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In the last decades Fe-doped SrTiO3 (Fe:STO) has become one of the best investigated mixed conducting materials. Nevertheless, the effect of UV irradiation at elevated temperatures on the material’s composition, more precisely on its oxygen content, has hardly been examined so far. UV illumination in oxygen causes an enhanced oxygen incorporation rate and therefore a decreased oxygen vacancy concentration of SrTiO3. Consequently, Fe3+ in Fe:STO is oxidized to Fe4+ to preserve charge neutrality. This oxidation may cause color changes in Fe:STO and a decline in the AC and DC resistivity, which can be investigated by UV/VIS spectroscopy, inplane impedance spectroscopy, van der Pauw measurements respectively. Oxygen can also be released again from Fe:STO by annealing without UV exposure. Therefore, reversibly switching between these described states can be obtained.

The impact of UV irradiation on Fe‐doped SrTiO3 (Fe:STO) single crystals is investigated at elevated temperatures. Illumination leads to incorporation of oxygen into the single crystals and thus to a decreasing oxygen vacancy concentration and oxidation of Fe3+ to Fe4+. The Fe4+ ions cause a color change from transparent/brownish to black. This photochromic blackening due to stoichiometry changes at elevated temperatures is irreversible at room temperature, but annealing at high temperatures, for example at 700 °C, can restore the original stoichiometry and color. Absorbance changes due to UV irradiation are monitored by ex situ and in situ UV/VIS spectroscopy experiments and changes in electrical properties are measured by van der Pauw measurements and in‐plane electrochemical impedance spectroscopy. After 1140 min of illumination at 440 °C, for example, electrical measurements reveal a conductivity increase by more than a factor of 5 due to the enhanced hole concentration in blackened Fe:STO. In addition, UV illumination increases the oxygen chemical potential up to a calculated p(O2) of more than 109 Pa in Fe:STO. Hence, UV light can be used to tune the color, but also electrical properties of Fe:STO by directly impacting the bulk defect concentrations.

Wide band gap semi-conductors such as SrTiO3 (STO) have attracted high interest for photoelectrochemical water splitting and as part of high temperature photovoltaic cells. However, the impact of UV irradiation on the composition (e.g. the oxygen content) of STO and Fe doped STO (Fe:STO) at elevated temperatures has hardly been studied. In Fe:STO, UV exposure causes an enhanced oxygen incorporation rate and, therefore, a decreased oxygen vacancy concentration in air at elevated temperatures. In this contribution we discuss such bulk stoichiometric changes in terms of optical and electrochemical (e.g. AC conductivity) properties. Moreover, the kinetics behind the incorporation were examined, more precisely chemical diffusion coefficients obtained from UV/VIS measurements were calculated.

Wide band gap semi-conductors such as SrTiO3 (STO) have attracted high interest for photoelectrochemical water splitting and as part of high temperature photovoltaic cells. However, the impact of UV irradiation on the composition (e.g. the oxygen content) of STO and Fe doped STO (Fe:STO) at elevated temperatures has hardly been studied. In Fe:STO, UV exposure causes an enhanced oxygen incorporation rate and, therefore, a decreased oxygen vacancy concentration in air at elevated temperatures. In this contribution we discuss such bulk stoichiometric changes in terms of optical and electrochemical (e.g. AC conductivity) properties. Moreover, the kinetics behind the incorporation were examined, more precisely chemical diffusion coefficients obtained from UV/VIS measurements were calculated.