Achieving High Thermoelectric Performance in Severely Distorted YbCd2Sb2

Alloying scattering of phonons is particularly effective in reducing the thermal conductivity. The alloying model considers the mass and strain fluctuations but the substitutional atoms are assumed to be positioned at the ideal lattice point, i.e., without lattice distortion. In the real case, the existence of the lattice distortion in the alloy is inevitable, and it should have an additional contribution to the phonon scattering. Such an effect, however, is usually ignored and can be partially ascribed to the difficulty of experimentally identifying and quantifying the lattice distortion. In this work, significant distortion of the crystal lattice is directly observed by the scanning transmission electron microscopy in YbCd2Sb2 with multiple elements alloying. These results show that the plane distance of adjacent Ytterbium atoms along the direction b fluctuates 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 scattering and 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 (Yb0.9Mg0.1)Cd1.2Mg0.4Zn0.4Sb2. These results indicate that tuning the lattice distortion can be a promising strategy for enhancing thermoelectric performance. Lattice distortion, a factor different from mass and strain field fluctuations, plays an important role in phonon scattering. Point defects cause severe lattice distortion in (Yb0.9Mg0.1)Cd1.2Mg0.4Zn0.4Sb2, resulting in a 53% decrease in the room‐temperature lattice thermal conductivity compared to that of the pristine sample. Eventually, an average thermoelectric figure of merit (300–700 K) of ≈0.92 is achieved.