Effect of Heat Treatment for Crystal Structure and Ferroelectric Properties of Sr_1-xBi_2+xTa₂O_9-δ (x=0, 0.2)

Abstract

Ferroelectric material of SrBi₂Ta₂O₉ consists of (Bi₂O₂)²⁺ layer and peseudoperovskite block, (SrTa₂O₇)^2-. The crystal structure, defect, oxygen nonstoichiometory, and ferroelectric properties change by heat treatment. In this study, we investigated the relation between crystal structure, physical properties and ferroelectric properties by various heat treatment of Sr_1-xBi_2+xTa₂O_9-δ (x=0, 0.2). From the results, the remanent polarization (P_r) and coercive field (E_c) increase by heat treatment at x=0. On the other hand, P_r is almost constant and E_c decreased with heat treatment of oxidation direction at x=0.2. The dielectric constant (ε_s) increase with heat treatment of oxidation direction and Curie temperature (T_c) decrease by heat treatment at x=0. On the other hand, ε_s decreased with heat treatment of oxidation direction and T_c decrease by heat treatment at x=0.2. From the results of structural analysis by the Rietveld method using the neutron powder diffraction data, we concluded that the distortion of (Bi₂O₂)²⁺ layer and TaO₄ plane, and tilting angle of TaO₆ octahedra on a-c plane affect E_c. The tilting angle of TaO₆ octahedra on b-c plane affects T_c.