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Study of molecular rotations in solids and liquids by the inelastic scattering of cold neutrons
Solid State Communications Vol. 2, pp. vi-x, 1964. Pergamon Press, Inc. Printed in the United States.
Abstracts of Articles to be Published in the Journal of the 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.
1.
AN INVESTIGATION INTO THE NUMBER
2.
OF NEIGHBOURING ATOMS TO BE INCLUDED iN CALCULATIONS OF THE SLOW NEUTRON SCATTERING CROSS SECTION OF DEFECTS IN SOL]DS D. G. Martin (Metallurgy Division, Atomic Energy Research Establishment, Harwell, Berkshire, England).
A MECHANISM OF AN ADDITIONAL DAMPING OF THE FERROMAGNETIC RESONANCE NEAR THE CURIE POINT IN DILUTE FERROMAGNETIC ALLOYS
Janusz Morkowski (Ferromagnetics Laboratory, Institute of Physics of the Polish Academy of Sciences, Poznan, Poland).
The calculated slow neutron scattering cross section of defects in solids possesses a term due to the core of the defect and another due to the relaxation of neighbouring atoms. In the present study an attempt is made to investigate how many of these relaxed atoms must be included in the calculations in order that the final result may be independent of the number of atoms considered.
A damping of the ferromagnetic resonance in dilute ferromagnetic alloys due to fluctuations in the local concentration is discussed. A highly simplified method for calculating this additional damping is adopted: the alloy is considered as being divided into small regions, with concentration constant inside the regions, but varying slightly from region to region, and the contribution to the resonance line-width determined by scattering of magnon-like excitations on boundaries of these regions is calculated. The mechanism proposed qualitatively accounts for the observed maximum of the resonance line-width at the Curie temperature.
The differential and also the total cross sections of an interstitial in a~cubic primitive lattice have been calculated for various numbers of neighboring atoms, assuming an elastic continuum approximation to describe these relaxations. A number of values of the relaxations were used in these calculations, some of which are believed to correspond to relaxations around interstitials and vacancies in metals, and therefore to be directly applicable in these cases.
(Received 9 March 1964) 3.
It is found that in all cases the general shape of the curve obtained for a very large number of atoms appears when about 30 atoms are considered. However, more atoms are required to obtain the more detailed shape; for the transmission cross sections about 60 atoms are needed, while for the differential cross sections as many as 300, depending on the amount of relaxation, may be necessary.
STUDY OF MOLECULAR ROTATIONS IN SOLIDS AND LIQUIDS BY THE INELASTIC SCATTERING OF COLD NEUTRONS* J. A. ianik~, J. M. Janikil, J. Mellor and H. Palevsky(Brookhaven National Laboratory, Upton, New York, U.S.A.).
____________
Work supported by the U. S. Atomic Energy Commission. § On leave from Institute of Nuclear Physics, Krakow, Poland. IE On leave from Laboratory of Physical Chemistry and Electrochemistry, Jagiello nian University, Krakow, Poland.
*
-
(Received 24 February 1964) vi
Vol. 2, No. 6
ABSTRACTS OF PAPERS TO APPEAR IN J. PHYS. CH~M.SOLIDS
The spectra of scattered neutrons from molecular crystals and liquids containing rotating molecular groups have been obtained. The materials studied were liquid CH.4, CH3I and dimethylacetylene; NH4C1O4, NH4PF6, H3OC1O4, and dimethoxylazoxybenzeñe. The observed spectrum from liquid CH4 was used as a comparison standard for freely rotating NH4~ions and the CH3I spectrum was used for comparison to H3O~and CR3 groups possessing single axis rotational freedom. All measured spectra are compared to those calculated from the Krieger- Nelkin, Sach-Teller theory. (Received 12 March 1964) 4.
ON THE SOLID SOLUTIONS OF BISMUTH TELLURIDE AND BISMUTH SELENIDE Sonmath Misra and M. B. Bever (Department of Metallurgy, Massachusetts Institute of Technology, Cambridge, Mass., U. S. A.).
The heats of formation at 0°Cof various solid solutions in the system Bi2Te3_X Sex(O< x <3) have been measured by liquid metal solution calorimetry with bismuth as solvent, Slowly cooled and quenched alloys near the cornposition Bi2Te2Se had different heats of formation; the difference is interpreted as the energy of an order-disorder transition. The heats of formation of the slowly cooled alloys based on the binary compounds and the energy of ordering were maxima at the composition Bi2Te2Se. The thermodynamic results are interpreted in terms of the nearest-neighbor bond theory. The postulated order-disorder transition was investigated by X-ray diffraction with briquettes of Bi2Te2Se. The powder patterns of slowly cooled specimens showed no superstructure reflections in agreement with a structure factor analysis and symmetry considerations, but the ratios of the integrated intensities of corresponding reflections from the slowly cooled and quenched specimens confirmed the occurrences of ordering, (Received 13 March 1964) 5.
