{
  "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.",
  "abstract_shown": true,
  "affiliations": [
    "National Taiwan University of Science and Technology , , ,",
    "National Science and Technology Council , , ,",
    "National Yang Ming Chiao Tung University , , ,",
    "Tamkang University , , Tamsui, ,"
  ],
  "article_type": null,
  "arxiv": null,
  "author_total": 8,
  "authors": [
    {
      "affs": [
        0,
        1
      ],
      "name": "Ching-Hwa Ho",
      "orcid": "0000-0002-7195-208X"
    },
    {
      "affs": [
        0
      ],
      "name": "Thalita Maysha Herninda"
    },
    {
      "affs": [
        2
      ],
      "name": "Li-Chu Chang"
    },
    {
      "affs": [
        0
      ],
      "name": "Yu-San Hsu"
    },
    {
      "affs": [
        3
      ],
      "name": "Chih-En Hsu"
    },
    {
      "affs": [
        0
      ],
      "name": "Anna Milatul Ummah"
    },
    {
      "affs": [
        2
      ],
      "name": "Shun-Jen Cheng",
      "orcid": "0000-0002-1721-7914"
    },
    {
      "affs": [
        3
      ],
      "name": "Hung-Chung Hsueh",
      "orcid": "0000-0003-2830-8771"
    }
  ],
  "bibtex": "https://research.draconitic.com/paper/apaxja0ekdshb.bib",
  "cited_by": 0,
  "doi": "10.1021/jacsau.6c01386",
  "fulltext_url": null,
  "id": "apaxja0ekdshb",
  "issns": [
    "2691-3704"
  ],
  "landing_url": "https://pubs.acs.org/jaaucr/article/doi/10.1021/jacsau.6c01386/5457333/Observation-of-Cu-Displacement-Effect-in-the-Ferro",
  "language": null,
  "licence": "CC-BY-4.0",
  "licence_label": "CC BY 4.0",
  "licence_source": "article",
  "licence_url": "https://creativecommons.org/licenses/by/4.0/",
  "metadata_licence": null,
  "native_subjects": [
    [
      "openalex",
      "2505|2D Materials and Applications"
    ]
  ],
  "openalex": "W7223260133",
  "pdf_url": "https://pubs.acs.org/doi/pdf/10.1021/jacsau.6c01386",
  "pmcid": null,
  "pmid": null,
  "published": "2026-10-23",
  "publisher": "American Chemical Society (ACS)",
  "ris": "https://research.draconitic.com/paper/apaxja0ekdshb.ris",
  "sources": [
    {
      "first_seen": "2026-10-30T12:18:36Z",
      "native_id": "10.1021/jacsau.6c01386",
      "source": "crossref",
      "url": "https://pubs.acs.org/jaaucr/article/doi/10.1021/jacsau.6c01386/5457333/Observation-of-Cu-Displacement-Effect-in-the-Ferro"
    }
  ],
  "subjects": [
    {
      "field": "chemistry",
      "origin": "openalex:2505|2D Materials and Applications",
      "subfield": "materials-polymers"
    }
  ],
  "title": "Observation of Cu + Displacement Effect in the Ferro-Ionic Order and Disorder of a Multilayered CuInP2Se6",
  "title_text": "Observation of Cu + Displacement Effect in the Ferro-Ionic Order and Disorder of a Multilayered CuInP2Se6",
  "type": "peer-reviewed",
  "updated_at": "2026-10-30T12:18:36Z",
  "url": "https://research.draconitic.com/paper/apaxja0ekdshb",
  "venue": "JACS Au",
  "versions": []
}