How UV light lowers the conductivity of SrTiO(3) by photochemical water splitting at elevated temperature

Nominally undoped SrTiO(3) single crystals were illuminated by UV light at 350 °C in oxidizing as well as reducing atmospheres. In N(2)/O(2) atmospheres, UV irradiation enhances the conductivity of SrTiO(3) by several orders of magnitude. In dry H(2) atmosphere UV exposure leads to the opposite conductivity effect, i.e., above band gap energy illumination surprisingly lowers the conductivity. This is discussed in the framework of a defect chemical model. We show that a shift in defect concentrations due to UV-driven oxygen incorporation from the gas phase into the oxide is the main cause of the measured conductivity changes. A model is introduced to illustrate the thermodynamic and kinetic drivers of the processes under UV irradiation. Noteably, in reducing H(2)/H(2)O atmospheres, the incorporation of oxygen into the investigated oxide under UV light takes place via water splitting. Owing to the predominant electron conduction of SrTiO(3) in equilibrium with H(2), oxygen incorporation upon UV and thus an increase of the oxygen chemical potential leads to a decrease of the majority electronic charge carrier, here electrons, which lowers the conductivity under UV irradiation.