Linking the Electrical Conductivity and Non-Stoichiometry of Thin Film Ce1-xZrxO2-δ by a Resonant Nanobalance Approach

Bulk ceria-zirconia solid solutions (Ce1-xZrxO2-delta, CZO) are highly suited for application as oxygen storage materials in automotive three-way catalytic converters (TWC) due to the high levels of achievable oxygen non-stoichiometry delta. In thin film CZO, the oxygen storage properties are expected to be further enhanced. The present study addresses this aspect. CZO thin films with 0 <= x <= 1 were investigated. A unique nano-thermogravimetric method for thin films that is based on the resonant nanobalance approach for high-temperature characterization of oxygen non-stoichiometry in CZO was implemented. The high-temperature electrical conductivity and the non-stoichiometry delta of CZO were measured under oxygen partial pressures pO(2) in the range of 10(-24)-0.2 bar. Markedly enhanced reducibility and electronic conductivity of CeO2-ZrO2 as compared to CeO2-delta and ZrO2 were observed. A comparison of temperature- and pO(2)-dependences of the non-stoichiometry of thin films with literature data for bulk Ce1-xZrxO2-delta shows enhanced reducibility in the former. The maximum conductivity was found for Ce0.8Zr0.2O2-delta, whereas Ce0.5Zr0.5O2-delta showed the highest non-stoichiometry, yielding delta = 0.16 at 900 degrees C and pO(2) of 10(-14) bar. The defect interactions in Ce1-xZrxO2-delta are analyzed in the framework of defect models for ceria and zirconia.