Occurrence and stability of trivalent zirconium in orthophosphate single crystals

EPR spectroscopy has been used in investigations of the unusual 3+ valence state of zirconium. The EPR spectrum of Zr3+, which was initially observed as a parasitic signal in Fe-doped single crystals of ScPO4, was definitively identified by preparing single crystals of ScPO4 doped with isotopically enriched (94.6%)91Zr. Single crystals of LuPO4 and YPO4 doped with both naturally abundant and isotopically enriched Zr were also grown and investigated. The EPR spectrum of Zr3+ could be observed at room temperature in the ''as-grown'' single crystals of both ScPO4 and LuPO4; and, accordingly, the 3+ state is stable at room temperature in these hosts. The spectrum of Zr3+ in the YPO4 host could only be observed following a γ irradiation at 77 K, and this spectrum decayed rapidly with increasing temperature. Axial spin-Hamiltonian parameters were determined for Zr3+ in all three hosts at a sample temperature of 77 K and at room temperature for the ScPO4 and LuPO4 hosts. In the case of the latter two hosts, the spin-Hamiltonian parameters were found to exhibit a small temperature dependence. The observed g values were not accounted for by previously published second-order expressions indicating that additional coupling mechanisms are operative