Polarization and leakage current properties of high quality bismuth sodium titanate single crystals and polycrystalline ceramics

Abstract

Investigation to obtain the high quality (Bi,Na)TiO3 (BNT) single crystals and polycrystalline ceramics and to reveal the polarization mechanism of rhombohedral BNT were performed. BNTsingle crystals were grown by the high-Po2 flux method and their polarization and piezoelectric properties were investigated along [100]c, [110]c and [111]c, where "c" denote cubic notation used. Strain measurements of rhombohedral BNT crystals suggest that the polarization reversal along [111]c is achieved by non-180° spontaneous polarization (Ps) rotation. The values of remanent polarization (Pr) obtained along these three directions provided a value of Ps of 55-60 μC/cm2 at 25°C for rhombohedral BNT. The aerosol deposition (AD) method with use of heat treatment supplied fully dense self-supported BNT polycrystalline films detached from substrates. The annealed self-supported BNT polycrystalline films indicated a superior low leakage current density (J) of approximately 10-8A/cm2 at 150 kV/cm, which was lower than that of sintered bulks. Also well-saturated hysteresis loops with a large Pr of 40μ/cm2 were confirmed, which was near value of maxmum Pr (4852 μ/cm2) estimated from the Ps of high quality BNT single crystals. The high-Po2 flux method and use of the AD method have been demonstrated to be effective for the obtaining high quality BNT single crystals and polycrystalline ceramics.