Electron-Paramagnetic-Resonance Study ofMn2+in Calcium Chlorophosphate

Single crystals of ${\mathrm{Ca}}_5$ ${\left(\mathrm{P}{\mathrm{O}}_4\right)}_3$Cl have been grown from solution in a melt of Ca${\mathrm{Cl}}_2$ doped with Mn${\mathrm{Cl}}_2$. The crystal structure is monoclinic and may be described as a modified apatite structure with a double-unit-cell volume. There are five inequivalent Ca sites in the unit cell as compared to two in the apatite structure. Divalent Mn has been observed by electron paramagnetic resonance to substitute for Ca at all five sites and the spin-Hamiltonian parameters have been determined for each site. A third-order perturbation expression for the fine-structure splitting in a rhombic crystal field is reported. The fine-structure parameters are compared with earlier results for divalent Mn in calcium fluorophosphate (apatite structure).