Temperature- and water-induced structural transformations in Pr- and Ho-doped Ba(Ce _0.7 Zr _0.1 Y _0.1 Yb _0.1 )O _3-δ proton conducting electrolyte

The crystal structure of the doped Ba(Ce0.7Zr0.1Y0.1Yb0.05M0.05)O3–δ (M =Pr and Ho) cerates was studied at various temperatures in dry and wet atmosphere using in situ high-temperature X-ray powder diffraction. A phase transition from tetragonal I4/mcm to cubic Pm m structure was shown to occur in all the cerates studied upon heating from 25 up to 1000 °C irrespective of air humidity. The cubic Pm m and tetragonal I4/mcm phases possess comparable coefficients of linear thermal expansion (CTEs), around 11·10–6 K–1. Even in very dry atmosphere (log /atm) = –4.0), chemical expansion caused by hydration was shown to contribute significantly to the observed structural transformations and temperature dependence of the unit cell volume of the doped cerates.