Strong Lattice Softening Induced by Atomic Mismatch in Meta-Phase Thermoelectrics

Area of Science:

• Materials Science
• Solid State Physics
• Thermoelectrics

Background:

• Conventional methods to reduce lattice thermal conductivity (κL) rely on phonon scattering, which has inherent limitations.
• Reducing phonon mean free path is a key strategy, but is constrained by interatomic spacing and phonon wavelength.

Purpose of the Study:

• To introduce a novel strategy for suppressing lattice thermal conductivity (κL) by reducing phonon velocity.
• To investigate the effect of atomic mismatch on lattice thermal conductivity and thermoelectric performance in specific meta-phases.

Main Methods:

• Incorporated atoms with significant atomic mismatch into the crystal lattices of Ag₈SnS₆, Cu₂S, and Mg₂Si.
• Substituted Tellurium (Te) for Sulfur (S) in Ag₈SnS₆ and Cu₂S, and Tin (Sn) for Silicon (Si) in Mg₂Si.
• Analyzed the impact of increased atomic mass and weakened chemical bonding on sound velocity and lattice thermal conductivity (κL).

Main Results:

• Achieved significant reductions in sound velocity due to atomic mismatch, leading to amorphous-like, extremely low lattice thermal conductivity (κL) across all temperatures.
• Demonstrated outstanding thermoelectric performance with maximum figure of merit (zT) values: 1.0 for Ag₈SnS_4.99Te, 1.1 for Mg₂Si_0.5Sn_0.5, and 2.0 for Cu₂S_0.5Te_0.5.

Conclusions:

• The study successfully demonstrates a new approach to manipulate thermal conductivity via lattice softening.
• This method provides a promising pathway for designing high-performance thermoelectric materials by effectively reducing lattice thermal conductivity (κL).