Electron spin resonance of CrO43− in Li3PO4, Li3VO4, and Li3AsO4

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Abstract
The single crystalelectron spin resonance of CrO4 3− in Li3PO4, Li3VO4, and Li3AsO4 has been studied at 4.2 K. The ESR data show highly unusual g values which have a much greater deviation from 2 than previously observed for Cr5+ in tetrahedral coordination. In all three compounds the 3d 1 electron has a d z 2ground state with a small admixture of higher states due to a distortion of the chromate tetrahedra which leaves only a mirror plane symmetry. The g values and hyperfine data for 53Cr are fitted to crystal field equations including higher order terms in the energy separation of the ground state doublet, and the crystal field parameters obtained reveal an extremely small distortion of the CrO3− 4 in the high temperature phase in Li3PO4. The distortions in the low temperature phase of Li3VO4 and Li3AsO4 are of a different nature and larger than in the phosphate but are still much smaller than in previously studied compounds containing CrO4 3−. There is no evidence for a Jahn–Teller distortion in any of the samples. The observed variation of linewidth with orientation in these systems which closely follows the angular variation of g values is attributed to small variations in the size of the distortion of the tetrahedra.