letters a, m, o, t, h and c mnemonic with the names of the six crystal systems, trichnic (anorthic), monoclinic, orthorhombic, tetragonal, hexagonal cubic, respectively to give the symbols listed in Table 8.1 below. Thus, for example, the centred monoclinic Bravais lattice is represented by the symbol mC, and this is followed by the number of atoms in the crystallographic cell to give a classification symbol such as mC24. Trigonal P lattices fall in the hexagonal P grouping. These classification symbols are, of course, not possible names for structure types, since there may be an indefinite number of structural types falling under a given class. The problem of giving simple systematic names to crystal structure types is one that has received much thought, but it seems also to be a problem without any ready solution. The best that can be done is to name each structure type after a representative substance, as for example Cu3Au, which has that structure. Strukturbericht type symbols are still fairly widely used and recognized for simple structures, but the regular system of attributing letters A, B or C to the structure type of compounds with 1,2 or 3 atoms in the formula has its own exceptions and seems to have broken down completely in the D 0 to 10 series of structure
* ASTM Designation: E157-63, 1965 of ASTM Standards, Part 31, p. 387. American Society for Testing and Materials, Philadelphia. See also ASTM Special Technical Publication No. 35.5. MetalsReference Book. C. .I. Smithells, 3rd edition, 1962, Butterworths, London.
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Metallic Shifts in NMU TABLE 8.1
Symbols used for the fourteen Bravais lattices?, quoted from PearsorJa2 3, Symbol
System
Lattice symbol
aP mP
triclinic(anorthic) monoclinic
P P*
mC OP
orthorhombic
P c F
tetragonal
P
hexagonal (and trigonal, P) rhombohedral
P R P F
C*
oc OF 01
tP
I
t1 hP hR CP cF
I
cubic
CI
I
* Second setting, y axis unique. t The ASTM symbols for the fourteen Bravais lattices are in fact used in a systematic nomenclature for alloy phases; the symbols which we use are only for classifying structure types for crystallographers and are not part of any nomenclature of structure types.
types. This fact and the extension of the Strukturberbericht series in Metals Reference Book by using small subscript letters, e.g. B,, b, B, - - - instead of numbers, e.g. B18, B19, B20 - - -, now means that we have not only an arbitrary system of structure type names, but also a somewhat arbitrary method of allotting the names. The Strukturbericht series of names has therefore passed beyond the stage where it can be extended and used sensibly. An arbitrary system of structure names could only be acceptable if the names were derived in a systematic way depending, say, on formula or structural characteristics”. (b) NMR Properties For the alloys there are a few added points to be discussed concerning evaluation procedures. Knight shifts: For an alloy system the end points (pure metals) have been determined separately and
are listed under the elemental metals. In evaluating s as a function of alloy composition, X(c), the endpoints have been considered fured at the preferred values. The indicated errors of theX(c) listings represent the errors in measuring a variation of X rather than their absolute value. The error indicated under the pure metal must be added to obtain absolute values of errors. This is a different procedure than was followed for elemental metal X(7’) listings, for which separate X(T) slopes of higher accuracy are listed when such a measurement was made. The reason is that X(T) is often deduced from separate measurements, rather than from direct relative changes whereas mostX(c) data are from direct relative change measurements using the pure metal resonance position as reference frequency. OftenX(c) reports give a conversion from these relative shifts,Ax(c), from the metal position to shifts with respect to a salt by employing a previously publishedX(metal) value. Problems arise here when theX(metal) value used is not mentioned in the paper, or when reference salts are not given. In contrast, reported AX(c) values are easily added onto our preferred X(meta1) values to give X(c) values, which, when the product AX x *metal) is large, must be done by employing eqn. (5.3). When the conversion is done in the literature, as a rule eqn. (5.3) has not been used. This is one place where errors may arise. This error is usually quite small and is only pointed out, or corrected where possible, in cases where it may be important. When r E 1X1- ‘(AX/AC) is calculated, another inconsistency (usually small) is introduced if a previously available X value which differs from our preferred value is employed. When the &value actually employed is not mentioned, a correction cannot be made. Generally, a comment concerning the source of theNmetal) value is made when the question arises and may be signiticant. A common error of larger magnitude is that introduced in measuring A.%@)from derivative zeros rather than centroids of the resonance, as discussed in previous chapters; Chapter 3 discusses this topic in connection with line asymmetries due to near neighbor environments (also satellite behavior), and
Description of the Critical Data Compilation and Tables
117
non-linear .X(c) behavior. Chapter 6 gives further details on data reduction procedures for asymmetric lines. Often line shapes and the method of x deduction are not mentioned by authors and data as reported must be reproduced as preferred values, as well as their reported errors, if the sources of these errors are not stated. If there is reason to change the error on a preferred value this reason is always noted in the tables, or the discussions. An example of uncertainties introduced in employing derivative zeros in alloys, when lineshape effects are present, was given by Rowland.(8*38) This is described in section 3.1. T1 T: The discussion under ‘Metals’ applies to the alloy tables as well. Korringa products are generally deleted for alloys as such a number is much less meaningful. It can be obtained simply by calculating from eqn. (23) the product 20.98 (+y/2n)* X*Tl T. Other properties: The discussion for the various other properties (under ‘Metals’) applies to alloys as well. References: The discussion under ‘Metals’holds for alloys as well. A problem encountered in the case of alloys, results from authors not stating explicitly the alloys studied, but rather mentioning a group of alloys identified; for example, as “dilute Al-X alloys”, or “V3X compounds,” etc. These reports cannot be indexed under specific alloys or compounds, and are thus irretrievable. Because this happens mostly in short reports and abstracts that usually provide qualitative rather than quantitative information, very little numerical data are lost. In several cases where such abstracts represented the sole source of data, the authors have been contacted for further details. Otherwise these reports that do not specifically identify the alloys studied are omitted from the lists of references.
References 8.1.
8.2. 8.3.
8.4. 8.5. 8.6. 8.1.
8.8. 8.9. 8.10. 8.11. 8.12.
8.13. 8.14. 8.15. 8.16. 8.17. 8.18. 8.19. 8.20.
