We report a melt spinning technique followed by a quick spark plasma sintering procedure to fabricate high-performance p-type Bi0.52Sb1.48Te3 bulk material with unique microstructures. The microstructures consist of nanocrystalline domains embedded in amorphous matrix and 5–15 nm nanocrystals with coherent grain boundary. The significantly reduced thermal conductivity leads to a state-of-the-art dimensionless figure of merit ZT∼1.56 at 300 K, more than 50% improvement of that of the commercial Bi2Te3 ingot materials.
Abstract In most semiconducting metal chalcogenides, a large deformation is usually accompanied by a phase transformation, while the deformation mechanism remains largely unexplored. Herein, a phase‐transformation‐induced deformation in Ag 2 Se is investigated by in situ transmission electron microscopy, and a new ordered high‐temperature phase (named as α ′‐Ag 2 Se) is identified. The SeSe bonds are folded when the Ag + ‐ion vacancies are ordered and become stretched when these vacancies are disordered. Such a stretch/fold of the SeSe bonds enables a fast and large deformation occurring during the phase transition. Meanwhile, the different SeSe bonding states in α‐, α ′‐, β‐Ag 2 Se phases lead to the formation of a large number of nanoslabs and the high concentration of dislocations at the interface, which flexibly accommodate the strain caused by the phase transformation. This study reveals the atomic mechanism of the deformation in Ag 2 Se inorganic semiconductors during the phase transition, which also provides inspiration for understanding the phase transition process in other functional materials.
Abstract Ordinary diamond presents the disadvantages of poor self-sharpening and concentrated grinding stress when it is used as an abrasive. Moreover, this kind of diamond cannot be well wetted by the vitrified bond, resulting in a lower holding force of the binder to the abrasives (i.e., the diamond is easy to detach from the binder matrix during grinding). These comprehensive factors not only reduce the surface quality of the processed workpiece, but also hinder the processing efficiency. In order to solve these problems, a new type of porous diamond with high self-sharpening properties was prepared using a thermochemical corrosion method in this study. Our results showed a great improvement in pore volume and specific surface area of the porous diamond compared with ordinary diamond abrasive particles, and the holding force and wettability of vitrified bond to the porous diamond abrasive particles were also improved. Compared with ordinary diamond abrasive tools, porous diamond abrasive tools showed a 29.6% increase in grinding efficiency, a 15.5% decreased in grinding ratio, a 27.5% reduction in workpiece surface roughness, and the scratches on the silicon wafer surface were reduced and refined.
Skutterudite materials have been considered as promising thermoelectric candidates due to intrinsically good electrical conductivity and tailorable thermal conductivity. Options for improving thermal-to-electrical conversion efficiency include identifying novel materials, adding filler atoms, and substitutional dopants. Incorporating filler or substitutional dopant atoms in the skutterudite compounds can enhance phonon scattering, resulting in reduction of thermal conductivity, as well as improving electrical conductivity. The structures, electronic properties, and thermal properties of double-filled Ca0.5Ce0.5Fe4Sb12 and Co4Sb12−2xTexGex compounds (x = 0, 0.5, 1, 2, 3, and 6) have been studied using density functional theory-based calculations. Both Ca/Ce filler atoms in FeSb3 and Te/Ge substitution in CoSb3 cause a decrease in lattice constant for the compounds. As Te/Ge substitution concentration increases, lattice constant decreases and structural distortion of pnictogen rings in the compounds occurs. This indicates a break in cubic symmetry of the structure. The presence of fillers and substitutions cause an increase in electrical conductivity and a gradual decrease in electronic band gap. A transition from direct to indirect band-gap semiconducting behavior is found at x = 3. Phonon density of states for both compounds indicate phonon band broadening by the incorporation of fillers and substitutional atoms. Both systems are also assumed to have acoustic-mode-dominated lattice thermal conductivity. For the Co4Sb12−2xTexGex compounds, x = 3 has the lowest phonon dispersion gradient and lattice thermal conductivity, agreeing well with experimental measurements. Our results exhibit the improvement of thermoelectric properties of skutterudite compounds through fillers and substitutional doping.
Although many thermoelectric materials, such as Bi2Te3, PbTe and CoSb3, possess excellent thermoelectric properties, they often contain toxic and expensive elements. Moreover, most of them are synthesized by processes such as vacuum melting, mechanical alloying or solid-state reactions, which are highly energy and time intensive. All these factors limit commercial applications of the thermoelectric materials. Therefore, it is imperative to develop efficient, inexpensive and non-toxic materials and explore rapid and low-cost synthesis methods. Herein we demonstrated a rapid, facile and low-cost synthesis route that combines thermal explosion (TE) with plasma-activated sintering and used it to prepare environmentally benign CuFeS2+2x. The phase transformation that occurred during the TE and correlations between the microstructure and transport properties were investigated. In a TE process, single-phase CuFeS2 was obtained in a short time and the thermoelectric performance of the bulk samples was better than that of the samples that were synthesized using traditional methods. Furthermore, the effect of phase boundaries on the transport properties was investigated and the underlying physical mechanisms that led to an improvement in the thermoelectric performance were revealed. This work provides several new ideas regarding the TE process and its utilization in the synthesis of thermoelectric materials. Thermoelectric materials can be rapidly formed into efficient structural phases using controlled thermal explosions. Many thermoelectric materials contain toxic and expensive elements and are synthesized by energy intensive processes. ’Fool's gold‘, or chalcopyrite, a copper iron sulfide (CuFeS2) mineral, exhibits promising thermoelectric activity and a low toxicity. Xinfeng Tang from Wuhan University of Technology, China and co-workers have developed a quick process to arrange the atoms inside CuFeS2 for optimal electrical conductivity and heat retention. Exposing powdered reagents in a quartz tube to brief periods of intense temperatures initiated a series of exothermic, explosive reactions that synthesized target crystals in under a minute. The researchers adjusted the initial sulfur content to fine tune the chalcopyrite crystal phases generated during explosions, and, following sintering, recovered one compound with 130% times the normal thermoelectric conversion efficiency. In a typical thermal explosion process, a single-phase CuFeS2 is obtained in a very short time and the thermoelectric performance of the fully condensed bulk samples is better than that of the samples synthesized by the traditional methods. The presence of phase boundaries in the CuFeS2−x has an effect on the transport properties: phase boundaries scatter low-frequency phonons and reduce the thermal conductivity of a composite structure. Moreover, large differences in the carrier concentration in CuFeS2 and Cu1.1Fe1.1S2 drive a redistribution of electrons in the composite and lead to an enhancement in the electronic transport properties.
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