Expansion Behavior of Ce[sub 1−y]Gd[sub y]O[sub 2.0−0.5y−δ] under Various Oxygen Partial Pressures Evaluated by HTXRD

Lattice constants and thermal expansion of Ce 1 − y Gd y O 2 − 0.5 y − δ ( y = 0 , 0.1 , 0.2 ) in the temperature range 25-1000°C were estimated with high-temperature X-ray diffraction (HTXRD) while oxygen partial pressure varied in 10 − 20 to 10 5 Pa. Under oxygen partial pressures higher than 1 Pa, linear thermal expansion was observed, and the expansion coefficient increased with Gd content. In atmospheres with oxygen partial pressures lower than 10 − 14 Pa, anomalous expansion due to reduction, which generates oxide-ion vacancies, was observed at temperatures higher than 600°C. By using the result of oxygen nonstoichiometry, lattice expansion behaviors with δ were analyzed. It was revealed that there exists two regions with different expansion behavior against δ in CeO 2 − δ and Ce 0.9 Gd 0.1 O 1.95 − δ , whereas only a single expansion behavior against δ was observed in Ce 0.8 Gd 0.2 O 1.9 − δ , showing correspondence with results of oxygen nonstoichiometry.