Study of the local environment around zirconium ions in polycrystalline α-alumina in relation with kinetics of grain growth and solute drag

The aim of the present work, made up of two parts, consists in studying the behaviour of the local environment of the doping zirconium, in the polycrystalline α-alumina related to the material microstructure. At first, the kinetics of grain growth has been studied, and local chemical analyses on thin foils at grain boundaries using the energy dispersive X-ray spectroscopy (EDXS) technique, were performed. In the second part, we shall consider the evolution of the local order around the doping element, related to the microstucture, by X-ray absorption spectroscopy (XAS) measurements. This study was performed on doped α-polycrystalline alumina (0.03 wt% ZrO2) samples. According to the experimental results, we can show a great interaction between the zirconium and the grain boundaries of the alumina: during the grain growth, grain boundaries drag most of the doping element in solid solution. A transition in the environmental configuration around the doping in grain boundaries is observed, when the segregation ratio of the zirconium in grain boundaries reaches the value of about (4±2)×103. In these conditions, a change in the local order is observed, around the segregated zirconium. This change varies from a statistical disorder to an ordered state, and can be described as an assembly of nanocrystalline metastable, tetragonal zirconia particles. This transition of the environmental configuration in grain boundaries is correlated to the increase of the grain growth velocity, according to the kinetics studies.