Structural characterization and magnetic property determination of nanocrystalline Ba3Fe2WO9 and Sr3Fe2WO9 perovskites prepared by a modified aqueous sol–gel route
Sr3Fe2WO9 and Ba3Fe2WO9 triple perovskites have been prepared in nanocrystalline form using a modified sol–gel route with citric acid as a chelating agent. These materials have been studied by X-ray powder diffraction (PXRD), energy-dispersive X-ray (EDX) spectroscopy, transmission electron microscopy (TEM), scanning electron microscopy (SEM), and unpolarized Raman spectroscopy, while their magnetic properties have been determined using SQUID measurements. At room temperature, the crystal structure of 6H-perovskite Ba3Fe2WO9 is hexagonal, space group P63/mmc, with a = 5.7577(2) and c = 14.1095(5) Å, whereas Sr3Fe2WO9 presents a tetragonal lattice, space group I4/m, with a = 5.5803(1) and c = 7.8745(3) Å. Both compounds are nanocrystalline with average crystallite sizes of 25.6(1) nm for Ba3Fe2WO9 and 35.9(1) nm for Sr3Fe2WO9 with moderate microstrain. They exhibit a disordered perovskite structure, in which Fe3+ and W6+ cations distribute randomly at the B-sites of the perovskite lattice: Sr2[Fe0.72W0.28]2a[Fe0.61W0.39]2bO6 and Ba6[Fe1.71W0.29]2a[Fe2.29W1.71]4fO18. The detected hysteresis loops with non-zero remanent magnetization and a rather large coercive field reveal ferrimagnetic ordering with ordering temperatures of 373 K for Sr3Fe2WO9 and 330 K for Ba3Fe2WO9. Magnetic measurements show the onset of ferrimagnetic ordering at relatively high temperatures of 717 and 711 K for the Sr and Ba compounds, respectively; however the magnetization isotherms at 2 K exhibit, for H = 50 kOe, maximum magnetization values close to 0.8 μB (f.u.)−1 and 0.35 μB (f.u.)−1 for Sr and Ba compounds, respectively, although full saturation is not reached.