TeI4掺杂量对n型Bi2Te3基烧结材料热电性能的影响

采用区熔法结合放电等离子体快速烧结(SPS)技术制备了n型Bi₂Te₃基热电材料.在300—500K的温度范围内测量了各热电性能参数，包括电导率(σ)、塞贝克系数(α)和热导率(κ)，研究了掺杂剂TeI₄的含量(质量百分比分别为0，0.05，0.08，0.10，0.13和0.15wt%)对热电性能的影响.结果表明：试样的载流子浓度(n)随TeI₄含量增加而增大，使电导率增大、塞贝克系数的绝对值先增大而后减小，从而导致品质因子(α²σ)呈先增加后降低的变化趋势；同时，由于异质离子(I^-)以及载流子对声子的散射作用增强，可显著降低其晶格热导率.烧结材料的性能优值(ZT=α²σT/κ)对应于TeI₄含量为0.08wt%有其最大值，约为0.92.此外，烧结材料的抗弯强度增加至80MPa左右，从而可以显著改善材料的可加工性以及元器件的使用可靠性. 关键词： 2Te₃')" href="#">Bi₂Te₃ 放电等离子体快速烧结 热电性能     

Bi2Te3 合金低温热电性能及冷能发电研究

利用机械合金化和冷压烧结法制备得到n型和p型Bi₂Te₃基热电材料,在80—300 K温度范围测量了电导率、Seebeck系数,结果表明其具有良好的低温热电性能.采用Bi₂Te₃基热电材料制备出半导体热电器件,并配合附属设备搭建出一套半导体温差发电装置.利用液氮汽化时释放的冷能,对半导体热电器件的发电性能进行实验研究,得出这种半导体热电器件输出电压、输出功率与电流关系式,测得最大的输出功率达到1.33 W,从而证明了冷     

(Sb2Te3)0.75(1－x)(Bi2Te3)0.25(1－x)(Sb2Se3)x机械合金化粉体的制备及其冷压烧结样品的热电性能研究

采用机械合金化法制备了p型赝三元(Sb₂Te₃-Bi₂Te₃-Sb₂Se₃)合金粉体，对其进行XRD分析表明Te，Bi，Sb，Se单质粉末，经100h球磨后实现了合金化；SEM分析表明所得机械合金化粉体材料颗粒均匀、细小，颗粒尺寸在10nm到100nm量级.使用这种粉体制备了冷压烧结块体样品，在室温下测量了温差电动势率(α)和电导率(σ)，研究了烧结温度对材料热电性能的影响，结果表明在低于300℃的烧结温区，样品室温下的热电性能随烧结温度的升高不断提高，功率因子(α²σ)由未烧结样品的0.59μW cm^-1K^-2升高到在300℃下烧结样品的15.9μW cm^-1K^-2，这一结果对确定材料的最佳烧结温度具有重要意义. 关键词： 赝三元热电材料 机械合金化 冷压 烧结     

Sb2Te3 纳米结构的制备与表征

以室温热电性能优异的传统热电材料Sb₂Te₃为研究对象,利用化学气相沉积法制备Sb₂Te₃单晶纳米结构,并研究其生长机理.实验结果表明,不加催化剂时Sb₂Te₃易生长成六方纳米盘,在金催化剂条件下定向生长成纳米线.Sb₂Te₃的形貌与其晶体结构和生长机理有关.Sb₂Te₃为三角结构,Sb和     

高压烧结法合成致密纳米BaTiO3陶瓷结构和铁电性能研究

 在6 GPa压力、1 000 ℃温度条件下制备了致密的纳米BaTiO₃陶瓷，合成样品的平均晶粒尺寸为50 nm，理论密度在97%以上。通过介电测量，观察到了样品宽化的相变峰，它与粗晶陶瓷的相变峰大不相同。由于90°电畴的减少和退极化场的存在，观察到了细长的电滞回线，它是样品铁电性存在的有力证据，表明钛酸钡陶瓷的临界尺寸在50 nm以下。     

n型Bi2Te3基化合物的类施主效应和热电性能

晶粒细化是提高Bi₂Te₃基热电材料力学性能的重要方法,但晶粒细化过程中伴随的类施主效应严重劣化了材料的热电性能,并且一旦产生类施主效应,就很难通过简单的热处理等工艺消除.本文系统研究n型Bi₂Te₃基化合物烧结前粉体颗粒尺寸对材料类施主效应和热电性能的影响规律.随着颗粒尺寸减小,氧诱导的类施主效应明显增强,载流子浓度从10 M烧结样品的3.36×10¹⁹ cm^-3急剧增加到120 M烧结样品的7.33×10¹⁹ cm^-3,严重偏离最佳载流子浓度2.51×10¹⁹ cm^-3,热电性能严重劣化.当粉体颗粒尺寸为1—2 mm时,烧结样品的Seebeck系数为–195 μV/K,载流子浓度为3.36×10¹⁹ cm^-3,与区熔样品沿着ab面方向的Seebeck系数为–203 μV/K和载流子浓度为2.51×10¹⁹     

