Anharmonicity in Thermal Insulators: An Analysis from First Principles.

Area of Science:

• Condensed Matter Physics
• Materials Science
• Solid-State Physics

Background:

• Atomic motion anharmonicity is a key factor limiting thermal conductivity in crystalline solids.
• A detailed microscopic understanding of mechanisms in strong thermal insulators is currently lacking.
• Existing models often use perturbative approaches, assuming dynamics around a single stable geometry.

Purpose of the Study:

• To classify materials based on anharmonicity and identify novel thermal insulators.
• To investigate the microscopic mechanisms governing thermal conductivity in strong insulators.
• To challenge the conventional perturbative approach by considering dynamics around multiple geometries.

Main Methods:

• Classification of 465 experimentally known materials based on anharmonicity.
• Fully anharmonic ab initio Green-Kubo calculations for 58 selected materials.
• Analysis of atomic dynamics and exploration of metastable intrinsic defect geometries.

Main Results:

• Identification of 28 thermal insulators with thermal conductivity (κ) below 10 W/mK.
• Discovery of 6 materials exhibiting ultralow thermal conductivity (κ ≤ 1 W/mK).
• Demonstration that strong anharmonic dynamics arise from exploring metastable defect geometries.

Conclusions:

• The exploration of metastable intrinsic defect geometries is the primary driver of strong anharmonic dynamics in thermal insulators.
• This finding contrasts with traditional perturbative methods that assume dynamics around a single stable geometry.
• The study provides a new understanding of heat transport in solids and identifies promising materials for thermal management applications.