Zur Kinetik der Spinellbildung von β-Ga2O3 mit zweiwertigen Oxiden. I. Die Festkörperreaktion von β-Ga2O3 mit NiO

The solid state reaction in a sandwich type diffusion couple of NiO and β-Ga₂O₃ has been investigated between 1240 and 1550°C in air and inert gas atmosphere.Optical microscope and X-ray methods are used to identify the reaction product, which is a singlephased spinel of the general formula $\text{Ni}{}_{\mathrm{1?y}}\text{Ga}{}_{\mathrm{<mtext>2+</mtext><mtext>2y</mtext><mtext>3</mtext>}}\text{O}{}_4$. The homogeneity range of the spinel phase was investigated by X-ray methods; there is a high solubility of β-Ga₂O₃ in the spinel lattice.The growth of the thickness of the reaction layer follows a parabolic rate law, and therefore a diffusion process must be rate determining. The activation energy of the rate controlling step is 82 kcal/mole.Pt-marker experiments are not sufficient for determining the reaction mechanism. Investigations with an electron-probe microanalyzer, an connection with a modified marker technique, resulted in a Wagner-mechanism of counterdiffusion of cations for formation of nickel-gallium spinel; the total amount in Ga³⁺ ions is lost for spinel formation before there is an appreciable solubility of gallium in NiO.