烧结温度对La0.9Sr0.1FeO3热电性能的影响

利用传统的固相反应分别在1250℃,1300℃,1350℃.烧结条件下制备出钙钛矿结构的La_0.9Sr_0.1FeO₃陶瓷样品.样品的XRD粉末衍射结果显示不同烧结温度的La_0.9Sr_0.1FeO₃陶瓷样品都是单相的正交结构,同时晶胞体积随着烧结温度的升高而减小.从样品的SEM结果看出,随着烧结温度的升高,晶粒逐渐变大,并且晶粒间的空隙逐渐减小,样品更加致密.在室温到800℃的 关键词： 铁酸镧陶瓷 热电性能 烧结温度     

粗糙界面对Bi2Te3/PbTe超晶格热电优值影响的理论分析

以Bi₂Te₃/PbTe超晶格薄膜为例,分析电子在Bi₂Te₃量子阱中的输运过程,综合了薄膜的经典散射效应和理想量子效应,并以此混合效应为基础,在PbTe障碍层厚度一定时,模拟计算了两种混合效应中量子效应占不同比例时,Bi₂Te₃/PbTe超晶格热电优值的变化.在镜面反射占混合效应的0.3时,得到的热电优值与当前报道的量子阱超晶格的实验值接近. 关键词： 超晶格 粗糙界面 热电优值     

PbTe纳米晶高压热电性能的研究

 利用自建的400 t四柱双缸液压机,研究了PbTe纳米晶在0~0.8 GPa压力范围内热电性能随压力的变化。实验结果表明：PbTe纳米晶电导率随压力的增加而增加,而热电动势随压力的增加而减小,两者随压力的变化具有可逆性;PbTe纳米晶具有极高的热电动势,在常压下达到565 μV/K,在0.8 GPa压力下,材料的电导率为常压下的4倍,热电动势仅降低20%,功率因子则达到常压下的3倍。研究表明,高压能显著提高PbTe纳米晶的热电性能。利用第一性原理计算了0.4~4.0 GPa压力范围内材料的简约费米能级,计算结果与实验结果相吻合。     

Bi2Te3/Sb超晶格纳米线的外延生长和热电测量

通过脉冲电沉积,外延生长出小单元长度的Bi₂Te₃/Sb超晶格纳米线.借助哈曼方法,测量了超晶格纳米线阵列的热电性能,330 K时的ZT值可达0.15.研究了Bi₂Te₃/Sb超晶格纳米线阵列器件的制冷或者加热能力,发现器件的上下表面的最大温差可以达到6.6 K.     

Superconductivity and non-metallicity induced by doping the topological insulators Bi2Se3 and Bi2Te3

We show that by Ca doping the Bi₂Se₃ topological insulator, the Fermi level can be fine tuned to fall inside the band gap and therefore suppresses the bulk conductivity. Non-metallic Bi₂Se₃ crystals are obtained. On the other hand, the Bi₂Se₃ topological insulator can also be induced to become a bulk superconductor, with T_c∼3.8 K, by copper intercalation in the van der Waals gaps between the Bi₂Se₃ layers. Likewise, an as-grown crystal of metallic Bi₂Te₃ can be turned into a non-metallic crystal by slight variation in the Te content. The Bi₂Te₃ topological insulator shows small amounts of superconductivity with T_c∼5.5 K when reacted with Pd to form materials of the type Pd_zBi₂Te₃.     

Effects of process parameters on electrical properties of n-type Bi2Te3 prepared by mechanical alloying and spark plasma sintering

n-Type Bi₂Te₃ thermoelectric materials were prepared by spark plasma sintering (SPS) using mechanically alloyed powders. Seebeck coefficient and electrical conductivity of the resultant materials were measured, with emphasis on the effects of sintering process parameters on the electrical properties. The power factor was improved from 1.5 to 1.6 mW/mK² when the SPS pressure was increased from 20 to 50 MPa at 623 K, and was further increased to 2.1 mW/mK² under 50 MPa by raising the SPS temperature from 623 to 673 K. The maximum power factor was obtained for the sample sintered under optimized SPS process parameters, in which the sintering temperature and the sintering pressure are 673 K and 50 MPa, respectively.     

