Preparation of Ba1−xLaxFeO3−δ (x = 0.1-0.6) with cubic perovskite phase and random distribution of oxide ion vacancy and their electrical conduction property and thermal expansion behavior

Single phase of Ba1−xLaxFeO3−δ (x = 0.1-0.6) with cubic perovskite structure and random arrangement of oxide ion vacancy was successfully prepared by sintering under N2 flow whose P(O2) was approximately 10−4 bar. It was revealed that chemical state of Fe was almost 3.0+ at room temperature regardless of La content, resulting in decrease of δ from 0.48 to 0.26 with increasing La content from 0.1 to 0.5. High temperature X-ray diffraction measurements indicated stability of the cubic structure from room temperature to 1000 °C under P(O2) of 10−2 bar. Electrical conductivity increased with increasing La content up to log (σ/S·cm−1) of about 1.5 for Ba0.5La0.5FeO3−δ, indicating high potential as electron and oxide ion mixed conducting material. The variation of electrical conduction behavior from semiconducting to semi-metallic and discontinuous variation of thermal expansion behavior at 300-400 °C under P(O2) of 10−2 bar could be attributed to abrupt oxygen uptake as large as Δδ = 0.185 at the temperature. The decrease of electrical conductivity with increasing temperature and deviation of linear thermal expansion above 400 °C could be ascribed to increase of δ above 400 °C.