CARTER, G. C., ef al, The NBS AIloy Data Center: Function, Bibliographic System, Related Data Centers, and Reference Books. NBS Technical Note 464, Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402 (1968). DRAIN, L. E., Metall. Rev. 119 (1967) 195. WEISMAN, I. D., SWARTZENDRUBER, L. J. and BENNETT, L. H., Nuclear Resonances in Metals: Nuclear Magnetic Resonance and MZissbauerEffect, in Techniques of Metals Research, Vol. 6, Part 2, p. 165, (Bunshah, R. F., ed.), Wiley, New York (1973). COHEN, M. H. and REIF, F., Quadrupole Effects in Nuclear Magnetic Resonance Studies of Solids, in Solid State Physics, VoL 5, p. 322, (Seitz, F. and Turnbull, D. T., eds.), Academic Press, New York (1957). DAS, T. P. and HAHN, E. L., Nuclear Quadrupole Resonance Spectroscopy, in Solid State Physics, Suppl. 1 (Seitz, F. and Turnbull, D. T., eds.), Academic Press, New York (1958). LUCKEN, E. A. C., Nuclear Quadrupole Coupling Constants, Academic Press, New York (1969). SEGEL, S. L. and BARNES, R. G., Catalog of Nuclear Quadrupole Interactions and Resonance Frequencies in Solids, Part I: Elements and Inorganic Compounds, Iowa State University Report No. IS-520, revised (1968), available from the Ames Laboratory, Iowa State University, Ames, Iowa 50010. FREEMAN, A. J. and WATSON,R. E., Hyperfine Interactions in Magnetic Materials, in Magnetism, VoL IIA, p. 168, (Rado, G. T. and SUN, H., eds.), Academic Press, New York (1965). PORTIS, A. M. and LINDQUIST, R. H., Nuclear Resonance in FerromagneticMaterials, ibid. (1965) 357. Hyperfine Interactions, (Freeman, A. J. and Frankel, R. B., eds.), Academic Press, New York (1967). Hyperfine Structure and Nuclear Radiations,Asilomar Conference (1967), (Matthias, E. and Shirley, D. A., eds.), North-Holland, Amsterdam; distributed in the U.S.A. by Wiley, New York (1968). Miissbauer Effect Data Index, 1958-1965, MUIR, A. H., JR., ANDO, K. J. and COQGAN, H. M., Wiley, New York (1966). 1969, STEVENS, J. G. and V. E., eds., Plenum Press, New York (1970). 1970, ibid. (1972). 1971, ibid. (1972). 1972, ibid. (1973). 1973, ibid. (1975). _~ Hyperfine Interactions in Excited Nuclei, Jerusalem Conference (1970), (Goldring, G. and Kalish, R., eds.), Gordon and Breach, New York (1971). Znt. Conf. Hyperfine Interactions Studied in Nuclear Reactions and Decay (1973), (Karlsson, E., and Wappling, R., eds.), Almqvist and Wiksel, Stockholm (1974); invited papers also in Phys. Scripta 11, issues 3,4 (1975). CARTER, G. C., KAHAN, D. J., BENNETT, L. H., CUTHILL, J. R. and DOBBYN, R. C., The NBS--Alloy Data Center: Permuted Materials Index, NBS Special Publication 324, Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402, Catalog No. C 13.0:324 (1970). Angular Correlations in Nuclear Disintegration,Delft Conference (1970), (van Krugten, H. and van Nooijen, B., eds.), Rotterdam University Press, Wolters-Noordhoff Publishing, Netherlands (1971). LOW, W., Paramagnetic Resonance in Solids, in Solid State Physics, Suppl. 2 (Seitz, F. and Turnbull, D. T., eds.), Academic Press, New York (1960). LUDWIG, G. W; and WOODBURY, H. H., Electron Spin Resonance in Semiconductors, ibid. 13 (1962) 223. YAFET, Y., g Factors and SpinLattice Relaxation of Conduction Electrons, ibid. 14 (1963) 2. Colloquia of the Groupement Atomes et Molecules Par Etudes Radio Electriques (proceedings of the Colloques Ampere).
118
8.21. 8.22.
8.23. 8.24.
8.25.
8.26. 8.27.
8.28. 8.29. 8.30. 8.31. 8.32. 8.33. 8.34. 8.35. 8.36. 8.37. 8.38.
Metallic Shifts in NMR 13th CoBoque Ampere (Leuven, 1964), (van Gerven, L., ed.), International Conference on Nuclear Magnetic Resonance and Relaxation in Solids. North-Holland, Amsterdam (1965). 14th COllOqUe Ampere (LjubBana, 1966), (Blinc, R., ed.), Magnetic Resonance and Relaxation. North-Holland, Amsterdam (1967). 15th Colloque Ampere (Grenoble, 1968), (Averbuch, P., ed.), Magnetic Resonance and Radiofrequency Spectroscopy, North-Holland, Amsterdam (1969). 16th Colloque Ampere (Buchurest, 1970), (Ursu, I., ed.), Magnetic Resonance and ReIaxation Phenomena. Academy of Sciences of the Socialist Republic of Romania, Bucharest (1971). 17th COBOqUeAmpere (Turku, 1972), (Hovi, V., ed.), Magnetic Resonance and Related Phenomena. North-Holland, Amsterdam (1973). 18th Colloque Ampere (Nottingham, 19741, (Allen, P. S., Andrew, E. R., and Bates, C. A., eds.) Magnetic Resonance and Related Phenomena, University of Nottingham Printing and Photographic Unit, Nottingham (1974). FULLER, G. H. and COHEN, V. W., Nuclear Data Tables 5A (1969) 433. HOLDEN, N. E. and WALKER, F. W., Chart of the Nuclides, Knolls Atomic Power Laboratory, Naval Reactors, U.S.A.E.C., distributed by Educational Relations, General Electric Co., Schenectady, N.Y. 12345. Revised to April 1972, dated October 1972. PEARSON, W. P., Handbook of Lattice Spacings and Structures of Metals, Vols. 1 and 2. Pergamon Press, Oxford (1958), (1967). HULTGREN, R., DESAI, P. D., HAWKINS, D. T., GLEISER, M., KELLEY, K. K. and WAGMAN, D. D., Selected Values of the Thermodynamic Properties of the Elements. American Society for Metals, Metals Park, Ohio,.44073 (1973). ROBERTS, B. W., Superconductive Materials and Some of their Properties, NBS Technical Note 408, Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402 (1966); ibid, NBS Technical Note 482 (1969), and ROBERTS, B. W., Properties of Selected Superconductive Materials, NBS TechnicalNote 724 (1972) and 825 (1974). GSCHNEIDNER, K. A., JR., Rare Earth Information Center, private communication (1972). CONNOLLY, T. F. and COPENHAVER, E. D., Bibliography of Magnetic Materialsand TabulationofMagnetic Trnnsition Temperatures, Research Materials Information Center, ORNL-RMIC-7 (Rev. 2), Oak Ridge National Laboratory, Oak Ridge, Tenn., 37831 (1970). LANDOLT-BORNSTEIN TABLES, II Band, 9. Teil, Magnetische Eigenschaften 1, (Hellwege, K.-H. and Hellwege, A. M., eds.), Springer Verlag, New York (1962). BUSCH, G. and YUAN, S., Phys. Kondens. Materie 1 (1963) 37. HURD, C. M. and COODIN, P., J. Phys. Chem Solids 28 (1967) 523. DUPREE, R. and SEYMOUR, E. F. W., Liquid Metals, Chap. 11, p. 461, (Beer, S. Z., ed.), Marcel Dekker, New York (1972). SEYMOUR, E. F. W., private communication. GSCHNEIDNER, K. A., Physical Properties and Interrelationships of Metallic and Semimetallic Elements, in Solid StatePhysics, Vol, 16, p. 275, (Seitz, F. and Turnbull, D. T., eds.), Academic Press, New York (1964). SIMMONS, G. and WANG, H., Single Crystal Elastic Constants and Calculated Aggregate Properties: A Handbook. M.I.T. Press, Cambridge, Mass., 02138 (1971). HANSEN, M. and ANDERKO, D., Constitution ofBinarv Alloys. McGraw-Hill, New York (1958). ELLIOTT, R. J., Constitution of Binary Alfoys, SuppL 1. McGraw-Hill, New York (1965). SHUNK, F. A, Constitution of Binary ABoys, SuppL 2. McGraw-Hill, New York (1969). ROWLAND, T. J.,Phys. Rev. 125 (1962) 459.