A COMPARATWE STUDY OF THE ELECTRICAL CONDUCTIVITY OF SOLE) AMMONIUM CHLORIDE AND OTHER AMMONIUM SALTS Thelma M. Herrington and L. A. K. Staveley (The Inorganic Chemistry Labora-
Vii
tory, Oxford University, Oxford, England). Measurements have been made of the conductivity of single crystals of pure and doped arnmonium chlor~ide,and of single crystals of caesium cl4oride and potassium chloride. Less detaile~1studies have been made of ammonium and pota~siurnbromides and iodides, tetramethylan~moniuxniodide, ammonium and potassium star~nichlorides,and ammonium and rubidiu~nfluophosphates. The conductivity of ammoni~zmchloride is significantly greater than thai of a comparable alkali chloride, and reasons ~.re given for believing that a conductivity mec~ianismoperates in the axnmonium salt which iS not possible for the alkali metal salts. It i$ suggested that this mechanism is a three-~tageprocess, involving (1) a proton switch fro4~an ammonium ion to a chloride ion adjacent to a vacancy, which produces an ammonia mol~culeand a hydrogen chloride molecule, (2) ~hemigration of one of these molecules into th~vacancy, (3) a reverse proton switch to refornj a pair of ions. Part of the evidence for this m$hanism comes from a consideration of the the~modynamicproperties of ammonium chloride, which are consistent with the view that even ~t room temperature and below the formatior~of molecules within the lattice takes place to a significant extent. (Received 26 March 1964) 6.
MECHANICAL R~LAXATIONASSOCIATED WITH PARED P(~INTDEFECTS N CUBIC LATTICES OF O~POINT GROUP SYMMETRY Roger Chang (Nor~thAmerican Aviation Science Center, Canoga Park, California, U.S.A.).
The mech~nicalrelaxation modes associated with paired j~ointdefects in cubic lattices of °hpoint groi~psymmetry are denved from group theory 4onsiderations. The following paired point d4fects are considered, s-a, i-i, v-v, s-i, and 5-v, where a is a substitutional impurity, us an interstitial, and v is a vacancy. Thç following crystal lattices are studied, fade-centered cubic, bodycentered cubic, dlamo$ cubic, NaCl, and CaF2. Relaxation freqt~enciesfor each of the mechanical relaxation n~odesare evaluated and tabulated for the paired ~Iefectin nearest neighbor and higher order nearest neighbor (second, third, etc.) coi~flgurations.
Abstracts of Articles to be Published in the Journal of the 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.
1.
AN INVESTIGATION INTO THE NUMBER
2.
OF NEIGHBOURING ATOMS TO BE INCLUDED iN CALCULATIONS OF THE SLOW NEUTRON SCATTERING CROSS SECTION OF DEFECTS IN SOL]DS D. G. Martin (Metallurgy Division, Atomic Energy Research Establishment, Harwell, Berkshire, England).
A MECHANISM OF AN ADDITIONAL DAMPING OF THE FERROMAGNETIC RESONANCE NEAR THE CURIE POINT IN DILUTE FERROMAGNETIC ALLOYS
Janusz Morkowski (Ferromagnetics Laboratory, Institute of Physics of the Polish Academy of Sciences, Poznan, Poland).
The calculated slow neutron scattering cross section of defects in solids possesses a term due to the core of the defect and another due to the relaxation of neighbouring atoms. In the present study an attempt is made to investigate how many of these relaxed atoms must be included in the calculations in order that the final result may be independent of the number of atoms considered.
A damping of the ferromagnetic resonance in dilute ferromagnetic alloys due to fluctuations in the local concentration is discussed. A highly simplified method for calculating this additional damping is adopted: the alloy is considered as being divided into small regions, with concentration constant inside the regions, but varying slightly from region to region, and the contribution to the resonance line-width determined by scattering of magnon-like excitations on boundaries of these regions is calculated. The mechanism proposed qualitatively accounts for the observed maximum of the resonance line-width at the Curie temperature.
The differential and also the total cross sections of an interstitial in a~cubic primitive lattice have been calculated for various numbers of neighboring atoms, assuming an elastic continuum approximation to describe these relaxations. A number of values of the relaxations were used in these calculations, some of which are believed to correspond to relaxations around interstitials and vacancies in metals, and therefore to be directly applicable in these cases.
(Received 9 March 1964) 3.
It is found that in all cases the general shape of the curve obtained for a very large number of atoms appears when about 30 atoms are considered. However, more atoms are required to obtain the more detailed shape; for the transmission cross sections about 60 atoms are needed, while for the differential cross sections as many as 300, depending on the amount of relaxation, may be necessary.
