A neutron diffraction study of the oxygen diffusion in molybdenum doped Ba2In2O5

The structures of molybdenum doped Ba2In2O5 were refined using X-ray and neutron diffraction data at room and high temperature with the aim to derive preferred oxygen diffusion pathways. At room temperature, refinement of composition Ba2In2 − xMoxO5 + 3x / 2 with x = 0.1 revealed that molybdenum atoms are preferentially located in the tetrahedral layers of the brownmillerite. At 700 °C, the structure can be viewed as the stacking of alternating In and In/Mo octahedral layers. The conduction process occurs preferentially in the latter which is highly oxygen deficient. Preferred oxygen diffusion pathways were deduced from Joint Probability Density Function (JPDF) and energy barriers were derived. It was in good agreement with the activation energy deduced from impedance spectroscopy for composition x = 0.1 at 950 °C. However, calculation of energy barrier assumes a dynamic disorder of oxide ions which is unlikely to occur at lower temperature and for sample containing a larger amount of molybdenum. Composition x = 0.5 is cubic on the whole range of temperature. At room temperature, JPDF revealed a static disorder of the oxygen atoms, which is likely due to the solution of molybdenum into the barium indium perovskite. When temperature increases the disorder becomes more and more dynamic.