A transition phase in the transformation from α-, β- And ∈- to δ-bismuth oxide

As an important functional material, Bi₂O₃ is found in seven polymorphs. We systematically analyze the transformation from α-, β- and ∈- 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 ∈-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.