Figure 4.

(a). Schematic coherent α to β phase transformation characterized by a smooth variation of lattice parameter in the single metastable state. There is no coexistence of the α and β PdHx phases. (b). Schematic incoherent α to β phase transformation characterized by nucleation of β PdHx phase in the dilute α PdHx phase accompanied with formation of dislocation in the crystalline structure. The two phases coexist. (c). Schematic incoherent β to α phase transformation. (d). Schematic coherent β to α phase transformation. Reprinted with permission from [27]. Copyright 2016 Nature Materials.