Merit Of Thermoelectric Materials Research Articles

Stepwise Ge vacancy manipulation enhances the thermoelectric performance of cubic GeSe

In thermoelectrics, the native point defect enables the delicate balance between carrier concentration and carrier mobility. The proper native point defect is prerequisite for the carrier concentration optimization. However, the carrier mobility is inevitable to be affected in case of the carrier mean free path approaches to the size of point defects. Herein, we reported the stepwise Ge vacancy manipulation as a point defect engineering to realize the zT enhancement in cubic GeSe. The pristine orthorhombic GeSe has the ultralow zT of 0.05 due to the inferior carrier concentration arising from the low Ge vacancy concentration, as well as the low carrier mean free path. Hence, we adopted InSnTe2 alloying to stabilize the cubic phase at ambient conditions and significantly increase the Ge vacancy concentration due to the generation of Ge precipitates, thereby increasing the carrier concentration by several orders of magnitude but damaging the carrier mobility. Subsequently, the moderate Te doping was adopted to make the Ge-precipitations to be dissolved into the matrix, thus mitigating the strong carrier scattering deriving from the Ge vacancy and enhancing the carrier mobility to some extent. Combined with the restrained thermal conductivity originating from the multiscale defects and the reduced sound velocity, the maximum zT of 0.62 at 573 K was achieved in cubic GeSeTe0.15(InSnTe2)0.2. These results demonstrated that the stepwise point defect manipulation is an effective strategy for enhancing the figure of merit in thermoelectric materials with intrinsic low carrier mobility.

Evaluate Dimensionless Figure of Merit for Thermoelectric Materials Based on the Intrinsic Carrier Concentration and Bipolar Effect

Evaluate Dimensionless Figure of Merit for Thermoelectric Materials Based on the Intrinsic Carrier Concentration and Bipolar Effect

Enhancing the figure of merit in thermoelectric materials by adding silicate aerogel

To achieve practical applications of thermoelectric materials in large scale, materials with high thermal conversion efficiency, low cost, and operating at a proper temperature range are required. Owing to the inversely relationship between electrical conductivity (σ) and Seebeck coefficient (S), it is a great challenge to improve high power factor (PF = σS2) of a thermoelectric material. Here, we show that by adding a small amount of silicate aerogel to existing promising materials, including Bi0.5Sb1.5Te3 (p-type), Cu0.01Bi2Te2.7Se0.3 (n-type), and p-type MgAgSb, significantly improves the figure of merit (zT) of the materials. For the BiTe-based materials, the primary gain in zT comes from a significant reduced thermal conductivity, while preserving high PF for the aerogel mixed composites. On the other hand, the enhancement of zT in aerogel-added p-type MgAg0.97Sb0.99 material is not due to the reduction in thermal conductivity but rather an enhancement in PF, which is important for practical applications. Furthermore, the materials we present in this work are bulk polycrystalline samples, which are relatively easy to produce without complicated synthesis processes.

Physical and chemical descriptors for predicting interfacial thermal resistance

Heat transfer at interfaces plays a critical role in material design and device performance. Higher interfacial thermal resistances (ITRs) affect the device efficiency and increase the energy consumption. Conversely, higher ITRs can enhance the figure of merit of thermoelectric materials by achieving ultra-low thermal conductivity via nanostructuring. This study proposes a dataset of descriptors for predicting the ITRs. The dataset includes two parts: one part consists of ITRs data collected from 87 experimental papers and the other part consists of the descriptors of 289 materials, which can construct over 80,000 pair-material systems for ITRs prediction. The former part is composed of over 1300 data points of metal/nonmetal, nonmetal/nonmetal, and metal/metal interfaces. The latter part consists of physical and chemical properties that are highly correlated to the ITRs. The synthesis method of the materials and the thermal measurement technique are also recorded in the dataset for further analyses. These datasets can be applied not only to ITRs predictions but also to thermal-property predictions or heat transfer on various material systems.

