Creation and Recombination of Frenkel Defects in AgBr

Abstract

Abstract Complete ionic conductivity spectra as well as quasielastic and inelastic neutron scattering spectra have been taken of solid silver bromide at various temperatures. High-amplitude vibrational move­ments, essentially of the silver ions, contribute to both kinds of spectra. In particular, a conductivity maximum, located at about 500 GHz, reflects oscillations of individual silver ions along directions. -The microwave and millimetre-wave conductivities are dominated by a thermally activated Debye-type relaxation process. The effect is consistently explained by the frequent hopping of silver ions from regular octahedral lattice sites into tetrahedral interstitial sites and back again, i.e., by the frequent creation and recombination of Frenkel pairs. -The effect is also responsible for the existence of thermally activated quasielastic components in the neutron scattering spectra. The width of the coherent quasielastic scattering shows that the forward-backward hopping of a silver ion is accompanied by fast correlated movements of ions in its immediate neighbourhood.