Effect of Ba substoichiometry on phase formation and electrical transport of Pr-substituted BaZr0.7Ce0.2Y0.1O3-d

The perovskite composition BaZr0.7Ce0.2Y0.1O3-δ (BZCY72) is of considerable interest as a stable and efficient proton-conducting ceramic membrane for protonic ceramic fuel cells (PCFCs) and hydrogen-separation applications... [ view full abstract ]

The perovskite composition BaZr_0.7Ce_0.2Y_0.1O_3-δ (BZCY72) is of considerable interest as a stable and efficient proton-conducting ceramic membrane for protonic ceramic fuel cells (PCFCs) and hydrogen-separation applications [1,2]. We recently reported the effects of substituting Pr in BZCY72 on the transport behaviour and defect chemistry with a view to improving the mixed-conducting properties for PCFC cathodes and separation membranes [3]. Here we report the synthesis of the related solid solution Ba(Zr_0.7Ce_0.2)_1-xPr_xY_0.1O_3-δ where Ba substiochiometry increases with x. The structural phase transitions have been mapped as a function of temperature and composition by high-resolution neutron powder diffraction and synchrotron X-ray diffraction revealing phase fields of higher symmetry for lower Pr contents and higher temperatures (Fig.1). The structural studies are complemented by magnetic measurments to elucidate the Pr oxidation state, site occupanices and prevailing charge-compensation mechanisms. The defect chemistry is employed to rationalise the electrical behaviour. Electron-hole transport predominates in both wet and dry oxidising conditions, with later members of the series exhibiting greater conductivity in dry conditions than the Ba stoichiometric analogues [3]. A further difference between the two series is that the conductivity is generally higher in wet in comparison to dry N₂ for the Ba substoichiometric analogues, indicating an important protonic contribution to electrical transport. The solid solution members of higher Pr content warrant further study as mixed-conducting materials for PCFC and membrane applications.