A Transition Phase in the Transformation from α-;, β- and ϵ- to δ-Bismuth Oxide

As an important functional material, Bi₂O₃ is found in seven polymorphs. We systematically analyze the transformation from α-, β- and ϵ- to δ-Bi₂O₃ by using crystallographic group theory and structural simulations. A transition phase is proved to exist in the transformation from the α-, β- and ϵ-Bi₂O₃ to δ-Bi₂O₃. The transition phase is supposed to be tetragonal phase Bi₂O_2.7 (Z=2) with the 139th I 4/m 2/m 2/m space group.