Structural position and oxidation state of nickel in SrTiO_(3)

The properties of Ni-doped strontium titanate are studied using X-ray diffraction and XAFS spectroscopy.It is shown that regardless of the preparation conditions,the SrTi_(1-x)Ni_(x)O_(3) solid solution and the NiTiO_(3) phase are the most stable phases which can coexist.According to the EXAFS data,in the single-phase sample of SrTi_(0.97)Ni_(0.03)O_(3),the Ni atoms substitute for the Ti ones and are oncenter.The distortion of the oxygen octahedra is not observed.The XANES spectra analysis shows that the oxidation state of nickel in NiTiO_(3) is 2+,and in the SrTi_(1-x)Ni_(x)O_(3) solid solution it is close to 4+.It is shown that the strongest light absorption in doped samples is associated with the presence of tetravalent nickel in the SrTi_(1-x)Ni_(x)O_(3) solid solution.This doping seems the most promising one for solar energy converters that exploit the bulk photovoltaic effect.