E.N.Kovalenko, V.K.Miloslavsky, O.N.Yunakova
Received April 20, 1998
Electron absorption spectrum of the superionic conductor
CsyRb1-yCu4Cl3I2 (y
= 0.5; 1) has been studied. The observed narrow absorption bands in
the 3.5-6 eV interval have been shown to be related to excitons
localized in Cu(II)Hal and Cu(III)Hal sublattices of the above
compounds. A larger forbidden gap as compared to Eg in
CuI and CuCl is found to be defined by smaller number of Cu
ions in the second coordination sphere of the compound crystal lattice. Some
specific features associated with gamma beta and beta alpha phase transitions
have been revealed in the temperature dependence of the spectral position
and half-width of the low-frequency excitonic band. The temperature-related
broadening of the excitonic band in the dielectric gamma-phase has
been shown to be defined by exciton-phonon interaction and generation
of Frenkel defects with low activation energy.