열전소재의 성능지수 측정법

열전소재의 성능지수 측정법

Synthesis and Characterization of Bulk Nanostructured Thermoelectric Ca3Co4O9

Nanostructuring has been proposed as an effective strategy for the reduction of the phonon contribution to the thermal conductivity, resulting in an increase in the figure of merit of thermoelectric materials. However, obtaining bulk samples presenting high relative density and nanometric grain size can be quite challenging, particularly in the case of ceramic phases. Only few examples have been reported and none in the case of Ca₃Co₄O₉. In this work, we used a sol–gel synthesis coupled with ball milling to prepare powders of Ca₃Co₄O₉ presenting a grain size as small as 4 nm. These nanopowders were then sintered at different temperature and pressures using the High-Pressure Field-Assisted Sintering Technique (HP-FAST). Relative densities up to 95 vol% where obtained while maintaining a nanometric grain size. The microstructural and electrical properties of the sintered samples have been characterized. The results show that in this oxide a reduction to the nanometric grain size produces a drastic reduction in the electrical conductivity, which cannot be compensated by the reduction in the thermal conductivity. The Seebeck effect, on the other hand, appears to be affected only marginally by the grain size and porosity.

Enhancement of figure of merit of thermoelectric materials: a new theoretical approach

Thermoelectric materials have attained importance because of the gargantuan energy crisis the world faces today. A thermoelectric material can be used efficiently and frequently, provided, its figure of merit ZT is increased. Also, easy availability, manufacturing, and low cost are the other factors to be considered for a novel thermoelectric material. A theoretical model is proposed in this paper for the enhancement of the figure of merit of thermoelectric materials.

Synthesis of alloyed Bi2TexSe(3-x) nanoparticles and thermoelectric characterization of bulk nanostructured materials obtained by their assembly

ABSTRACTThe optimization of the figure of merit of thermoelectric materials requires the simultaneous control of the material composition and microstructure. Assembly of nanoparticles obtained by a solution route is an attractive bulk fabrication method because size and shape of the nanoparticles can be tuned by variation of the synthesis conditions. Recently, new synthetic pathways were reported among which reducing agent assisted, surfactant free processes. We report here the evaluation of this method for the synthesis of Bi2TexSe3-x alloyed nanoparticles with varying selenium concentrations. X-ray diffraction studies conducted on powder and pellet samples show that two alloyed phases are present in the sample even at low selenium content. The careful study of the position of the diffraction peaks as function of the formulation shows that this behaviour could arise from the difference in reactivity of selenium and tellurium. Moreover, the electrical conductivity of the samples is shown to increase upon selenium addition while the Seebeck coefficient is reduced. Power factor shows an optimum value around 20% selenium content with a large tolerance in composition.

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The Study of Solvothermal Synthesis of Nano-Engineered CoSb3 Skutterudite Thermoelectric Materials

AbstractNanostructured materials have been shown to enhance phonon scattering and improve the figure of merit of thermoelectric materials. Solvothermal syntheses of nano-engineered CoSb3 skutterudite have been studied in the present work in which CoCl2 and SbCl3 were used as precursors and NaBH4 as a reductant. Elemental, structural and morphology characterization techniques including: XRD, SEM, TEM and EDAX were used to identify and characterize the products. NaBH4 was found to be a necessary factor in forming cobalt antimonide. It was detected the products' phase transited from Sb2Co to CoSb3 in conjunction with the amount increase of NaBH4. The change of synthesis time and temperature contributed little on the products' phases under the present experimental routes. Single-phased CoSb3 skutterudites was obtained from the solvothermal syntheses combined with an acid wash. The as-prepared CoSb3 powders consist of irregular nanoparticles with 15∼20 nm in size. A possible chemical mechanism was also discussed.

Solvothermal synthesis of nanosized CoSb3 skutterudite

Nanostructures enhance phonon scattering and improve the figure of merit of thermoelectric materials. Nanosized CoSb(3) skutterudite was synthesized by solvothermal methods using CoCl(2) and SbCl(3) as the precursors. A "two-step" model was suggested for the formation of CoSb(3) based on the X-ray diffraction analysis. The first step is the formation of cobalt diantimonide in the earlier stage during the synthesis process. Diantimonide was then combined with antimony atoms to form the skutterudite structured triantimonide, CoSb(3), in the later stage of the synthesis process as the second step. The synthesized CoSb(3) powders consist of irregular particles with sizes of about 20 nm and sheets of about 80 nm.

Note on maximum figure of merit of thermoelectric materials

Note on maximum figure of merit of thermoelectric materials