EPR and dielectric relaxation of Fe3+ in KTaO3

Modeling local structure using crystal field and spin Hamiltonian parameters: the tetragonal FeK3+–OI2−defect center in KTaO3crystal

“…A perfect KTaO 3 crystal has cubic structure resulting in cubic site symmetry around the cations, namely the 6-fold cubic coordination for Ta 5+ sites, whereas it has 12-fold cubic coordination for K + sites (see figure 1) [2,3]. Trivalent Fe 3+ ions doped in KTaO 3 crystal can substitute for both Ta 5+ and K + ions [4][5][6]. However, in addition to the two cubic sites, two axial (tetragonal) defect sites have been observed in EMR spectra [4,7].…”

“…However, in addition to the two cubic sites, two axial (tetragonal) defect sites have been observed in EMR spectra [4,7]. These Fe 3+ sites are characterized by surprisingly large values of the second-rank axial zero-field-splitting (ZFS) parameter D. The values D = 4.30 cm −1 [8], D = 4.44 ± 0.014 cm −1 (and g = 1.92 ± 0.02) [5] and D = 4.46 cm −1 (independently determined in [9] and [10]) were assigned to the Fe 3+ K -O 2− I defect centers, where O 2− I denotes an oxygen ion on the nearest interstitial site acting as a compensator for the Fe 3+ K center. The values D = 1.33 cm −1 at room temperature and 1.44 cm −1 at 77 K [9] were assigned to the Fe 3+ Ta -V O defect center [5,7,9], where V O denotes an oxygen vacancy acting as the nearest-neighbor compensator.…”

“…the Fe 3+ Ta centers. However, the experiments [5,[8][9][10] show that the D values for the Fe 3+ K center are remarkably larger in magnitude than those for the Fe 3+ Ta center. The ionic radius of Fe 3+ (R Fe = 0.064 nm) is approximately half that of K + (R K = 0.133 nm) [29] and the K + ion is replaced by an impurity Fe 3+ ion having different charge.…”

An alternative interpretation of the optical spectra for Fe3+-doped KTaO3 crystals

“…The experimental values aE345 Â 10 -4 cm À1 [17] for Fe 3+ at the Ta 5+ site of KTaO 3 and aE30 Â 10 -4 cm À1 [12,17] for Fe 3+ at the K + site suggest that the parameter jDqj of Fe 3+ at the Ta 5+ site is much larger compared with that of Fe 3+ at the K + site.…”

Behaviour of manganese impurity in b-ZnP2

“…One can see that the width and the intensity of the band vary weakly with temperature. The magnitude of an activation energy of the band, determined from a temperature dependence of a line width (∆B = ∆B o exp (E a /kT) [22], is equal 0.03 åV. The obtained low value of an activation energy indicates an asymmetrical paramagmetic center (PC) configuration [15].…”