Ferroelectric and dielectric properties of bismuth-layered structural Sr2Bi4−xLnxTi5O18 (Ln=La, Nd, Sm and Dy) ceramics

La, Nd, Sm, and Dy-doped Sr2Bi4Ti5O18 (SBTi) ceramic samples have been prepared by the solid-state reaction method. The X-ray diffraction reveals that all of the ceramic samples are single phase compounds. Their remnant polarization (2Pr) increases at first, and then decreases with the increase of doping content. When doping content is 0.01, Sm and Dy-doped SBTi samples exhibit the maximum 2Pr of 18.2 and 20.1 μC/cm2, respectively. While La and Nd-doped SBTi samples display the maximum 2Pr value of 18.4 and 19.1 μC/cm2 with doping content of 0.05 and 0.10, respectively. The ferroelectric properties of Sr2Bi4−xLnxTi5O18 are found to be dominated by the competition of the decrease of oxygen vacancy concentration and the relief of structural distortion.