Stress-induced phase transitions in nanoscale CuInP2S6

Abstract

Using Landau-Ginsburg-Devonshire approach and available experimental results we constructed multiwell thermodynamic potential of the layered ferroelectric CuInP2S6 (CIPS). The analysis of temperature dependences of the dielectric permittivity and lattice constants for different applied pressures unexpectedly reveals the critically important role of a nonlinear electrostriction in this material. With the nonlinear electrostriction included we calculated the temperature and pressure phase diagrams and spontaneous polarization of a bulk CIPS, within the assumed range of applicable temperatures and applied pressures. Using the developed thermodynamic potential, we revealed the strain-induced phase transitions in thin epitaxial СIPS films, as well as the stress-induced phase transitions in СIPS nanoparticles, which shape varies from prolate needles to oblate disks. We also revealed the strong influence of a mismatch strain, elastic stress and shape anisotropy on the phase diagrams and polar properties of a nanoscale CIPS, and derived analytical expressions allowing for elastic control of the nanoscale CIPS polar properties.Hence obtained results can be of particular interest for the strain-engineering of nanoscale layered ferroelectrics.

Stress and Curvature Effects in Layered 2D Ferroelectric CuInP2S6

“…F ijkl is the flexoelectric stress tensor determined by the microscopic properties of the material. , Einstein summation over repeated indexes is used hereinafter. The values T C , α T , β, γ and δ, Q ijkl and Z ijkl , given in Table AI in the Supporting Information, were defined in ref .…”

“…At the same time, stress is one of the well-recognized control parameters in ferroelectric thin films that can couple to polarization and induce transitions between structural variants. For Cu-based layered chalcogenides, stress-induced phase transitions and strain engineering , become especially important in ultrathin films of CuInP 2 (S,Se) 6 , ,, Despite the significant fundamental and practical interest in bulk and nanosized CuInP 2 (S,Se) 6 , the influence of stress and strains on the local switching of its spontaneous polarization is explored only weakly. From a theoretical perspective, there has been very little effort on both mesoscopic and atomistic levels of theory.…”

Anomalous polarization enhancement in a van der Waals ferroelectric material under pressure

“…In the HP phase, the spontaneous polarization is greatly enhanced (∼12.24 µC cm −2 ) compared to the ground state (∼3.34 µC cm −2 with full intralayer sites occupancy of Cu 1+ ). On the other hand, giant negative piezoelectricity and nonlinear electrostriction in CIPS also suggest a strong correlation between spontaneous polarization and strain [26][27][28] . These earlier reports prompted us to investigate the spontaneous polarization of CIPS under pressure.…”