In the previous work of Kuang et al., two novel bismuth-rich phases in the Bi 1-x V x O 1.5+x system (x = 0.087, 0.095) were found to have high oxide ion conductivity between 573-773 K, competitive with the best-performing Bi 2 O 3 -based materials currently known. Subsequent studies involving ab initio molecular dynamics (AIMD) simulations found that for these materials, as well as a related phase with x = 0.148 (also known as β -Bi 46 V 8 O 89 ), distinct structural features, such as variably-coordinated VO x polyhedra, played key roles in the ionic migration pathways through the material, in particular facilitating oxygen exchange between the polyhedra and the Bi-O sublattice. The structure of the higher-substituted material Bi 0.852 V 0.148 O 1.648 is shown in Figure , highlighting the layers containing Bi and O interspersed with layers containing VO 4 polyhedra. This phase can be thought of as a monoclinic, ordered fluorite superstructure where V 5+ replaces some of the Bi 3+ sites in δ -Bi 2 O 3 , with concomitant reordering of oxygen vacancies to preserve fourfold coordination around the V atoms. Darriet et al. reported a very similar structure in the same monoclinic C2/m space group for the P-substituted analogue Bi 0.852 P 0.148 O 1.648 (also reported as Bi 46 P 8 O 89 ), with layers of PO 4 tetrahedra rather than VO 4 . At lower doping levels, such as in the x = 0.087 (Bi 0.913 V 0.087 O 1.587 ) phase, a long-range ordered pseudo-cubic 3 × 3 × ordering of vacancies and dopants leads to a disruption of the underlying cubic symmetry of the Bi 2 O 3 sublattice, which by comparison is essentially maintained in Bi 0.913 V 0.087 O 1.587 .