Improvement of dielectric and ferroelectric properties in bismuth sodium titanate based relaxors through Bi non-stoichiometry

Abstract

Influence of Bi-non-stoichiometry is studied on the dielectric and ferroelectric properties of 0.72Bi0.5+xNa0.5TiO3-0.22SrTi0.875Nb0.1O3-0.06BaTiO3 (BNBSNT) lead-free relaxors. All compositions exhibit high symmetry phase structure with dynamic polar nano regions. An enhanced degree of disorder is revealed and more polarization can be induced in Bi deficiency, which is related to the difficulty in the formation of a neutral defect complex between cations and oxygen vacancies. The relaxation of the two anomalies on temperature dependent permittivity is greatly affected by Bi non-stoichiometry especially that around the first dielectric anomaly temperature that can be deconvoluted by phenomenological models. The materials display a remarkable stability of high ε′ (∼3000) over a wide temperature range (>320 °C) with considerably low loss (≤0.003) in the ergodic relaxor state. Significant improvement on energy storage properties as well as electrostrictive strain (Wrec = 0.86 J/cm3, η = 83%; S = 0.235%, strain hysteresis of 7.34% at a low electric field of 80 kV/cm for bipolar P-E loops) is achieved due to chemical disorder and strong random field caused by Bi3+ deficiency.