An experimental and theoretical study of Ni impurity centers in Ba0.8Sr0.2TiO3

Abstract

The local environment and the charge state of a nickel impurity in cubic Ba0.8Sr0.2TiO3 are studied by XAFS spectroscopy. According to the XANES data, the mean Ni charge state is ∼2.5+. An analysis of the EXAFS spectra and their comparison with the results of first-principle calculations of the defect geometry suggest that Ni 2+ ions are in a high-spin state at the B sites of the perovskite structure and the difference of the Ni 2+ and Ti 4+ charges is mainly compensated by distant oxygen vacancies. In addition, a considerable amount of nickel in the sample is in a second phase BaNiO 3−δ . The measurements of the lattice parameter show a decrease in the unit cell volume upon doping, which can indicate the existence of a small amount of Ni 4+ ions at the B sites.

Electronic and magnetic properties of structural defects in SrTiO3(Co)

“…We note that the behavior of cobalt in SrTiO 3 is very different from that of its neighbor in the Periodic Table -nickel [20,43]. First, only for cobalt its appreciable amount can be incorporated into the A site.…”

“…Based on our previous studies of Ni-doped SrTiO 3 and BaTiO 3 [20,43], we deliberately used low concentration of Co in our calculations to avoid the appearance of broad impurity bands. First-principles calculations of Ref.…”

On the possibility of incorporation of the iron impurity into $A$ sites in SrTiO$_3$

“…The energy corresponding to the inflection point on the µ(E) curve was taken as the photoelectron energy origin E 0 . The EXAFS spectra were processed with a widely used IFEFFIT software package [32] similarly to [21,33]. For each sample, 3-4 spectra were recorded, they were then independently processed, and the obtained χ(k) curves were averaged.…”