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 first spectrum with cubic symmetry was shown to be that of Gd3+ substituted for K+. The analysis of the spectrum line intensities and widths gave no evidence about the quasi-static displacements of tantalum ions in the lattice assumed earlier. The second spectrum had axial symmetry and its source was identified as a new off-centre impurity ion Fe+ substituted for K+ in KTaO3. The surrounding oxygen ion displacements were shown to be the main reason for the Fe+ ESR spectra axiality. The estimation of these displacements Delta x was carried out in the framework of crystalline-field theory and appeared to be about 0.2 Angstrom.