Phase Transition Kinetics of Ge from dc Phase to β-Sn Phase under High Pressure

Germanium is a semiconductor with good performances of high carrier mobility and narrow band gap at ambient conditions. Under high pressure, it undergoes serials of polymorphs similar to the case of silicon, and the attractive characteristics in its high pressure phases such as metallization and superconducting transition make it one of the most appealing materials in high pressure research. However, its fundamental phase transition kinetics has been rarely studied. In this work, we present our experimental observations on the phase transition of germanium via a novel designed rapid compression tool and ultrafast time-resolved X-ray diffraction (XRD) acquisition system. The compression rate reaches to tens of TPa/s which is realized by combining gas membrane and piezoceramics compression methods in a symmetrical dynamic diamond anvil cell (dDAC). The time-resolved XRD with high resolution in microseconds is achieved by integrating the high flux pink beam diffraction, an X-ray scintillator to convert diffracted X-rays to visible lights and a high-speed optical camera. It is found that there is a time sequence for diffraction planes disappearing and appearing of dc and $\,\beta$-Sn phases, showing a displacive feature for this phase transition. In addition, the XRD evolution under static compression is also given for comparing with the dynamic compression, the results demonstrate our novel designed rapid compression and ultrafast time-resolved XRD setup shows a great potential for studying the high pressure phase transition kinetics.