Chemical and physical properties of Al 1− xFe xPO 4 alloys : Part I. Thermal stability, magnetic properties and related electrical conductivity

Abstract

A series of samples of the nominal compositions Al 1− x Fe x PO 4 with 0≤ x≤0.8 calcined at various temperatures have been synthesized by the co-precipitation method. The structural changes during calcination were investigated by using X-ray powder diffraction and differential thermal analysis. The electrical conductivity and the magnetic properties were studied. Detailed X-ray studies showed that the solid solution formation between FePO 4 and AlPO 4, which are not isostructural, takes place by incorporation of Fe 3+ ions into the AlPO 4 structure for Al 0.8Fe 0.2PO 4 and Al 0.6Fe 0.4PO 4. This solid solution formation is accompanied with a phase transformation of AlPO 4 from a tridymite to an orthorhombic phase. In Al 0.2Fe 0.8PO 4, the incorporation of AlPO 4 into the FePO 4 lattice occurred at 800 °C. The electrical properties of uncalcined samples exhibit a metallic behavior. A semiconductor trend has been revealed when the samples were calcined at lower temperatures (up to 600 °C). The magnetic behavior of all uncalcined samples shows a paramagnetic trend. Samples calcined at temperatures ≥600 °C exhibit a ferromagnetic behavior at rich FePO 4 content.