ELECTRON-SPIN RESONANCE OF CRO43- IN STRONTIUM CHLOROAPATITE, SR5(PO4)3CL

The electron spin resonance of CrO4 3- has been studied at 4.2°K in single crystals of Sr5(PO4)3Cl. It is shown that strontium chloroapatite has the hexagonal P63 m structure down to 4.2°K. No phase transition to the monoclinic P21 b symmetry, observed in the Ca5(PO4)3Cl and Ca5(PO4)3OH analogs, has been found in Sr5(PO4)3Cl. The principal values of g and A tensors are gx = 1.9348, gy = 1.9430, gz = 1.9822, Ax = 26.5 × 10-4cm-1, Ay = 22.1 × 10-4cm-1, and Az = 6.7 × 10-4cm-1. The principal axes of g and A are found to be rotated by 8.6° relative to each other about the common y axis which is parallel to the crystallographic c axis. The ground state of the d1 electron is dz with considerable admixture of the higher-level d orbitals. The difference in the orientation of the x and z principal axes of the g and A tensors is due to this admixture. Crystal field parameters are extracted assuming a distortion of the oxygen tetrahedron which leaves only xz mirror plane (Cs) symmetry. An angular dependence of the linewidth is observed which is attributed to a distribution of distortions within the crystal. © 1979.