Herein we report the electrical transport properties of a series of ordered mesoporous ceria-zirconia (CexZr1-xO2, referred to as mp-CZO) thin films with both a cubic structure of (17±2) nm diameter pores and nanocrystalline walls. Samples over the whole range of composition, including bare CeO2 and ZrO2, were fabricated by templating strategies using the large diblock copolymer KLE as the structure-directing agent. Both the nanoscale structure and the chemical composition of the mesoporous materials were analyzed by a combination of scanning and transmission electron microscopy, grazing incidence small-angle X-ray scattering, X-ray photoelectron spectroscopy, and time-of-flight secondary ion mass spectrometry. The total conductivity as a function of the film composition, temperature, and oxygen partial pressure was measured using impedance spectroscopy. The mesoporous solid solutions of CeO2-ZrO2 prepared in this work showed a higher stability against thermal ripening than both binary oxides, making them ideal model systems to study both the charge transport properties and the oxygen storage at elevated temperatures. We find that the redox properties of nanocrystalline mp-CZO thin films differ significantly from those of bulk CZO materials reported in the literature and, therefore, propose a defect chemical model of surface regions.

Mayenite (Ca12Al14O33) is a highly interesting functional material not only in view of its unique crystal structure as a cage compound but also for its variety of possible applications. Its ability to incorporate foreign ions into the cage structure opens the possibility to create new types of solid electrolytes and even electrides. Therefore, the conductivity of various anion substituted mayenites was measured as a function of temperature. Due to controversial reports on the stability of mayenite under specific thermodynamic conditions (dry, wet, reducing, and high temperature), a comprehensive study on the stability was performed. Mayenite is clearly not stable under dry conditions (ppm H2O < 100) at temperatures above 1050 °C, and thus, the mayenite phase vanishes from the calcium aluminate phase diagram below a minimum humidity. Two decomposition reactions were observed and are described in detail. To get further insight into the mechanism of hydration of mayenite, the conductivity was measured as a function of water vapour pressure in a range of -5 ≤ lg[pH2O/bar] ≤ -1.6 at temperatures ranging from 1000 °C ≤ θ ≤ 1200 °C. The hydration isotherms are described with high accuracy by the underlying point defect model, which is confirmed in a wide range of water vapour pressure.

The ternary solid solution CeO 2 -ZrO 2 is known for its superior performance as an oxygen storage catalyst in exhaust gas catalysis (e.g. TWC), although the defect chemical background of these outstanding properties is not fully understood quantitatively. Here, a comprehensive experimental study is reported regarding defects and defect-related transport properties of cubic stabilized single crystalline (Ce x Zr 1Àx ) 0.8 Y 0.2 O 1.9Àd (0 r x r 1) solid solutions as a model system for CeO 2 -ZrO 2 . The constant fraction of yttria was chosen in order to fix a defined concentration of oxygen vacancies and to stabilize the cubic fluorite-type lattice for all Ce/Zr ratios. Measurements of the total electrical conductivity, the partial electronic conductivity, the ionic transference number and the non-stoichiometry (oxygen deficiency, oxygen storage capacity) were performed in the oxygen partial pressure range À25 o lg pO 2 /bar o 0 and for temperatures between 500 1C and 750 1C. The total conductivity at low pO 2 is dominated by electronic transport.A strong deviation from the widely accepted ideal solution based point defect model was observed.An extended point defect model was developed using defect activities rather than concentrations in order to describe the point defect reactions in CeO 2 -ZrO 2 -Y 2 O 3 properly. It served to obtain good quantitative agreement with the measured data. By a combination of values for non-stoichiometries and for electronic conductivities, the electron mobility could be calculated as a function of pO 2 , ranging between 10 À2 cm 2 V À1 s À1 and 10 À5 cm 2 V À1 s À1. Finally, the origin of the high oxygen storage capacity and superior catalytic promotion performance at a specific ratio of n(Ce)/n(Zr) E 1 was attributed to two main factors: (1) a strongly enhanced electronic conductivity in the high and medium pO 2 range qualifies the material to be a good mixed conductor, which is essential for a fast oxygen exchange and (2) the equilibrium constant for the reduction exhibits a maximum, which means that the reduction is thermodynamically most favoured just at this composition.