Modeling local distortions around Fe3+ ions doped into TlGaS2 crystal using superposition model analysis of the zero-field splitting parameters

Superposition model (SPM) is employed to investigate the local environment around the Fe3+ centers located at the two sites 1 and 2 in TlGaS2 single crystal exhibiting nominally triclinic symmetry. Modeling of the local distortions around Fe3+ 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=2k=2, q=−2q=−2 to 2 and k=4,q=−4k=4,q=−4 to 4 derived by us, and crystallographic data and model parameters taken from the literature, the triclinic ZFSPs bkq are calculated for the two Fe3+ centers in the undistorted TlGaS2 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 b20 and b22 and thus determination of the local distortions around Fe3+ ions arising due to doping, while preserving the observed orthorhombic site symmetry. The present modeling results support earlier suggestions that Fe3+ ions substitute for Ga3+ ions in TlGaS2. The fourth-rank ZFS parameters b4q, 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 Fe3+ ions in TlGaS2 may be carried out when the experimental values of b4q become available.