Pressure-Driven Structural Phase Competition and Functional Response in Layered LiInP2S6

Abstract

Understanding how hydrostatic pressure modifies interlayer interactions and competing ionic configurations is essential for controlling the emergent functional properties of layered quantum materials. Here, using first-principles density-functional theory calculations, we investigate the pressure-dependent structural, mechanical, electronic, and optical properties of three competing LiInP2S6 polymorphs: the monoclinic C2/c phase and the trigonal P-31c phase in both in-layer and in-gap configurations. Our results reveal a pressure-induced structural phase transition from the monoclinic ground-state C2/c phase to a trigonal P-31c in-layer phase at ~0.38 GPa, driven by enhanced interlayer coupling and anisotropic lattice compression. In contrast, the trigonal P-31c in-gap phase remains energetically unfavorable due to its stronger interlayer ionic interactions and reduced compressibility. All phases remain mechanically stable under compression (0-26 GPa) and exhibit enhanced mechanical rigidity, elastic wave velocities, and Debye temperatures with increasing pressure. Remarkably, the electronic and optical properties within each phase remain highly robust under pressure, with only moderate changes in the band gap and optical absorption edge (UV-Visible range) under pressure; however, substantial modifications emerge across the pressure-induced structural phase transition. These findings establish LiInP2S6 as a pressure sensitive ionic-vdW material in which subtle changes in interlayer interactions govern structural stability and functional properties.

13 pages, 9 figures

References in corpus (12)

• Restoring the density-gradient expansion for exchange in solids and surfaces
• Generalized gradient approximation for solids and their surfaces
• Van der Waals heterostructures
• VASPKIT: A User-friendly Interface Facilitating High-throughput Computing and Analysis Using VASP Code
• PyProcar: A Python library for electronic structure pre/post-processing
• Pressure-induced electronic mixing and enhancement of ferromagnetic ordering in EuX (X=Te, Se, S, O) magnetic semiconductors
• Vibrational properties of CuInP2S6 across the ferroelectric transition
• Disentangling stress and curvature effects in layered 2D ferroelectric CuInP2S6
• Stress-Induced Phase Transitions in Nanoscale CuInP${}_2$S${}_6$
• Unconventional ferroelectric domain switching dynamics in CuInP2S6 from first principles
• Pressure-driven phase transformations and phase segregation in ferrielectric CuInP${}_2$S${}_6$-In${}_{4/3}$P${}_2$S${}_6$ self-assembled heterostructures
• Cyclic Ferroelectric Switching and Quantized Charge Transport in CuInP${}_2$S${}_6$