The phase transitions, thermal expansions, chemical expansions, and CO₂ resistances of Ba(Ce_0.7Zr_0.1Y_0.1Yb_0.1)O_3-δ (BCZYYb7111) and Ba(Ce_0.4Zr_0.4Y_0.1Yb_0.1)O_3-δ (BCZYYb4411) have been investigated via high-temperature X-ray diffraction in controlled atmospheres (dry N₂, wet N₂, and dry 33.3 vol% CO₂ − 66.6 vol% N₂) 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 (I2/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 N₂) showed trigonal (R 3 ¯ c) and cubic (Pm 3 ¯ m) symmetries, respectively, at 298 K in dry N₂. 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 N₂ 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 CO₂ resistance than BCZYYb7111.