Enhanced Second-Harmonic Generation of van der Waals CuInP₂S₆ via Pressure-Regulated Cationic Displacement

Abstract

Design and exploration of high-performance nonlinear optical (NLO) materials have long been sought with the goal of tunable local structures and NLO properties for advanced laser technology. Thus far, the design strategies for second-order NLO materials have been mainly focused on anionic groups that have made great progress in the development of new NLO compounds. However, few studies have focused on the effects of cationic components and their contributions to NLO properties have long been underappreciated and remain unclear. Here, by introducing pressure to continuously tune the Cu displacement, we demonstrate the significant role of the cationic configuration in NLO properties, and a remarkable enhancement by one order of magnitude in second-harmonic generation (SHG) has been achieved at 3.4 GPa in thiophosphate CuInP 2 S 6 (CIPS). In situ high-pressure structural characterization indicates that Cu cations move from the van der Waals edge to the cages of S 6 octahedra during compression and subsequently form highly distorted [CuS 6 ] octahedra at 3.2 GPa. We quantitively demonstrate the contributions of cationic displacement on the octahedral distortion and interband dipole moments, which dominate optical nonlinearity and determine the enhanced SHG. This work deepens the fundamental understanding of the relationship between cationic displacement and SHG properties, thus providing new paths to NLO material design by optimizing the cationic configurations.

Anomalous polarization enhancement in a vdW ferroelectric material under pressure

“…Previous studies 24,25 reported that CIPS maintains the ambient conditions phase up to 4-5 GPa then a phase transition from the monoclinic (Cc) to centrosymmetric trigonal (P-31m) structure occurs. However, the sharp increase in spontaneous polarization up to about 0.26 GPa has not been reported.…”

“…33 However, the increased optical band gap under high pressure indicates that the coupling is weakened, and the migration of Cu cations to the center of the S octahedron becomes the dominant factor. 25 The competition between the two factors likely give rise to the plateau of remanent polarization between 0.26 and 1.4 GPa.…”

Significant Enhancement of Optoelectronic Properties in CuInP2S6 via Pressure-Induced Structural Phase Transition

“…25 The band gap obtained by the Tauc plot method is 2.8 eV (Figure 1d, inset), consistent with a previous result. 22 In situ high-pressure optoelectronic experiments were conducted on CIPS. The photoresponse was measured first at 0.6 GPa with different voltages and light power intensities.…”

“…It has been proved that the ferroelectric phase transition temperature T c of CIPS can be modulated by hydrostatic pressure. , In addition, a pressure-induced phase transition from monoclinic to trigonal has been demonstrated at 4.0 GPa . Recently, a remarkable enhancement of second-harmonic generation in CIPS has been realized by applying pressure, which is related to Cu cation movement during the phase transition . The significant pressure-tuning properties of CIPS inspire us that high pressure may provide a potential way to regulate its optoelectronic properties.…”

“…21 Recently, a remarkable enhancement of second-harmonic generation in CIPS has been realized by applying pressure, which is related to Cu cation movement during the phase transition. 22 The significant pressure-tuning properties of CIPS inspire us that high pressure may provide a potential way to regulate its optoelectronic properties.…”