Abstract
Materials with very low thermal conductivity are of high interest for both thermoelectric and optical phase-change applications. Synthetic nanostructuring is most promising to suppress thermal conductivity by scattering phonons, but challenges remain in producing bulk samples. We show that in crystalline AgSbTe2, a spontaneously-forming nanostructure leads to a suppression of thermal conductivity to a glass-like level. Our mappings of phonon mean-free-paths provide a novel bottom- up microscopic account of thermal conductivity, and also reveal intrinsic anisotropies associated with the nanostructure. Ground-state degeneracy in AgSbTe2 leads to the natural formation of nanoscale domains with different orderings on the cation sublattice, and correlated atomic displacements, which efficiently scatter phonons. This mechanism is general and points to a new avenue in nano- scale engineering of materials, to achieve low thermal conductivities for efficient thermoelectric converters and phase-change memory devices.
