Modeling local distortions around ions doped into crystal using superposition model analysis of the zero-field splitting parameters

Superposition model (SPM) is employed to investigate the local environment around the Fe 3 + centers located at the two sites 1 and 2 in TlGaS 2 single crystal exhibiting nominally triclinic symmetry. Modeling of the local distortions around Fe 3 + ions is carried out using triclinic and orthorhombic SPM analysis of the second-rank zero-field splitting (ZFS) parameters (ZFSPs) fitted from electron paramagnetic resonance (EPR) spectra at room temperature. Using SPM expressions for k = 2 , q = − 2 to 2 and k = 4 , q = − 4 to 4 derived by us, and crystallographic data and model parameters taken from the literature, the triclinic ZFSPs b k q are calculated for the two Fe 3 + centers in the undistorted TlGaS 2 host. The low symmetry aspects involved in SPM analysis of ZFSPs, which have commonly been omitted in previous studies, are considered. Then a reduction of the crystallographic data for the host crystal is carried out to reflect the ascent from triclinic to orthorhombic symmetry observed in the EPR spectra of doped crystal. This approximation enables matching the SPM-calculated ZFSPs with the experimental values of b 2 0 and b 2 2 and thus determination of the local distortions around Fe 3 + ions arising due to doping, while preserving the observed orthorhombic site symmetry. The present modeling results support earlier suggestions that Fe 3 + ions substitute for Ga 3 + ions in TlGaS 2 . The fourth-rank ZFS parameters b 4 q , firstly determined theoretically in this study, have not been measured by EPR as yet. More comprehensive modeling of the local distortions and ZFS parameters for Fe 3 + ions in TlGaS 2 may be carried out when the experimental values of b 4 q become available.