Thermoelectric Performance of Tetrahedrite Synthesized by a Modified Polyol Process

Abstract

Tetrahedrite, a promising thermoelectric material composed of earth-abundant elements, has been fabricated utilizing the rapid and low energy modified polyol process. Synthesis has been demonstrated for undoped and zinc-doped tetrahedrite samples on the gram scale requiring only 1 h at 220°C. This method is capable of incorporating dopants and producing particles in the 50−200 nm size regime. For determination of bulk thermoelectric properties, powders produced by this solution-phase method were densified into pellets by spark plasma sintering. Thermopower, electrical resistivity, and thermal conductivity were obtained for temperatures ranging from 323 to 723 K. Maximum ZT values at 723 K were found to be 0.66 and 1.09 for the undoped and zinc-doped tetrahedrite samples, respectively. These values are comparable to or greater than those obtained using time and energy intensive conventional solid-state methods. Consolidated pellets fabricated using nanomaterial produced by this solution-phase method were found to have decreased thermal conductivity, increased electrical resistivity, and increased thermopower. Exceptionally low total thermal conductivity values were found (below 0.7 W m −1 K −1 for undoped tetrahedrite and 0.5 W m −1 K −1 for zinc-doped tetrahedrite), with both having lattice thermal conductivities below 0.4 W m −1 K −1. This study explores how nanostructuring and doping of tetrahedrite via a solution-phase polyol process impacts thermoelectric performance.

Scalable synthesis of Cu–Sb–S phases from reactive melts of metal xanthates and effect of cationic manipulation on structural and optical properties

“…These images indicate the formation of pseudo-spherical particles at the nano-scale with an average size of 61 ± 8 nm. Similar morphologies for tetrahedrite nanoparticles (in the range of 50–200 nm) synthesised by modified polyol process have been reported 35 . The EDX spectra for tetrahedrite (Supporting Information Fig.…”

“…A layer thickness of 50–100 nm was achieved by spin coating and 1–2 µm by drop casting. Weller et al 35 reported the solution-phase synthesis of tetrahedrite using a polyol process, which produced a nanostructured product (50–200 nm) 35 . It was shown that for these materials the thermopower was enhanced and thermal conductivity was decreased as compared to bulk tetrahedrite.…”

Copper Sulfides: Earth‐Abundant and Low‐Cost Thermoelectric Materials

“…Hence, such simple synthetic routes are very useful to make the production of thermoelectric materials in a cost‐effective manner. Similarly, a solution‐phase combined solid‐state synthesis called the modified polyol process is demonstrated to synthesize undoped and zinc‐doped tetrahedrites by Weller et al Here, the complete synthesis of tetrahedrite has been carried out in only 1 h. The maximum values of zT obtained are 0.66 (with S = 210 µV K −1 , ρ = 1.1 × 10 −2 Ω cm, and k = 0.45 W m −1 K −1 ) for undoped tetrahedrite and 1.09 (with S = 240 µV K −1 , ρ = 1.25 × 10 −2 Ω cm, and k = 0.35 W m −1 K −1 ) for Zn‐doped tetrahedrite, which are achieved at 723 K. Both the undoped and doped samples have shown the low thermal conductivity values of less than 0.7 and 0.5 W m −1 K −1, respectively, in the temperature range of 323–723 K. Another advantage of this work is the fabrication of a nanostructured material, which is confirmed by the SEM and TEM analysis, as shown in Figure . These features helped in the increased thermopower with slightly decreased thermal conductivity as compared to most of the bulk values that are reported.…”

“…a) FESEM and b) TEM images of undoped tetrahedrite compound. Reproduced with permission . Copyright 2017, American Chemical Society. …”

Recent developments in Earth-abundant copper-sulfide thermoelectric materials

“…The majority of copper sulfides investigated to date have been prepared by high-temperature synthesis, typically in sealed, evacuated fused silica ampoules. This has inherent limitations on scale, restricting the amounts of material to < 20 g. Both mechanochemical 153 and solution-based methods 169,170 have been investigated as alternative scalable synthetic routes to tetrahedrites and each has been shown to produce material with comparable performance to that produced by small-scale high-temperature synthesis. Similarly, up-scaling consolidation by SPS has also been achieved.…”