Lanthanum distribution and dielectric properties of intergrowth Bi5−xLaxTiNbWO15 ferroelectrics

Abstract

Bi 5 − x La x Ti Nb W O 15 (x=0–1.50) ceramics prepared by conventional solid-state reaction were studied using x-ray diffraction (XRD), dielectric spectroscopy and Raman scattering techniques. The XRD analysis implied that single-phase intergrowth bismuth layered perovskite structure was obtained for all the samples and when x=0.75, the Bi3+ in (Bi2O2)2+ layer begins to be substituted by La3+. The dielectric spectra showed that, when Bi3+ in (Bi2O2)2+ is substituted, the Curie temperature becomes diffusive and the dielectric permittivity at room temperature is increased in a wide frequency range. Especially when x=1.50, the dielectric permittivity reaches its maximum of 270, nearly two times larger than that of the La3+ undoped sample. The Raman scattering experiments evidenced further that Bi3+ in (Bi2O2)2+ is substituted when x⩾0.75 and revealed the orthorhombic distortion of the octahedra is responsible for the increase of the dielectric permittivity at x⩾1.25.