X-ray absorption fine structure studies of Mn coordination in doped perovskite SrTiO3

The coordination of Mn in doped SrTiO3 ceramics having nominal compositions SrTi0.98Mn0.02O3 and Sr0.98Mn0.02TiO3 was analyzed using x-ray absorption fine structure (XAFS) measurements. As expected, Mn4+ substitution for Ti4+ leads to Mn occupancy of the octahedral B-sites of ABO3 perovskite lattice with a Mn–O bond distance of 1.902 Å (compared to 1.953 Å for Ti–O) and no significant local distortions around the Mn atoms. In contrast, for the composition Sr0.98Mn0.02TiO3, Mn segregates to both the A-sites (as Mn2+) and the B-sites (predominantly as Mn4+). Extended XAFS confirms strong (≈0.77 Å) displacements of Mn2+ cations off the ideal A-site positions along ⟨001⟩ directions with a significant distortion of several coordination shells around the dopant atoms.