Detection of charge transfer processes in Cr-doped SrTiO3 single crystals

An insulator-to-metal transition is observed in Cr-doped SrTiO3 single crystals upon extended exposure to a high electric field, namely, electroconditioning (EC). Electron paramagnetic resonance (EPR) and transport measurements under laser irradiation show anticorrelation between the Cr3+ EPR signal and the electrical current. This proves that the Cr3+ ions are responsible for the photocurrent that initiates the EC process. We observe the presence of Cr3+∕Cr4+ mixed valencies in the bulk in the conducting state. The EPR characterization of the spectra in the conducting state excludes the possibility of a Cr3+-oxygen vacancy complex in the bulk as a result of the EC.