Identification of Light Induced Charge Transfer Processes in BaTio sub 3 by Combined ESR and Optical Measurements,
OSNABRUECK UNIV (GERMANY F R) FACHBEREICH PHYSIK
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What are the defects responsible for the photorefractive effect in Barium titanate What charge conversion processes involving these defects are taking place during illumination Along which energetic paths are charges transported These questions have to be answered if one wants to understand the outstanding photorefractive properties of BaTiO3 on a microscopic basis. The necessary information can be obtained from ESR studies, if these are combined with optical investigations. We report on such measurements. It was found that the optical behavior of the defects identified by ESR varied from specimen to specimen, even if these were nominally undoped. Even for the same crystal the results depended strongly on the history of illumination and heat treatments. We can give so far only representative results, mostly obtained with crystals cut from one boule, which was nominally undoped. ESR investigations of defects in BaTiO3 in relation to the photorefractive behavior of the material have been performed earlier. We extend such measurements by observing ESR with BaTiO3 single crystals also at low temperatures and by simultaneously monitoring the light induced changes of ESR and optical absorption.