Observation of Cu + Displacement Effect in the Ferro-Ionic Order and Disorder of a Multilayered CuInP2Se6
4 affiliations
- 1National Taiwan University of Science and Technology , , ,
- 2National Science and Technology Council , , ,
- 3National Yang Ming Chiao Tung University , , ,
- 4Tamkang University , , Tamsui, ,
Abstract
Two-dimensional ferro-ionic materials belong to an emerging class of van der Waals systems with promising optoelectronics and memory functionalities. Here we present layered CuInP2Se6, a typical ferro-ionic semiconductor, whose optical transitions and charge transport reflect the structural changes associated with Cu+ ordering and local off-centering. Temperature-dependent Raman spectroscopy reveals pronounced symmetry breaking and in-plane vibrational anisotropy with Cu+ off-centering in a ferroelectric (FE) phase. Microthermoreflectance identifies an optical critical-point transition at 1.59 eV at 300 K, which evolves into resonances at 1.81, 1.91, and 2.05 eV at 20 K, accompanying the development of the low-temperature symmetry-broken state. In contrast, microphotoluminescence is dominated by a Cu+ defect-bound exciton at ∼1.35 eV and a band-edge emission of ∼1.81 eV at 20 K, evidencing a substantial reconstruction of the band edge by Cu+ displacement in a FE state. Electrical measurements exhibit hysteretic current switching behavior between the 120 and 220 K order–disorder crossover window, consistent with polarization-modulated transport in a ferro-ionic semiconductor. First-principles calculations reveal a double-well energy profile along the intralayer Cu-displacement coordinate and a Berry-phase polarization of 2.49 μC cm–2. For the relaxed low-temperature ferrielectric structure, GW+BSE calculations yield a dominant bright excitation at 1.81–1.84 eV, quantitatively supporting the A1 resonance at 1.81 eV, while the structural dependence of the band-edge states and the assignments of A2 and A3 remain qualitative. These findings establish CuInP2Se6 as a prototypical ferro-ionic semiconductor and provide fundamental insights into the interplay between Cu off-centering, band-edge reconstruction, and electronic transport across the order–disorder crossover.
Related
- Gradient multilayered RTV silicone rubber composites with carbonyl iron, conductive carbon, and ZnS for broadband microwave absorption and infrared stealth.
- One-pot electrodeposition of multilayered 3D PtNi/polymer nanocomposite. H2O2 determination in aerosol phase
- Systematic investigation of cationic monomeric, dimeric, and trimeric surfactants for self-assembly, adsorption thermodynamics, and enhanced oil displacement
- Epitaxial Displacement-etched GaAsSb Quantum Dots Emitting at Telecom Wavelengths
- High-speed in situ observation of transient bubble dynamics during molten salt electrolysis using laser Shadowgraphy
BibTeX
@article{ho2026observation,
title = {{Observation of Cu + Displacement Effect in the Ferro-Ionic Order and Disorder of a Multilayered CuInP2Se6}},
author = {Ching-Hwa Ho and Thalita Maysha Herninda and Li-Chu Chang and Yu-San Hsu and Chih-En Hsu and Anna Milatul Ummah and Shun-Jen Cheng and Hung-Chung Hsueh},
journal = {JACS Au},
year = {2026},
month = oct,
doi = {10.1021/jacsau.6c01386},
url = {https://pubs.acs.org/jaaucr/article/doi/10.1021/jacsau.6c01386/5457333/Observation-of-Cu-Displacement-Effect-in-the-Ferro},
note = {CC BY 4.0},
}
RIS
TY - JOUR
TI - Observation of Cu + Displacement Effect in the Ferro-Ionic Order and Disorder of a Multilayered CuInP2Se6
AU - Ching-Hwa Ho
AU - Thalita Maysha Herninda
AU - Li-Chu Chang
AU - Yu-San Hsu
AU - Chih-En Hsu
AU - Anna Milatul Ummah
AU - Shun-Jen Cheng
AU - Hung-Chung Hsueh
PY - 2026
DA - 2026/10/23
JO - JACS Au
DO - 10.1021/jacsau.6c01386
UR - https://pubs.acs.org/jaaucr/article/doi/10.1021/jacsau.6c01386/5457333/Observation-of-Cu-Displacement-Effect-in-the-Ferro
AB - Two-dimensional ferro-ionic materials belong to an emerging class of van der Waals systems with promising optoelectronics and memory functionalities. Here we present layered CuInP2Se6, a typical ferro-ionic semiconductor, whose optical transitions and charge transport reflect the structural changes associated with Cu+ ordering and local off-centering. Temperature-dependent Raman spectroscopy reveals pronounced symmetry breaking and in-plane vibrational anisotropy with Cu+ off-centering in a ferroelectric (FE) phase. Microthermoreflectance identifies an optical critical-point transition at 1.59 eV at 300 K, which evolves into resonances at 1.81, 1.91, and 2.05 eV at 20 K, accompanying the development of the low-temperature symmetry-broken state. In contrast, microphotoluminescence is dominated by a Cu+ defect-bound exciton at ∼1.35 eV and a band-edge emission of ∼1.81 eV at 20 K, evidencing a substantial reconstruction of the band edge by Cu+ displacement in a FE state. Electrical measurements exhibit hysteretic current switching behavior between the 120 and 220 K order–disorder crossover window, consistent with polarization-modulated transport in a ferro-ionic semiconductor. First-principles calculations reveal a double-well energy profile along the intralayer Cu-displacement coordinate and a Berry-phase polarization of 2.49 μC cm–2. For the relaxed low-temperature ferrielectric structure, GW+BSE calculations yield a dominant bright excitation at 1.81–1.84 eV, quantitatively supporting the A1 resonance at 1.81 eV, while the structural dependence of the band-edge states and the assignments of A2 and A3 remain qualitative. These findings establish CuInP2Se6 as a prototypical ferro-ionic semiconductor and provide fundamental insights into the interplay between Cu off-centering, band-edge reconstruction, and electronic transport across the order–disorder crossover.
SN - 2691-3704
ER -