DESCRIPTION
OF THE CRITICAL
COMPILATION
DATA
AND TABLES
8.1. Scope The tables in this critical compilation present the available quantitative Knight shift data as accurately as possible. A high degree of Knight shift data evaluation was attained both by experts at the Alloy Data Center performing critical reviews, as well as via direct communications with several of the authors of the original source documents, who on the one hand helped review the final tables and on the other hand assisted in arriving at “best values” for several cases where discrepancies or uncertainties could be resolved. The literature sources include both published and unpublished data that have become available to us in Technical Reports, theses, and private communications. The literature search was done by scanning “Current Contents” and by using various abstracting journals and services. Defense Documentation Center automated bibliographic searches were performed to obtain the report literature. In addition, various journals were scam-red directly and secondary referencing (relevant references given in papers dealing with NMR) was used extensively for locating source papers. The search is thought to be approximately 97-98% complete for the published literature through 1972 and somewhat less comprehensive for unpublished documents and for articles published through 1975. Using this file of data, as arranged in an automated reference system described in NBS Technical Note No. 4154,(~*‘)we have compared the available literature for each metal, and each alloy system separately. This compilation has been prepared over a period of several years. As a result evaluations for different metals or alloys have different cut-off dates for the literature search, since our policy has been to make as much accurate data available as possible, rather than adhering to a straightforward cut-off date for the whole compilation. Thus, some recent papers may not be cited under each of the alloys they deal with. A list of pertinent papers that have been added to our files by end 1975, since each writeup has been completed, is given at the end of the data compilation, under “Addenda”. These addenda at times give quantitative updates or added descriptions to the metal and alloy evaluations as well. The data that in our judgment are the more accurate ones are tabulated, followed by discussions of the evaluations as well as additional tables and figures. Throughout this compilation we have used the definition of the Knight shift described in the earlier chapters. Interpretations of the NMR results in terms of theoretical knowledge of the materials, or in terms of the constitution of the samples (phase diagram information) or magnetic origins, etc., as discussed in these chapters, are noted in the evaluations. These interpretations as well as other related NMR data are not evaluated to the same degree as the Knight shift. No attempt has been made to prepare complete bibliographies for the other NMR properties. They are listed in the sense of “additional information”, rather than added critical evaluations, although these numbers have been screened to some degree by us and both the critically evaluated Knight shifts as well as the other NMR data have undergone valuable reviewing prior to publication, by several authors in the field of NMR. Additionally, when discrepancies were encountered which could not be resolved from the source papers, the authors of these reports were usually contacted directly to obtain needed information. Further details relating to the degree of coverage and evaluation are discussed in the next section. In order for the NMR results to be related to the other properties of the material, and in order to interpret the NMR data and arrive at the best X-values, it is often necessary to have a knowledge of several of the other physical properties of the materials. To present the NMR data to its best utility, several other available properties have been listed. Similarly, where the NMR data enhance the 109
110
Metallic Shifts in NMR
understanding of some of the other properties of the materials, such interconnections are often noted in the evaluations. For certain materials very little information is available and no Knight shift data are reported. For some of these materials, related information has been included, although our files are not complete for such other subjects. This is in an attempt to give the reader some information to help locate literature pertinent to NMR research. Examples of related information are FNR hyperfme fields, NQR, and perturbed angular correlation data. Also, in a few selected cases, where the materials may have some more practical applications (either experimentally, theoretically, or technologically), hyperfme fields determined by the Mossbauer effect are noted. It should always be kept in mind; however, that these related data are not evaluated. Most of the evaluations, especially for those systems where ample NMR data are available, do not include non-NMR data. The size of the present compilation at this time prohibits more comprehensive inclusion of these topics. For clarity of presentation, topics discussed in the more lengthy descriptions of the evaluations are noted as marginal notes, whenever they do not bear on the room temperature Y values. These marginal notes also bring to the reader’s attention any non-NMR techniques discussed in the paragraphs, or any conclusions about other properties of the materials from the NMR experiments. Finally, this compilation encompasses in its scope all metallic materials. This includes liquid ammonia solutions of the alkali metals, hydrides, superconductors, and materials with semiconductorto-metal transitions. For some nonmetallic elemental substances data are given, so that a comparison can be made when these substances are alloyed with metals. In addition, a substantial number of compounds have been included that show relatively large NMR shifts, of the order of Xvalues, which are likely to be due to magnetic origins (e.g., AlaC00~). These shifts are not Knight shifts in the ordinary sense, since these materials are not metallic. Only those cases that have come to our attention are listed and the literature search for this type of compound is not complete. These compounds have been included in this compilation as examples of large shifts due to mechanisms described in sections 2.10 and 3.4. Semiconductors are generally excluded from this compilation. In the literature, the NMR shifts in semiconductors are often called Knight shifts. These shifts are due to the conduction electrons in impurity bands, outside of any chemical shifts, and are thus very sensitive to the purity, or the amount of doping of the material. However, a few systems showing semiconducting properties have been given in this compilation as examples. The Knight shift in semiconductors gives information concerning the type of interactions of the charge carriers with the nuclei of their constituent elements. Again, completeness is not attempted as semiconductors fall outside the scope of completeness of this data compilation.
