Phase Transitions, Thermal Expansions, Chemical Expansions, and CO 2 Resistances of Ba(Ce 0.8-x Zr x Y 0.1 Yb 0.1 )O 3-δ (x = 0.1, 0.4) Perovskite-Type Proton Conductors

The phase transitions, thermal expansions, chemical expansions, and CO 2 resistances of Ba(Ce 0.7 Zr 0.1 Y 0.1 Yb 0.1 )O 3- δ (BCZYYb7111) and Ba(Ce 0.4 Zr 0.4 Y 0.1 Yb 0.1 )O 3- δ (BCZYYb4411) have been investigated via high-temperature X-ray diffraction in controlled atmospheres (dry N 2 , wet N 2 , and dry 33.3 vol% CO 2 − 66.6 vol% N 2 ) on cooling from 1173 to 298 K. Two phase transitions (cubic ( Pm 3 ¯ m ) to trigonal ( R 3 ¯ c ) and trigonal ( R 3 ¯ c ) to monoclinic ( I 2/ m )) were observed for BCZYYb7111, whereas one phase transition (cubic ( Pm 3 ¯ m ) to trigonal ( R 3 ¯ c )) was observed for BCZYYb4411 when the samples were prepared at 1873 K in air. Dehydrated BCZYYb7111 and BCZYYb4411 (by firing at 1273 K for 10 h in dry N 2 ) showed trigonal ( R 3 ¯ c ) and cubic ( Pm 3 ¯ m ) symmetries, respectively, at 298 K in dry N 2 . BCZYYb7111 and BCZYb4411 exhibited linear thermal expansion coefficients (LTECs) of 10.7 × 10 −6 K −1 and 10.1 × 10 −6 K −1 , respectively, from 973 to 1173 K in dry N 2 and maximum chemical expansion rates (CERs) of 0.33% and 0.29%, respectively, at 773 K. BCZYYb7111, which has a higher Ce/Zr ratio, exhibited larger LTEC and CER values than BCZYYb4411, whereas BCZYYb4411, which has a lower Ce/Zr ratio, exhibited higher CO 2 resistance than BCZYYb7111.