An electron spin-resonance study of Cr3+ in LiSrxCa1-xAlF6 with x = 0, 0.5, 0.8, and 1

Electron spin-resonance (ESR) spectra of Cr3+ ions in LiSrxCa1-xAlF6 crystals with x = 0, 0.5, 0.8, and 1 have been measured at X-band microwave frequencies in the temperature range 1.3-300 K. The intense ESR lines from Cr3+ ions in these crystals have been fitted to a trigonal spin Hamiltonian to determine values of the g-tensor (gparallel, gperpendicular) and zero-field splitting, 2D. The principal g-values (gparallel approx =. gperpendicular approx =. 1.974) are almost the same in all cases whereas 2D increases sequentially for x = 0, 0.5, 0.8, and 1. The value of vertical bar 2D vertical bar for Cr3+:LiCaAlF6 decreases gradually as the temperature is increased from 1.3 K to 300 K. Over this same temperature range the value of vertical bar 2D vertical bar for Cr3+:LiSrAlF6 increases. The ESR spectra for Cr3+ in LiSr0.5Ca0.5AlF6 and LiSr0.8Ca0.2AlF6 are inhomogeneously broadened by discrete centres with pseudo-trigonal symmetry, different configurations of which correspond to the random occupation of the second-nearest-neighbour cation sites by Ca2+ and Sr2+ ions. (author)