8.2. Organization and Degree of Evaluation of the Data In this compilation the elemental metals are treated first, in order to give a fully evaluated basis set of Yvalues from which variations upon alloying can be presented. In order for the metals to be properly understood in terms of the NMR research, some nuclear and solid state properties are tabulated. These will now be discussed in the order in which they appear. The extent of their evaluations, or literature sources, will be indicated. 8.2.1. Metals (a) NMR Properties Knight shifts: This compilation presents a complete and m-depth evaluation of all reported Knight shifts. The data are made as self-consistent as possible and whenever enough information is available, the data have been adjusted to the use of the Ydetinitions given in previous chapters. Unfortunately the majority of the literature reviewed in our evaluations lack adequate descriptions of the criteria used in X deductions (e.g., centroid of a resonance versus derivative zero, etc.) or descriptions of sample preparation and characterization, so that comparison between disagreeing data and adjustment to a uniform .X definition was often not possible. In several cases authors have been contacted in order to be able to tabulate more accurate data. Mostly, for metals with little available data, the numerical values are presented as reported. The reliability of these data will be evident from the discussion of the data, or the
Description of the Critical Data Compilation and Tables
111
source, which may be no more than an abstract. It is not possible for us to estimate reasonable errors for these data SOthat such values are often accompanied by the note N.E.(no errorsgiven). Errorsare denoted in this compilation by the numbers in brackets immediately following the numerical value, and signify the uncertainty of the digit(s) immediately preceding the bracket, i.e. .$ = 0.20(2)$% stands for $= (0.20 + 0.02)%. This notation is used for all parameters given in this compilation. When stating errors separately for X, this is denoting by AX= f . . . %, which should not be confused with an alternate method of denoting the error in percent of the absolute Xvalue. Since% itself is expressed in percent, this notation is confusing, and therefore not used in this compilation. When errors are given in the literature they may be representative of the root mean square deviation of the scatter of the values obtained from several runs, using the same equipment, the same sample, and the same conditions. This is a calculable number, and when presented in the source papers has usually been included in this compilation along with the reported values. Because these numbers represent precision rather than total error due to various experimental conditions, we have given estimated errors whenever the reported error seemed unreasonably small in view of the description of the experiment. However, at times insufficient information has been given to estimate a reasonable error. In the discussions the sources of the errors or reasons for their choice, if different from the author’s, is included in the discussion. Whenever an average of two or more reported Xvalues was thought to give the most probable X value, the error was chosen so as to include all these numbers plus a possible error connected with each value, as was deemed necessary for individual cases. In evaluating the X values for the elemental metals, the best room temperature value was first determined, when available. Once this point was determined the variation with temperature or pressure was evaluated. As there is an error associated with the absolute value of the$(300”K), the error of the X(2’) variation was added onto the room temperature error. Thus, the tabulated metal .X-valuesand their errors are in terms of absolute values. Often the variation of Xhas been determined more accurately. Such higher precision determinations are represented in our tables by giving separately values for (qTi) -L%!(Ti))/(Tj - Ti) with the error associated with that measurement. Pressure dependences have been treated in a similar way. Instrumentation is not described explicitly in the evaluation discussions, except for those cases where this may be a cause of discrepancy of the data. As a result, the notation N.I. (no instrumentation description given) is only used occasionally in this compilation. Similarly, sample analysis is not described unless pertinent to the evaluation. The notation N.A. is used to indicate that sample analysis was not discussed in the reference. However, since NMR itself can be a probe of the sample quality, often the experimental results themselves could be used as indicator for certain aspects of sample quality in the data evaluations. Several paragraphs in the previous chapters, especially Chapters 6 and 7, discuss this topic. A common adjustment made in this compilation is that of chemical shifts. Whenever values for chemical shifts have come to our attention they are mentioned in the text, or in a few cases tables are given. Adjustments of svalues for chemical shifts have been made when possible; these corrections are noted in the discussions. The notation of AX= . . . % is used to indicate the value of the adjustment. Again, these corrections are given in terms of additions or subtractions to the XvaIues, and not in terms of a percentage of the original Xvalue. As Y has not been convincingly proven to be dependent on isotopes (except possibly for Rb, and Sb in GaSb, see section 2.9), no effort is made in this compilation to identify specific isotopes for theX measurements, except in those cases where a deliberate attempt has been made to determine the presence of such an effect. Unless special experimental efforts are made, the accuracy of Knight shift measurements is lower than any anticipated isotope effect. For other NMR parameters that do depend on isotopes, such as relaxation times, the isotope is indicated. Often data have been published in the form of graphs. Such graphs have generally not been reproduced, but rather, short tables with values read from the graphs have been prepared. Figures including private communications, unpublished data, or graphs drawn for this compilation are included, however, as they are not readily available in the published literature. At times, numerical data are difficult to obtain from graphs. Such cases are noted, and often cause representation of errors larger than those of the actual measurements. Obtaining s(T) data from Y vs. x graphs is an example of complications encountered in X deductions from graphical representations: if x(T) is not known,NT) cannot be deduced. TIT: Although no attempt has been made to completely evaluate TIT, or to give a complete set of
112
Metallic Shifts in A4MR
literature references, we have given these data some consideration so that the listed value, or range of values, are reasonably accurate. Quantitative knowledge of Tt T is important as this NMR parameter is connected to the Knight shift by the Korringa relation and thus can give insight into the Knight shift behavior (see section 2.8). In order not to expand our scope of Knight shift evaluations into a project of unmanageable scope, we have used some of the TIT values given by Drain(*.‘) for pure metals. These values have been reconsidered, often in view of more recent results. Employing our newly evaluated sand y values and our reconsidered T1 T values, we have recalculated the Korringa product. The results are similar to the numbers given by Drain for the metals listed in his review, and are summarized in Table 2.4. Tz, e2qQ/h: Values for the parameters have been included only when they were mentioned in readily available literature. However, no attempt has been made for completeness, nor have they been evaluated. Methods for obtaining T2 values experimentally are discussed in a comprehensive review by Weisman et a1.;(8.3) Chapter 6 of the present review discusses methods of obtaining quadrupole coupling constants, e2qQ/h, from experimental NMR spectra. An earlier review on quadrupole effects is given by Cohen and Reif,cs4) and pure NQR is treated by Das and Hahn. (8*5) Earlier tables of numerical values for quadrupole coupling constants include those by Lucken(8*6) and by Segel and Barnes,(‘*‘) although these deal to a large extent with nonmetallic materials. Line width: The line width values are approximate. They are not evaluated and a detailed literature search has not been made for this quantity. Our listings are not complete, nor are they deduced in a uniform fashion from the spectra. Nm: For elemental metals we have attempted to note reports of pure NQR, and some unevaluated results have been included in some cases. A review on this subject has been written by Das and H&.(8.5)
