Effects of Sn2+ Ion Size on Sn Doped SrTiO3

Abstract

We discuss the doping effect of Sn2+ on ATiO3 perovskites by comparing with those of Pb and Ba. The solution energy of Sn into A sites of ATiO3 perovskites shows minimum when the lattice size is almost the same as that of SrTiO3 (STO), as determined by first-principles calculations. In dielectric measurements of these STO-based ceramics, the Sn2+-doped STO ceramics showed a higher peak temperature than the Pb2+- or Ba2+-doped STO ceramics at the same doping amount. In addition, the maximum polarization obtained in the Sn2+-doped STO ceramics was larger than that obtained in the Pb2+- or Ba2+-doped ceramics in terms of the relationship between the polarization and electric field curve measurement at room temperature. The piezoresponse was also observed in the Sn2+-doped STO ceramics at room temperature by piezoresponse force microscopy. We propose that these effects originate from the bond length between Sn2+ and O2- which is smaller than that between Pb2+ and O2-. The Sn2+ ion prefers the off-center position at the Sr2+ site because of the retention of the stable bond length between Sn2+ and O2-. These leads to the formation of polar regions and which can assist in the generation of a larger polarization.