Manifestation of Nb dynamics in Raman, microwave, and infrared spectra of the AgTaO3-AgNbO3 mixed system

The results of an extended investigation of the monoclinic (M(2))-monoclinic (M(3)) phase transition in the mixed AgNbxTa1-xO3 system (ATN) with high concentration of niobium (Nb) are presented in this paper. ATN's dielectric properties make it promising for microwave technologies and stimulate investigations of the niobium contribution to the dielectric response. The strong quasielastic diffusion and a significant softening of a low-frequency phonon mode, both observed by light scattering measurements on single crystals, are analyzed in the vicinity of this nonferroelectric phase transition. The quasielastic diffusion is confirmed to be caused by the relaxation mode related with Nb dynamics, the parameters of which are determined. The origin of the relaxational mode and possible mechanisms of the phase transition are discussed in connection with the dielectric dispersion and the infrared reflectivity. (C) 1996 American Institute of Physics.