Evidence for impurity-induced polar state in Sr1-xMnxTiO3 from density functional calculations

We have performed density functional calculations for 40- and 90-atom supercells of SrTiO3 doped by manganese. We use the all-electron, full-potential local-orbital scheme. We show that Mn ion substituting for Sr occupies the off-central position. The ions of the host lattice also change their equilibrium positions when the material is doped, and the ground-state structure becomes polar. The calculated spontaneous magnetic moment of Sr1-xMnxTiO3 is 5 mu(B)/Mn ion, in contrast to SrTi1-xMnxO3 which exhibits the moment of 3 mu(B)/Mn. The calculation results are in accordance with the data of recent ESR and dielectric susceptibility measurements in SrTiO3:Mn ceramics and support the interpretation of observed dielectric anomalies as impurity-induced transition to a polar phase caused by Mn substituting for Sr.