High-pressure dissociation of selenium and tellurium.

Pressure-induced molecular dissociation provides significant insights into chemical bonding, governing the physical properties of molecular solids. Here the typical molecular solids, selenium and tellurium, have been explored experimentally to unearth the process of pressure-induced molecular dissociation. Before molecular dissociation, both commensurately and incommensurately modulated structures have been observed in these two elements. Upon compression, the successive commensurate-incommensurate phase transitions are proved by the soft amplitude (AMP) mode. The fitted critical pressure suggests that the molecular dissociation of Te is inferred to occur at 26.1 GPa in agreement with our XRD and Raman data. The current precise structural studies before pressure-induced molecular dissociation demonstrated in the elements selenium and tellurium will help in clarifying the mechanisms of molecular dissociation in related molecular solids.