Local Structure of Proton-Conducting Lanthanum Tungstate La_28–xW_4+xO_54+δ: a Combined Density Functional Theory and Pair Distribution Function Study

Abstract

‡ Note that h111i is the group of directions and the correct vector for this vac-vac distance in the fluorite structure would be 1/2 Â h111i, and for the pyrochlore 1/4 Â h111i. However, to avoid confusion when comparing different unit cells we only use the group of directions related to an oxygen cube as illustrated in Fig. 1.

Recent advances in the application of total scattering methods to functional materials

“…Following these results, and the extremely complex oxygen distribution, several different structural configurations of varying total energy obtained by molecular dynamic simulations, were fitted against the experimental X-ray and neutron PDFs. The interplay between molecular dynamics simulation results and PDF fitting allowed to identify the most plausible oxygen distribution as demonstrated by both X-ray and neutron PDF fitting agreement reported in Figure 6 25 . The use of DFT calculations in order to derive energetically stable structural starting models has led to a good description of the experimental PDFs of this complex oxide.…”

“…Neutron and X-rays total scattering experiments were carried out and initially compared to the (average) structural models available in literature leading to the evidence of a significant grade of disorder in the oxygen sublattice, which is also evident from the marked background modulation in the neutron diffraction patterns. In addition, the fit of the experimental PDFs in the short range lead to unsatisfactory results, as can be seen in Figure 5 25 , showing a strong discrepancy between the average crystallographic structure and the local range order. Following these results, and the extremely complex oxygen distribution, several different structural configurations of varying total energy obtained by molecular dynamic simulations, were fitted against the experimental X-ray and neutron PDFs.…”

“…A recent example is the work by Kalland et al 25 where a neutron and X-ray total scattering study has been coupled to extensive molecular dynamic simulation. In particular, object of such work was to shed light on the actual structure of the most recent discovered oxide ion conductor, the lanthanum tungstate, which was initially described in the literature with the chemical formula La 6 WO 12 , similarly to other rare earth tungstates.…”

Diffusion of Nd and Mo in lanthanum tungsten oxide

“…To promote the understanding of the diffusion mechanisms in LWO, a schematic of the defective fluorite-type structure of LWO [21,35] is presented in Fig. 5.…”

“…Illustration of the three different cation sites in the LWO structure, taken from[35]. The La2 site depicted here is edge sharing with other La2 sites in the b-direction, forming a continuous network for transport.…”