Crystal Structure and Ferroelectric Behaviors of Ba5SmTi3Ta7O30 and Ba4Sm2Ti4Ta6O30 Tungsten Bronze Ceramics.

The crystal structure and dielectric characteristics were evaluated for Ba4Sm2Ti4Ta6O30 and Ba5SmTi3Ta7O30 ceramics. The X-ray diffraction patterns confirmed the tetragonal tungsten bronze structure with space group P4 bm. A normal ferroelectric phase transition was observed at 332 K for the former, while the typical relaxor ferroelectric behavior with a spin glass nature was determined for the latter, where a broad permittivity peak with a strong frequency dispersion was observed around 150 K, which followed the Vogel–Fulcher relationship well. These different dielectric behaviors originated from the different crystal structures governed by the occupancy configuration of cations at A1 and A2 sites. [ABSTRACT FROM AUTHOR]