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On the “anomalous” curvature of the diffusion plot of bromine in AgBr
Author(s) -
Varotsos P.,
Alexopoulos K.
Publication year - 1979
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.2220920237
Subject(s) - curvature , diffusion , vacancy defect , arrhenius plot , gibbs free energy , ion , melting point , chemistry , thermodynamics , bromine , activation energy , materials science , crystallography , physics , organic chemistry , geometry , mathematics
The excessive increase of cation Frenkel defects in AgBr near the melting point should supress the number of anion vacancies through the mass action law. Therefore a downward curvature in the bromine diffusion plot would be expected whereas the experiments show a strong upward curvature. It is shown that this “anomaly” is a consequence of the usual assumption that the Schottky‐Gibbs formation energy g S fdecreases linearly with temperature. Furthermore it is shown that g S fhas to decrease (with temperature) faster than linearly in such a way that the term ( g S f /2) — g F fexhibits an excessive decrease with temperature. Therefore the concentration of anion vacancies shows an excessive increase nea the melting poing and hence the bromine diffusion plot has to show an upward curvature. Another contribution — but a smaller one — to this curvature is the non‐linear decrease of the migration Gibbs energy of a free anion vacancy with the temperature.