Achieving High Thermoelectric Performance in Severely Distorted YbCd_2Sb_2

摘要

Alloying scattering of phonons is particularly effective in reducing the thermalconductivity. The alloying model considers the mass and strain fluctuationsbut the substitutional atoms are assumed to be positioned at the ideal latticepoint, i.e., without lattice distortion. In the real case, the existence of the latticedistortion in the alloy is inevitable, and it should have an additional contributionto the phonon scattering. Such an effect, however, is usually ignoredand can be partially ascribed to the difficulty of experimentally identifyingand quantifying the lattice distortion. In this work, significant distortion ofthe crystal lattice is directly observed by the scanning transmission electronmicroscopy in YbCd_2Sb_2 with multiple elements alloying. These results showthat the plane distance of adjacent Ytterbium atoms along the direction bfluctuates in the range between 0.34 and 0.46 nm, a distortion from ≈?11.7%to ≈16.0%. The lattice distortion plays a remarkable role in phonon scatteringand substantially reduces the lattice thermal conductivity to ≈0.45 Wm~(-1) K~(–1)at 700 K. As a result, a peak zT of ≈1.4 is achieved in (Yb_(0.9)Mg_(0.1))Cd_(1.2)Mg_(0.4)Zn_(0.4)Sb_2. These results indicate that tuning the lattice distortioncan be a promising strategy for enhancing thermoelectric performance.