Structure, proton incorporation and transport properties of ceramic proton conductor Ba(Ce_0.7Zr_0.2Yb_0.1)O_3−δ

Abstract

Dense ceramics with composition Ba(Ce_0.7Zr_0.2Yb_0.1)O_3−δ(BCZY) were synthesized by solid state reactions, and their structures were characterized by Rietveld refinements of time-of-flight (TOF) neutron diffraction data collected for the samples at high-temperature and controlled atmospheres. The structure phase transition from orthorhombic Imma to cubic Pm3m was observed at the temperature between 500 and 700°C and in flowing 100ppm H₂/Ar gases. At 900°C, the sample was subsequently exposed to different oxygen partial pressures (pO₂, ranging from ~10⁻¹⁷ to ~10⁻²³ atm) and water vapor pressures (pH₂O) up to ~0.18 atm. The expansion of lattice parameters of BCZY, instead of following the normally expected relationship with pO₂, was actually correlated with the increase of pH₂O, implying proton incorporation into the structures. The presence of H-containing species in the structure was confirmed by comparing both inelastic neutron scattering spectra and neutron diffraction data collected for dry and “wet” samples at 10K. The observed vibrational peaks at 104 and 150 meV and absence of a peak around 420 meV indicate the hydrogen occupation in the structure but the absence of any hydroxyl groups (hydrogen covalently bonded to oxygen). Electrical conductivities of BCZY were investigated at different temperatures in both dry and wet conditions.