Germanium under high pressure: <i>In</i> <i>situ</i> and <i>ex situ</i> inelastic neutron scattering

The fundamentally interesting semiconductor germanium exhibits a rich phase behavior under high pressure. Upon compression to ~11 GPa, diamond-cubic Ge (Fd-3m) transforms to a dense metallic phase (I4₁/amd). This transition is not reversible upon decompression. Instead several metastable phases with altered band-gap characteristics are recovered. One phase, simple tetragonal st12-Ge (P4₃2₁2) possesses a relatively large band gap and relatively high thermal stability making it technologically interesting. While these phases and their transitions have been studied with experimental diffraction techniques, theoretical density functional theory (DFT) and other probes, they have not yet been characterized with inelastic neutron scattering (INS), which has prevented detailed correlation to computational understanding.
This work here addresses this short-coming through INS performed at ORNL’s ARCS spectrometer. For the first time, in situ INS is performed during compression to the metallic phase and an INS spectrum of metallic Ge is observed, while detailed ex situ INS is performed on recovered st12-Ge. These experimental data are directly correlated to DFT.