- Email: [email protected]
Experimental equations of state for the rare gas solids
Solid State Communications, Vol. 15,, pp. iii-vi, 1974.
Pergamon Press.
Printed in Great Britain
Abstracts of Articles to be Published in The Journal of Physics and Chemistry of Solids 'J Phys. Chem. Solids (to be published)' should be cited in references to material quoted from this section prior to the publication of the relevant article. .
CALCULATION OF STATIC CORRELATIONS IN A FLUID OF LINEAR MOLECULES R. Pynn, Brookhaven National Laboratory, Upton, New York 11973, U.S.A.
Recently, both X-ray and neutron diffraction data have been obtained for liquid crystalline materials. While these results contain information about the in stantaneous correlations of molecular postions and oreientations in such fluids, no relevant calculations are available to aid the interpretation of the data. In this paper a formalism which may be used to describe static, molecular correlations in isotropic or anisotropic fluids of linear molecules is developed. To obtain the theory, the direct and total correlation functions of two molecules are expanded as series of spherical harmonics the argument:~ ofwhich describe the molecular orientations. A relation between the expansion coefficients of these series is obtained by making use of the Ornstein-Zernike equation. It is shown that this equation may be solved in the Percus-Yevick or Optimized-Randim-Phase approximations by a variational technique. This technique is used to find the total correlation function in the Percus-Yevick approximation of hard, linear molecules of various length-tobreadth ratios at several fluid densities.
Lattice parameter measurements were made on the tetragonal compounds U6 Mn, U6 Fe, U6 Co and U6Ni and alloys between them. Parameter {a} was found to have a minimum at U6Fe while {c} decreased steadily from U6Mn to U6Ni. There appea_~s to be a correlatio:a between {a} and the ,~uperconducting transition temperature.
Received 19 November 1973 Revised 13 March 1974
.
EXPERIMENTAL EQUATIONS OF STATE FOR THE RARE GAS SOLIDS M.S. Anderson and C.A. Swenson, Ames Laboratory, USAEC and Department of Physics, Iowa State University, Ames, Iowa 50010, U.S.A.
Piston-replacement equations of state (EOS) for the the rare gas solids neon, argon, krypton and xenon have been determined to 20 kbar at temperatures from 4.2 K to the triple point in each case, with V(P, T) relations which are believed to be accurate to roughly 0.1 per cent. The present papaer describes the results for the three heavier solids, argon, krypton and exnon, and indicates consistency between these results and other low pressure experiments at all temperatures.- In particular, the individual isotherms can be represented by P(V) relations which are suggested by the form of the Lennard-Jones potential, the bulk moduli are only slightly temperature dependent at constant volume, and the data for the three solids appear to obey a
Received 28 January 1974 Revised 29 April 1974
.
Physical Sciences, University of California, San Diego, La Jolla, California 92037, U.S.A.
LATTICE PARAMETERS AND SUPERCONDUCTIVITY OF THE COMPOUNDS U6 Mn, U6Fe, U6Co AND U6Ni AND ALLOYS BETWEEN THEM J.J. Engelhardt, Institute for Pure and Applied iii
iv
ABSTRACTS OF PAPERS TO APPEAR IN J. PHYS. CHEM. SOLIDS
reduced EOS both at T = 0 and near the triple point.
Received 13 May 1974
.
Semi-empirical spin-projected open-shell molecular orbital calculations are used to estimate the electron density and electric field gradient at the iron nucleus of the iron-oxygen complexes FeO69 and FeO~ 1° from Fe s7 -doped MgO, FeO~ 7 from BaFet2Oi9, and FeO~ 6 from BaFeSi4Olo. The calculations indicate that the inclusion of covalency effects can provide a consistent interpretation of the M6ssbauer data.
Received 4May 1973 Revised 7 March 1974
5.
of Fe sT. This is in agreement with M6ssbauer measurements, molecular-orbital studies and previous X-ray data.
Received 8 June 1973 Revised 7March 1974
MOLECULAR ORBITAL AND MOSSBAUER STUDY OF IRON OXYGEN COMPOUNDS A. Trautwein, E. Kreber and U. Gonser, Fachbereich Angewandte Physik,'Universit~it des Saarlandes 66 Saarbriicken, West Germany; and F.E. Harris, Department of Physics, University of Utah, Salt Lake City, Utah 84112, U.S.A.
Mt3SSBAUER MEASUREMENTS OF THE BIPYRAMIDAL LATTICE SITE IN BaFe 12O 19 E. Kreber, U. Gonser and A. Trautwein, Fachbereich 12.1, Werkstoffphysik und Werkstofftechnologie, Universit~it des Saarlandes, 66 Saarbriicken, West Germany; and F.E. Harris, Department of Physics, University of Utah, Salt Lake City, Utah 84112, U.S.A.
