Octahedral distortion due to oxygen vacancy reduction in La3+ modified BNT-BTO solid solutions near morphotropic phase boundary

Abstract

Currently, there is great interest in perovskite compounds (ABO3) due to their various applications as well as fundamental research that has taken place. However, oxygen vacancy in the perovskite is a very important parameter to control its physical properties. Hence, the polycrystalline ((Bi1−xLax)0.5Na0.5)0.94Ba0.06TiO3 (BLNBTO) with x = 0.00, 0.02, 0.04, 0.06, 0.08 and 0.10 solid solutions was synthesized via a conventional solid-state reaction process to study the oxygen vacancies and its influence on dielectric property. Structural phase formation of the solid solutions has been studied by x-ray diffraction (XRD) technique. Rietveld analysis of the XRD pattern reveals the decrease of octahedral distortion with the increase of La3+ concentration in BNBTO (x = 0.00) solid solution. The reduction of octahedral distortion in the solid solutions was also supported by Raman spectra analysis. The presence of oxygen vacancy has been observed from the analysis of x-ray photoelectron spectroscopy spectra corresponding to the different elements of the solid solutions. Furthermore, the distinct peak at high-temperature range (250 °C–350 °C) in impedance plots is ascribed to the presence of oxygen vacancy related dielectric relaxation phenomenon. The activation energy increases from 0.99 to 1.53 eV with the increase of La3+ mole fraction in BNBTO solid solution, which is obtained from impedance data using the Arrhenius equation. The increase of activation energy has been correlated with the reduction of oxygen vacancy.