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Shell Model Calculation of Microscopic Grüneisen Parameters for Rocksalt‐Type Materials
Author(s) -
Barsch G. R.,
Achar B. N. N.
Publication year - 1969
Publication title -
physica status solidi (b)
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.51
H-Index - 109
eISSN - 1521-3951
pISSN - 0370-1972
DOI - 10.1002/pssb.19690350239
Subject(s) - brillouin zone , polarizability , halide , dielectric , shell (structure) , alkali metal , condensed matter physics , transverse plane , chemistry , thermodynamics , k nearest neighbors algorithm , materials science , physics , molecule , composite material , inorganic chemistry , optoelectronics , organic chemistry , structural engineering , engineering , artificial intelligence , computer science
The microscopic Grüneisen parameters have been calculated for the two optical modes in the Brillouin zone center and for the four modes at the Brillouin zone edge in [100] for nine alkali halides and MgO. A six parameter shell model which takes into account anion polarizability, non‐central first nearest neighbor interaction and central forces between second neighbors has been used, and the pressure dependence of the frequencies is obtained from the assumption of a pressure independent core‐shell force constant. The parameters of the model are determined from experimental data of the elastic constants, from the high and low frequency dielectric constants, from the pressure derivatives of these quantities, and from the zero pressure value of the transverse optical frequency in the zone center. Good to fair agreement with the available experimental data is found. It is suggested that the discrepancies are mainly due to the limited experimental accuracy. The results confirm that the B1 → B2 phase transformation in alkali halides is not due to an instability of the TA mode at the [100] zone boundary.