Commensurate stacking phase transitions in an intercalated transition metal dichalcogenide

Xiaohui Yang,Jin-Ke Bao,Zhefeng Lou,Peng Li,Chenxi Jiang,Jialu Wang,Tulai Sun,Yabin Liu,Wei Guo,Sitaram Ramakrishnan,Surya Rohith Kotla,Martin Tolkiehn,Carsten Paulmann,Guang-Han Cao,Yuefeng Nie,Wenbin Li,Yang Liu,Sander van Smaalen*,Xiao Lin*,Zhu-An Xu*

Intercalation and stacking-order modulation are two active ways in manipulating the interlayer interaction of transition metal dichalcogenides (TMDCs), which lead to a variety of emergent phases and allow for engineering material properties. Herein, the growth of Pb-intercalated TMDCs–Pb(Ta1+xSe2)2, the first 124-phase, is reported. Pb(Ta1+xSe2)2 exhibits a unique two-step first-order structural phase transition at around 230 K. The transitions are solely associated with the stacking degree of freedom, evolving from a high-temperature (high-T) phase with ABC stacking and R3m symmetry to an intermediate phase with AB stacking and P3m1, and finally to a low-temperature (low-T) phase again with R3msymmetry, but with ACB stacking. Each step involves a rigid slide of building blocks by a vector [1/3, 2/3, 0]. Intriguingly, gigantic lattice contractions occur at the transitions on warming. At low-T, bulk superconductivity with Tc ≈ 1.8 K is observed. The underlying physics of the structural phase transitions are discussed from first-principle calculations. The symmetry analysis reveals topological nodal lines in the band structure. The results demonstrate the possibility of realizing higher-order metal-intercalated phases of TMDCs and advance the knowledge of polymorphic transitions, and may inspire stacking-order engineering in TMDCs and beyond.

Advanced Materials. Vol.34, Issue6.2108550 (2022)

The published article is available at https://onlinelibrary.wiley.com/doi/10.1002/adma.202108550