Chemical and physical properties of Al1−xFexPO4 alloys: Part I. Thermal stability, magnetic properties and related electrical conductivity

A series of samples of the nominal compositions Al1−xFexPO4 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 FePO4 and AlPO4, which are not isostructural, takes place by incorporation of Fe3+ ions into the AlPO4 structure for Al0.8Fe0.2PO4 and Al0.6Fe0.4PO4. This solid solution formation is accompanied with a phase transformation of AlPO4 from a tridymite to an orthorhombic phase. In Al0.2Fe0.8PO4, the incorporation of AlPO4 into the FePO4 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 FePO4 content.