Linking the Electrical Conductivity and Non-Stoichiometry of Thin Film Ce(1−x)Zr(x)O(2−δ) by a Resonant Nanobalance Approach

Bulk ceria-zirconia solid solutions (Ce(1−x)Zr(x)O(2−δ), 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 δ. 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 δ 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 CeO(2)-ZrO(2) as compared to CeO(2−δ) and ZrO(2) were observed. A comparison of temperature- and pO(2)-dependences of the non-stoichiometry of thin films with literature data for bulk Ce(1−x)Zr(x)O(2−δ) shows enhanced reducibility in the former. The maximum conductivity was found for Ce(0.8)Zr(0.2)O(2−δ), whereas Ce(0.5)Zr(0.5)O(2-δ) showed the highest non-stoichiometry, yielding δ = 0.16 at 900 °C and pO(2) of 10(−14) bar. The defect interactions in Ce(1−x)Zr(x)O(2−δ) are analyzed in the framework of defect models for ceria and zirconia.