From Two-, One-, to Zero-Dimensional Vacancies: A Densification Pattern for a Typcial Transition-Metal Dichalcogenide of TiSe2

In the areas of condensed matter physics, geoscience, material science, and inorganic chemistry, how the crystal structures evolve under an external field such as high-pressure is a fundamental question. By taking TiSe2 as the case, we investigate the phase transformations of the layered transition-metal dichalcogenides (TMDs) under high-pressure. The ambient 6-fold P-3m1 TiSe2 undergoes a transformation into the monoclinic 8-fold coordinated C2/m phase at 15 GPa and then into the hexagonal 9-fold Fe2P-type structure at 34 GPa. The above phase transitions can be unitedly described as the evolution of the vacancies: from a layered structure with two-dimensional (2D) vacancies to the structure with one-dimensional (1D) and zero-dimensional (0D) vacancies. The proposed densification model of TiSe2 reveals the processes how the symmetry breaking phase of spatial chemical bonding restores the symmetry under the isotropic external pressure.

Automated summary

By investigating the phase transformations of layered transition-metal dichalcogenides under high pressure, using TiSe2 as a case study, it was found that the evolution of vacancies plays a crucial role. The proposed densification model reveals how the symmetry-breaking phase of spatial chemical bonding restores symmetry under isotropic external pressure.