Thermoelectric properties of Cu₂Ga₄Te₇ based compounds with Zn substitution for Cu and Ga

Abstract

We present two series of Cu2Ga4Te7‐based compounds with Zn substituting for Cu (Cu‐poor) and Ga (Ga‐poor), and have observed enhanced thermoelectric performance. Generally, the Seebeck coefficient (α) and lattice thermal conductivity (κL) increase and electrical conductivity (σ) decreases with the Zn content increasing. The variation in electrical properties might be mainly due to the formation of antisite defects (normalVCu−1 and ZnormalnGa−1), the acceptors. The defects increase the local density of states (DOS) near the Fermi level and effective mass, leading to the increase in α, while on the other hand, they widen the bandgap (Eg) leading to the degradation of the electrical conductivity. The gradual enhancement in κL is attributed to the reduced phonon scattering resulting from the decrease in vacancy concentration. As a result, we attained the maximum ZT value of 0.46 for Cu‐CGT and 0.47 for Ga‐CGT at ∼770 K with a proper Zn content, which is about 20–22% higher than that of intrinsic Cu2Ga4Te7.

Thermoelectric Enhancement of Different Kinds of Metal Chalcogenides

“…The thermoelectric performances of I B –III A –VI A compounds are listed in Table 4 . To further enhance their performance, doping is a widely used as an effective method . A notable example is CuInTe 2 doped with Mn, which modifies its band structure .…”

“…Deficiency of elements, alloying, and the formation of nanocomposites are also effective routes for enhancing their thermoelectric performance. [62h,]…”

“…In contrast to the chalcopyrite structure, abundant ordered defects exist in this structure. [62a] By doping with Zn, the concentration and type of defects were optimized to achieve a ZT of 0.47 at 770 K.[62a]…”

Increased effective mass and carrier concentration responsible for the improved thermoelectric performance of the nominal compound Cu2Ga4Te7 with Sb substitution for Cu

“…24,25 Although the n H value is close to the optimal one with respect to the TE performance, 26 the compound Cu 2 Ga 4 Te 7 has a relatively high electrical resistivity and thermal conductivity. 24,25 It was reported that the highest ZT value of Cu 2 Ga 4 Te 7 is less than 0.47 at $770 K, 25,27 and 0.64 at 940 K. 28 Therefore, there is a requirement to further improve its TE performance.…”

“…That is why we have observed a general reduction in k L as the Sb content increases. The high k L values at x ¼ 0.2 at high temperatures might be due to the donor Sb Cu defect along with the visible Sb impurity neutralizing the inherent p-type cation vacancy, thus reducing the vacancy scattering centers of phonons 27.…”