Phase segregation and miscibility of TiOx nanocomposites in Gd‐doped ceria solid electrolyte material

• Published in: Journal of synchrotron radiation Vol. 30; no. 4; pp. 758 - 765
• Main Authors: Li, Junying, Routh, Prahlad K., Li, Yuanyuan, Plonka, Anna, Makagon, Evgeniy, Lubomirsky, Igor, Frenkel, Anatoly
• Format: Journal Article
• Language: English
• Published: 5 Abbey Square, Chester, Cheshire CH1 2HU, England International Union of Crystallography 01-07-2023; John Wiley & Sons, Inc
• Subjects: Absorption spectroscopy; Actuators; Anatase; Cerium oxides; Deformation; Dimensional changes; electro-chemo-mechanical effect; Electrolytes; Gadolinium; local structural disorder; Miscibility; Nanocomposites; Oxidation; Room temperature; Solid electrolytes; Synchrotrons; Titanium dioxide; Titanium oxides; X‐ray absorption spectroscopy
• ISSN: 1600-5775; 0909-0495; 1600-5775
• DOI: 10.1107/S1600577523003636

Electro‐chemo‐mechanical (ECM) coupling refers to mechanical deformation due to electrochemically driven compositional change in a solid. An ECM actuator producing micrometre‐size displacements and long‐term stability at room temperature was recently reported, comprising a 20 mol% Gd‐doped ceria (20GDC), a solid electrolyte membrane, placed between two working bodies made of TiOx/20GDC (Ti‐GDC) nanocomposites with Ti concentration of 38 mol%. The volumetric changes originating from oxidation or reduction in the local TiOx units are hypothesized to be the origin of mechanical deformation in the ECM actuator. Studying the Ti concentration‐dependent structural changes in the Ti‐GDC nanocomposites is therefore required for (i) understanding the mechanism of dimensional changes in the ECM actuator and (ii) maximizing the ECM response. Here, the systematic investigation of the local structure of the Ti and Ce ions in Ti‐GDC over a broad range of Ti concentrations using synchrotron X‐ray absorption spectroscopy and X‐ray diffraction is reported. The main finding is that, depending on the Ti concentration, Ti atoms either form a cerium titanate or segregate into a TiO2 anatase‐like phase. The transition region between these two regimes with Ti(IV) concentration between 19% and 57% contained strongly disordered TiOx units dispersed in 20GDC containing Ce(III) and Ce(IV) and hence rich with oxygen vacancies. As a result, this transition region is proposed to be the most advantageous for developing ECM‐active materials.
The local structure of titania–ceria composites in a Gd‐doped ceria solid electrolyte material is obtained by a combination of X‐ray absorption fine structure and X‐ray diffraction over the entire range of Ti composition. A compositional region (between 19 and 57%) with strongly distorted TiO6 units and coexistence of Ce(III) and Ce(IV) was discovered, i.e. optimized for oxygen transport conduction and in agreement with the enhanced electro‐chemo‐mechanical effect previously observed in this composition range.