Electronic structures of Co(II) and Co(III) impurities in cubic perovskite hosts

The spin-polarized option of the multiple-scattering Xα method is used to obtain the electronic structures of divalent and trivalent cobalt ions in SrTiO₃ and BaTiO₃ samples. Various clusters account for the different charge-compensation mechanisms (oxygen vacancies, fluorine ions) and different spin configurations are considered for Co(II) and Co(III) centers. Transition-state computations are carried out to get the various multiplet levels of Co(II) and CO(III) cubic centers. The high-spin ⁵T2g and the low-spin ¹A1g terms are, respectively, the Co(III) ground terms in BaTiO₃ and SrTiO₃ hosts. The 10Dq crystal-field parameter of Co(III) increases from 1.9 eV (BaTiO₃) to 2.1 eV (SrTiO₃). In the light of Xα energy diagrams, the possible interpretations of the absorption spectra relevant to Reimeika BaTiO₃: Co and SrTiO₃: Co crystals are reviewed.