Raman-spectroscopic investigations on the crystal structure and phonon modes of Ba(RE1/2Ta1/2)O3 microwave ceramics

Complex Ba(RE1/2Ta1/2)O3 [RE = rare earth] ceramics have been prepared by solid state ceramic route and their microwave dielectric responses were measured in the GHz range. In general, the resonators showed high dielectric constants, high quality factors and good thermal stability of the resonance frequency. However, these properties are found to depend nonlinearly on the tolerance factor, indicating structural modifications with chemical substitution. The structure of Ba(RE1/2B″1/2)O3Ba(RE1/2B″1/2)O3 [B″ = Nb, Ta] compounds has been a matter of debate for many years, because X-ray structural data and vibrational-spectroscopic ones are controversial. In order to contribute to this debate and discuss the relationship between structure and dielectric properties, a systematic investigation of the phonon modes of several ceramics with varying RE ion was carried out. In this paper, the results of the Raman analysis and crystal structure of Ba(RE1/2Ta1/2)O3 samples are presented, and correlated with the observed microwave dielectric properties.