How does voltage or light affect point defects in metal oxides?

by Jürgen Fleig (Inst. of Chemical Technologies and Analytics, TU Wien, Austria)

Thursday 21 Jul 2016, 11:00 → 12:00 Europe/Berlin

room BAH 2, bldg. 03 (DESY Hamburg)

Metal oxides find broad application in very different fields of technology including energy conversion and (micro-)electronics. They are used as electrodes and electrolytes in electrochemical cells (fuel cells, electrolyzers) but also in resistive switching devices. Further examples include piezoelectric ceramics in actuators and semiconductors for varistors or sensors. Many of those metal oxides are mixed ionic and electronic conductors, at least to a certain degree. This mixed conductivity plays a functional role in numerous applications (e.g. in fuel cells or ReRAMs) but may also lead to severe degradation of devices in other cases. An in-depth understanding of point defects in metal oxides, causing ion transport, and of the role of defects in electrochemical reactions is therefore of vital importance. Voltage and light are two important drivers of defect chemical processes or solid state electrochemical reactions in metal oxides and this talk gives an overview of multiple defect related phenomena in oxides that are caused by voltage or light. For example, a voltage affects the width of reaction zones of solid state electrochemical electrodes, leads to unusual electrode migration in PZT, triggers metallic Fe formation on LaFeO3 surfaces or modifies local conductivities in SrTiO3 thin films. Similarities are emphasized between oxides used in different fields, e.g. in piezo actuators and solid oxide fuel cells. The effect of light on defect chemical processes, on the other hand, is essential when aiming at solid state photo-electrochemical cells. An oxide based high temperature solar cell, operating at >400°C, is introduced which can be used to chemically store energy. Moreover, oxygen stoichiometry changes in SrTiO3 under UV illumination lead to a voltage in an electrochemical cell and thus kind of light-driven charging of a battery could be realized.