Correlation between thermal properties, electrical conductivity, and crystal structure in the BaCe0.80Y0.20O2.9 proton conductor

In this paper, we report an extensive neutron diffraction investigation at high temperature on the BaCe0.80Y0.20O2.9 proton conducting material. Our results precisely define the structural evolution of this compound as a function of temperature which evolves from the monoclinic structure found at room temperature to the orthorhombic symmetry (Imma space group) at 500 °C; then it adopts a rhombohedral structure from 600 to 700 °C and finally transforms into the more symmetric cubic structure at the highest investigated temperature (800 °C). This progressive increase in the symmetry of the system is not accompanied by any first order phase transition as also confirmed by thermal analysis. Finally, combined neutron data and TGA measurement shows that the oxygen content in the sample is stable up to about 700 °C. Above this temperature, the oxygen content reduces from the nominal content of about 2.9 to about 2.8.