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Mixed proton-electron conductors (MPEC) can be used as gas separation membranes to extract hydrogen from a gas stream, for example, in a power plant. From the different MPEC, the ceramic material lanthanum tungstate presents an important mixed protonic-electronic conductivity. Lanthanum tungstate La(6-x)WO(12-y) (with y = 1.5x + δ and x = 0.5-0.8) compounds were prepared with La/W ratios between 4.8 and 6.0 and sintered at temperatures between 1300 and 1500 °C in order to study the dependence of the single-phase formation region on the La/W ratio and temperature. Furthermore, compounds substituted in the La or W position were prepared. Ce, Nd, Tb, and Y were used for partial substitution at the La site, while Ir, Re, and Mo were applied for W substitution. All substituents were applied in different concentrations. The electrical conductivity of nonsubstituted La(6-x)WO(12-y) and for all substituted La(6-x)WO(12-y) compounds was measured in the temperature range of 400-900 °C in wet (2.5% H2O) and dry mixtures of 4% H2 in Ar. The greatest improvement in the electrical characteristics was found in the case of 20 mol % substitution with both Re and Mo. After treatment in 100% H2 at 800 °C, the compounds remained unchanged as confirmed with XRD, Raman, and SEM.

Structural changes in a 0.5Li 2 MnO 3 $0.5LiCoO 2 cathode material were investigated by X-ray absorption spectroscopy. It is observed that both Li 2 MnO 3 and LiCoO 2 components of the material exist as separate domains, however, with some exchange of transition metal (TM) ions in their slab layers. A large irreversible capacity observed during activation of the material in the 1 st cycle can be attributed to an irreversible oxygen release from Li 2 MnO 3 domains during lithium extraction. The average valence state of manganese ions remains unchanged at 4+ during charge and discharge. In the absence of conventional redox processes, lithium extraction/reinsertion from/into Li 2 MnO 3 domains occurs with the participation of oxygen anions in redox reactions and most likely involves the ion-exchange process. In contrast, lithium deintercalation/intercalation from/into LiCoO 2 domains occurs topotactically, involving a conventional Co 3+ /Co 4+ redox reaction. The presence of Li 2 MnO 3 domains and their unusual participation in electrochemical processes enable LiCoO 2 domains of the material to sustain a higher cut-off voltage without undergoing irreversible structural changes.

This article reports a comprehensive investigation of the average and local structure of La 5.6 WO 12À , which has excellent mixed proton, electron and oxide ion conduction suitable for device applications. Synchrotron X-ray and neutron powder diffraction show that a cubic fluorite supercell describes the average structure, with highly disordered lanthanum and oxide positions. On average, the tungsten sites are sixfold coordinated and a trace [3.7 (1.3)%] of anti-site disorder is detected. In addition to sharp Bragg reflections, strong diffuse neutron scattering is observed, which hints at short-range order. Plausible local configurations are considered and it is shown that the defect chemistry implies a simple 'chemical exchange' interaction that favours ordered WO 6 octahedra. The local model is confirmed by synchrotron X-ray pair distribution function analysis and EXAFS experiments performed at the La K and W L 3 edges. It is shown that ordered domains of $3.5 nm are found, implying that mixed conduction in La 5.6 WO 12À is associated with a defective glassy-like anion sublattice. The origins of this ground state are proposed to lie in the nonbipartite nature of the face-centred cubic lattice and the pairwise interactions which link the orientation of neighbouring octahedral WO 6 sites. This 'function through frustration' could provide a means of designing new mixed conductors. research papers J. Appl. Cryst. (2016). 49, 997-1008 Tobias Scherb et al. Nanoscale order in La 5.6 WO 12À 999 Figure 1Observed, calculated and difference profiles for the Rietveld fit to the synchrotron X-ray diffraction profile of La 5.6 WO 12À , highlighting the region of the 10 6 2 reflection. The peak asymmetry is well fitted by the minimal broadening model discussed in the text.

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