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Structure and dehydration mechanism of the proton conducting oxide Ba2In2O5(H2O)(x)

Johan Bielecki (Institutionen för fysik (Chalmers) ; Institutionen för fysik, Kondenserade materiens fysik (Chalmers)) ; S. F. Parker ; Laura Mazzei (Institutionen för fysik, Kondenserade materiens fysik (Chalmers)) ; Lars Börjesson (Institutionen för fysik, Kondenserade materiens fysik (Chalmers)) ; Maths Karlsson (Institutionen för fysik, Kondenserade materiens fysik (Chalmers))
Journal of Materials Chemistry A (2050-7488). Vol. 4 (2016), 4, p. 1224-1232.
[Artikel, refereegranskad vetenskaplig]

The structure and dehydration mechanism of the proton conducting oxide Ba2In2O5(H2O)(x) are investigated by means of variable temperature (20-600 degrees C) Raman spectroscopy together with thermal gravimetric analysis and inelastic neutron scattering. At room temperature, Ba2In2O5(H2O)(x) is found to be fully hydrated (x = 1) and to have a perovskite-like structure, which dehydrates gradually with increasing temperature and at around 600 degrees C the material is essentially dehydrated (x approximate to 0.2). The dehydrated material exhibits a brownmillerite structure, which is featured by alternating layers of InO6 octahedra and InO4 tetrahedra. The transition from a perovskite-like to a brownmillerite-like structure upon increasing temperature occurs through the formation of an intermediate phase at ca. 370 degrees C, corresponding to a hydration degree of approximately 50%. The structure of the intermediate phase is similar to the structure of the dehydrated material, but with the difference that it exhibits a non-centrosymmetric distortion of the InO6 octahedra that is not present in the dehydrated material. The dehydration process upon heating is a two-stage mechanism; for temperatures below the hydrated-to-intermediate phase transition, dehydration is characterized by a homogenous release of protons over the entire oxide lattice, whereas above the transition a preferential desorption of protons originating in the nominally tetrahedral layers is observed. Furthermore, our spectroscopic results point towards the co-existence of two structural phases, which relate to the two lowest-energy proton configurations in the material. The relative contributions of the two proton configurations depend on how the sample is hydrated.



Denna post skapades 2016-02-24. Senast ändrad 2016-08-26.
CPL Pubid: 232411

 

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