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Higher manganese silicides have evolved as an efficient thermoelectric material because of their exceptional thermoelectric performance at intermediate temperatures. In this work, we report the ultralow-thermal conductivity with improved thermoelectric properties of Mn 1-x Cr x Si 1.8 (x = 0, 0.025, 0.05 and 0.1) prepared by induction melting followed by ball milling and uni-axial induction hot-pressing. Bragg diffraction patterns confirmed that the as-synthesized compound belongs to the Mn 15 Si 26 phase along with the solid solubility of Cr in the HMS lattice. In addition, the backscattered electron micrographs revealed the precipitation of excess Si in the HMS matrix, originating from Si-rich stoichiometry. Furthermore, an elevation in electrical conductivity with increasing Cr content has been observed because of its acceptor dopant behaviour at the Mn site. On the contrary, the Seebeck coefficient decreased upon an increase in Cr content, and bulk MnSi 1.8 has shown the highest Seebeck coefficient of 220 μV/K at 773 K. Impressively, nanostructuring along with the generated point defects as a result of Cr dopant facilitates an intensified phonon scattering at the nanostructured grain boundaries that results in a very low κ total of 0.99 W/mK at 773 K for ball-milled Mn 0.9 Cr 0.1 Si 1.8 , leading to an elevated zT of 0.46 at 773 K. [ABSTRACT FROM AUTHOR]

Higher manganese silicide (HMS) is a promising thermoelectric (TE) semiconductor that operates effectively at medium temperatures. It is characterized by its abundance, environmental friendliness, and desirable impact resistance properties. To enhance the TE properties of HMS, this study employs isoelectronic anion and cation codoping, combined with embedded quantum dot (QD) techniques. The introduction of element doping and nanoinclusions, such as Mn 0.96 Re 0.04 (Si 0.96 Ge 0.04) 1.79 +1.5%Ag 2 Pt QDs sample, leads to an approximately 85% increase in electrical conductivity. This boost is attributed to the adjustment of the band structure through Re, Ge, and Ag element doping and the charge transfer facilitated by MnSi, Si, and Pt precipitates. Furthermore, the enhanced PF of 1.85 × 10−3 W m−1 K−2 at 773 K is approximately 29% higher than that of pure HMS. Simultaneously, the increase in point defects hampers the improvement of lattice thermal conductivity (κ l) by intensively scattering short-wave phonons. This effect is complemented by the precipitation of Si, MnSi, Ag, and Pt nanoparticles, which increases the density of grain boundaries, enhances medium-wave phonon scattering, and substantially reduces κ l to 1.45 W m–l K−1 (at 773 K), ∼30% lower than that of pure HMS. The figure of merit of the sample containing 1.5%Ag 2 Pt QDs at 823 K attains a value of 0.69, which is ∼52% and ∼19% higher than that of pure HMS and Re-Ge-double-doped samples, respectively. The incorporation of isoelectronic codoping, along with the integration of metastable QDs, is demonstrated as an effective strategy for enhancing TE properties. [ABSTRACT FROM AUTHOR]

To our knowledge, this is the first study to successfully synthesise high-temperature-phase copper selenide (β -Cu 2 Se) at room temperature using rapid microwave hybrid heating (MHH). Controlling the starting Cu/Se ratio is the critical parameter for adjusting the content of α - and β -phases in the as-synthesised sample. The relatively low Cu composition causes impurities to form in the Cu 3 Se 2 phase, deteriorating the thermoelectric (TE) properties of the Cu 2 Se material. The β phase formation at room temperature promotes electrical conductivity. The thermal conductivities of the Cu 2.0 Se samples were 0.5–0.8 Wm−1K−1 at 303–673 K. A strong electronic-phonon interaction may potentially couple electronic thermal conductivity (κ e) and lattice thermal conductivity (κ L), resulting in incomplete separability of κ L and κ e in the β -Cu 2.0 Se sample. The Cu 2.0 Se exhibited a ZT value of 0.65 at 523 K because of its considerably lowered thermal conductivity. [ABSTRACT FROM AUTHOR]

Thermoelectric (TE) materials have attracted considerable interest for their potential and the figure of merit ZT serves as a crucial metric for evaluating TE performance. Chalcogenide materials, such as tellurium (Te) and selenium (Se), have been favored for high-performance TE applications. However, their toxic nature raises concerns, demanding exploration of non-toxic alternatives suitable for human-contacting devices. This study focused on antimony trioxide (Sb 2 O 3) due to its high Seebeck coefficient and explored the potential of layered double hydroxide (LDH) materials as a non-toxic alternative for efficient TE materials. Composites of Sb 2 O 3 nanowires integrated with 2D CaAl-LDH were synthesized to reduce thermal conductivity and improve TE performance. The composites displayed enhanced electrical conductivity, resulting in a significantly improved power factor. The introduction of CaAl-LDH facilitated the charge carrier transport paths, leading to better electrical performance. Furthermore, the composites exhibited reduced thermal conductivity due to phonon scattering at the heterointerfaces between Sb 2 O 3 and CaAl-LDH. As a result, the Sb 2 O 3 /CaAl-LDH_70 composite achieved a maximal ZT value of 0.0485 at 473 K, demonstrating promising potential for LDH-based composites as environmentally friendly TE materials. These findings contribute to sustainable energy conversion technologies, ensuring progress towards more efficient and biocompatible TE materials. [ABSTRACT FROM AUTHOR]

