Photochromic Fe⁵⁺ (3d³) in SrTiO₃ evidence from paramagnetic resonance

Using paramagnetic resonance it is shown that a photochromic center in SrTiO3 is Fe5+ (3d3). Its resonance parameters are g = 2.0131 ±0.0008, A(57Fe) = (8.6 ± 0.1) x 10-4cm-1. As a function of valency the positive g-shift of Fe5+ lies nearly on a straight line joining those of the isoelectronic Cr3+ and Mn4+. The hyperfine fields of V2+, Cr3+, Mn4+ and Fe5+ are close to one another (Geschwind's rule). Simultaneous observation of Fe3+ and Fe4+ proves indirectly the existence of Fe3+ which can act as a hole trap. © 1971.