Spark Plasma synthesis and diffusion of Cu and Ag in vanadium mixed valence oxides

Spark Plasma sintering (SPS) technique allows powders to be compacted at low temperature with a very short holding time. The powder loaded into a carbon die is heated via direct current pulses and simultaneously submitted to an uni-axial pressure of several MPa. Full density of the sample is achieved within minutes. This process is used to study Cu and Ag metals interactions with V2O5 oxide. Syntheses of MxV2O5 phases (M = Cu, Ag) have been achieved within minutes. Thus Cu and Ag atoms penetrate microcrystals of V2O5 oxide at a high speed, shearing its crystal network and simultaneously rebuilding the crystal structures of the prototype networks b, b0, e or d MxV2O5. To account for the formation of these phases identified by X-ray diffraction, structural mechanisms are proposed. Cu and Ag atomic diffusion parameters have been determined from energy dispersive X-ray spectroscopy (EDX) and electron micropobe analysis (EPMA) line scans. High values of diffusion coefficients have been determined. Cu atoms diffuse faster than Ag, DCu & 4 9 10-8 m2/s and DAg & 0.5–1 9 10-9 m2/s in e and d MxV2O5 phases, respectively. Their formation may also be used as a model for further investigations into the diffusion mechanisms of atoms in solids and for a better understanding of the SPS process.