IMPURITIES IN NOMINALLY PURE KTAO3 - EVIDENCE FROM ELECTRON-SPIN-RESONANCE

The ESR investigation of nominally pure KTaO3 was carried out at 4.2 K < T < 77 K. Two ESR spectra were observed for the first time. The fir st spectrum with cubic symmetry was shown to be that of Gd3+ substitut ed for K+. The analysis of the spectrum line intensities and widths ga ve no evidence about the quasi-static displacements of tantalum ions i n the lattice assumed earlier. The second spectrum had axial symmetry and its source was identified as a new off-centre impurity ion Fe+ sub stituted for K+ in KTaO3. The surrounding oxygen ion displacements wer e shown to be the main reason for the Fe+ ESR spectra axiality. The es timation of these displacements Delta x was carried out in the framewo rk of crystalline-field theory and appeared to be about 0.2 Angstrom.