Nature of polar state in 0.67BiFeO3–0.33BaTiO3

This study was conducted to further understand the nature of the polar state in 0.67BiFeO3–0.33BaTiO3 (0.67BF–0.33BT). A typical relaxor-type dielectric anomaly was observed (Tf = ~627 K, TB = ~820 K). The remnant polarization (Pr), maximum value of electrostrain (Sm) and magnitude strain at Ec in the bipolar mode (Sneg) increase clearly during heating (Pr, ~40 mC/cm2; Sm, 0.191 % under 40 kV/cm at 453 K). The first-cycle bipolar electrostrain loops indicate that the minimum strain on the negative side of the bipolar strain curves is negative. The slopes of the relative permittivity versus log frequency plots in unpoled (–21) and poled (–23) specimens are similar. The transition between the ergodic relaxor state and ferroelectric-like state does not involve a clear dielectric anomaly even in the poled specimen. Analyses based on the Rietveld refinement of XRD patterns, bright-field images and selected-area electron diffractions (SAED) demonstrate that the formation of the long-range ferroelectric domains is difficult under the poling field.