Defect Chemistry, Chemical Kinetics and Diffusion in Oxides: Simultaneous measurements of optical absorption and electrical conductivity under in-situ conditions

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The understanding of the kinetic behavior, performance, and degradation mechanisms of chemical and electrochemical devices, e.g., sensors, fuel cells, and batteries based on ionic solids requires the knowledge of electronic and ionic point defects and of their transport properties in these materials. In this proposal, point defect-induced optical absorptions in transition metal-containing oxides will be investigated at high temperatures and various oxygen activities mainly by means of optical in-situ spectroscopy. Simultaneous measurements of optical absorption and electrical conductivity of selected oxides will be established and performed in order to precisely understand defect structures and to develop a deeper understanding of the specific contribution of optical-active electronic defects to the electrical conductivity. Time dependent variations of optical absorption and conductivity upon sudden changes in temperature or oxygen activity in the atmosphere surrounding the sample, i. e. by the T-jump or aO2-jump relaxation technique, will be monitored and analyzed using various kinetic models involving surface exchange reaction and/or bulk diffusion. Thermodynamic and kinetic parameters of defect formation reactions and defect transport processes will be determined in several complex oxide systems including battery materials LiMPO4.