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Elastic constants of some NaCl type alkali halides
Author(s) -
Lincoln R. C.,
Koliwad K. M.,
Ghate P. B.
Publication year - 1966
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.19660180127
Subject(s) - van der waals force , halide , alkali metal , chemistry , thermodynamics , cauchy distribution , lattice constant , ionic bonding , van der waals radius , ion , physics , quantum mechanics , molecule , mathematical analysis , inorganic chemistry , mathematics , organic chemistry , diffraction
Second and third order elastic constants of NaCl, NaBr, KF, KCl, KBr, and RbBr have been calculated using the Born model of ionic solids. Short range repulsive interactions have been included up to second nearest neighbors using an expression of the form A exp (‐ r/b ) where b is the repulsive parameter. A distinction is made between the like and unlike ion interactions. Van der Waals terms are also included. When the room temperature lattice parameter is used, the elastic constants satisfy the Cauchy relations. Experimental data show that many of the alkali halides fail to satisfy the Cauchy relations. This aspect is examined by using the quasi‐harmonic approximation as developed by Leibfried and his associates. Linear temperature coefficients of the elastic constants are also calculated in the high temperature limit. In order to assess the contributions of the van der Waals terms, elastic constants are also calculated by dropping the van der Waals terms in the expressions for the elastic constants. Calculated values of the elastic constants are compared with the available experimental data.