Single crystal and powder EPR study of trivalent gadolinium in Cs2NaBiCl6 in the 30–300 K interval Original Research Article

A crystalline electric field cubic symmetry site has been reported for Gd3+ in Cs2NaBiCl6 at room temperature. This host exhibits an apparent structural transformation below 100 K that is completely reversible. However, an EPR examination for a powdered sample of Cs2NaBiCl6:Gd3+ clearly demonstrates that there are no new large crystalline electric field symmetry sites arising between the transition temperature (100 K) and 30 K, suggesting, therefore, that the site symmetry remains predominantly cubic even at temperatures close to 30 K. In order to substantiate this statement, a computer EPR powder simulation was performed using the single-crystal-spin-Hamiltonian parameters obtained from the three different sites that emerge from the original site while observed at 30 K. A remarkable agreement is observed while comparing the computer-simulated data with that of powdered experimental data. It is important to mention here that several attempts were done trying to fit the observed new spectra to lower crystalline field symmetries, however, our best analytical adjustment was obtained with the cubic spin-Hamiltonian. Below 30 K, new structural transitions are present and the lattice loses its original cubic nature. However, at 10 K the EPR spectrum of the crystal again shows only seven lines that are very broad. This new spectrum cannot be fitted with previously used cubic spin-Hamiltonian parameters.