FNR: All metals and alloys for which FNR reports are available are included. Numerical Herr values as obtained by FNR, using the relation I&-(FNR) = v(FNR)/(y/2 7~ ) , are noted when readily available. These values are generally not critically evaluated (also see under Heff, next paragraph), but when possible they have been made consistent with our preferred y/271values. For metals or alloys for which a large number of FNR reports are available, short summarizing tables have been prepared giving only a small fraction of the total data and a limited bibliography. Additional references can be obtained from compilations and bibliographies such as given in references 8.8 through 8.15. Some more recent references are available in the NBS Alloy Data Center files. H ,_ft: Heff values resulting from NMR, ferromagnetic resonance (FNR), and at times perturbed angular correlation (PAC), have been noted, although full coverage or evaluation of these parameters has not been attained. The listed Heff values have been adjusted to our preferred y values when possible. Those determined by%(T) vs. x(T) plots (see discussion in section 3.4.1) have been presented in units of kilogauss (kc) for each aligned Bohr magneton @n, or spin l/2) rather than for each aligned spin (spin 1). Those cases for which adjustments to these units were made are so noted. Heff values as determined by other methods such as FNR are given in units of kG. For the important metals such as Fe, Co and Ni care has been taken in presenting accurate Heff values, although the bibliographies are by no means complete (see FNR paragraph, above). PAC, Nuclear specific heat, Miissbauer effect: Unevaluated hyperfme fields obtained by these methods have occasionally been included when such information was readily available in our files. No attempt has been made to give details, or completeness in these areas, although increased coverage of these topics has been given for relatively important materials, when essentially no other NMR data were available. For any of these types of experiments other compilations and bibliographies are available. References 8.8 through 8.15 include numerical Heff values obtained with these techniques (see especially the review article by Lounasmaa in reference 8.10 for nuclear specific heat values and also see reference 8.16 which deals with PAC only). Other NMR parameters: Some other parameters derived from NMR measurements and discussed in the previous chapters are at times noted, when they have been given in the literature (e.g. t, or jsr values). No attempt has been made here to extract such parameters from existing data, nor have the numerical values been evaluated. EPR: When EPR has been reported for a metal; this is often noted in a paragraph of the evaluation text. Completeness on EPR bibliographies has not been attempted, however. The availability of EPR reports is mentioned since these may be of interest in NMR research, mostly in connection with obtaining Pauli susceptibilities (see section 2.3). Some reviews dealing with EPR for both metals and
Description of the ch’tical Data Compilation and Tables
113
semiconductors are given in the articles by Low,(~*’‘1 Ludwig and Woodbury,(8*‘8) and Yafet.(8*’ 9, Electron-nuclear and other double resonances are at times also brought to the attention of the reader when these reports were encountered in our files. Again for these topics our bibliographies are not intended to be complete, but rather representative. The conference series “Colloque Ampt%e”(8*20) covers the topics of NMR, EPR as well as ENDOR and other double resonances. Additional references are available from reference 8.15 and the Alloy Data Center files. (b) Properties of the Nucleus Nuclear properties themselves do not vary when the environment is varied. Their values are listed with each metal for convenience, but not repeated under the alloys. n, y/2n, Z, Q: The magnetic moments, ZL,not corrected for core diamagnetism, and the magnetogyric ratios, y, derived therefrom (more commonly referred to as gyromagnetic ratios), the nuclear spins, and electric quadrupole moments have been taken from Fuller and Cohen,(8.2*) unless otherwise stated. Only those isotopes of possible interest in NMR research are given. Since $values are derived from shifts of y’ (or r_l’)as seen in the metal with respect to our preferred y, or n reference values for the nucleus, and since these magnitudes are often in the range of uncertainty of the absolute 7 (or cc)values, some 7 values were reevaluated. Thus the present set of 7 values represents a listing of fully evaluated numbers, for use in NMR. Those cases for which reevaluation was indicated are described in the discussions of the Knight shift evaluations for elemental metals. Table 2a lists our preferred r/2n values in the format of the periodic tables. Table 2b lists these values by increasing ~/2rr value. This is a format often convenient in resonance identification in a spectrum or in search of a suitable reference for Smeasurements. In this compilation we have employed the value for the nuclear magneton, /.IN= 5.05050 x 1o-24 erg/C, used by Fuller and Cohen(8.2 ‘) in order to retain consistency with their listed nuclear moments. This same listing gives for the proton, corrected for the diamagnetism of water, ZJ= 2.79278 &v, and a conversion factor to y of y/2n = 0.762273(~#, giving y/2n = 4.25772 kHz/G for the proton. The choice of these quantities affects the factor converting ccto y/2n for any nucleus in the last significant figure. For example, 1965 internationally accepted values give y/2n = 0.7622750 and a set of values proposed later gives y/2n = 0.762269(n/Z). A consistent set of fundamental constants adopted internationally by CODATA ( see CODATA Bulletin 11, Dec. 1973) lists &,, = 5.050824(20) x 1O-24 erg/G and for the proton (corrected for the diamagnetism of water), /.l= 2.7928456(11) BN and y/27r = 4.25771 l(12) kHz/G, resulting in a conversion of y/2n = 0.7622530 These 1973 values became available too late to incorporate in the present compilation. Numerically, X measurements made directly between a metal and a salt for a particular nuclear species are not affected by the choice of these constants. However, when X is measured with respect to an intermediate chemical, such as described under Nb metal in Chapter 9, then the choice of the above values can make a significant difference in the numerical results. This is so because (a) the unit of ~1,c(N, is different in different listings, thus changing the value of Z.L, and (b) the ratio for conversion, r/(‘Ln~), is different. For example, if the 1973 set of constants are used, then all the 7 values given under the metals in Chapter 9, which were derived from Fuller and Cohen’&‘** ‘) ZJvalues, will be smaller according to the new r/(%m) ratio. Xmeasurements involving the use of y or n values often fail to state the numerical VdUeS of c(N, p or 7, or the ‘Y//Jratio employed. It is not possible to critically compare and evaluate numerical results, or to adjust to new standards of fundamental constants, unless the physical constants used in the original data reductions are specifically stated. Other fundamental constants listed in this compilation do not affect the critically evaluated Knight shift data, however, and those listed are taken from the 1973 CODATA list of fundamental constants. A correction for the diamagnetism of water has been included for the nuclear moment of the proton and the deuteron (i.e., the chemical shift correction). No further core diamagnetism exists for the proton or the deuteron. For all other isotopes, no core diamagnetism corrections have been made. It is very nearly the same for a given isotope in any environment. Furthermore, the corrections are a result of calculations for the atomic states, which are the same for a given nucleus in any solid, and thus cancel out in shift measurements. As relative shifts are usually measured in NMR, it is often useful to employ a reference 7 value of figh precision SOthat data can be compared, although the absolute accuracy may be lower. For this reason Cc values from which the listed y values were obtained were not always taken from the rounded values given by Fuller and Cohen,(8*2’1 but rather from their other tables, mostly Table E, giving p values
114
Metallic Shifts in NMR
