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Evidence for impurity-induced polar state in Sr1-x Mnx TiO3 from density functional calculations

Abstract:

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-x Mnx TiO3 is 5 μB /Mn ion, in contrast to SrTi1-x Mnx O3 which exhibits the moment of 3 μB /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. © 2009 The American Physical Society.