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

Abstract

A-cation deficiency has a significant impact on the properties of proton-conducting perovskites (ABO3), 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-δ (BCY20). Neutron powder diffraction is employed to determine a monoclinic symmetry (space group I2/m) for Ba0.95Ce0.8Y0.2O3-δ (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 ≈1.4 and 1 S m−1 in dry conditions of O2 and N2, respectively, at 600 °C. Partial conductivities determined by a defect-chemistry-based method indicate that proton conductivity is dominant in wet air for temperatures <700 °C and greater for B95CY20 (≈0.95 S m−1 at 600 °C) in comparison to BCY20 (≈0.58 S m−1 at 600 °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.