The segregation behavior in 3 and 10 mol % polycrystalline yttria stabilized zirconia ͑YSZ͒, calcined at temperatures ranging from 300 to 1600°C, is characterized using low-energy ion scattering ͑LEIS͒. In order to be able to separate the Y and Zr LEIS signals, YSZ samples have been prepared using isotopically enriched 94 ZrO 2 instead of natural zirconia. The samples are made via a special precipitation method at a low temperature. The segregation to the outermost surface layer is dominated by impurities. The increased impurity levels are restricted to this first layer, which underlines the importance of the use of LEIS for this study. For temperatures of 1000°C and higher, the oxides of the impurities Na, Si, and Ca even cover the surface completely. The performance of a device like the solid oxide fuel cell which has an YSZ electrolyte and a working temperature around 1000°C, will, therefore, be strongly hampered by these impurities. The reduction of impurities, to prevent accumulation at the surface, will only be effective if the total impurity bulk concentration can be reduced below the 10 ppm level. Due to the presence of the impurities, yttria cannot accumulate in the outermost layer. It does so, in contrast to the general belief, in the subsurface layer and to much higher concentrations than the values reported previously. The difference in the interfacial free energies of Y 2 O 3 and ZrO 2 is determined to be Ϫ21Ϯ3 kJ/mol.

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The growth and thermal stability of an iron oxide overlayer on yttria-stabilized zirconia (YSZ) have been studied using atomic layer deposition (ALD), mainly in combination with low-energy ion scattering (LEIS). These techniques form a powerful combination, where ALD is designed for controlled (sub)monolayer deposition, while LEIS selectively probes the altered outermost atomic layer. The Fe(acac) 3 precursor reacts already at room temperature with YSZ. The reaction proceeds until saturation, which is characteristic for ALD. After the results of repeated ALD cycles, which consist of Fe(acac) 3 deposition followed by an oxidation treatment, have been studied, a model could be proposed which describes the growth mode of the iron oxide layer on YSZ. Oxidation at temperatures of 800 °C and higher causes a migration of Fe 2 O 3 into the bulk, limiting its usefulness in surface catalytic processes at these temperatures. At 800 °C the diffusion coefficient of Fe in YSZ is determined to be 10 -23 m 2 /s. The reaction mechanism of Fe(acac) 3 with the YSZ surface is studied using infrared diffuse reflectance. The results reveal more than one reaction mechanism, but there seems to be a preference for the reaction via coordinatively unsaturated sites.

The formation and composition of room-temperature surface oxides on (1 10) orientated lnSb samples was studied with ESCA and AES. The oxides are composed of a mixture of In,03 and Sb205. It is shown that the Sb oxide is Sb2O5 and not Sb2O3, as has been previously generally assumed. Four surface-preparation techniques were compared: free etching, mechanical polishing, chemo-mechanical polishing and anodic oxidation. Chemo-mechanical polishing and free etching yield comparable oxide thicknesses of about 30 A. Mechanical polishing produces a 100 A thick disturbed oxide layer. Anodic oxidation allows a choice of the thickness but introduces a strong carbon contamination. The first monocell layer of natural oxide grows very fast, within 80 S a 15 A layer has formed. Thereafter the oxidation is diffusion controlled and much slower. From renormalisation curves it is concluded that the oxide mainly consists of In203 with some Sb205. The In oxide stays near the oxide/bulk interface and finally after some 25 days stops further oxidation, while the Sb oxide moves towards the oxide/air interface. In contrast to thermal oxides no Sb layer is found at the oxide/bulk interface.commercially Czochralski grown material (Cominco Ltd