STUDY OF MOLECULAR ROTATIONS IN SOLIDS AND LIQUIDS BY THE INELASTIC SCATTERING OF COLD NEUTRONS* J. A. ianik~, J. M. Janikil, J. Mellor and H. Palevsky(Brookhaven National Laboratory, Upton, New York, U.S.A.).
____________
Work supported by the U. S. Atomic Energy Commission. § On leave from Institute of Nuclear Physics, Krakow, Poland. IE On leave from Laboratory of Physical Chemistry and Electrochemistry, Jagiello nian University, Krakow, Poland.
*
-
(Received 24 February 1964) vi
Vol. 2, No. 6
ABSTRACTS OF PAPERS TO APPEAR IN J. PHYS. CH~M.SOLIDS
The spectra of scattered neutrons from molecular crystals and liquids containing rotating molecular groups have been obtained. The materials studied were liquid CH.4, CH3I and dimethylacetylene; NH4C1O4, NH4PF6, H3OC1O4, and dimethoxylazoxybenzeñe. The observed spectrum from liquid CH4 was used as a comparison standard for freely rotating NH4~ions and the CH3I spectrum was used for comparison to H3O~and CR3 groups possessing single axis rotational freedom. All measured spectra are compared to those calculated from the Krieger- Nelkin, Sach-Teller theory. (Received 12 March 1964) 4.
ON THE SOLID SOLUTIONS OF BISMUTH TELLURIDE AND BISMUTH SELENIDE Sonmath Misra and M. B. Bever (Department of Metallurgy, Massachusetts Institute of Technology, Cambridge, Mass., U. S. A.).
The heats of formation at 0°Cof various solid solutions in the system Bi2Te3_X Sex(O< x <3) have been measured by liquid metal solution calorimetry with bismuth as solvent, Slowly cooled and quenched alloys near the cornposition Bi2Te2Se had different heats of formation; the difference is interpreted as the energy of an order-disorder transition. The heats of formation of the slowly cooled alloys based on the binary compounds and the energy of ordering were maxima at the composition Bi2Te2Se. The thermodynamic results are interpreted in terms of the nearest-neighbor bond theory. The postulated order-disorder transition was investigated by X-ray diffraction with briquettes of Bi2Te2Se. The powder patterns of slowly cooled specimens showed no superstructure reflections in agreement with a structure factor analysis and symmetry considerations, but the ratios of the integrated intensities of corresponding reflections from the slowly cooled and quenched specimens confirmed the occurrences of ordering, (Received 13 March 1964) 5.
A COMPARATWE STUDY OF THE ELECTRICAL CONDUCTIVITY OF SOLE) AMMONIUM CHLORIDE AND OTHER AMMONIUM SALTS Thelma M. Herrington and L. A. K. Staveley (The Inorganic Chemistry Labora-
Vii
tory, Oxford University, Oxford, England). Measurements have been made of the conductivity of single crystals of pure and doped arnmonium chlor~ide,and of single crystals of caesium cl4oride and potassium chloride. Less detaile~1studies have been made of ammonium and pota~siurnbromides and iodides, tetramethylan~moniuxniodide, ammonium and potassium star~nichlorides,and ammonium and rubidiu~nfluophosphates. The conductivity of ammoni~zmchloride is significantly greater than thai of a comparable alkali chloride, and reasons ~.re given for believing that a conductivity mec~ianismoperates in the axnmonium salt which iS not possible for the alkali metal salts. It i$ suggested that this mechanism is a three-~tageprocess, involving (1) a proton switch fro4~an ammonium ion to a chloride ion adjacent to a vacancy, which produces an ammonia mol~culeand a hydrogen chloride molecule, (2) ~hemigration of one of these molecules into th~vacancy, (3) a reverse proton switch to refornj a pair of ions. Part of the evidence for this m$hanism comes from a consideration of the the~modynamicproperties of ammonium chloride, which are consistent with the view that even ~t room temperature and below the formatior~of molecules within the lattice takes place to a significant extent. (Received 26 March 1964) 6.
MECHANICAL R~LAXATIONASSOCIATED WITH PARED P(~INTDEFECTS N CUBIC LATTICES OF O~POINT GROUP SYMMETRY Roger Chang (Nor~thAmerican Aviation Science Center, Canoga Park, California, U.S.A.).
The mech~nicalrelaxation modes associated with paired j~ointdefects in cubic lattices of °hpoint groi~psymmetry are denved from group theory 4onsiderations. The following paired point d4fects are considered, s-a, i-i, v-v, s-i, and 5-v, where a is a substitutional impurity, us an interstitial, and v is a vacancy. Thç following crystal lattices are studied, fade-centered cubic, bodycentered cubic, dlamo$ cubic, NaCl, and CaF2. Relaxation freqt~enciesfor each of the mechanical relaxation n~odesare evaluated and tabulated for the paired ~Iefectin nearest neighbor and higher order nearest neighbor (second, third, etc.) coi~flgurations.