TY - JOUR A1 - Scherb, Tobias A1 - Kimber, S. A. J. A1 - Stephan, Christiane A1 - Henry, P. F. A1 - Schumacher, G. A1 - Escolástico, S. A1 - Serra, J. M. A1 - Seeger, J. A1 - Just, J. A1 - Hill, A.H. A1 - Banhart, J. T1 - Nanoscale order in the frustrated mixed conductor La5.6WO12-Delta JF - Journal of Applied Crystallography N2 - This article reports a comprehensive investigation of the average and local structure of La5.6WO12-δ, 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 WO6 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 similar to 3.5 nm are found, implying that mixed conduction in La5.6WO12-δ 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 WO6 sites. This 'function through frustration' could provide a means of designing new mixed conductors. KW - neutron diffraction KW - x-ray diffraction KW - proton conductors PY - 2016 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-366756 DO - https://doi.org/10.1107/S1600576716006415 SN - 1600-5767 VL - 49 IS - Issue 3 SP - 997 EP - 1008 PB - International Union of Crystallography CY - Chester, UK AN - OPUS4-36675 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Scherb, T. A1 - Fantin, Andrea A1 - Checcia, S. A1 - Stephan-Scherb, Christiane A1 - Escolástico, S. A1 - Franz, A. A1 - Seeger, J. A1 - Meulenberg, W. A. A1 - d'Acapito, F. A1 - Serra, J. M. T1 - Unravelling the crystal structure of Nd5.8WO12-d and Nd5.7W0.75Mo0.25O12-d mixed ionic electronic conductors JF - Journal of Applied Crystallography N2 - Mixed ionic electronic conducting ceramics Nd6-yWO12-d (d is the Oxygen deficiency) provide excellent stability in harsh environments containing strongly reactive gases such as CO2, CO, H2, H2O or H2S. Due to this chemical stability, they are promising and cost-efficient candidate materials for gas separation, catalytic membrane reactors and protonic ceramic fuel cell technologies. As in La6-yWO12-d, the ionic/electronic transport mechanism in Nd6-yWO12-d is expected to be largely controlled by the crystal structure, the conclusive determination of which is still lacking. This work presents a crystallographic study of Nd5.8WO12-d and molybdenum-substituted Nd5.7W0.75Mo0.25O12-d prepared by the citrate complexation route. High-resolution synchrotron and neutron powder diffraction data were used in combined Rietveld refinements to unravel the crystal structure of Nd5.8WO12-d and Nd5.7W0.75Mo0.25O12-d. Both investigated samples crystallize in a defect fluorite crystal structure with space group Fm3m and doubled unit-cell parameter due to cation ordering. Mo replacesWat bothWyckoff sites 4a and 48h and is evenly distributed, in contrast with La6-yWO12-d. X-ray absorption spectroscopy as a function of partial pressure pO2 in the near-edge regions excludes oxidation state changes of Nd (Nd3+) and W(W6+) in reducing conditions: the enhanced hydrogen permeation, i.e. ambipolar conduction, observed in Mo-substituted Nd6-yWO12-d is therefore explained by the higher Mo reducibility and the creation of additional – disordered – oxygen vacancies. KW - Powder diffraction KW - Mixed conductors KW - X-ray absorption spectroscopy PY - 2020 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-514607 DO - https://doi.org/10.1107/S1600576720012698 VL - 53 SP - 1471 EP - 1483 AN - OPUS4-51460 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -