High Thermoelectric Figure of Merit Achieved in Cu₂S_1–xTe_x Alloys Synthesized by Mechanical Alloying and Spark Plasma Sintering

Abstract

Chalcogenides have been considered as promising thermoelectric materials because of their low cost, nontoxicity, and environmental benignity. In this work, we synthesized a series of CuSTe (0 ≤ x ≤ 1) alloys by a facile, rapid method of mechanical alloying combined with spark plasma sintering process. The CuSTe system provides an excellent vision of the competition between pure phase and phase transformation, entropy-driven solid solution, and enthalpy-driven phase separation. When the Te concentration increases, the CuSTe system changed from the pure monoclinic CuS at x = 0 to monoclinic CuSTe solid solution at 0.02 ≤ x ≤ 0.06 and then transforms to hexagonal CuSTe solid solution at 0.08 ≤ x ≤ 0.1. The phase separation of hexagonal CuTe in the hexagonal CuS matrix occurs at 0.3 ≤ x ≤ 0.7 and finally forms the hexagonal CuTe at x = 1. Owing to the changed band structure and the coexisted CuS and CuTe phases, greatly enhanced power factor was achieved in all CuSTe (0< x < 1) alloys. Meanwhile, the point defect introduced by the substitution of Te/S atoms strengthened the phonon scattering, resulting in a lowered lattice thermal conductivity in most of these solid solutions. As a consequence, CuSTe exhibits a maximum ZT value of 1.18 at 723 K, which is about 3.7 and 14.8 times as compared to the values of pristine CuS (0.32) and CuTe (0.08), respectively.

Promising and Eco‐Friendly Cu2X‐Based Thermoelectric Materials: Progress and Applications

“…However, deriving from simultaneously deteriorated carrier transport properties, the zT values cannot be effectively enhanced, as shown in Figure d. Similar influence of nanoengineering in Cu 2 S has also been found . Although nanoengineering can effectively reduce κ l of Cu 2 Se, high crystallinity is important for maintaining high electrical performance in nanoengineered Cu 2 Se and subsequently a high zT.…”

“…[229][230][231][232] However, in Cu 2 X-based thermoelectric materials, some controversial phenomena have been observed. For example, heavy element doping on anion site can reduce κ l of Cu 2 Se, such as using I, [233] Te, [203,234] and S. [171] In contrast, Zhao et al [235] observed increased κ l after I and Te doping in Cu 2 Se. When the doping is on cation (Cu) site, for example, Guan et al [207] substituted Cu with Ag, inducing a large amount of CuAgSe secondary phase, which became solid-solution with the Cu 2 Se matrix when temperature was increased above 400 K, reduced the κ l .…”

“…Similar influence of nanoengineering in Cu 2 S has also been found. [174,234,241,242] Although nanoengineering can effectively reduce κ l of Cu 2 Se, high crystallinity is important for maintaining high electrical performance in nanoengineered Cu 2 Se and subsequently a high zT.…”

Recent Advances in Liquid‐Like Thermoelectric Materials

“…Figures 9 and 10). [8l,o, [26][27][28][29] When the solubility x is low, the low symmetry monoclinic crystal structure of the Cu 2−δ M matrix is well maintained at room temperature; when the solubility x is high, a high symmetry trigonal or hexagonal structure would form (cf. Figure 9).…”

eview on the general technical approaches as an effective ways to fabricate inorganic nanomaterials

“…Mechanical alloying has, recently, been applied for industrializing a wide range of nanostructured materials through top down process and favor process for producing of intermetallic compounds such as Ni-Al, Ti-Al, Fe-Al, Nb-Al and pure metallic of Cr, Fe, Ti, Cu, Co, Nb as well as alloys of Ni-Si, Ni-Mo, Ni-Zr, Cu-Ta, Cu-W nanocrystals 136,137 . Fig.9 illustrates the Cu2-Te, Sm0.9 Mg0.1FeAsO0.8F0.2, p-type SnSe, Ti-B, Ti0.5V1.2Co0.3, Fe50Se50, TiFe and La-SrTiO3 nanocrystals were attended in this ways [138][139][140][141][142][143][144][145] . Using this technique, the oxide becomes dispersed along the boundaries of the alloy grains, resulting in an alloy with increased crawling strength compared to the same alloys without the oxide being dispersed in them 146 .…”