A reversible structural transition at 300 K to a low-symmetry polytype of hafnium disulfide atomic layers. (March 2021)

• Record Type: Journal Article
• Authors: Peng, Jie; Najmaei, Sina; Dubey, Madan; Chung, Peter W.
• Is Part Of: Materials today communications. Volume 26(2021)
• Publication Date: 2021-03
• Subjects: Phase transition -- Transition metal dichalcogenide -- Low enthalpy -- Non-centrosymmetry -- Anharmonic phonons; Materials science -- Periodicals; 620.11
• DOI: 10.1016/j.mtcomm.2020.101722
• Languages: English
• ISSNs: 2352-4928

Abstract

Graphical abstract: Highlights: Temperature-dependent anharmonic phonons enable a symmetry-breaking phase transformation in a 2D material. The low enthalpy transition is reversible, at room temperature, and does not involve mass or charge transfer. Raman measurements can give the false appearance of a change in sign of the thermal expansion coefficient. Abstract: Materials with multiple structural phases can be highly desirable because the transition can drive properties between phases. Low enthalpy transitions can particularly enable reconfigurable behaviors due to their low energy cost. In this work, a reversible thermally induced phase transformation is found near room-temperature between centrosymmetric and a previously unobserved non-centrosymmetric hafnium disulfide polytype. The symmetry-breaking mechanism requires no diffusion, intercalation, or charge transfer. A combination of experiments and simulations is used to determine that anharmonic phonons, weaker interlayer interactions, and variable metal atom coordination play important mediating roles in creating a pathway accessible to a lower free energy configuration. The transition occurs at 300 K and is marked by stacked AAA planes shifting into an ABC stacking and the shift is reversible in repeated cool-down experiments. The results demonstrate a reversible a phase transition that offers a unique mechanism for reconfigurability in a two dimensional material.