determined by NMR, or from double or triple resonances. In the cases of NMR determinations the reference salt used for the /L measurements could be stated. The method of measuring fi has also been indicated for each listed /J value. The standard isotope notation, giving the isotope value to the upper left of the chemical symbol or nuclear property symbol, is adhered to in this manuscript (e.g. 27Al). Abundance: The % abundance or half-life of the isotopes were taken directly from Holden and Walker.(8*22) In our listings we have given the stable (or near-stable) isotopes of non-zero spin. Those radioactive isotopes that are of possible interest in NMR have also been listed, and are indicated with an asterisk to the upper right of the chemical symbol (e.g. 2 3OPti*). Abundances are included in Tables 2a and 2b. (c) Solid State Properties All listed solid state properties have been taken from existing compilations and have not been evaluated anew. For a few indicated systems, new data have been taken directly from recent publications when these new data have come to our attention, and included when the existing compilations gave no data. No specific searches have been done for these properties. All data not referenced specifically were taken from the the following sources: Ckystal structures: All data were taken from Pearson (8*23) unless otherwise noted. For details of notation see below under Alloys: “Crystal Structures, Point Symmetries and Metallurgical Information”. Melting points and other phase transition temperatures: Melting points (abbreviated m.p.) and other phase transition temperatures were taken from Hultgren et a1,(8*24) or from Pearson(8.23) when not available from Hultgren et aL(8.24) (Pearson’s thermodynamic data are mostly unevaluated.) Superconducting transition temperatures: For the superconducting elemental metals the superconducting transition temperatures, T,, are listed as given by Roberts. (8.2 ‘) The lowest temperature at which superconductivity tests show other metals to be normal are noted when given by Roberts. Magnetic transition temperatures: For the rare earths Gschneidner(8.26) has supplied the data; Conn~lly(~*~~) was consulted for other metals with a few noted exceptions. The paramagnetic Pauli susceptibilities: @’ values have been derived directly from electronic specific heat coefficients, ycp, listed by Hultgren (8.241 using the relation, xFp = 3(/+/7~k)~7c~, which is rigorously true only for the case of free electrons (see section 2.3). In addition, for several cases, xp values are noted using an alternate estimate simply to give an idea of the range of values one may obtain using different estimates. Section 2.3 discusses the shortcomings of the various methods of estimating xp. For the alkalis, Bi and Sb, the alternate xp values are derived using xexp listed in the Landolt-Bornstein Tables.(8.2 ‘) For other metals Busch and Yuan(8*29) gave xex n values. These were then used to compute xp = 3/2 [xexp - x~~~~], employing x~~~e values given by Hurd and Coodin.(8.30) Later experimental values may give some improvement, and at times alternate estimates of x~~~e may result in better xp values. Our listed xr, values thus represent a set deduced in a somewhat uniform fashion, rather than the best value for each individual case, since even “best estimates” may not be accurate. For liquid metals a more recent survey by Dupree and Seymour(8.31) is available, and it appears(a.3i9 8.321 t h at use of the Hurd and Coodin(s*30) x~~~ values generally leads to lower apparent electronic susceptibilities for liquid metals, than are suggested by Dupree and Seymour.(8.3 ‘) Li and Na metals are two exceptions for which direct measurements of x,, have been made in the solid state, using EPR and a more indirect method was used for Be metal (see section 2.3). The numerical values are listed under the metals. Compressibilities: Compressibility data were taken from Gschneidner,(8.33) and are representative room temperature values. A later extensive listing of compressibilities by Simmons is also available,(8.34) but as these data are unevaluated they are not used in our listing. References: The references have been generated by computerized techniques using our automated NMR files described in reference 8.1. For each metal or alloy system all papers indexed under Knight shift are listed, whether they are discussed in the text or not. In addition, a list of “Related References” is given which lists those papers dealing with other topics discussed in the evaluations. These “Related References” are used in our evaluation process and do not represent a listing of all papers in our files on
Description of the Oitical Data Compilation and Tables
115
the related subjects. NBS Special Publication 324 (‘J ‘) of the Ahoy Data Center can be consulted for additional references for properties other than K All the authors, full titles, and citations are given, together with a few descriptive words for subtopics such as “single crystal” work, or sample also studied in the “superconducting state”. For those papers noted as “Theory” or “Review” this signifies that the paper gives only theory or review for this metal. Papers including any experimental data (Knight shift or other) for a material are considered as experimental so that some papers may not be denoted as theory or review because the property Knight shift (or other) is indexed as experimental, although the paper may give a theory or a review as well.
8.2.2. Alloys
(a) Solid State Properties All alloys are listed in alphabetical order, following the elemental metals. Phase diagrams are presented with the element of first alphabetic occurrence on the left-hand side. Compounds are written in alphabetic order, e.g. GaVs, rather than VsGa, to conform with the phase diagram, with a few exceptions, such as the oxides and phosphides, where the second element is clearly a non-metallic constituent. The alloys have been written in the following sequence: for an ahoy A-B, first the A resonance (denoted by underlining the A, A--B) is treated. The tables of preferred data, a description of the evaluation, and the figures are given. Then the B resonance, A-B, is treated in the same sequence. When only few data are available, only a brief comment, or only a table or a figure is presented. Phase diagrams: The phase diagrams for nearly all binary systems were taken from the series of Hansen,(8*3s) Elliott,(8*36) Shunk,(8.37) and unpublished addenda. Where other data have been included, reference to such material is given in the text. Crystal structures, point symmetries, and metallurgical information: Pearson(8.23) has been used throughout for this information, and his classification and designation system for the structures has been adopted. A section of the description of this system, given by Pearson!8*23) reads as follows: “The structures are primarily classified according to the fourteen Bravais lattices and then the number of atoms in the conventional crystallographic unit cell for the standard space group and setting. Secondary classification within these groups follows the numerical order of the 230 space groups, and finally, if necessary, within any space group structures follow the alphabetical order of their names. This classification is in some ways similar to that adopted by the ASTM* for naming or describing alloy phases. But whereas the ASTM uses a single arbitrary capital letter to characterize each of the fourteen Bravais lattices, we have chosen to use two characters and thus retain the crystallographic letters P, C, F, I, and R for primitive, one-face-centred, all-face-centred, body-centred and rhombohedral lattices respectively, combining with these the small letters a, m, o, t, h and c mnemonic with the names of the six crystal systems, trichnic (anorthic), monoclinic, orthorhombic, tetragonal, hexagonal cubic, respectively to give the symbols listed in Table 8.1 below. Thus, for example, the centred monoclinic Bravais lattice is represented by the symbol mC, and this is followed by the number of atoms in the crystallographic cell to give a classification symbol such as mC24. Trigonal P lattices fall in the hexagonal P grouping. These classification symbols are, of course, not possible names for structure types, since there may be an indefinite number of structural types falling under a given class. The problem of giving simple systematic names to crystal structure types is one that has received much thought, but it seems also to be a problem without any ready solution. The best that can be done is to name each structure type after a representative substance, as for example Cu3Au, which has that structure. Strukturbericht type symbols are still fairly widely used and recognized for simple structures, but the regular system of attributing letters A, B or C to the structure type of compounds with 1,2 or 3 atoms in the formula has its own exceptions and seems to have broken down completely in the D 0 to 10 series of structure
* ASTM Designation: E157-63, 1965 of ASTM Standards, Part 31, p. 387. American Society for Testing and Materials, Philadelphia. See also ASTM Special Technical Publication No. 35.5. MetalsReference Book. C. .I. Smithells, 3rd edition, 1962, Butterworths, London.
