ESR investigations of nominally pure KTaO3

An ESR investigation of nominally pure KTaO3 was carried out at 4.2 < T < 77 K. Two new ESR spectra were observed. The first, with cubic symmetry, was shown to be that of Gd3+ substituted for K+. The analysis of the spectrum had axial symmetry and its widths gave no evidence about Ta ions displacements at low temperature. The second spectrum had axial symmetry and its source was identified as a new off-center impurity ion Fe+ substituted for K+ i KTaO3. The surrounding oxygen ion displacements were shown to be the main reason for the Fe+ ESR spectra axiality. The possible origin of the pure KTaO3 low temperature anomalies is discussed.