Tin sulfide (SnS), as a low-cost and eco-friendly thermoelectric (TE) material, exhibits relatively poor phonon and charge transport capacities when the long-range ordered layered crystal structure is broken by the grain boundaries of polycrystalline. Nevertheless, doping and compositing are effective strategies for improving the electrical and thermal conductivity. Herein, utilizing the composite powders synthesized via Cu-doped SnS nanosheets grown in-situ on the surface of Cu-doped SnS nanofibers, we design a homogeneous nanofibers composited Cu-doped SnS polycrystalline bulk to boost its TE performance. Comparing with pure phase SnS, Cu doping can effectively increase the carrier concentration and mobility of SnS, realizing an increase of electrical conductivity from 4.11 S·cm−1 to 31.57 S·cm−1. Simultaneously, quite a number of fiber/matrix composite interfaces for phonon scattering are formed due to incorporating of composite nanofibers, which significantly reduce the lattice thermal conductivity of Cu-doped SnS polycrystalline bulk. The results show that thermal conductivity reduced as low as 0.64 W·m−1 K−1 at 324 K when the additive amount of nanofibers was fix at 2 wt%. Ultimately, the power factor and ZT value are markedly enhanced at low and medium temperature ranges (300–500 K) compared with SnS polycrystalline bulk without fiber incorporation. This provides an effective strategy for optimizing the thermoelectric performance of SnS-based polycrystalline. [Display omitted] • In-situ growth of SnS-based nanofiber composite thermoelectric materials synthesized using a simple approach. • Cu doping increased the carrier concentration and increased the conductivity from 4.11 S·cm−1 to 31.57 S·cm−1. • The composite SnS fibers reduced the thermal conductivity from 1.38 W·m−1·K−1. to 0.64 W m−1·K−1. [ABSTRACT FROM AUTHOR]

The electron and phonon thermal transport behavior of Ag + doped KSr 2 Nb 5 O 15 were discussed by using the first-principles calculations. The band gap was reduced after Ag+ doping, and the electrons near the Fermi level had stronger transition capability, which effectively increased the carrier concentration and electrical conductivity and reduced the thermal conductivity, thereby improving the ZT of the doped KSr 2 Nb 5 O 15 from 0.6298 to 0.7214 (1200 K) under ideal conditions. In addition, the solid-state reaction method was used to prepare Ag nanoparticle added KSr 2 Nb 5 O 15 samples, and their thermoelectric performance was tested. The experimental results and the calculated results showed a good consistent trend in which Ag improved the thermoelectric properties of KSr 2 Nb 5 O 15. When the amount of addition of nanosized Ag was 20 wt%, the power factor and ZT of the material were the highest at 1073 K, which were 0.228 mW/(K2·m) and 0.1090, respectively. This research shows how to improve the thermoelectric performance of KSr 2 Nb 5 O 15 ceramics and broaden their temperature range for application. [Display omitted] [ABSTRACT FROM AUTHOR]

In this paper, thermoelectric (TE) properties of n- type InSb 1-x Bi x (x = 0.00, 0.02, 0.05 and 0.10) polycrystalline samples, synthesized by single-step vacuum melting reaction, have been studied in the temperature range of 300–623 K. P-XRD confirms the phase purity and preferred orientation of (220) plane. FE-SEM back-scattered electron (BSE) micrographs reveal surface morphology and phase homogeneity, and elemental mapping with EDS is used to identify the chemical composition. The elemental existence and oxidation state of In3+, Sb3+, and Bi3+ in InSb 1-x Bi x are rechecked through XPS analysis. With Bi substitution, the electrical conductivity of InSb increases, whereas Seebeck coefficient starts decreasing. However, the maximum Seebeck coefficient, S of −241 μV/K at 423 K, was achieved for the composition of InSb 0.98 Bi 0.02. Interestingly, a huge reduction in lattice thermal conductivity, κ lattice from ∼17.5 W/mK (InSb) to 13.1 W/mK (InSb 0.9 Bi 0.10) at 300 K is observed due to increased phonon scattering from mass-fluctuation and created point defects. Further, the maximum thermoelectric figure of merit, zT was achieved as ∼0.56 at 623 K with higher Vickers micro-hardness values of ∼140 H V for the composition of InSb 0.98 Bi 0.02 which is notably higher than the recently reported InSb based materials. [ABSTRACT FROM AUTHOR]

