Dielectric relaxation and ultrasonic attenuation of Sr4La2Ti4Nb6O30 tungsten bronze ceramics

Dielectric relaxation and ultrasonic attenuation spectra of Sr4La2Ti4Nb6O30 tungsten bronze ceramics were investigated over a broad temperature range. A broad permittivity peak with strong frequency dispersion was observed around 200 K, which followed well the Vogel-Fulcher relationship, and is attributed to relaxor ferroelectric behavior with spin glass nature. The ultrasonic investigation provided further evidence on this thermally activated process, and both the dielectric relaxation and the freezing of polar clusters were clearly observed in the ultrasonic velocity shift and ultrasonic attenuation spectra. (C) 2007 American Institute of Physics.