- Petr Doležal: Crystal structure of van der Walls materials
- 9. 11. 2022, 14:10
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Intensive research of the van der Waals materials TX3 (T is a transition metal and X is a halogen anion) in recent years is motivated by their possible use in spintronic and optoelectronic devices. Besides the promising application possibilities, these materials have also very interesting and complex structural properties.
The crystal structure of trihalides is usually dimorphic. At room temperature the VI3 and VBr3 compounds have a rhombohedral lattice, which is modified by a subtle structural distortion upon cooling through a structural transition at 79 K and 90 K, respectively. The connections of structural transitions with magnetic phenomena in VI3 suggest a considerable role of magnetoelastic interactions. As an exception seems to be the CrI3 compound, its crystal structures have almost opposite order than the rest of trihalides. At room temperature the symmetry of the CrI3 lattice is monoclinic and during cooling below 180 K it undergoes a structural transition. It is uncommon, that the low-temperature lattice symmetry is rhombohedral, higher than room-temperature one. The transition has also 40 K hysteresis, which is in strong contrast of the rest trihalides, where the hysteresis is negligible.