Tang Xinfeng

Phase transition and high temperature thermoelectric properties of copper selenide Cu 2-x Se （0 ≤ x ≤ 0.25）

With good electrical properties and an inherently complex crystal structure, Cu2−xSe is a potential “phonon glass electron crystal” thermoelectric material that has previously not attracted much interest. In this study, Cu2−xSe (0 ≤ x ≤ 0.25) compounds were synthesized by a melting-quenching method, and then sintered by spark plasma sintering to obtain bulk material. The effect of Cu content on the phase transition and thermoelectric properties of Cu2−xSe were investigated in the temperature range of 300 K–750 K. The results of X-ray diffraction at room temperature show that Cu2−xSe compounds possess a cubic structure with a space group of F m3m (#225) when 0.15 < x ≤ 0.25, whereas they adopt a composite of monoclinic and cubic phases when 0 ≤ x ≤ 0.15. The thermoelectric property measurements show that with increasing Cu content, the electrical conductivity decreases, the Seebeck coefficient increases and the thermal conductivity decreases. Due to the relatively good power factor and low thermal conductivity, the nearly stoichiometric Cu2Se compound achieves the highest ZT of 0.38 at 750 K. It is expected that the thermoelectric performance can be further optimized by doping appropriate elements and/or via a nanostructuring approach.

Synthesis and Thermoelectric Properties of Polyaniline

Electrical conductivity and seebeck coefficient at different temperatures, and thermal conductivity at room temperature for various doped polyaniline (PAn) samples were measured, and the thermoelectric figure of merit ZT was calculated. The effects of preparation methods and temperature on thermoelectric properties were discussed. The results show that the electrical conductivity and the seebeck coefficient of PAn are strongly dependent on the preparation conditions and temperature. The electrical conductivity becomes larger and the seebeck coefficient becomes smaller as PAn molecular weight increase. Redoping by organic acid and HCl results in an increase in both electrical conductivity and Seebeck coefficient of PAn, and therefore ZT value. The electrical conductivity increases and the seebeck coefficient decreases as the temperature increases when T<Td (dedoping temperature). The decreasing of the electrical conductivity and increasing of the seebeck coefficent take place by dedoping when T>Td. The thermal conductivity is lower, and insensitive to the sample preparation conditions.

Fast preparation and thermal transport property of TiCoSb-based half-Heusler compounds

TiCoSb-based half-Heusler compounds with the substitution of Zr for Ti have been prepared quickly by combining high-energy ball milling method with spark plasma sintering technique, and their thermal transport properties have been investigated. With the increase of the concentration of Zr, the thermal conductivity of Ti1-xZrxCoSb compounds decreases significantly. Compared with the thermal conductivity of TiCoSb compound, that of Ti0.5Zr0.5CoSb decreases by 200% at 1000 K.

Quick preparation and thermal transport properties of nanostructured β-FeSi2 bulk material

This paper reports that the nanostructured β-FeSi2 bulk materials are prepared by a new synthesis process by combining melt spinning (MS) and subsequent spark plasma sintering (SPS). It investigates the influence of linear speed of the rolling copper wheel, injection pressure and SPS regime on microstructure and phase composition of the rapidly solidified ribbons after MS and bulk production respectively, and discusses the effects of the microstructure on thermal transport properties. There are two crystalline phases (α-Fe2Si5 and -FeSi) in the rapidly solidified ribbons; the crystal grains become smaller when the cooling rate increases (the 20 nm minimum crystal of e-FeSi is obtained). Having been sintered for 1 min above 1123 K and annealed for 5min at 923 K, the single-phase nanostructured β-FeSi2 bulk materials with 200–500 nm grain size and 98% relative density are obtained. The microstructure of β-FeSi2 has great effect on thermal transport properties. With decreasing sintering temperature, the grain size decreases, the thermal conductivity of β-FeSi2 is reduced remarkably. The thermal conductivity of β-FeSi2 decreases notably (reduced 72% at room temperature) in comparison with the β-FeSi2 prepared by traditional casting method.

Synthesis and high temperature thermoelectric transport properties of Si-based type-I clathrates

N-type Si-based type-I clathrates with different Ga content were synthesized by combining the solid-state reaction method, melting method and spark plasma sintering (SPS) method. The effects of Ga composition on high temperature thermoelectric transport properties were investigated. The results show that at room temperature, the carrier concentration decreases, while the carrier mobility increases slightly with increasing Ga content. The Seebeck coefficient increases with increasing Ga content. Among all the samples, Ba7.93Ga17.13Si28.72 exhibits higher Seebeck coefficient than the others and reaches -135 μV.K-1 at 1000 K. The sample prepared by this method exhibits very high electrical conductivity, and reaches 1.95×105 S.m-1 for Ba8.01Ga16.61Si28.93 at room temperature. The thermal conductivity of all samples is almost temperature independent in the temperature range of 300–1000 K, indicating the behaviour of a typical metal. The maximum ZT value of 0.75 is obtained at 1000 K for the compound Ba7.93Ga17.13Si28.72.

