Cation disorder in AgSbTe2 leads to glasslike ultralow lattice thermal conductivity

초록

Thermoelectric efficiency benefits from suppressing lattice thermal conductivity (kappa l), yet the microscopic origin of the glasslike ultralow kappa l in AgSbTe2 remains debated. Here we combine first-principles simulation of anharmonic lattice dynamics with the unified theory of thermal transport to quantify how Ag-Sb cation disorder controls heat conduction. We find that compared with cation-ordered L11 and D4 phases, disordered structures exhibit a strongly reduced kappa l across a wide temperature range [approximately equal to 0.48 W/(m K) at 300 K] and a much weaker temperature dependence (proportional to T-0.40). Our detailed analysis of the phonon spectrum and mode-resolved transport properties reveals that cation disorder disrupts the Te-centered octahedral network, softens phonons, lowers group velocities, and enhances low-frequency scattering, thus dramatically suppressing the diagonal (particlelike) contribution [approximately equal to 0.07 W/(mK)] while making the off-diagonal (wavelike) term dominant. Moreover, we performed a statistical analysis of kappa l of 434 dynamically stable cation-disordered configurations, which reveals a robust positive correlation between kappa l and the average frequency of acoustic modes. In addition, acoustic softening further correlates with increased Ag and Te participation and reduced participation ratios, indicating disorder-induced localization of heat-carrying modes. These results identify cation-disorder-driven localization and low-frequency scattering as key to the phonon-glass behavior of AgSbTe2, and suggest disorder engineering as a route to tune kappa l in multication thermoelectrics.

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