Abstract: A series of MgO-ZrO₂ composites with various compositions were prepared by co-precipitation with NH4OH from mixed aqueous solution of nitrates and calcination at 500 ℃ and 600 ℃ respectively. The samples were characterized by XRD, XPS, BET, TEM, EXAFS and DTA measurements. The results exhibit that MgO tends to dissolve into the bulk phase of ZrO₂ to form solid solution as Mg/Zr molar ratio is lower than 1. After the dissolution reaches saturation, MgO starts to disperse onto the surface of the solid solution, and at the same time the separate crystalline phase of MgO appears. However, when the content of MgO is high, ZrO₂ does not dissolve into the bulk phase of MgO and not form the separate crystalline phase of ZrO₂, but disperses onto the surface of the crystallite of MgO. And the properties of the surfaces of the samples were obviously affected by the dispersion of ZrO₂. These results suggest that in the samples prepared by co-precipitation, one component can disperse as a monolayer onto the surface of the separate crystalline phase of the other component or the solid solutions composed of the two components in a certain content range. This phenomenon might exist in many binary oxide systems and deserves much more attention.

Key words: ZrO₂, MgO, Binary oxide, Monolayer dispersion, Co-precipitation, Solid solution