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))-mono clinic (M(3)) phase transition in the mixed AgNbxTa1-xO3 system (ATN) with high concentration of niobium (Nb) are presented in this paper. A TN's dielectric properties make it promising for microwave technologie s and stimulate investigations of the niobium contribution to the diel ectric response. The strong quasielastic diffusion and a significant s oftening of a low-frequency phonon mode, both observed by light scatte ring 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 relaxation al mode and possible mechanisms of the phase transition are discussed in connection with the dielectric dispersion and the infrared reflecti vity. (C) 1996 American Institute of Physics.