Crystal Structures and Thermoelectric Properties of Sm-Filled Skutterudite Compounds Smy Fex Co4 - x Sb12

Abstract Polycrystalline samples of Sm partially filled skutterudites Sm y Fe x Co 4 - x Sb 12 were prepared by melting and Spark Plasma Sintering technique. The results of Rietveld refinement showed that the obtained Sm y Fe x Co 4 - x Sb 12 samples possessed filled skutterudite structures. The thermal parameter ( B ) of Sm is larger than that of Sb, Fe, and Co, indicating that Sm “rattled” in Sb-icosahedron voids. The effects of filling atom Sm on thermoelectric properties of these compounds were investigated. With the increase of Sm filling fraction ( y ), electrical conductivity decreased, Seebeck coefficient increased and had a maximum value when y was 0.38; thermal conductivity reduced and had a minimum value when y was 0. 32. At 750 K, the highest figure of merit of 0.68 was obtained for Sm 0.32 Fe 1.47 Co 2.53 Sb 12 .

Optimization of p-type Segmented Bi2Te3/CoSb3 Thermoelectric Material Prepared by Spark Plasma Sintering

A kind of p-type segmented Bi2Te3/CoSb3 thermoelectric material was prepared by spark plasma sintering (SPS). When the segmented materials were used at the temperature ranging from 300 Koto 800K, the junction temperature was optimized, which is about 500 K, and the corresponding length ratio of CoSb3 to Bi2Te3 is about 15∶2. The measured maximum power output of segmented materials is about 320 W·m−2, which is about 1.8 times as high as that of monolithic material CoSb3 under the same measuring conditions.

Effect of Ba filling fraction on thermoelectric properties ofp-type BayFe1.6Co2.4Sb12

Effects of Ba filling fraction on the thermoelectric properties of p-type filled skutterudite compounds BayFe1.6Co2.4Sb12 (y=0−0.63) were investigated. BayFe1.6Co2.4Sb12 showed p-type conduction. The hall coefficient (Rh) and seebeck coefficient (α) increased with increasing Ba filling fraction. But hole concentration (p) and electrical conductivity (σ) decreased. While Ba filling fraction was about 0.4, the lattice thermal conductivity (kL) reached the minimum value. The results show that effect of Ba rattling on phonon scattering is the strongest as Sb-icosahedron partial voids are filled by Ba. A maximum dimensionless thermoelectric figure of merit (ZT) value of 0.7 was obtained for Ba0.38Fe1.6Co2.4Sb12 at 750 K.

Gama-Na x CoO 2 粉体的聚丙烯酸钠凝胶法制备及其表征

本研究发展了一种用于制备氧化物热电材料γ-Na x CoO 2 粉体的化学合成方法——聚丙烯酸钠(PAAS)凝胶法。主要研究了PAAS/Co 2+ 摩尔比、原料浓度和煅烧温度对产物相组成及微观形态的影响规律, 探讨了物相形成机制, 同时用该方法结合SPS制备了不同Na离子浓度的Na x CoO 2 多晶样品, 并对其热电性能进行了表征。结果表明, PAAS/Co 2+ 摩尔比对产物相组成产生了显著影响, 随着PAAS/Co 2+ 摩尔比的增加, 样品的相组成由Co3O4相向单相γ-Na x CoO 2 转变, 合适的PAAS/Co 2+ 摩尔比为0.8~1.1。而反应原料浓度对产物相组成的影响存在一个临界值(0.025 mol/L), 大于临界值抑制单相形成, 小于临界值促进单相形成。煅烧温度的升高有助于γ-Na x CoO 2 单相的形成, 800℃煅烧得到γ-Na x CoO 2 单相, 晶粒形态呈片状, 平均厚度约200 nm, 片状方向的尺寸在1~4 μm之间。随着Na含量的增加, 样品的Seebeck系数增大, 电导率增加, 热导率降低, 最终导致ZT值大幅增加。

Preparation and Characterization of Gama-Na

本研究发展了一种用于制备氧化物热电材料γ-Na x CoO 2 粉体的化学合成方法——聚丙烯酸钠(PAAS)凝胶法。主要研究了PAAS/Co 2+ 摩尔比、原料浓度和煅烧温度对产物相组成及微观形态的影响规律, 探讨了物相形成机制, 同时用该方法结合SPS制备了不同Na离子浓度的Na x CoO 2 多晶样品, 并对其热电性能进行了表征。结果表明, PAAS/Co 2+ 摩尔比对产物相组成产生了显著影响, 随着PAAS/Co 2+ 摩尔比的增加, 样品的相组成由Co3O4相向单相γ-Na x CoO 2 转变, 合适的PAAS/Co 2+ 摩尔比为0.8~1.1。而反应原料浓度对产物相组成的影响存在一个临界值(0.025 mol/L), 大于临界值抑制单相形成, 小于临界值促进单相形成。煅烧温度的升高有助于γ-Na x CoO 2 单相的形成, 800℃煅烧得到γ-Na x CoO 2 单相, 晶粒形态呈片状, 平均厚度约200 nm, 片状方向的尺寸在1~4 μm之间。随着Na含量的增加, 样品的Seebeck系数增大, 电导率增加, 热导率降低, 最终导致ZT值大幅增加。