Cinthia Antunes Corrêa^1,2, Jiří Volný², Klára Uhlířová², Tim Verhagen²

¹ Institute of Physics of the Czech Academy of Sciences, Department of Structure Analysis, Na Slovance 2, Prague, 182 00, Czech Republic

² Faculty of Mathematics and Physics, Charles University, Ke Karlovu 5, Prague, 121 16, Czech Republic

The misfit material (PbS)_1.11VS₂ is a compound consisting of intercalating layers of the transition metal dichalcogenide (VS₂) and monochalcogenide (PbS). The weak inter-layer van der Waals interactions and strong in-layer bonds allow for a slight twist of individual layers, creating an out-of-plane spontaneous polarization that leads to sliding ferroelectricity. Sliding ferroelectricity in two-dimensional materials has been recently shown theoretically [1] and experimentally [2]. However, most of it was observed on artificially prepared layered materials by stacking the exfoliated layers with a slight twist between them.  (PbS)_1.11VS₂ naturally grows as a stacking of the TMD and TMM, forming a van der Waals superlattice.

In this work, (PbS)_1.11VS₂ was grown by chemical vapor transport and is stable at ambient conditions. The crystal structure was elucidated using single-crystal X-ray diffraction and is an incommensurate modulated composite with the layers stacked along the c-axis. The interaction between the two subsystems works as a perturbation potential that generates satellite reflections on the diffraction patterns. Intrinsic twin formation with a relative rotation of less than one degree leads to sliding ferroelectricity at room temperature. Triangular and lamellar ferroelectric domains vary from a few nanometers to tens of micrometers. We will present the crystal structure of (PbS)_1.11VS₂ using the superspace formalism for a composite structure.

References:
[1]  L. Li and M. Wu, ACS Nano 11 (6), 6382-6388 (2017)
[2] D. Zhang et al., Nature Reviews Materials 8, 25-40 (2023)