Yielding under compression and the polyamorphic transition in silicon
Physical review materials(2023)
Abstract
We investigate the behavior of amorphous silicon under hydrostatic compression using molecular simulations. During compression, amorphous silicon undergoes a transformation from a low-density to a high-density structure. Depending on the temperature and the compression rate, the transformation occurs in a pressure range between 6 and 16 GPa. Ensemble-averaged density and elastic constants change discontinuously across the transition. Densification of individual glassy samples occurs through a series of discrete plastic events, each of which is accompanied by a vanishing shear modulus. This is the signature of a series of elastic instabilities, similar to shear transformation zones observed during shear yielding of glasses. We compare the structure obtained during compression with a quasiequilibrium form of amorphous silicon obtained by quenching a melt at constant pressure. This gives structures identical to compression at low and high pressure, but the transition between low- and high-pressure structures occurs gradually rather than discontinuously. Our observations indicate that the polyamorphic transition has the characteristics of a yield transition that occurs under compression instead of shear.
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Key words
silicon,polyamorphic transition,compression
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