Structural, microstructural and dielectric properties of Ba1−xLaxTi(1−x∕4)O3 prepared by sol gel method

Abstract

Detailed structural and dielectric properties of Lanthanum-doped barium titanate [Formula: see text]Lax[Formula: see text]O3 ceramic powders BLTx (where [Formula: see text]; 0.10; 0.20; 0.30 and 0.40)/BT, BLT10, BLT20, BLT30 and BLT40, synthesized by the sol gel process, calcined at 900∘C for 3[Formula: see text]h and sintered at 1250∘C for 6[Formula: see text]h, have been investigated. The phase formation and crystal structure of the samples were checked by X-ray diffraction (XRD) and Raman spectroscopy. The samples crystallize in the pure perovskite structure that transforms from tetragonal to pseudocubic under doping with La; results that have been confirmed by Rietveld Refinement technique. The estimated average crystallite size of the samples was about 23[Formula: see text]nm. Dielectric parameters (dielectric permittivity and losses) were determined in the temperature range room temperature (RT) — 280∘C and in the frequency range 500[Formula: see text]Hz–2[Formula: see text]MHz. La doping gives rise to a strong decrease of the ferro-to-paraelectric transition temperature, and the frequency dependence of the permittivity shows that the samples with [Formula: see text] and [Formula: see text] reach their resonance frequency. The frequency dependence of impedance and electric modulus properties were studied over a wide frequency range from 1[Formula: see text]kHz to 2[Formula: see text]MHz at various temperatures to confirm the contributions from grains and grain-boundaries. The complex impedance analysis data have been presented in the Nyquist plot which is used to identify the corresponding equivalent circuit and fundamental circuit parameters; it was found that the grain boundaries resistance is dominant at room temperature. The frequency dependence of the parameters permittivity, losses and AC conductivity reveals that the relaxation process is of the Maxwell–Wagner type of interfacial polarization.