Journal
CHEMISTRY OF MATERIALS
Volume 25, Issue 11, Pages 2378-2384Publisher
AMER CHEMICAL SOC
DOI: 10.1021/cm401466r
Keywords
proton conductors; diffraction; pair distribution function analysis; DFT
Funding
- Norwegian metacenter for computational science (Notur) [NN4604k]
- MIUR through the FIRB [RBFR12CQP5]
- Los Alamos Neutron Science Centre
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Lanthanum tungstate (La28-xW4+xO54+delta) is a good proton conductors and exhibits a complex fluorite-type structure. To gain further understanding of the short-range order in the structure we correlate the optimized configurations obtained by density functional theory (DFT) with the experimental atomic pair distribution function analysis (PDF) of time-of-flight neutron and synchrotron X-ray data, collected at room temperature. The local atomic arrangements cannot be described by means of any average symmetric structure. Tungsten forms WO6 octahedra in alternating directions, La1 is mainly 8-fold coordinated in relatively symmetric cubes, and La2 is coordinated with 6 or 7 oxygens in heavily distorted cubes. Both DFT and PDF confirm that the excess tungsten (x) is incorporated in La2 (1/4,1/4,1/4) sites in the La27W5O55.5 composition. This additional tungsten can be considered as a donor self-dopant in the material and has implications to the conducting properties and the defect structure.
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