Premium
Nanoscale order in the frustrated mixed conductor La 5.6 WO 12−δ
Author(s) -
Scherb Tobias,
Kimber Simon A. J.,
Stephan Christiane,
Henry Paul F.,
Schumacher Gerhard,
Escolástico Sonia,
Serra José M.,
Seeger Janka,
Just Justus,
Hill Adrian H.,
Banhart John
Publication year - 2016
Publication title -
journal of applied crystallography
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.429
H-Index - 162
ISSN - 1600-5767
DOI - 10.1107/s1600576716006415
Subject(s) - pair distribution function , crystallography , neutron diffraction , hollandite , neutron scattering , condensed matter physics , chemistry , octahedron , frustration , extended x ray absorption fine structure , crystal structure , scattering , materials science , molecular physics , physics , absorption spectroscopy , optics , quantum mechanics
This article reports a comprehensive investigation of the average and local structure of La 5.6 WO 12−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 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 12−δ is associated with a defective glassy‐like anion sublattice. The origins of this ground state are proposed to lie in the non‐bipartite 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.