Spectroscopic studies of high-temperature processes in solids

Results are reported of spectroscopic investigations of various high-temperature processes in oxides. The redox behaviour of the garnet Yb3Al5O12 is studied by means of optical spectroscopy. The reoxidation kinetics of reduced single crystalline Yb3Al5O12 is found to provide an example of an internal oxidation process which differs significantly from the behaviour observed during reduction. The observation of a well-defined colour front is discussed. Manganese-doped barium titanate, BaTiO3, represents an important electroceramic material where the valency of the dopant plays an essential role. We have studied the charge state of manganese ions in the barium titanate by electron paramagnetic resonance (EPR) spectroscopy at 1073 K as a function of oxygen partial pressure.