An electron spin resonance study was made of Ti3+ centers in SrTiO3 single crystals. The Ti3+ centers were created in perturbed regular Ti4+ sites by trapping a photoelectron from the conduction band after ultraviolet irradiation of the sample at low temperature (T < 180K). The centers were stable below about 180K. This was apparently the first observation of such Ti3+ defects in a SrTiO3 lattice. At T > Tc (where Tc was about 105K and corresponded to the temperature of the cubic-tetragonal phase transition), the Ti3+ center exhibited an orthorhombic symmetry of the g-tensor with its principal axes oriented exactly along <001> and <110> crystal directions: g[110] = 1.9920, g[1¯10] = 1.9375, g[001] = 1.8843. At T < Tc, due to a structural phase transition, two of the Ti3+ principal axes were tilted relative to the <110> directions by up to ±8º in the (001) crystal plane. The spectroscopic data were explained assuming Jahn-Teller orthorhombic distortions of the O octahedron with non-linear T2g x (eg + t2g) vibronic coupling.

The Photo-Induced Ti3+ Centre in SrTiO3. V.V.Laguta, M.D.Glinchuk, R.O.Kuzian, S.N.Nokhrin, I.P.Bykov, J.Rosa, L.Jastrabík, M.G.Karkut: Journal of Physics - Condensed Matter, 2002, 14[50], 13813-25