High-entropy compounds with compositional complexity can be designed as new thermoelectric materials. Here a data-driven model was developed, which chose suitable elements to reduce the enthalpy of formation and hence to increase the chance of single phase formation. Using this model, two high-entropy sulfides were designed, metallic Cu5SnMgGeZnS9 and semiconducting Cu3SnMgInZnS7. They were then successfully fabricated as single-phase dense ceramics with homogeneously distributed cations, and their phase stability and atomic local structures were investigated using density functional theory calculations. Finally, a zT value of 0.58 at 773 K was obtained for Cu5Sn1.2MgGeZnS9, where additional Sn was used to tune the carrier concentration. This work provides a simple approach to find new high-entropy functional materials in the largely unexplored multielement chemical space.

We report a remarkably high and stable thermoelectric zT ∼ 2 by manipulating the electronic bands in hybrid flash-SPSed Ga–Sb codoped GeTe.

A comprehensive study on the thermoelectric effect of Ag substitution in GeTe solid solutions, a congenital base for high efficient TAGS-m [(GeTe) m (AgSbTe 2 ) 100-m ] thermoelectric materials, was performed. First-principles calculations were carried out to probe the changes arising from doping on the electronic band structure of GeTe, which exhibits a rhombohedral (r) structure at temperatures lower than 700 K. Aliovalent Ag substitution in GeTe increases the hole concentration and decreases the thermoelectric figure of merit (zT) due to the reduction of the Seebeck coefficient, which is ascribed mainly to the lowering of the Fermi level together with the loss of band degeneracy. Band structure and effective mass calculations of these doped materials also point to a soaring contribution from several hole pockets in the valence band. First-principles calculations carried out with two other group-11 transition metals (Cu, Au) reveal that silver substitution has the lowest impact on the thermopower of r- Page 1 of 32 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 2 GeTe. A mean zT of ∼0.85 at 773 K is achieved for Ge 1-x Ag x Te (x ≤ 0.04) solid solutions. The study highlights the limits in doping just a coinage metal to GeTe and recapitulates the need for pair substitution to enhance the thermoelectric properties of GeTe-based solid-state solutions.

The quaternary AgPb18SbTe20 compound (abbreviated as LAST) is a prominent thermoelectric material with good performance. Endotaxially embedded nanoscale Ag-rich precipitates contribute significantly to decreased lattice thermal conductivity (latt) in LAST alloys. In this work, Ag in LAST alloys was completely replaced by the more economically available Cu. Herein, we conscientiously investigated the different routes of synthesizing CuPb18SbTe20 after vacuum-sealed tube melt processing, including: (i) slow cooling of the melt; (ii) quenching and annealing; (iii) consolidation by spark plasma sintering (SPS); and also by the state-of-the-art (iv) Flash-SPS. Irrespective of the method of synthesis, the electrical (σ) and thermal (tot) conductivities of CuPb18SbTe20 samples were akin to that of LAST alloys. Both the flash-SPSed and the slow cooled CuPb18SbTe20 samples with nanoscale dislocations and Cu-rich nanoprecipitates exhibited an ultra-low latt  0.58 W/mK at 723 K, comparable with that its Ag counterpart, regardless of differences in their size of the precipitates, type of precipitate-matrix interfaces and other nanoscopic architectures.The sample processed by flash sintering manifested higher figure of merit (zT  0.9 at 723 K), due to better optimization and trade-off between the transport properties by decreasing the carrier concentration and latt without degrading the carrier mobility. In spite of their comparable σ and tot, the zT of the Cu samples were low compared to the Ag samples due to their contrasting thermopower values. First-principles calculations attribute this variation in Seebeck to the dwindling of the energy gap (from 0.1 eV to 0.02 eV) between the valence and conduction bands in MPb18SbTe20 (M = Cu or Ag), when Cu replaces Ag. Materials and Methods ReagentsPb (Strem Chemicals, 99.999%), Sb (Alfa Aesar, 99.999%), Cu (Alfa Aesar, 99.999%) and Te (JGI, 99.999%) were used for synthesis without any further purification. SynthesisIn this work, several different processing routes were investigated, however, the first step (synthesis) was common to all of the processing routes. Samples of CuPb18SbTe20 were synthesized using the vacuumsealed tube melt processing. Stoichiometric amounts of the starting elements of Cu, Pb, Sb and Te were introduced into a fused silica tube. The tube was prepared by cleaning with hydrofluoric (HF) acid and distilled water, then dried under vacuum. The ampoules were sealed under a vacuum of 10 -6 Torr, then placed in a rocking furnace and slowly heated to 1223 K over a period of 12 hours, then held at that temperature for 15 hours. Four different batches of samples were prepared, the first two were produced directly from the molten material, followed by: (i) cooling the melt to room temperature over a period of 18 hours (samples denoted as 'SS'); (ii) rapidly quenching the tube in water, followed by annealing at 973 K for 8 hours (denoted as 'MQ'). The other two batches used the material produced by method (i), which was crushed and milled. The powders were then ...