Thermal stability of Ba(Zr0.8-xCexY0.2)O2.9 ceramics in carbon dioxide

In situ x-ray diffraction spectra (25-1000 degrees C) have been measured as a function of temperature for proton-conducting Ba(Zr0.8-xCexY0.2)O-2.9 (x=0.0-0.4) ceramics in CO2 atmosphere. Atomic vibrations before and after exposure to CO2 were obtained by using the micro-Raman scattering (150-1600 cm(-1)). Ba(Zr0.8Y0.2)O-2.9 and Ba(Zr0.6Ce0.2Y0.2)O-2.9 reveal a promising thermal stability in CO2 without apparent decomposition up to 1000 degrees C. However, Ba(Zr0.5Ce0.3Y0.2)O-2.9 and Ba(Zr0.4Ce0.4Y0.2)O-2.9 exhibit thermally stable below 550 degrees C and then proceed an obvious chemical decomposition of BaCO3 and Zr0.8-xCexY0.2O2 above 550 degrees C, which were clearly evidenced by the Raman vibrations of 1057 and 466 cm(-1), respectively. A first-order orthorhombic-hexagonal structure transition was confirmed in BaCO3 in the region of 810-850 degrees C upon heating. This study suggests that the Ba(Zr0.8-xCexY0.2)O-2.9 ceramics with x <= 0.2 are promising candidates for proton-conducting applications in CO2-containing environment.