116
Metallic Shifts in NMU TABLE 8.1
Symbols used for the fourteen Bravais lattices?, quoted from PearsorJa2 3, Symbol
System
Lattice symbol
aP mP
triclinic(anorthic) monoclinic
P P*
mC OP
orthorhombic
P c F
tetragonal
P
hexagonal (and trigonal, P) rhombohedral
P R P F
C*
oc OF 01
tP
I
t1 hP hR CP cF
I
cubic
CI
I
* Second setting, y axis unique. t The ASTM symbols for the fourteen Bravais lattices are in fact used in a systematic nomenclature for alloy phases; the symbols which we use are only for classifying structure types for crystallographers and are not part of any nomenclature of structure types.
types. This fact and the extension of the Strukturberbericht series in Metals Reference Book by using small subscript letters, e.g. B,, b, B, - - - instead of numbers, e.g. B18, B19, B20 - - -, now means that we have not only an arbitrary system of structure type names, but also a somewhat arbitrary method of allotting the names. The Strukturbericht series of names has therefore passed beyond the stage where it can be extended and used sensibly. An arbitrary system of structure names could only be acceptable if the names were derived in a systematic way depending, say, on formula or structural characteristics”. (b) NMR Properties For the alloys there are a few added points to be discussed concerning evaluation procedures. Knight shifts: For an alloy system the end points (pure metals) have been determined separately and
are listed under the elemental metals. In evaluating s as a function of alloy composition, X(c), the endpoints have been considered fured at the preferred values. The indicated errors of theX(c) listings represent the errors in measuring a variation of X rather than their absolute value. The error indicated under the pure metal must be added to obtain absolute values of errors. This is a different procedure than was followed for elemental metal X(7’) listings, for which separate X(T) slopes of higher accuracy are listed when such a measurement was made. The reason is that X(T) is often deduced from separate measurements, rather than from direct relative changes whereas mostX(c) data are from direct relative change measurements using the pure metal resonance position as reference frequency. OftenX(c) reports give a conversion from these relative shifts,Ax(c), from the metal position to shifts with respect to a salt by employing a previously publishedX(metal) value. Problems arise here when theX(metal) value used is not mentioned in the paper, or when reference salts are not given. In contrast, reported AX(c) values are easily added onto our preferred X(meta1) values to give X(c) values, which, when the product AX x *metal) is large, must be done by employing eqn. (5.3). When the conversion is done in the literature, as a rule eqn. (5.3) has not been used. This is one place where errors may arise. This error is usually quite small and is only pointed out, or corrected where possible, in cases where it may be important. When r E 1X1- ‘(AX/AC) is calculated, another inconsistency (usually small) is introduced if a previously available X value which differs from our preferred value is employed. When the &value actually employed is not mentioned, a correction cannot be made. Generally, a comment concerning the source of theNmetal) value is made when the question arises and may be signiticant. A common error of larger magnitude is that introduced in measuring A.%@)from derivative zeros rather than centroids of the resonance, as discussed in previous chapters; Chapter 3 discusses this topic in connection with line asymmetries due to near neighbor environments (also satellite behavior), and
Description of the Critical Data Compilation and Tables
117
non-linear .X(c) behavior. Chapter 6 gives further details on data reduction procedures for asymmetric lines. Often line shapes and the method of x deduction are not mentioned by authors and data as reported must be reproduced as preferred values, as well as their reported errors, if the sources of these errors are not stated. If there is reason to change the error on a preferred value this reason is always noted in the tables, or the discussions. An example of uncertainties introduced in employing derivative zeros in alloys, when lineshape effects are present, was given by Rowland.(8*38) This is described in section 3.1. T1 T: The discussion under ‘Metals’ applies to the alloy tables as well. Korringa products are generally deleted for alloys as such a number is much less meaningful. It can be obtained simply by calculating from eqn. (23) the product 20.98 (+y/2n)* X*Tl T. Other properties: The discussion for the various other properties (under ‘Metals’) applies to alloys as well. References: The discussion under ‘Metals’holds for alloys as well. A problem encountered in the case of alloys, results from authors not stating explicitly the alloys studied, but rather mentioning a group of alloys identified; for example, as “dilute Al-X alloys”, or “V3X compounds,” etc. These reports cannot be indexed under specific alloys or compounds, and are thus irretrievable. Because this happens mostly in short reports and abstracts that usually provide qualitative rather than quantitative information, very little numerical data are lost. In several cases where such abstracts represented the sole source of data, the authors have been contacted for further details. Otherwise these reports that do not specifically identify the alloys studied are omitted from the lists of references.
References 8.1.
8.2. 8.3.
8.4. 8.5. 8.6. 8.1.
8.8. 8.9. 8.10. 8.11. 8.12.
8.13. 8.14. 8.15. 8.16. 8.17. 8.18. 8.19. 8.20.
