Acoustic emissions and shear instabilities during phase transformations in Si and Ge at ultrahigh pressures

TLDR: In this paper, the authors describe acoustic emissions and shear instabilities that are associated with the β-Sn → simple-hexagonal phase transformation in Si and Ge to pressures as high as 70 GPa, well above the brittle-ductile transitions of both elements.

Abstract: ACOUSTIC emissions are commonly observed at low pressures as they are characteristic of brittle deformation1,2. Most solids are ductile above a few gigapascals (GPa), and acoustic emissions have not been recorded from solids above 5 GPa. Here we describe acoustic emissions and shear instabilities that are associated with theβ-Sn → simple-hexagonal phase transformation in Si and Ge to pressures as high as 70 GPa, well above the brittle–ductile transitions of both elements. We propose that the events are driven by rapid atomic motions across displacive phase transformations, and not by fracturing or cracking of the samples. These phenomena may be relevant to the processes that generate deep-focus seismicity in the Earth's mantle.