The influence of hydrogen gas anneals on the electrical properties of nominally undoped, oxygen-deficient SrTiO3−x single crystals was investigated. Titanium getter layers and vacuum anneals were used to obtain oxygen-deficient SrTiO3−x with a low electrical resistivity. These crystals showed an optical absorption peak at 2.92 eV and strong midinfrared absorption. Subsequent anneals at 800 °C in forming gas, which contained 10% hydrogen, returned the crystals into the insulating, transparent state. The mechanisms by which hydrogen anneals can compensate for the effects of oxygen vacancies in SrTiO3−x are discussed. The results show that forming gas anneals of stoichiometric SrTiO3 can lead to complex electrical conduction behavior