M6ssbauer measurements have been made on polycrystalline barium ferrite samples. The subspectrum corresponding to the iron ion in the bypyramidal lattice site in the temperature range from T = 4.2 K up to T = 870 K was obtained. Based on the temperature dependence of the unusually large quadrupole splitting due to ferric iron in the bypyramidal position, a model of this lattice site is proposed in which the iron ion is located at one of two equvalent positions of Wyckhoff notation 4e, separated by a potential barrier. At sufficiently high temperature the ion jumps between the two 4e sites with a jump frequency which is greater than the invers of the lifetime of the 14.14 keV state
Vol. 15, No. 7
.
POLYMORPHIC TRANSITIONS IN MOLECULAR CRYSTALS - III. TRANSITIONS EXHIBITING UNUSUAL BEHAVIOR Yu.V. Mnyukh, N.A. Panifilova, N.N. Petropavlov,and N.S. Uchvatova, Institute of Biophysics, Academy of Sciences of the U.S.S.R., Poustchino, Moscow Region, U.S.S.R.
Some polymorphic transitions in molecular crystals, among the few classified earlier as displacive or martensitic on the basis of the existence of a definite orientation relationship between the lattices of the phases and the "instantaneous" transformation rate, have been experimentally investigated. The investigation showed no evidence of a high rate of transition. All occurred through nucleation at the latttice imperfections and continuous growth of the ne phase at a rate depending on AT = Ttr -- To, where Ttr is the actual transition temperature and To is the temperature of the thermodynamic equilibrium of the phases. The interface can be observed; its motion can be controlled to as small an extent as is desirable, or stopped. The "instantaneous transformations" reported in the literature are caused by temperature delays in nucleation in the absence of appropriate lattice defects. In reality these are polymorphic transitions which appear to be instantaneous only when observed through an optical microscope; actually they occur at the rate corresponding to ordinary temperazure dependence. It was established that lamination or cleavage of the crystals in a definite direction is a common feature of the substances exhibiting "atypical" behavior. (Typical behavior has been described in references I and 2). The observed characteristics of the polymorphic transitions (uniform direction of the interfaces, definite orientation relationship of the lattices, small temperature hysteresis of the transition, etc.) can be readily explained in terms of
epitaxial growth of the new phase on the cleavage planes of the original phase. At the same time the ;ole of the proximity of crystal structural parameters is elucidated. Simple model calculations showed that
Pergamon Press.
Printed in Great Britain
Abstracts of Articles to be Published in The Journal of Physics and Chemistry of Solids 'J Phys. Chem. Solids (to be published)' should be cited in references to material quoted from this section prior to the publication of the relevant article. .
CALCULATION OF STATIC CORRELATIONS IN A FLUID OF LINEAR MOLECULES R. Pynn, Brookhaven National Laboratory, Upton, New York 11973, U.S.A.
Recently, both X-ray and neutron diffraction data have been obtained for liquid crystalline materials. While these results contain information about the in stantaneous correlations of molecular postions and oreientations in such fluids, no relevant calculations are available to aid the interpretation of the data. In this paper a formalism which may be used to describe static, molecular correlations in isotropic or anisotropic fluids of linear molecules is developed. To obtain the theory, the direct and total correlation functions of two molecules are expanded as series of spherical harmonics the argument:~ ofwhich describe the molecular orientations. A relation between the expansion coefficients of these series is obtained by making use of the Ornstein-Zernike equation. It is shown that this equation may be solved in the Percus-Yevick or Optimized-Randim-Phase approximations by a variational technique. This technique is used to find the total correlation function in the Percus-Yevick approximation of hard, linear molecules of various length-tobreadth ratios at several fluid densities.
Lattice parameter measurements were made on the tetragonal compounds U6 Mn, U6 Fe, U6 Co and U6Ni and alloys between them. Parameter {a} was found to have a minimum at U6Fe while {c} decreased steadily from U6Mn to U6Ni. There appea_~s to be a correlatio:a between {a} and the ,~uperconducting transition temperature.
Received 19 November 1973 Revised 13 March 1974
.
EXPERIMENTAL EQUATIONS OF STATE FOR THE RARE GAS SOLIDS M.S. Anderson and C.A. Swenson, Ames Laboratory, USAEC and Department of Physics, Iowa State University, Ames, Iowa 50010, U.S.A.
Piston-replacement equations of state (EOS) for the the rare gas solids neon, argon, krypton and xenon have been determined to 20 kbar at temperatures from 4.2 K to the triple point in each case, with V(P, T) relations which are believed to be accurate to roughly 0.1 per cent. The present papaer describes the results for the three heavier solids, argon, krypton and exnon, and indicates consistency between these results and other low pressure experiments at all temperatures.- In particular, the individual isotherms can be represented by P(V) relations which are suggested by the form of the Lennard-Jones potential, the bulk moduli are only slightly temperature dependent at constant volume, and the data for the three solids appear to obey a
Received 28 January 1974 Revised 29 April 1974
.
