Proton-Containing Yttrium-Doped Barium Cerate: A Simultaneous Structural and Dynamic Study by Neutron Scattering

The structural response to proton incorporation in a yttrium-doped barium cerate (BCY), a perovskite exhibiting high protonic and low oxide ion conductivity, and the proton motion therein are investigated in situ as a function of temperature and surrounding atmosphere (flow of moist or dry air). Undoped barium cerate (BC) is taken as a nonproton-conducting reference. Using simultaneous neutron diffraction and quasielastic neutron scattering measurements, we determine and correlate the phase transitions in the BCY lattice, the hydrogen content, and the relative mean square displacement (MSD) of hydrogen atoms over the temperature range of 150-900 C. Presence of OH groups in the BCY system affects the temperature of the high-temperature rhombohedral-cubic phase transition. Uptake of hydrogen occurs from room temperature up to 500-600 C, beyond which the system dehydrates. Onset of dehydration is observed before the rhombohedral-cubic phase transition at 700 C. The relative MSD follows the trend of hydrogen content, peaking also at 500-600 C. Decrease in MSD over a large range of temperatures (500-800 C) suggests a corresponding significant variation of the bonding strengths between the hydrogen atoms and the lattice.