Engineering Multiple Microstructural Defects for Record‐Breaking Thermoelectric Properties of Chalcopyrite Cu1‐xAgxGaTe2

Defect engineering for vacancies, holes, nano precipitates, dislocations, and strain are efficient means of suppressing lattice thermal conductivity. Multiple microstructural defects are successfully designed in Cu1‐xAgxGaTe2 (0 ≤ x ≤ 0.5) solid solutions through high‐ratio alloying and vibratory ball milling, to achieve ultra‐low thermal conductivity and record‐breaking thermoelectric performance. Extremely low total thermal conductivities of 1.28 W m−1 K−1 at 300 K and 0.40 W m−1 K−1 at 873 K for the Cu0.5Ag0.5GaTe2 are observed, which are ≈79% and ≈58% lower than that of the CuGaTe2 matrix. Multiple phonon scattering mechanisms are collectively responsible for the reduction of thermal conductivity in this work. On one hand, large amounts of nano precipitates and dislocations are formed via vibrating ball milling followed by the low‐temperature hot press, which can enhance phonon scattering. On the other hand, the difference in atomic sizes, distorted chemical bonds, elements fluctuation, and strained domains are caused by the high substitution ratio of Ag and also function as a center for the strong phonon scattering. As a result, the Cu0.7Ag0.3GaTe2 exhibits a record high ZTmax of ≈1.73 at 873 K and ZTave of ≈0.69 between 300–873 K, which are the highest values of CuGaTe2‐based thermoelectric materials. The multiple microstructural defects in Cu1‐xAgxGaTe2 (x = 0–0.5) solid solutions are successfully designed through high ratio alloying and high energy vibratory ball milling, which to achieve ultra‐low thermal conductivity and record‐breaking thermoelectric performance.