Magnetism and decarburization-like diffusion process on V2O5-doped ZnO ceramics

Abstract

We report on vanadium-doped ZnO ceramics to be used as sputtering targets. Prior to a sintering process, ZnO and V2O5 powders were milled in stoichiometric proportion to obtain Zn0.95V0.05O1+δ composition. Sintering process of compressed powders was carried out at 900, 1000 and 1100°C in air for 1, 2, 4, 6, 10 and 14h. During the sintering process, decarburization-like diffusion of V2O5 (i.e. reduction of the V concentration in the pellet) leads to a non-homogeneous distribution of V. The solution of second Fick׳s law for a decarburization process C(z,t)=(C0−Cs)erf(z/2δDgbt)+Cs was used to find δDgb, where Dgb is the grain boundary diffusion coefficient and δ the grain boundary width. δDgb strongly depends on sintering time, given that ZnO grain growth is accomplished with a simultaneous reduction of high diffusivity paths. X-ray diffraction analysis shows that residual V2O5 react with ZnO to produce γ-Zn3(VO4)2 and ZnV2O4 secondary phases that nucleate during cooling in interstitial sites between ZnO grains. Energy Dispersive X-Ray Spectroscopy (EDS) analysis was used to obtain vanadium concentration profiles. No vanadium was observed in the lattice of ZnO grains, the only diffusion mechanism corresponds to Harrison׳s C-type kinetics. Ceramics exhibit a very low magnetization, reaching a maximum saturation magnetization Ms=14.6×10−3emu/cm3 on the sample annealed at 1100°C for 1h. Magnetic signals are originated at the interface between the V-based secondary phases and ZnO grains, where a composition near to Zn0.95V0.05O is obtained.