Ferroelectric properties of mixed bismuth layer-structured Na0.5Bi8.5Ti7O27 ceramic and SrxNa0.5−x/2Bi8.5−x/2Ti7O27 solid solutions

Mixed bismuth layer-structured Na0.5Bi8.5Ti7O27 ceramic and SrxNa0.5−x/2Bi8.5−x/2Ti7O27 solid solutions were prepared by the solid-state reaction method and the ferroelectric properties of the samples were characterized in this study. As for the Na0.5Bi8.5Ti7O27 ceramic, a single phase (orthorhombic crystal structure with B2cb space group) was produced at the sintering temperature of 1150 °C. The maximum remanent polarization (Pr) of the Na0.5Bi8.5Ti7O27 ceramic was obtained at the sintering temperature of 1150 °C. On the other hand, the coercive field (Ec) of the sample sintered at 1050 °C for 2 h in air was approximately 100 kV/cm, whereas the values of the samples remained unaltered at the sintering temperatures higher than 1075 °C. From these results, the bulk densities of the samples were connected with the Pr values, because it was recognized that the variations in the bulk density of the samples showed the same tendency as that of the Pr values caused by the increase in the sintering temperature. Also, the Sr substitution for Na and Bi is effective in improving the Pr values of SrxNa0.5−x/2Bi8.5−x/2Ti7O27 solid solutions. The Curie temperatures (Tc) of the solid solutions decreased slightly, depending on the composition x, and then the variations in the Tc values are related to the structural distortion caused by the Sr substitution for Na and Bi.