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 V 2 O 5 powders were milled in stoichiometric proportion to obtain Zn 0.95 V 0.05 O 1+ 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 14 h. During the sintering process, decarburization-like diffusion of V 2 O 5 (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 ) = ( C 0 − C s ) e r f ( z / 2 δ D g b t ) + C s was used to find δD gb , where D gb is the grain boundary diffusion coefficient and δ the grain boundary width. δD gb 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 V 2 O 5 react with ZnO to produce γ-Zn 3 (VO 4 ) 2 and ZnV 2 O 4 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 M s =14.6×10 −3 emu/cm 3 on the sample annealed at 1100 °C for 1 h. Magnetic signals are originated at the interface between the V-based secondary phases and ZnO grains, where a composition near to Zn 0.95 V 0.05 O is obtained.