Linking the Electrical Conductivity and Non-Stoichiometry of Thin Film Ce_1-xZr_xO_2-δ by a Resonant Nanobalance...

Bulk ceria-zirconia solid solutions (Ce_1-xZr_xO_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 pO₂ in the range of 10^-24-0.2 bar. Markedly enhanced reducibility and electronic conductivity of CeO₂-ZrO₂ as compared to CeO_2-δ and ZrO₂ were observed. A comparison of temperature- and pO₂-dependences of the non-stoichiometry of thin films with literature data for bulk Ce_1-xZr_xO_2-δ shows enhanced reducibility in the former. The maximum conductivity was found for Ce_0.8Zr_0.2O_2-δ, whereas Ce_0.5Zr_0.5O_2-δ showed the highest non-stoichiometry, yielding δ = 0.16 at 900 °C and pO₂ of 10^-14 bar. The defect interactions in Ce_1-xZr_xO_2-δ are analyzed in the framework of defect models for ceria and zirconia.