Magnetic properties of the M(PO3)3 (M=Ti, V) metaphosphates

Abstract

Two metaphosphates with the formula M(PO₃)₃ (M=Ti and V) have been synthesized and characterized. Their crystal structures consist of isolated MO₆ octahedra linked through infinite [PO₃ ]_∞ chains of PO₄ tetrahedra. The IR and UV–VIS results for these compounds are consistent with chain structures in which the Ti^III and V^III cations exhibit octahedral symmetry. The EPR spectrum of the titanium metaphosphate at 4.2 K shows a nearly Lorentzian signal centred at g=1.77, which disappears at 100 K. EPR results obtained for the doped Sc(PO₃)₃:0.1% Ti^III metaphosphate are discussed on the basis of an effective trigonal symmetry. For the vanadium metaphosphate, the EPR spectrum exhibits a weak signal attributed to V³⁺ ions, with a zero-field splitting parameter D estimated at between 2 and 8 cm^–1 . Magnetic measurements show ferromagnetic and antiferromagnetic interactions for the titanium and vanadium metaphosphates, respectively. A value of J/k=–0.92(2) K has been obtained by fitting the experimental magnetic curve for V(PO₃)₃ to an analytical expression deduced for a three-dimensional Heisenberg model.