Effect of Phase Transitions on the Exciton Absorption Spectrum of Rb_(x)K_(1-x)Ag_(4)I_(5) Superionic Conductors

摘要

The absorption spectrum of thin films of solid solutions of Rb_(x)K_(1-x)Ag_(4)I_(5) superionic conductors is investigated in the energy range 3-6 eV at temperatures from 90 to 290 K upon heating and cooling. It is established that the temperature dependences of the spectral position E_(m) and the half-width GAMMA of the long-wavelength exciton band are determined by the exciton-phonon interaction and the generation of Frenkel defects at phase transitions to the superionic state. Fluctuations of the composition of solid solutions do not affect the behavior of the dependences E_(m)(x) and GAMMA(x) at 90 K, which is indicative of the localization of excitons in the AgI sublattice of these compounds. A difference in the dependences T_(c1)(x) and T_(c2)(x) (the gamma -> beta and beta -> alpha phase transitions, respectively) is revealed: the curve T_(c1)(x) has a minimum at x approx= 0.5, whereas the curve T_(c2)(x) shows a weak maximum.