Surface and Grain Boundary Segregation in Metal Oxides

Experimental approaches in studies of surface and grain boundary segregation in ionic solids are considered. The experimental material on both intrinsic and extrinsic segregation is discussed from the viewpoint of predominant driving forces of segregation. The direct effect of segregation involves an increased solubility limit within the interface region and resulting formation of bidimensional structures of extraordinary properties such as transport, magnetic and optical properties. The effect of segregation on properties of materials is considered in terms of phase diagrams of fine powder ceramics and sintering mechanism of ceramics. Also the catalytical aspect of the problem is briefly discussed.Experimental data on surface and grain boundary segregation are reviewed for several oxide materials such as ZrO₂; Al₂O₃, MgO, SnO₂, NiO, CoO and their solid solutions. Possible effect of interfaces on critical parameters of high T_c oxide superconductors is also considered. Most urgent research pathways in the surface and grain boundary chemistry are discussed.