Impact of lattice distortions and overdamped vibrations on the structural properties and thermal transport of strongly anharmonic <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:msub> <mml:mi>AgSnSbTe</mml:mi> <mml:mn>3</mml:mn> </mml:msub> </mml:mrow> </mml:math> crystals

Abstract

Understanding and predicting the anharmonic lattice dynamics of strongly anharmonic crystals remain significant challenges in condensed-matter physics and materials science. The high-entropy strategy offers a promising pathway in realizing ``phonon glass electron crystal'' (PGEC), yet the mechanisms underpinning the ultralow lattice thermal conductivity $({\ensuremath{\kappa}}_{\mathrm{L}})$ are still largely intuitive and lack a clear physical picture. Here, we investigate the anharmonic lattice dynamics and the microscopic mechanism of the ultralow ${\ensuremath{\kappa}}_{\mathrm{L}}$ in ${\mathrm{AgSnSbTe}}_{3}$ single crystals leveraging the Wigner formalism, the compressed sensing lattice dynamics, and the anharmonic phonon renormalization. Neuroevolution potential is developed for homogeneous nonequilibrium molecular dynamics simulations to evaluate the effectiveness of the Wigner transport theory in describing the thermal transport of overdamped phonons. Our findings reveal that the off-centering effect significantly scatters the low-frequency optical phonon branches, while the large displacement vibrational modes of the Ag atoms result in extreme values of the Gr\"uneisen parameters (\ensuremath{\gamma}). This study provides physical confirmations that the off-centering effect can attenuate the phonon intensity, and the vibration or diffusion of the weakly interacted atoms can enhance the anharmonicity. We also supply fundamental insights into the realization of the stable PGEC by employing the high-entropy strategy.

Topics & Concepts