Enhanced proton conductivity and stability of Ba-deficient BaCe0.8Y0.2O3-δ

A-cation deficiency has a significant impact on the properties of proton-conducting perovskites (ABO(3)), depending on factors such as the ionic radius, concentration of dopant and degree of substoichiometry of the A-site cation. Here, we focus on the influence of Ba deficiency on the structure, stability and partial electrical conductivities of the perovskite BaCe0.8Y0.2O3-delta (BCY20). Neutron powder diffraction is employed to determine a monoclinic symmetry (space group I2/m) for Ba0.95Ce0.8Y0.2O3-delta (B95CY20), with greater distortion and specific free volume than BCY20. Confocal Raman microscopy integrated with atomic force microscopy and X-ray diffraction confirm improved resistance to carbonate formation in the Ba-deficient material. Electrical conductivity is also greater for B95CY20 in both wet and dry oxidising and moderate reducing conditions, reaching approximate to 1.4 and 1 S m(-1) in dry conditions of O-2 and N-2, respectively, at 600 degrees C. Partial conductivities determined by a defect-chemistry-based method indicate that proton conductivity is dominant in wet air for temperatures <700 degrees C and greater for B95CY20 (approximate to 0.95 S m(-1) at 600 degrees C) in comparison to BCY20 (approximate to 0.58 S m(-1) at 600 degrees C), with an associated hydration enthalpy of -128 kJ mol(-1). Mixed oxide ionic-electronic conductivity dominates in dry oxidising conditions and, again, is greater for Ba substoichiometric material.