Ferroelectric transitions and relaxor behavior in Ba4Sm2(Ti1-xZrx)4Ta6O30 tungsten bronze ceramics

Abstract

Ferroelectric transitions of Ba4Sm2(Ti1-xZrx)4Ta6O30 (x = 0, 0.1, 0.3, 0.5, 0.7, 1) tetragonal tungsten bronze ceramic samples were investigated systematically with the crystal structure, dielectric properties, and Raman vibrations. For x = 0 and x = 0.1, the tetragonal tungsten bronze structure with space group P4bm was determined. A first order ferroelectric transition with a sharp, frequency independent dielectric permittivity maximum was indicated for x = 0 and x = 0.1, while a strong low temperature dielectric relaxation was also determined for x = 0.1. For x = 0.3, 0.5, 0.7, and 1, a tetragonal tungsten bronze structure with space group P4/mbm was determined. Relaxor ferroelectric behavior with strong frequency dispersion becomes dominating for compositions of x ≥ 0.3. Compositions of x = 0 and 0.1 exhibited nonlinear polarization electric-field (P-E) hysteresis loops at room temperature, while other compositions only exhibited linear curves. Raman spectra presented distinct vibration modes for x = 0 and x = 1, and the intensity of some modes showed sudden rising or falling with increasing x from x = 0 to x = 0.1. The abrupt change from normal ferroelectric to relaxor behavior at x = 0.1 in this system is quite different from the gradual change in the Ba4Sm2Zr4(NbxTa1-x)6O30 system, and both the different electron configuration and ion size mismatch between Zr and Ti should play important roles in the crossover here.