Glassy thermal conductivity in Cs₃Bi₂I₆Cl₃ single crystal

Area of Science:

• Materials Science
• Solid-State Physics
• Crystallography

Background:

• Destroying long-range order in crystals reduces lattice thermal conductivity (κL).
• Achieving ultralow, glass-like κL in crystalline materials is vital for applications like thermoelectrics.
• Layered halide perovskites offer potential for novel thermal transport properties.

Purpose of the Study:

• To demonstrate ultralow and glass-like lattice thermal conductivity in a single crystal of Cs3Bi2I6Cl3.
• To investigate the underlying mechanisms responsible for the observed thermal transport behavior.

Main Methods:

• Measurement of lattice thermal conductivity (κL) from 2 to 400 K.
• Synchrotron X-ray pair-distribution function analysis.
• Phonon analysis including cut-off frequency and sound velocity.

Main Results:

• Ultralow κL of ~0.20 W/m·K at room temperature was achieved.
• A glass-like temperature dependence of κL was observed between 2-400 K.
• Low cut-off frequency acoustic phonons, soft elastic properties, strong anharmonicity from Cs atom vibrations, and local structural distortions were identified.

Conclusions:

• Cs3Bi2I6Cl3 exhibits exceptionally low lattice thermal conductivity with glass-like behavior.
• Hierarchical chemical bonding and selective sublattice vibrations contribute to the low κL.
• The findings offer insights into lattice dynamics and potential applications in thermal management.