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.
Competing Interests: There are no conflicts to declare.
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