The SrTiO 3 perovskites n -doped with Sm3+, Dy3+, and Nb5+ were prepared via the conventional solid state reaction route (SSR) followed by spark plasma sintering (SPS) process. The SPS in dynamic vacuum promotes formation of Ti3+ and Nb4+ species, as verified by the XPS analysis. Presence of the reduced cations, primarily Ti3+, is in agreement with the observed color changes and enhanced electrical conductivity of the samples. The Sr-site substitution by Sm and Dy is highly effective in phonon scattering and reducing the lattice thermal conductivity. Besides, this substitution significantly increases the electron mobility and electrical conductivity, by reducing the lattice strain imposed by the Ti/Nb substitution. Thermoelectric measurements indicated that a doubly doped sample with the Sr 0.95 Sm 0.05 Ti 0.9 Nb 0.1 O 3 loading chemical composition reached the figure of merit (zT) value of 0.41 at 873 K. Such a high zT value originates primarily from a high carrier mobility of 24 cm2/V s and a low thermal conductivity of 2.4 W/m K. [ABSTRACT FROM AUTHOR]

Microstructure control for Bi 2 O 3 -added WO 3 ceramics is explored by changing the atomic ratio of Bi/W and the firing temperature. Densified WO 3 ceramics with two distinct microstructures are obtained for Bi/W = 0.005; the ceramic fired at 1123 K consists of WO 3 fine grains measuring several micrometers in size, whereas those fired at 1173 K and 1223 K consist of large WO 3 grains measuring several 10 μm in size. The grain growth is enhanced by a Bi 2 W 2 O 9 liquid phase formed among the WO 3 particles during the firing. Seebeck coefficient S , electrical conductivity σ , and thermal conductivity κ are measured at high temperatures for the three ceramics to elucidate the dimensionless figure of merit ZT , where Z is defined as S 2 σκ −1 and T is the absolute temperature. The ceramics consisting of larger WO 3 grains display higher power factors S 2 σ due to the higher electron carrier concentrations. The ZT values are consequently higher for these ceramics because the κ values are lower, due most likely to the larger phonon scattering by the grain boundaries developed among the larger WO 3 grains. The highest ZT is 2.4 × 10−3 at 873 K for the ceramic fired at 1223 K. [ABSTRACT FROM AUTHOR]

Bi 2 Sr 2 Co 2 O y with excellent thermoelectric properties has received extensive attention from scientific researchers. In this study, Bi 2 Sr 2 Co 2 O y ceramic samples were prepared using the solid-phase sintering method. By Ag + substitution for Bi3+, the hole concentration and electrical conductivity were optimised. On this basis, nano-SiC particles were introduced to increase grain boundaries, improve phonon scattering, reduce the mean free path of phonons, and reduce the lattice thermal conductivity. A sample with a nominal composition of Bi 1.8 Ag 0.2 Sr 2 Co 2 O y + 0.025 wt% SiC had a maximum ZT value of 0.35 at 923 K, which was approximately 67 % higher than the ZT value of pure Bi 2 Sr 2 Co 2 O y. These results confirmed that under the combined action of Ag substitution and SiC doping, the thermoelectric performance of Bi 2 Sr 2 Co 2 O y was significantly improved. [ABSTRACT FROM AUTHOR]

BiSe has emerged as a promising Te-free high-performance thermoelectric (TE) material base owing to its ultra-low lattice thermal conductivity caused by the Bi bilayers in its lattice. Herein, the TE properties of BiSe were modified by Sn doping and ball milling to improve its performance. The ball milling process reduced the grain size of the samples and affected their anisotropy during the pressing process, leading to the random arrangement of the (00 l) plane, which improved the electrical conductivity of the samples in the direction parallel to the spark plasma sintering direction and increased the Seebeck coefficient. The increased defects and smaller grain size of the samples due to Sn doping and ball milling enhanced the scattering of phonon transport, thereby decreasing the lattice thermal conductivity. The improvement in the ZT of the samples was realized through the improvement in their thermal and electrical transport. The Spark plasma-sintered bulk of the ball-milled Bi 0. 9 Sn 0. 1 Se sample exhibited a high-power factor of 8.4 μW · cm−1 · K−2 at 473 K and an ultra-low lattice thermal conductivity of 0.43 W · m−1 · K−1 at 673 K along with the maximum ZT value of 0.32 at 473 K, which is 31.6% higher than that of the pristine BiSe sample. [ABSTRACT FROM AUTHOR]

