Emergent coherent-incoherent phonon crossover enables ultralow lattice thermal conductivity in 3D double perovskite
The interplay between coherent (wave-like) and incoherent (particle-like) phonon transport is central to heat conduction, yet experimental evidence of their crossover in bulk three-dimensional (3D) crystals remains scarce. Here, we report intrinsically ultralow lattice thermal conductivity ( κ l ) in the lead-free double perovskite Cs 2 AgBiCl 6 , reaching 0.52 and 0.28 W m −1 K −1 in single crystal and polycrystals, respectively, at room temperature. Combining thermal transport, low-temperature heat capacity, Raman spectroscopy, synchrotron x-ray pair distribution function analysis, and anharmonic lattice-dynamics calculations, we uncover the microscopic origin of this anomalous heat transport. Chemical bonding heterogeneity, weakly bound rattling-like Cs vibrations, anisotropic Cl dynamics, and soft lattice modes generate low-energy localized optical phonons that strongly interact with acoustic modes. Enhanced three- and four-phonon scattering suppresses phonon lifetimes, while anharmonic renormalization flattens optical branches and reduces group velocities. Coherent contributions account for ∼50% of κ l near room temperature and exceeding incoherent contributions above ∼200 K, revealing an emergent coherent-incoherent phonon crossover in a fully crystalline 3D solid.
Authors
- Abhishek Das (ORCID: https://orcid.org/0000-0002-2362-0195)
- Moinak Dutta (ORCID: https://orcid.org/0000-0001-7166-7206)
- Subhajit Roychowdhury (ORCID: https://orcid.org/0000-0002-1808-9432)
- P. Lemmens (ORCID: https://orcid.org/0000-0002-0894-3412)
- D. S. Ukolov (ORCID: https://orcid.org/0000-0002-0780-9115)
- Koushik Pal (ORCID: https://orcid.org/0000-0002-5426-9748)
- Naveen Kumar Tailor (ORCID: https://orcid.org/0000-0001-7479-872X)
- Pranav Negi (ORCID: https://orcid.org/0009-0005-1810-3993)
- Krishnendu Maji (ORCID: https://orcid.org/0009-0008-0372-8589)
- Yu Pan (ORCID: https://orcid.org/0000-0002-8769-4193)
- María Ibáñez (ORCID: https://orcid.org/0000-0001-5013-2843)
- Shuai Wu (ORCID: https://orcid.org/0000-0003-1818-0831)
- Shantanu Semwal (ORCID: https://orcid.org/0009-0007-4483-9157)
- Koushik Medhi (ORCID: https://orcid.org/0009-0005-7335-3565)
- Kshyama Sagar Nag
- Divij Gupta (ORCID: https://orcid.org/0009-0006-1959-1690)
Institutions
- Indian Institute of Technology Jodhpur (IN)
- Institute of Science and Technology Austria (AT)
- Indian Institute of Science Education and Research, Bhopal (IN)
- Tata Steel (India) (IN)
- Indian Institute of Technology Kanpur (IN)
- Technische Universität Braunschweig (DE)
Publication Details
- Journal
- Science Advances
- Published
- 2026-10-14
- DOI
- https://doi.org/10.1126/sciadv.aej9757
- Primary Topic
- Thermal properties of materials
- Type
- article
- Field-Weighted Citation Impact
- 0.00
Funders
- Deutsche Forschungsgemeinschaft
- Horizon 2020 Framework Programme
- National Key Research and Development Program of China Stem Cell and Translational Research