Unexpected substitution in the Li1-3xFexNiPO4 (0 < x < 0.15) solid solution.: Weak ferromagnetic behaviour

Li1 - 3xFexNiPO4 (0 < x < 0.15) solid solution phases have been synthesized by solid state reaction. X-Ray studies on polycrystalline samples show that all phases are isostructural with the parent LiNiPO4 compound, crystallizing in the orthorhombic system, space group Pnma. The evolution of the lattice parameters with the iron content follows Vegard's law. The IR spectra show split bands for the phosphate groups, in good agreement with the distortion observed in the crystal structure. The EPR spectra for all phases show a broad band centred at zero field. The absence of a signal corresponding to Fe3+ ions suggests the presence of Fe-III-Ni-II interactions strongly affected by the zero field splitting of the nickel(ii) ions. The magnetic behaviour of the Li1 - 3xFexNiPO4 (0 < x < 0.15) phases can be described as antiferromagnetic with the presence of weak ferromagnetism below the ordering temperature. The magnitude of the remanent ferromagnetic moment is indicative of the existence of iron clustering in the samples. The FeO6 octahedra form finite chains in which the magnetic moments of the Fe3+ ions are antiferromagnetically aligned with a small canting angle.