Understanding the Correlation between Oxide Ion Mobility and Site Distributions in Ba₃NbWO_8.5

Abstract

A correlation between oxygen site distributions and ionic conductivity has been established in the recently discovered family of oxide-ion conductors Ba3M2O8.5±δ (M = Nb, V, Mo, W). We rationalise this observation on the basis of structural insights gained from the first single-crystal neutron diffraction data collected for a member of this family, Ba3NbWO8.5, and theoretical considerations of bonding and O site energies.

Oxide-Ion Occupational Disorder, Diffusion Path, and Conductivity in Hexagonal Perovskite Derivatives Ba3WNbO8.5 and Ba3MoNbO8.5

“…The structural parameters refined by the Rietveld analysis of neutron-powder-diffraction data of Ba 3 WNbO 8.5 in this work agree well with those from single-crystal neutron diffraction experiments in the literature. 45,59 Thus, there is no influence of the impurity phase and surface absorption on the structural parameters in our polycrystalline samples.…”

“…The present split-atom model with the 6c W,Nb2 and 18h O3 sites is consistent with the single-crystal X-ray, single-crystal, and powder neutron diffraction analyses in the literature. 37,45,58 Total neutron scattering studies demonstrated the possibility of the presence of five-fold (Mo,Nb)O 5 polyhedra in Ba 3 MoNbO 8.5−δ . 59 Here, we have shown the large spatial distribution of the O3 atom through the split-atom models also in Ba 3 MoNbO 8.5−δ , 18 which is consistent with the presence of the five-fold (Mo,Nb)O 5 polyhedra.…”

“…The apical O3 atoms are sandwiched by the Ba2 and M,Nb1 atoms (M = W and Mo); thus, the shorter Ba2−W,Nb1 distance would make the O3 atom unstable. Fop et al 44 and Auckett et al 45 pointed out that the higher bond-valence-based energy near the O3 site in Ba 3 WNbO 8.5 corresponds to the lower O3 occupancy, compared to that in Ba 3 MoNbO 8.5 .…”

Structure–property correlation in oxide-ion and proton conductors for clean energy applications: recent experimental and computational advancements

“…37 Moving instead from BNMO to BNWO, E1 increases dramatically, likely because of the lower fraction of tetrahedral units. In this respect, Auckett et al 48 suggested that it is the energy difference between the two O sites that drive the occupancies observed experimentally, not the opposite. Gilane et al applied BVEL to Ba 3 VWO 8.5 (BVWO), which exhibits ordered vacancies on the B2 site.…”

Exploring the nature of the fergusonite–scheelite phase transition and ionic conductivity enhancement by Mo6+doping in LaNbO4

“…We note that both Mo 6+ and W 6+ dopants introduce the same number of interstitial O 2À ions, yet the conductivity enhancement is observed to be greater in Mo 6+ -doped LaNbO 4 ; this is perhaps related to a stronger trapping effect near the W 6+ dopant ions (which our BVEL analysis does not quantify) or to the greater tendency for Mo 6+ to tolerate a variety of coordination geometries and low coordination numbers than W 6+ , 65 which has been identied as a factor contributing to the superior oxide-ionic conductivity of Mo-based analogues of other conductive oxides. 66 A further consequence of the above nding is that the enhancement of oxide-ionic conductivity in Mo 6+ -doped LaNbO 4 is likely to reach an upper limit when the concentration of oxide-trapping dopant cations becomes high enough to disrupt a signicant proportion of conduction pathways in the material. The close similarity of the conductivity data recorded for LNMO16 and LNMO20 (Fig.…”