V2+ in SrTiO3: an extreme double acceptor

Vanadium-doped SrTiO3 reduced above 1200 degrees C and then quenched is shown to contain a V2+ double acceptor level about 40 meV below the conduction band from resistivity measurements. Electron spin resonance (ESR) central hyperfine and g-shift values both indicate a 40% delocalisation of the spin density onto Ti conduction band levels. Upon cooling below 130 K, the ESR intensity freezes out. An exponential linewidth narrowing is observed with an activation energy ED of 200 meV, which can be accounted for by the thermally activated hopping between V2+ and V3+ single acceptors. All data are compatible with the tight-binding calculations of Selme, Pecheur and Toussaint (1986) for the vanadium-impurity in SrTiO3.