From Two-, One-, to Zero-Dimensional Vacancies: A Densification Pattern for a Typcial Transition-Metal Dichalcogenide
Kai Hu1, Li-Min Guan1, Dong Han2
1School of Physics and Electronics, Hunan University, Changsha 410082, China.
Abstract:
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.
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