Synthesis, Characterization, and Magnetic Properties of A(2)Co(2)Fe(VO4)(3) (A = Ag or Na) Alluaudite-Type Vanadates

Abstract : We successfully synthesized the polycrystalline form of vanadates A(2)Co(2)Fe(VO4)(3) (A = Ag or Na) using sol-gel method. Powder X-ray diffraction analysis allowed the identification of the alluaudite-type vanadate structure. The morphology and the elemental composition of the synthesized powders were analyzed by scanning electron microscopy (SEM) and energy-dispersive X-ray spectrometer (EDS). The two vanadates A(2)Co(2)Fe(VO4)(3) (A = Ag or Na) were further characterized by infrared and Raman spectroscopies to get complementary structural information. The infrared and Raman spectroscopy-observed bands were assigned to VO43- vibration modes. The room temperature Fe-57 Mossbauer spectroscopy confirmed the +III oxidation state of iron. Magnetic properties of these vanadates were investigated. The magnetic susceptibility data reveal that the predominant interactions in these vanadates are antiferromagnetic with a Curie-Weiss constant of theta=-125.6K for Na2Co2Fe(VO4)(3) and theta=-104.5K for Ag2Co2Fe(VO4)(3). The magnetic interactions in these vanadates were discussed according to semiempirical Goodenough-Kanamori-Anderson rules (GKA).