Kristof Szot

Spectroscopic study of the electric field induced valence change of Fe-defect centers in SrTiO3

The electrochemical changes induced by an electric field in Fe-doped SrTiO(3) have been investigated by X-ray absorption spectroscopy (XANES and EXAFS), electron paramagnetic resonance (EPR) and Raman spectroscopy. A detailed study of the Fe dopant in the regions around the anode and cathode reveals new insights into the local structure and valence state of Fe in SrTiO(3) single crystals. The ab initio full multiple-scattering XANES calculations give an evidence of the oxygen vacancy presence in the first coordination shell of iron. Differences in the length and disorder of the Fe-O bonds as extracted from EXAFS are correlated to the unequivocal identification of the defect type by complementary spectroscopical techniques to identify the valence state of the Fe-dopant and the presence of the Fe - V(Ö) complexes. Through this combinatorial approach, novel structural information on Fe - V(Ö) complexes is provided by X-ray absorption spectroscopy, and the relation of Fe-O bond length, doping level and oxidation state in SrTi(1-x)Fe(x)O(3) is briefly discussed.

Restructuring the surface region of donor doped SrTiO3 single crystals under oxidizing conditions

Abstract The cation-vacancy-compensation mechanism of donor doped SrTiO3 single crystals has been investigated on a 2.3at% La doped specimen. Slices with surface smoothness at atomic scale were treated in oxygen at 1380°C for 100h. Thereafter, crystallites of characteristic shape have been found on the surface. Several techniques such as optical microscope, SEM with EDX, AFM and SIMS have been used to describe the reformation of the surface and to analyze the structural composition of the new phases. SrO-rich compositions have been found. The surface seemed to be enriched with Sr and yielded steps which could be interpreted in terms of Ruddlesden Popper-phases ((SrTiO3)n*SrO). These results were compared with similar experiments on donor doped ceramics. Finally, an interpretation with respect to point defect chemistry and the formation of extended defects is proposed.