Realizing high thermoelectric performance in Cu₂Te alloyed Cu_1.15In_2.29Te₄

Controlling the chemical and physical structure at the atomic level is of paramount importance for decreasing the thermal conductivity by enhancing phonon scattering in thermoelectic materials. Additional enhancement in the figure of merit (ZT) can be achieved by improving the electron transport properties. Cu-deficient ternary I-III-VI compounds receive an increasing attention because they can easily form solid solutions and thereby can readily engineer their own thermoelectric performance. In this work, we present a novel thermoelectric compound Cu1.15In2.29Te4 with the dimensionless figure of merit ZT ~1.0 through alloying with Cu2Te. The enhanced ZT value is mainly attributed to the ultralow lattice thermal conductivity (κL=0.24 WK-1m-1 at 825 K), caused by a pronounced local lattice disorder as a result of the interstitial residing of extra Te. Density Functional Theory based first-principles calculations further elucidate that the creation of the resonant states at Fermi level and impurity levels near the valence band edge have increased the effective mass and carrier concentration: resulting in the improved electrical properties. Moreover, the localized modes of the Te interstitial defect hybridize with the acoustic modes of stoichiometric In, Te and lead to the enhanced scattering of the thermal phonons resulting in the significant low κL. The above findings substantiate that the proper doping of Cu2Te in the newly developed Cu1.15In2.29Te4 compound can effectively manipulate both electron and phonon transport and thereby promises high thermoelectric performance