制备工艺对p型碲化铋基合金热电性能的影响

利用区熔法、机械合金化、放电等离子烧结(SPS)技术、热压法等多种工艺制备了p型碲化铋基热电材料.在300—500K的温度范围内测量了各热电性能参数，包括电导率(σ)、塞贝克系数(α)和热导率(κ)，研究了制备工艺对热电性能的影响.结果表明，所制备的块体材料与同组成区熔晶体相比，性能优值ZT均有不同程度的提高.其中，利用区熔法结合SPS技术可获得热电性能最佳的块体材料，其ZT值达1.15. 关键词： 碲化铋 放电等离子烧结 区熔法 热电性能     

烧结温度对La0.1Sr0.9TiO3陶瓷热电性能的影响

利用传统固相反应方法, 分别在1440℃, 1460℃, 1480℃和1500℃烧结条件下, 制备了钙钛矿结构的La_0.1Sr_0.9TiO₃陶瓷样品. 样品的粉末X射线衍射结果显示, 不同烧结温度的La_0.1Sr_0.9TiO₃ 陶瓷样品均为单相的正交结构. 从样品的扫描电子显微照片来看, 随着烧结温度的增加, 平均晶粒尺寸逐渐增大. 在室温至800℃的测试温区, 测试了样品的电阻率和Seebeck系数, 系统地研究了不同烧结温度对样品热电性能的影响. 结果表明, 样品的电阻率在测试温区内随着测试温度的升高先略微降低, 然后逐渐升高;总体来看, 样品的电阻率随烧结温度的升高先增大后降低. 在测试温区内, Seebeck系数均为负值, 表明样品的载流子为电子; 随着测试温度的升高, Seebeck系数绝对值均有所增大;随烧结温度升高, Seebeck系数绝对值逐渐增大后显著降低. 1480℃制备的样品因其相对较低的电阻率和相对较高的Seebeck系数绝对值, 在165℃时得到最大的功率因子21 μW·K^-2·cm^-1.     

The effect of the Bi source on optical properties of Bi2Te3 nanostructures

nanostructures were synthesized by using different Bi sources via a simple solvothermal process, in which and BiCl₃ were used as the Bi sources. Optical properties of nanostructures prepared with and BiCl₃ as the Bi sources were investigated by micro-Raman spectroscopy. The Raman scattering spectrum of hexagonal nanoplates prepared by using as the Bi source shows that the infrared (IR) active mode A_1u, which must be odd parity and is Raman forbidden for bulk crystal due to its inversion symmetry, is greatly activated and shows up clearly in the Raman scattering spectrum. We attribute the appearance of the infrared active A_1u mode in the Raman spectrum to crystal symmetry breaking of hexagonal nanoplates. However, the Raman scattering spectrum of nanostructures with irregular shape prepared by using as the Bi source only exhibits the two characteristic Raman modes of crystals. Micro-Raman measurements on nanostructures with different morphologies offer us a potential way to tailor optical properties of nanostructures by controlling the morphologies of the nanostructures, which is very important for practical applications of nanostructures in thermoelectric devices.     

Lanthanum-doped Bi4Ti3O12 ceramics prepared by high-pressure technique

We present an effective way in this paper to increase the density of lanthanum doped bismuth titanate ceramics, Bi4-xLaxTi3O12 (BLT), thereby significantly improving the performance of the BLT ceramics. Dense BLT ceramicses, Bi4-xLaxTi3O12 (x = 0.25, 0.5, 0.75, 1.0), are prepared by using nanocrystalline powders fabricated by a-gel method and high-pressure technique. The microstructures of the BLT ceramicses prepared separately by conventional-pressure and high-pressure techniques are investigated by using x-ray diffraction and transmission electron microscope. The influence of La-doping on the densification of bismuth titanate ceramics is investigated. The experimental results indicate that the phase compositions of all samples with various lanthanum dopings sintered at 900°C possess layer-structure of Bi4Ti3O12 . The green compacts are pressed under 2.5 GPa, 3.0 GPa, 3.5 GPa and 4.0 GPa, separately. It is found that the density of BLT ceramics is significantly increased due to the decreasing of porosity in the green compacts by high-pressure process.     

Electro- and thermoreflectance of Bi2Te3 and Bi2Se3

Electroreflectance measurements in Bi₂Te₃ and Bi₂Se₃ with the electric field vector of the incident light both inclined and perpendicular to the C-axis have been made at room temperature. The structures found by other workers in the reflection measurements are observed in the present experiment, together with new structures at 0.91 eV, 1.18 eV, 1.78 eV, and 2.61 eV in Bi₂Se₃ which are not related to formerly observed transitions. From these measurements, the selection rules for direct optical transitions in Bi₂Te₃ and Bi₂Se₃ are studied. Thermoreflectance measurements are also made at both room and liquid-nitrogen temperatures. The positions of the peaks obtained in the present work are compared with the electroreflectance and reflection data.     

Thermoelectric properties of Bi0.9Sb0.1 prepared by high pressure

The Bi_0.9Sb_0.1 powders were prepared by mechanical alloying and then pressed under 6 GPa at different pressing temperatures. X-ray diffraction spectra showed that the single phase was formed. The nanostructure of grain was observed by bright-field imaging. Electrical conductivity, Seebeck coefficient, and thermal conductivity had been investigated in the temperature range of 80-300 K. The absolute Seebeck coefficient value of 120.3 μV/K was measured at 130 K. The figure-of-merit reached a maximum value of 0.90×10⁻³ K⁻¹ at 140 K.