{
  "abstract": "Mixed halide perovskites are highly versatile semiconductors with applications in photovoltaics, light-emitting diodes, and photodetectors. Understanding their thermodynamic phase behavior is central to guiding compositional design and improving device stability. Here, we train machine-learned interatomic potentials (MLIPs) on density functional theory reference data for CsxRb1-xPbBr3yI3-3y, CsxRb1-xPbBr3yCl3-3y, and CsxRb1-xPbCl3yI3-3y halide perovskites, enabling large-scale hybrid Monte Carlo-molecular dynamics simulations that sample both configurational and vibrational degrees of freedom. All three binary halide systems exhibit a miscibility gap, the extent of which correlates with halide ion size mismatch. The gaps in Br-Cl and Br-I close at low temperatures, while the Cl-I gap extends above room temperature. At temperatures above the miscibility gap (200 K to 500 K), all systems show a tendency toward layered halide ordering, with halide species preferentially occupying apical or equatorial octahedral sites. In CsPbBr3yI3-3y, this ordering occurs in a device-relevant temperature regime and is linked to the structural phase transitions, shifting transition temperatures by up to 100 K relative to randomly mixed structures. We attribute the strongly non-linear composition dependence of the orthorhombic-tetragonal phase boundary observed experimentally (a linear decrease followed by a plateau) to halide ordering. Introducing Rb on the A-site weakens halide ordering and eliminates the non-linear behavior, while narrowing the miscibility gap in both the Br-I and Br-Cl systems. These results establish halide ordering as a key determinant of structural phase stability in mixed-halide perovskites.",
  "abstract_shown": true,
  "affiliations": [],
  "article_type": null,
  "arxiv": "2609.09956",
  "author_total": 6,
  "authors": [
    {
      "name": "Felix Uddén"
    },
    {
      "name": "Erik Fransson"
    },
    {
      "name": "Julia Wiktor"
    },
    {
      "name": "Benjamin M. Gallant"
    },
    {
      "name": "Dominik J. Kubicki"
    },
    {
      "name": "Paul Erhart"
    }
  ],
  "bibtex": "https://research.draconitic.com/paper/34z4y32ys9pp1.bib",
  "cited_by": 0,
  "doi": "10.48550/arxiv.2609.09956",
  "fulltext_url": null,
  "id": "34z4y32ys9pp1",
  "issns": [],
  "landing_url": "https://arxiv.org/abs/2609.09956",
  "language": null,
  "licence": "CC-BY-4.0",
  "licence_label": "CC BY 4.0",
  "licence_source": "article",
  "licence_url": "http://creativecommons.org/licenses/by/4.0/",
  "metadata_licence": "CC0-1.0",
  "native_subjects": [
    [
      "arxiv",
      "cond-mat.mtrl-sci"
    ],
    [
      "openalex",
      "2208|Perovskite Materials and Applications"
    ]
  ],
  "openalex": "W7212151112",
  "pdf_url": "https://arxiv.org/pdf/2609.09956",
  "pmcid": null,
  "pmid": null,
  "published": "2026-09-09",
  "publisher": null,
  "ris": "https://research.draconitic.com/paper/34z4y32ys9pp1.ris",
  "sources": [
    {
      "first_seen": "2026-10-30T12:20:12Z",
      "native_id": "2609.09956",
      "source": "arxiv",
      "url": "https://arxiv.org/abs/2609.09956"
    }
  ],
  "subjects": [
    {
      "field": "physics",
      "origin": "arxiv:cond-mat.mtrl-sci",
      "subfield": "condensed-matter"
    }
  ],
  "title": "Strong Impact of Halide Ordering on Structural Phase Transitions in Mixed Perovskites",
  "title_text": "Strong Impact of Halide Ordering on Structural Phase Transitions in Mixed Perovskites",
  "type": "preprint",
  "updated_at": "2026-10-30T12:20:12Z",
  "url": "https://research.draconitic.com/paper/34z4y32ys9pp1",
  "venue": "arXiv",
  "versions": []
}