Pseudolocalized vibrations of M2+-vacancy complex and thermal conductivity of alkali halides

Abstract

Frequencies of pseudolocalized vibrational modes of alkali-halide lattices containing impurity complexes have been determined as a function of defect mass. In particular, the vibrations of complexes of divalent metal ions and positive-ion vacancies are determined in the acoustic frequency range. It is found that the vibrational frequency of certain of these modes is essentially independent of defect mass for all physically realizable M2+ ions of mass greater than the mass of the lattice ions. This result is shown to be an inherent property of strongly damped pseudolocalized modes. It is suggested that recent thermal-conductivity measurements by Schwartz and Walker, which indicate an insensitivity to defect mass, can be accounted for in this way. © 1966 The American Physical Society.