Structure and electrical properties of BaCe1−xLaxO3−δ mixed conductors

In this study, BaCe 1− x La x O 3− δ ( x  = 0.05, 0.10, 0.20, and 0.30) oxides synthesized using citrate–nitrate combustion method were calcined at 1100 °C for 5 h and subsequently sintered at 1550 °C for 5 h. Crystal structure, conductivity, and chemical properties were investigated via X-ray diffraction (XRD), alternating current (AC) impedance spectroscopy , and X-ray photoelectron spectroscopy (XPS). XRD analysis shows that all samples have orthorhombic perovskite-type structure, and lattice volume increases with increasing La content. XPS results show that Ba and La valence states are bivalent, and trivalent, respectively. Mixed Ce 4+ and Ce 3+ valence states can be identified in the samples. Furthermore, there are two types of O binding states in perovskite structure: (i) O–H groups/oxygen vacancies and (ii) lattice oxygen. AC impedance spectra reveal that all samples are proton–oxide ion–electron hole conductors at 400–800 °C in wet O 2 atmosphere and proton–electron conductors at 400–800 °C in wet Ar atmosphere. Among these samples, BaCe 0.90 La 0.10 O 3− δ and BaCe 0.95 La 0.05 O 3− δ display the highest conductivities at temperatures below and above 500 °C, respectively. Furthermore, BaCe 0.95 La 0.05 O 3− δ exhibits the highest total conductivity of 1.06 × 10 −2  S cm −1  at 800 °C under P O2 ≈ 1 atm and P H2O  = 0.006 atm.