Doping distribution in Skutterudites with ultra-high filling fractions for achieving ultra-low thermal conductivity

Low lattice thermal conductivity is of great importance for thermoelectric materials and thermal barrier materials. Interstitial or substitutional atoms in the host lattice fundamentally introduce point defects to scatter phonons, which is, however, not sufficient for achieving glass-like thermal conductivity. Here, we fabricated the Yb-filled CoSb₃ skutterudites with an ultra-high Yb filling fraction, in which the coexistence of ordered superstructures and nano/sub-nano scale inhomogeneous Yb interstitials was revealed. An ultra-low lattice thermal conductivity approaching the glass limit was achieved due to the enhanced rattling effect from the ultra-high Yb filling fraction and extra phonon scattering from the ordered superstructures, nanoscale inhomogeneous Yb fillers, and high-density lattice strain caused by the ordered and modulated fillers. Modulating the distribution of doping atoms opens a new dimension for doping atoms to achieve ultra-low thermal conductivities for thermoelectric materials and thermal barrier materials beyond the point defects scattering perspective.