Ta 2 O 5 nanoparticles were synthesized by thermal decomposition of tantalum (V) ethoxide, and Ca 3 Co 4 O 9 /Ta 2 O 5 composites were fabricated by ball milling. The volume percentage of Ta 2 O 5 nanoparticles in the composites was controlled as 0, 2%, 4%, and 6% in four samples. The existence and dispersion of Ta 2 O 5 nanoparticles in the composites were confirmed by electron microscopies. The Ca 3 Co 4 O 9 /Ta 2 O 5 composite particles were hot-pressed into pellets and sintered for thermoelectric property measurement. The impacts of the Ta 2 O 5 volume percentage on the lattice/electronic thermal conductivity, Seebeck coefficient, electrical conductivity, and thermoelectric Figure of Merit (ZT) of the Ca 3 Co 4 O 9 /Ta 2 O 5 composites were investigated. The results indicated that an increased Ta 2 O 5 volume percentage resulted in decreased electrical conductivity and thermal conductivity. When the Ta 2 O 5 was 4 vol %, the highest Seebeck coefficient, and maximum ZT were observed in the Ca 3 Co 4 O 9 /Ta 2 O 5 composite. [ABSTRACT FROM AUTHOR]

Bi 2 Mo 2 O 9 nanoparticles were introduced into bismuth antimony tellurium (BST) alloys by ball milling, and the composite particles were then fabricated into pellets by hot press for thermoelectric property measurement. Both elemental mapping and TEM image confirmed that Bi 2 Mo 2 O 9 nanoparticles were evenly distributed among BST matrix. The impacts of Bi 2 Mo 2 O 9 volume percentage on the electrical resistivity, Seebeck coefficient, thermal conductivity, and thermoelectric figure of merit (ZT) of BST/Bi 2 Mo 2 O 9 composites were investigated. The results told that the composite presented the highest thermoelectric ZT when Bi 2 Mo 2 O 9 was 0.3 vol%, which was increased by 12.15% from the ZT of pure BST at room temperature. This could be attributed to the balance between the decreased thermal conductivity and increased electrical resistivity, and phonons could are blocked when charge carriers passing through the dispersed Bi 2 Mo 2 O 9 nanoparticles. [ABSTRACT FROM AUTHOR]

Bi 2 Sr 2 Co 2 O y (BSCO) is a layered cobalt-based oxide whose thermoelectric properties have been extensively studied recently because its layer structure of CoO 2 gives good electrical conductivity. SiC, with larger Seebeck coefficients and higher electrical conductivity, is also widely concerned in the field of thermoelectricity. In this paper, the effects of alkali metal element doping and SiC dispersion on thermoelectric properties of BSCO are studied for two series samples of Bi 1·85 Na 0·15 Sr 2 Co 2 O y + m wt% SiC (m = 0, 0.025, 0.05, 0.1, and 0.15) and Bi 1·9 K 0·1 Sr 2 Co 2 O y + z wt% SiC (z = 0, 0.025, 0.05, 0.1, and 0.15). After Na+ and K+ replacing Bi3+ sites, the electrical resistivity of BSCO is reduced by the increased hole concentration. On the basis of the optimized Na+ and K+ doping, nano-SiC particles are dispersed on the BSCO matrix, which increases the phonon scattering at the interface and greatly reduces the thermal conductivity. Meanwhile, the Seebeck coefficients of Bi 2 Sr 2 Co 2 O y materials are basically unchanged under the combined action of cation doping and SiC dispersion. The maximum ZT values of 0.26 and 0.24 at 923 K are obtained for m = 0.025 and z = 0.05 Bi 2 Sr 2 Co 2 O y -based samples, respectively. [ABSTRACT FROM AUTHOR]

In this paper, we determined an effective substitution of Ge at Sb sites in Nd-filled p-type skutterudites, a series of Nd .9 Fe 2 Co 2 Sb 12-x Ge x compounds with compositions of x = 0, 0.1, 0.2, 0.3 and 0.4 were synthesized by home-made induction melting, assembled inside the glove box and followed by spark plasma sintering process (SPS). The thermoelectric properties are investigated as a function of Ge doping content with fixed Nd-filler at 0.9 and the formation of skutterudite phase is characterized by X-ray diffraction. All samples possess positive Seebeck coefficients, representing effective p-type doping. It is observed that the electrical conductivity decreases with decreasing Ge doping concentrations while increased with temperature due to bipolar effect. The lightly doped samples (x = 0.1 and 0.2) have lower lattice thermal conductivity over the entire temperature range, in which x = 0.2 sample shows the highest ZT value of 0.82 at 700 K, which is 30% higher than that of the Ge-free sample. The improvement in ZT can be attributed to the optimized carrier concentration and reduced thermal conductivity. The enhancement of ZT through Ge doping, coupled with drastically reduced processing time, shows that these compounds may have great potential in application as p-type segments of the thermoelectric devices. [ABSTRACT FROM AUTHOR]