Nontrivial nanostructure, stress relaxation mechanisms, and crystallography for pressure-induced Si-I → Si-II phase transformation

Crystallographic theory based on energy minimization suggests austenite-twinned martensite interfaces with specific orientation, which are confirmed experimentally for various materials. Pressure-induced phase transformation (PT) from semiconducting Si-I to metallic Si-II, due to very large and anisotropic transformation strain, may challenge this theory. Here, unexpected nanostructure evolution during Si-I → Si-II PT is revealed by combining molecular dynamics (MD), crystallographic theory, generalized for strained crystals, and in situ real-time Laue X-ray diffraction (XRD). Twinned Si-II, consisting of two martensitic variants, and unexpected nanobands, consisting of alternating strongly deformed and rotated residual Si-I and third variant of Si-II, form $$\{111\}$$ { 111 } interface with Si-I and produce almost self-accommodated nanostructure despite the large transformation volumetric strain of $$-0.237$$ − 0.237 . The interfacial bands arrest the $$\{111\}$$ { 111 } interfaces, leading to repeating nucleation-growth-arrest process and to growth by propagating $$\{110\}$$ { 110 } interface, which (as well as $$\{111\}$$ { 111 } interface) do not appear in traditional crystallographic theory.