The photoinduced Ti3+ centre in SrTiO3

We report the results of an electron spin resonance study of V, centres in SrTiO3 single crystals. The V, centres are created in perturbed regular Ti4+ sites by trapping a photoelectron from the conduction band after ultraviolet irradiation of the sample at low temperature (T < 180 K). The centres are stable below similar to180 K. To our knowledge this is the first observation of such Ti3+ defects in a SrTiO3 lattice. At T > T-c, (T-c approximate to 105 K corresponds to the temperature of the cubic-tetragonal phase transition), the V, centre exhibits an orthorhombic symmetry of the g-tensor with its principal axes oriented exactly along (00 1 and (I 10) crystal directions: g [110] = 1.9920, g[110] = 1.9375, g [001] = 1.8843. At T < T-c, due to a structural phase transition, two of the Ti3+, principal axes are tilted relative to the (110) directions by up to +/-8degrees in the (001) crystal plane. The spectroscopic data are explained assuming Jahn-Teller orthorhombic distortions of the oxygen octahedron with non-linear T(2)g x (e(g) + t(2g)) vibronic coupling.