Femtosecond Electron Diffraction Reveals Local Disorder and Local Anharmonicity in Thermoelectric SnSe.

Area of Science:

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

Background:

• Local disorder, deviating from average lattice structure, profoundly influences crystalline functional materials' properties.
• Experimentally characterizing 3D atomic configurations of local disorder and linking them to material functions is challenging.

Purpose of the Study:

• To experimentally identify and characterize 3D local disorder and local anharmonicity in thermoelectric tin selenide (SnSe).
• To elucidate the role of local disorder in the ultralow thermal conductivity of SnSe.

Main Methods:

• Utilized femtosecond electron diffraction, structure factor calculations, and time-dependent density functional theory molecular dynamics simulations.
• Investigated ultrafast structural dynamics to reveal local atomic configurations and anharmonicity.

Main Results:

• Exclusively identified static local disorder and local anharmonicity in SnSe, characterized by off-symmetry Sn displacements (≈0.4 Å).
• Observed ultrafast atomic displacements within 100 fs, indicative of THz Einstein oscillators, driven by local disorder anharmonicity.
• Correlated identified local disorder and anharmonicity with a glass-like thermal transport channel.

Conclusions:

• The study provides a novel method for revealing 3D local disorder and interactions using ultrafast structural dynamics.
• Findings update fundamental understanding of SnSe's ultralow thermal conductivity.
• The approach offers inspiration for establishing structure-property relationships in materials science.