Zhao Xinbing

Nanostructured Bi2Te3 synthesized by low temperature aqueous chemical route

Chemical and physical reactions during the low temperature aqueous chemical synthesis of nanostructured Bi2Te3 powders were investigated in-situ by pH measurement, color observation of the solution and X-ray diffraction analysis of the powders. It was found that Bi2Te3 could be synthesized only in a strong alkaline solution. Bi2Te3 nanocapsules were synthesized by the aqueous chemical route at 65 °C with the addition of disodium ethylenediaminetetraacetate salt. High-resolution transmission electron microscopy observation indicates that the nanocapsules are hollow-structured with a wall thickness of about 6 nm.

Effect of GaSb Addition and Sb Doping on the Thermoelectric Properties of Mg2Si0.5Sn0.5 Solid Solutions

Abstract Mg 2 Si 0.487-2 x Sn 0.5 (GaSb) x Sb 0.013 (0.04 ≤ x ≤ 0.10) solid solutions were synthesized by a B 2 O 3 flux method followed by hot pressing. X-ray power diffraction analysis confirms that single-phased samples are obtained. It is found that the Sb-doping effectively enhances the electrical conductivity. The Seebeck coefficients increase while the electrical conductivity decreases for Mg 2 Si 0.487-2 x Sn 0.5 (GaSb) x Sb 0.013 with the increase of temperature. With increasing of GaSb content the electrical conductivity first increases and then decreases. Among all the samples, Mg 2 Si 0.287 Sn 0.5 (GaSb) 0.1 Sb 0.013 sample has the lowest lattice thermal conductivity which is about 15% lower than that of Mg 2 Si 0.5 Sn 0.5 [11] at room temperature. A maximum dimensionless figure of merit of 0.61 at 720 K has been obtained for Mg 2 Si 0.327 Sn 0.5 (GaSb) 0.08 Sb 0.013 mainly due to its high electrical conductivity, which is obviously higher than that (0.019 at 540 K) of Mg 2 Si 0.5 Sn 0.5 [11] .

Ag 2 Te掺杂对p型Bi 0.5 Sb 1.5 Te 3 块状合金热电性能的影响

采用真空熔炼、机械球磨及放电等离子烧结技术 (SPS) 制备得到了(Ag 2 Te)x(Bi 0.5 Sb 1.5 Te 3 ) 1- x ( x = 0, 0.025, 0.05, 0.1) 系列样品, 性能测试表明, Ag 2 Te的掺入可以显著改变材料的热电性能变化趋势, 掺杂样品在温度为450~550 K范围内具有较未掺杂样品更优的热电性能. 适当量的Ag2Te掺入能够有效地提高材料的声子散射, 降低材料的热导率. 在测试温度范围内, (Ag 2 Te) 0.05 (Bi 0.5 Sb 1.5 Te 3 ) 0.95 具有最低的晶格热导, 室温至575 K范围内保持在0.2 ~ 0.3 W/(m·K)之间, 在575 K时, (Ag 2 Te) 0.05 (Bi 0.5 Sb 1.5 Te 3 ) 0.95 试样具有最大热电优值 ZT = 0.84, 相较于未掺杂样品提高了约20%.采用真空熔炼、机械球磨及放电等离子烧结技术 (SPS) 制备得到了(Ag 2 Te)x(Bi 0.5 Sb 1.5 Te 3 ) 1- x ( x = 0, 0.025, 0.05, 0.1) 系列样品, 性能测试表明, Ag 2 Te的掺入可以显著改变材料的热电性能变化趋势, 掺杂样品在温度为450~550 K范围内具有较未掺杂样品更优的热电性能. 适当量的Ag2Te掺入能够有效地提高材料的声子散射, 降低材料的热导率. 在测试温度范围内, (Ag 2 Te) 0.05 (Bi 0.5 Sb 1.5 Te 3 ) 0.95 具有最低的晶格热导, 室温至575 K范围内保持在0.2 ~ 0.3 W/(m·K)之间, 在575 K时, (Ag 2 Te) 0.05 (Bi 0.5 Sb 1.5 Te 3 ) 0.95 试样具有最大热电优值 ZT = 0.84, 相较于未掺杂样品提高了约20%.

Preparation and interface analyses of a P-type segmented FeSi/sub 2//Bi/sub 2/Te/sub 3/ material

P-type segmented FeSi/sub 2//Bi/sub 2/Te/sub 3/ thermoelectric material has been prepared by the dip coating procedure using Sn/sub 95/Ag/sub 5/ as the bridge material. An apparent Seebeck coefficient of about 225 /spl mu/V/K is obtained, which is significantly higher than those of both homogeneous materials /spl beta/-FeSi/sub 2/ and Bi/sub 2/Te/sub 3/ in the same temperature range. The maximum power output of the segmented FeSi/sub 2//Bi/sub 2/Te/sub 3/ is approximately 2.5 times that of the monolithic material /spl beta/-FeSi/sub 2/ in the same temperature range. This implies that not only does the segmented material benefit from Bi/sub 2/Te/sub 3/ at the low temperature side, but it also makes fully use of the characteristics of /spl beta/-FeSi/sub 2/ at high temperature. SEM and EDAX analyses revealed that interdiffusions do to some extent exist in all interfaces. A eutectic mixture could easily be formed since its melting point is lower than the annealing temperature, which trigger the exfoliation in the interface between Sn/sub 95/Ag/sub 5/ and Bi/sub 2/Te/sub 3/ under the stress due to the thermal expansion coefficient mismatch of both materials. Although the maximum power output of the material with a Ni layer sandwiched between Sn/sub 95/Ag/sub 5/ and Bi/sub 2/Te/sub 3/ is a little lower than those of the materials without Ni layer, the thermal stability can be significantly improved.