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.