CARTER, G. C., ef al, The NBS AIloy Data Center: Function, Bibliographic System, Related Data Centers, and Reference Books. NBS Technical Note 464, Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402 (1968). DRAIN, L. E., Metall. Rev. 119 (1967) 195. WEISMAN, I. D., SWARTZENDRUBER, L. J. and BENNETT, L. H., Nuclear Resonances in Metals: Nuclear Magnetic Resonance and MZissbauerEffect, in Techniques of Metals Research, Vol. 6, Part 2, p. 165, (Bunshah, R. F., ed.), Wiley, New York (1973). COHEN, M. H. and REIF, F., Quadrupole Effects in Nuclear Magnetic Resonance Studies of Solids, in Solid State Physics, VoL 5, p. 322, (Seitz, F. and Turnbull, D. T., eds.), Academic Press, New York (1957). DAS, T. P. and HAHN, E. L., Nuclear Quadrupole Resonance Spectroscopy, in Solid State Physics, Suppl. 1 (Seitz, F. and Turnbull, D. T., eds.), Academic Press, New York (1958). LUCKEN, E. A. C., Nuclear Quadrupole Coupling Constants, Academic Press, New York (1969). SEGEL, S. L. and BARNES, R. G., Catalog of Nuclear Quadrupole Interactions and Resonance Frequencies in Solids, Part I: Elements and Inorganic Compounds, Iowa State University Report No. IS-520, revised (1968), available from the Ames Laboratory, Iowa State University, Ames, Iowa 50010. FREEMAN, A. J. and WATSON,R. E., Hyperfine Interactions in Magnetic Materials, in Magnetism, VoL IIA, p. 168, (Rado, G. T. and SUN, H., eds.), Academic Press, New York (1965). PORTIS, A. M. and LINDQUIST, R. H., Nuclear Resonance in FerromagneticMaterials, ibid. (1965) 357. Hyperfine Interactions, (Freeman, A. J. and Frankel, R. B., eds.), Academic Press, New York (1967). Hyperfine Structure and Nuclear Radiations,Asilomar Conference (1967), (Matthias, E. and Shirley, D. A., eds.), North-Holland, Amsterdam; distributed in the U.S.A. by Wiley, New York (1968). Miissbauer Effect Data Index, 1958-1965, MUIR, A. H., JR., ANDO, K. J. and COQGAN, H. M., Wiley, New York (1966). 1969, STEVENS, J. G. and V. E., eds., Plenum Press, New York (1970). 1970, ibid. (1972). 1971, ibid. (1972). 1972, ibid. (1973). 1973, ibid. (1975). _~ Hyperfine Interactions in Excited Nuclei, Jerusalem Conference (1970), (Goldring, G. and Kalish, R., eds.), Gordon and Breach, New York (1971). Znt. Conf. Hyperfine Interactions Studied in Nuclear Reactions and Decay (1973), (Karlsson, E., and Wappling, R., eds.), Almqvist and Wiksel, Stockholm (1974); invited papers also in Phys. Scripta 11, issues 3,4 (1975). CARTER, G. C., KAHAN, D. J., BENNETT, L. H., CUTHILL, J. R. and DOBBYN, R. C., The NBS--Alloy Data Center: Permuted Materials Index, NBS Special Publication 324, Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402, Catalog No. C 13.0:324 (1970). Angular Correlations in Nuclear Disintegration,Delft Conference (1970), (van Krugten, H. and van Nooijen, B., eds.), Rotterdam University Press, Wolters-Noordhoff Publishing, Netherlands (1971). LOW, W., Paramagnetic Resonance in Solids, in Solid State Physics, Suppl. 2 (Seitz, F. and Turnbull, D. T., eds.), Academic Press, New York (1960). LUDWIG, G. W; and WOODBURY, H. H., Electron Spin Resonance in Semiconductors, ibid. 13 (1962) 223. YAFET, Y., g Factors and SpinLattice Relaxation of Conduction Electrons, ibid. 14 (1963) 2. Colloquia of the Groupement Atomes et Molecules Par Etudes Radio Electriques (proceedings of the Colloques Ampere).
118
8.21. 8.22.
8.23. 8.24.
8.25.
8.26. 8.27.
8.28. 8.29. 8.30. 8.31. 8.32. 8.33. 8.34. 8.35. 8.36. 8.37. 8.38.
Metallic Shifts in NMR 13th CoBoque Ampere (Leuven, 1964), (van Gerven, L., ed.), International Conference on Nuclear Magnetic Resonance and Relaxation in Solids. North-Holland, Amsterdam (1965). 14th COllOqUe Ampere (LjubBana, 1966), (Blinc, R., ed.), Magnetic Resonance and Relaxation. North-Holland, Amsterdam (1967). 15th Colloque Ampere (Grenoble, 1968), (Averbuch, P., ed.), Magnetic Resonance and Radiofrequency Spectroscopy, North-Holland, Amsterdam (1969). 16th Colloque Ampere (Buchurest, 1970), (Ursu, I., ed.), Magnetic Resonance and ReIaxation Phenomena. Academy of Sciences of the Socialist Republic of Romania, Bucharest (1971). 17th COBOqUeAmpere (Turku, 1972), (Hovi, V., ed.), Magnetic Resonance and Related Phenomena. North-Holland, Amsterdam (1973). 18th Colloque Ampere (Nottingham, 19741, (Allen, P. S., Andrew, E. R., and Bates, C. A., eds.) Magnetic Resonance and Related Phenomena, University of Nottingham Printing and Photographic Unit, Nottingham (1974). FULLER, G. H. and COHEN, V. W., Nuclear Data Tables 5A (1969) 433. HOLDEN, N. E. and WALKER, F. W., Chart of the Nuclides, Knolls Atomic Power Laboratory, Naval Reactors, U.S.A.E.C., distributed by Educational Relations, General Electric Co., Schenectady, N.Y. 12345. Revised to April 1972, dated October 1972. PEARSON, W. P., Handbook of Lattice Spacings and Structures of Metals, Vols. 1 and 2. Pergamon Press, Oxford (1958), (1967). HULTGREN, R., DESAI, P. D., HAWKINS, D. T., GLEISER, M., KELLEY, K. K. and WAGMAN, D. D., Selected Values of the Thermodynamic Properties of the Elements. American Society for Metals, Metals Park, Ohio,.44073 (1973). ROBERTS, B. W., Superconductive Materials and Some of their Properties, NBS Technical Note 408, Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402 (1966); ibid, NBS Technical Note 482 (1969), and ROBERTS, B. W., Properties of Selected Superconductive Materials, NBS TechnicalNote 724 (1972) and 825 (1974). GSCHNEIDNER, K. A., JR., Rare Earth Information Center, private communication (1972). CONNOLLY, T. F. and COPENHAVER, E. D., Bibliography of Magnetic Materialsand TabulationofMagnetic Trnnsition Temperatures, Research Materials Information Center, ORNL-RMIC-7 (Rev. 2), Oak Ridge National Laboratory, Oak Ridge, Tenn., 37831 (1970). LANDOLT-BORNSTEIN TABLES, II Band, 9. Teil, Magnetische Eigenschaften 1, (Hellwege, K.-H. and Hellwege, A. M., eds.), Springer Verlag, New York (1962). BUSCH, G. and YUAN, S., Phys. Kondens. Materie 1 (1963) 37. HURD, C. M. and COODIN, P., J. Phys. Chem Solids 28 (1967) 523. DUPREE, R. and SEYMOUR, E. F. W., Liquid Metals, Chap. 11, p. 461, (Beer, S. Z., ed.), Marcel Dekker, New York (1972). SEYMOUR, E. F. W., private communication. GSCHNEIDNER, K. A., Physical Properties and Interrelationships of Metallic and Semimetallic Elements, in Solid StatePhysics, Vol, 16, p. 275, (Seitz, F. and Turnbull, D. T., eds.), Academic Press, New York (1964). SIMMONS, G. and WANG, H., Single Crystal Elastic Constants and Calculated Aggregate Properties: A Handbook. M.I.T. Press, Cambridge, Mass., 02138 (1971). HANSEN, M. and ANDERKO, D., Constitution ofBinarv Alloys. McGraw-Hill, New York (1958). ELLIOTT, R. J., Constitution of Binary Alfoys, SuppL 1. McGraw-Hill, New York (1965). SHUNK, F. A, Constitution of Binary ABoys, SuppL 2. McGraw-Hill, New York (1969). ROWLAND, T. J.,Phys. Rev. 125 (1962) 459.