Physical Sciences, University of California, San Diego, La Jolla, California 92037, U.S.A.
LATTICE PARAMETERS AND SUPERCONDUCTIVITY OF THE COMPOUNDS U6 Mn, U6Fe, U6Co AND U6Ni AND ALLOYS BETWEEN THEM J.J. Engelhardt, Institute for Pure and Applied iii
iv
ABSTRACTS OF PAPERS TO APPEAR IN J. PHYS. CHEM. SOLIDS
reduced EOS both at T = 0 and near the triple point.
Received 13 May 1974
.
Semi-empirical spin-projected open-shell molecular orbital calculations are used to estimate the electron density and electric field gradient at the iron nucleus of the iron-oxygen complexes FeO69 and FeO~ 1° from Fe s7 -doped MgO, FeO~ 7 from BaFet2Oi9, and FeO~ 6 from BaFeSi4Olo. The calculations indicate that the inclusion of covalency effects can provide a consistent interpretation of the M6ssbauer data.
Received 4May 1973 Revised 7 March 1974
5.
of Fe sT. This is in agreement with M6ssbauer measurements, molecular-orbital studies and previous X-ray data.
Received 8 June 1973 Revised 7March 1974
MOLECULAR ORBITAL AND MOSSBAUER STUDY OF IRON OXYGEN COMPOUNDS A. Trautwein, E. Kreber and U. Gonser, Fachbereich Angewandte Physik,'Universit~it des Saarlandes 66 Saarbriicken, West Germany; and F.E. Harris, Department of Physics, University of Utah, Salt Lake City, Utah 84112, U.S.A.
Mt3SSBAUER MEASUREMENTS OF THE BIPYRAMIDAL LATTICE SITE IN BaFe 12O 19 E. Kreber, U. Gonser and A. Trautwein, Fachbereich 12.1, Werkstoffphysik und Werkstofftechnologie, Universit~it des Saarlandes, 66 Saarbriicken, West Germany; and F.E. Harris, Department of Physics, University of Utah, Salt Lake City, Utah 84112, U.S.A.
M6ssbauer measurements have been made on polycrystalline barium ferrite samples. The subspectrum corresponding to the iron ion in the bypyramidal lattice site in the temperature range from T = 4.2 K up to T = 870 K was obtained. Based on the temperature dependence of the unusually large quadrupole splitting due to ferric iron in the bypyramidal position, a model of this lattice site is proposed in which the iron ion is located at one of two equvalent positions of Wyckhoff notation 4e, separated by a potential barrier. At sufficiently high temperature the ion jumps between the two 4e sites with a jump frequency which is greater than the invers of the lifetime of the 14.14 keV state
Vol. 15, No. 7
.
POLYMORPHIC TRANSITIONS IN MOLECULAR CRYSTALS - III. TRANSITIONS EXHIBITING UNUSUAL BEHAVIOR Yu.V. Mnyukh, N.A. Panifilova, N.N. Petropavlov,and N.S. Uchvatova, Institute of Biophysics, Academy of Sciences of the U.S.S.R., Poustchino, Moscow Region, U.S.S.R.
Some polymorphic transitions in molecular crystals, among the few classified earlier as displacive or martensitic on the basis of the existence of a definite orientation relationship between the lattices of the phases and the "instantaneous" transformation rate, have been experimentally investigated. The investigation showed no evidence of a high rate of transition. All occurred through nucleation at the latttice imperfections and continuous growth of the ne phase at a rate depending on AT = Ttr -- To, where Ttr is the actual transition temperature and To is the temperature of the thermodynamic equilibrium of the phases. The interface can be observed; its motion can be controlled to as small an extent as is desirable, or stopped. The "instantaneous transformations" reported in the literature are caused by temperature delays in nucleation in the absence of appropriate lattice defects. In reality these are polymorphic transitions which appear to be instantaneous only when observed through an optical microscope; actually they occur at the rate corresponding to ordinary temperazure dependence. It was established that lamination or cleavage of the crystals in a definite direction is a common feature of the substances exhibiting "atypical" behavior. (Typical behavior has been described in references I and 2). The observed characteristics of the polymorphic transitions (uniform direction of the interfaces, definite orientation relationship of the lattices, small temperature hysteresis of the transition, etc.) can be readily explained in terms of
epitaxial growth of the new phase on the cleavage planes of the original phase. At the same time the ;ole of the proximity of crystal structural parameters is elucidated. Simple model calculations showed that