EPR and ENDOR analysis of Fe3+ impurity centers in fluoroelpasolite lattices

F. Loncke, H. De Cooman, N.M. Khaidukov, H. Vrielinck, E. Goovaerts, P. Matthys, F. Callens
Physical Chemistry Chemical Physics (PCCP)
9 (39), 5320-5329


Fe3+ ions in hexagonal and cubic fluoroelpasolite crystals (AI2BIMIIIF6) have been investigated in a combined Electron Paramagnetic Resonance (EPR) and Electron Nuclear Double Resonance (ENDOR) study. A detailed analysis of the ENDOR spectra for the nearest 19F and 23Na shells in X (9.5 GHz) and Q band (34 GHz) allowed the complex EPR spectra to be disentangled and to determine the spin Hamiltonian parameters for the various S = 5/2 Fe3+ centres. W-band (95 GHz) EPR measurements as a function of temperature were performed to provide unambiguous evidence about the absolute signs of the Zero Field Splitting (ZFS) and SuperHyperFine (SHF) parameters for Fe3+ in Cs2NaAlF6 as already determined from the ENDOR work. It could be concluded that all principal 19F hyperfine values were positive, in agreement with earlier assignments in the literature for related systems. A comparative analysis of the 19F SHF data for Fe3+ at a perfectly octahedral site in the cubic crystal, and at two slightly trigonally distorted environments in the hexagonal crystals, indicates that the metal-to-ligand distance changes upon doping. The obtained set of parameters concerning one defect in various analogous environments can furthermore be used to test different methods of theoretical calculations for ZFS and SHF values.