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A simple model for the calculation of heat of formation for high‐concentration substitutional defects in alkali halide crystals
Author(s) -
Paul S.,
Sengupta S.
Publication year - 1977
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.2220830233
Subject(s) - alkali metal , halide , polarizability , ion , thermodynamics , substitution (logic) , chemistry , standard enthalpy of formation , crystal (programming language) , lattice (music) , solid solution , simple (philosophy) , inorganic chemistry , physics , organic chemistry , philosophy , epistemology , molecule , computer science , acoustics , programming language
An analytical expression for the heat of formation of substitutional defects in high concentration is developed on the basis of a simple model. In a previous paper the authors developed a simple formula for the heat of formation of substitutional defects with low concentration which convenient formula is utilized for calculating the heat of formation when the defect concentration is high. In this model the defect concentration is developed stepwise and in every step the defect crystal is considered as equivalent to a perfect crystal with a modified lattice parameter determined by the Vegard's law. Values for the heat of formation over the entire composition range are calculated and compared to experimental values for eight different solid solutions. For negative ion substitution, the values are in good agreement with the experimental results. The reason for the slightly larger discrepancy for the positive ion substitution may be ascribed to the effect of polarizability of the negative ions.