Ge₂Bi₂Te₅ (Germanium Bismuth Telluride)

A layered van der Waals chalcogenide belonging to the (GeTe)_n(Bi₂Te₃)_m homologous series, built from ordered stacking of GeTe and Bi₂Te₃ building blocks. It is simultaneously a candidate magnetically/compositionally tunable topological insulator and a phase-change material, with its topological surface states and reversible amorphous-crystalline switching both of interest. This dual functionality makes Ge₂Bi₂Te₅ an important platform for studying topological phase-change memory and the interplay between topology and structural order.