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

Abstract Single phase of Ba 1− x La x FeO 3− δ ( x  = 0.1–0.6) with cubic perovskite structure and random arrangement of oxide ion vacancy was successfully prepared by sintering under N 2 flow whose P (O 2 ) 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 (O 2 ) of 10 −2  bar. Electrical conductivity increased with increasing La content up to log (σ/S·cm −1 ) of about 1.5 for Ba 0.5 La 0.5 FeO 3− 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 (O 2 ) of 10 −2  bar could be attributed to abrupt oxygen uptake as large as Δ δ  = 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.