Reaction kinetics during synthesis of CuxV2O5 and AgyV2O5 by spark plasma sintering

The kinetics of ultra-fast reaction rates in Cu–V2O5 and Ag–V2O5 diffusion couples during synthesis by SPS is investigated for temperatures ranging from 500 °C to 600 °C. The diffusion coefficient of the Cu and Ag ions in the CuxV2O5 and AgyV2O5 phases exhibit values comparable or higher than that of diffusion in liquids. However, the high values of activation energies (113 and 149 kJ/mol for Cu and Ag in ε-CuxV2O5 and δ-AgyV2O5, respectively) are not compatible with liquid-like diffusion mechanisms. We interpret the fast diffusion kinetics observed as resulting from repulsive interactions between diffusing species, as reported in the literature. The role of repulsive interactions can also account for the lower diffusion coefficient of Ag with respect of Cu, the former existing in the + 1 valence state, whereas the latter potentially exists in the + 1 and + 2 valence states. The higher activation energy of Ag with respect of Cu is interpreted as resulting from differences in diffusion paths in δ-AgyV2O5 and ε-CuxV2O5.