Effects of Sn2+ Ion Size on Sn Doped SrTiO3

We discuss the doping effect of Sn 2+ on ATiO 3 perovskites by comparing with those of Pb and Ba. The solution energy of Sn into A sites of ATiO 3 perovskites shows minimum when the lattice size is almost the same as that of SrTiO 3 (STO), as determined by first-principles calculations. In dielectric measurements of these STO-based ceramics, the Sn 2+ -doped STO ceramics showed a higher peak temperature than the Pb 2+ - or Ba 2+ -doped STO ceramics at the same doping amount. In addition, the maximum polarization obtained in the Sn 2+ -doped STO ceramics was larger than that obtained in the Pb 2+ - or Ba 2+ -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 Sn 2+ -doped STO ceramics at room temperature by piezoresponse force microscopy. We propose that these effects originate from the bond length between Sn 2+ and O 2- which is smaller than that between Pb 2+ and O 2- . The Sn 2+ ion prefers the off-center position at the Sr 2+ site because of the retention of the stable bond length between Sn 2+ and O 2- . These leads to the formation of polar regions and which can assist in the generation of a larger polarization.