EPR-Investigations of defects in ferroelectric ceramic material

Dr. R.-A. Eichel (University Freiburg, Institute for Physical Chemistry)
Prof. Dr. K-P. Dinse (Institute for Physical Chemistry)
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The main reason for the fatigue of ferroelectric oxide materials is, apart from mechanical damage by microcracks, the agglomeration of defects. Their formation and the change of macroscopic characteristics on longer time scales and/or under loading is caused by relocation of point defects, which are induced by cyclic domain movements. The kinetics of this agglomeration and the initial formation of isolated defects has not yet been clarified to a satisfactory degree. For a classification of both isolated defects and defect clusters electron paramagnetic resonance (EPR) is to be used in this subproject.

In close coordination with subproject B5 (Lupascu/Rödel) samples are to be examined with respect to the relocation and agglomeration of point defects. Therefore the concentration of point defects is adjusted in all samples by doping. During cyclic electrical loading point defects are most likely diminished locally and piled up at other locations, which can lead to agglomeration. The changes of the local spin parameters such as spin multiplicity and the number and nature of directly coupled nuclei are to be monitored during the cyclic loading. On a long-term basis additional investigations on the agglomeration kinetics under the influence of optical activation of the defects in order to investigate the influence of short living electronic excitation states is planned.