Thermoelectric Performance Enhancement in BiSbTe Alloy by Microstructure Modulation via Cyclic Spark Plasma Sintering with Liquid Phase

The widespread application of thermoelectric (TE) technology demands high-performance materials, which has stimulated unceasing efforts devoted to the performance enhancement of Bi₂Te₃-based commercialized thermoelectric materials. This study highlights the importance of the synthesis process for high-performance achievement and demonstrates that the enhancement of the thermoelectric performance of (Bi,Sb)₂Te₃ can be achieved by applying cyclic spark plasma sintering to Bi_xSb_2–xTe₃-Te above its eutectic temperature. This facile process results in a unique microstructure characterized by the growth of grains and plentiful nanostructures. The enlarged grains lead to high charge carrier mobility that boosts the power factor. The abundant dislocations originating from the plastic deformation during cyclic liquid phase sintering and the pinning effect by the Sb-rich nano-precipitates result in low lattice thermal conductivity. Therefore, a high ZT value of over 1.46 is achieved, which is 50% higher than conventionally spark-plasma-sintered (Bi,Sb)₂Te₃. The proposed cyclic spark plasma liquid phase sintering process for TE performance enhancement is validated by the representative (Bi,Sb)₂Te₃ thermoelectric alloy and is applicable for other telluride-based materials.     

Size Effect on Properties of Varistors Made From Zinc Oxide Nanoparticles Through Low Temperature Spark Plasma Sintering

Conditions for the elaboration of nanostructured varistors by spark plasma sintering (SPS) are investigated, using 8‐nm zinc oxide nanoparticles synthesized following an organometallic approach. A binary system constituted of zinc oxide and bismuth oxide nanoparticles is used for this purpose. It is synthesized at room temperature in an organic solution through the hydrolysis of dicyclohexylzinc and bismuth acetate precursors. Sintering of this material is performed by SPS at various temperatures and dwell times. The determination of the microstructure and the chemical composition of the as‐prepared ceramics are based on scanning electron microscopy and X‐ray diffraction analysis. The nonlinear electrical characteristics are evidenced by current–voltage measurements. The breakdown voltage of these nanostructured varistors strongly depends on grain sizes. The results show that nanostructured varistors are obtained by SPS at sintering temperatures ranging from 550 to 600 °C.     

脉冲激光淀积高电流密度的YBCO超导带材

采用脉冲激光加辅助离子源的方法在长为６．０ｃｍ的ＮｉＣｒ合金基带上制备０．１３μｍ厚的Ｙ－ＺｒＯ２（ＹＳＺ）隔离层，再用脉冲激光在ＹＳＺ／ＮｉＣｒ带上制备１．５μｍ厚的ＹＢａ２Ｃｕ３Ｏ７－ｘ超导厚膜形成ＹＢＣＯ／ＹＳＺ／ＮｉＣｒ超导带材。实验测得在７７Ｋ，０Ｔｅｓｌａ下其临界电流密度为８．７５×１０４Ａ／ｃｍ２，超导转变温度为８８．６Ｋ。     

<Emphasis Type="Italic">p</Emphasis>-Type PbTe Thermoelectric Bulk Materials with Nanograins Fabricated by Attrition Milling and Spark Plasma Sintering

This work reports a manufacturing process that combines attrition milling and spark plasma sintering (SPS) in the preparation of PbTe bulk materials with nanosize grains. The process involves milling raw PbTe ingots into nanocrystalline powders and subsequent compacting of these powders into dense bulk materials by spark plasma sintering. Sintered samples with relative densities of over 95% and grain sizes as small as 80 nm to 1 μm were obtained through this process. The thermoelectric properties of the samples were measured and compared with those of raw ingots at temperatures from 300 K to 400 K to demonstrate the influence of grain size on thermoelectric properties. The results reveal that reducing the grain size improved thermoelectric performance.     

烧结温度对YBCO陶瓷常温物理性能的影响

采用固相烧结法制备YBa2Cu3O7-x(YBCO)陶瓷,研究其在常温下电导率特性及烧结温度对电导率和热膨胀系数的影响。研究结果表明,YBa2Cu3O7-x相形成的温度为930℃、940℃烧结的YBCO陶瓷电导率最佳(达到9.742×105S/m),电导率具有随环境温度的变化呈正温度系数特点;烧结温度越高,电导率的环境热稳定性越好,烧结温度为950℃时,电导率基本不随环境温度变化而变化。不同烧结温度制备的YBCO陶瓷,热膨胀系数基本一致(为13.60~14.06μK-1),与铁素体不锈钢接近。     

PLZT厚膜研究

研究了用Sol-Gel法制备PLZT-7.5/70/30微粉的工艺,进行了相应厚膜的制备.探讨了微粉团聚问题及防止团聚的有关措施.由X射线衍射分析可知,在700℃下制备的PLZT-7.5/70/30厚膜为纯钙钛矿相.从铁电与热释电性测量结果可知,纯钙钛矿相PLZT-7.5/70/30厚膜的矫顽场Ec在28℃和43℃下分别为24.25kV/cm和18.13kV/cm,热释电系数p=0.46nC/cm2@℃.以上数据表明,PLZT-7.5/70/30厚膜材料是一种优选的热释电材料.     

烧结工艺对PMS-PNN-PZT压电厚膜性能的影响

采用丝网印刷法制备了PMS-PNN-PZT四元系压电厚膜陶瓷材料。研究了压电厚膜的烧结温度、烧结气氛对其压电、介电等性能及微观结构的影响。用XRD和SEM分析材料的相组成、厚膜定位及显微结构,结果表明,在密封埋粉的PbO气氛中,烧结温度1060℃,保温时间2 h,制得一种性能良好的压电厚膜陶瓷材料。其中,该压电厚膜压电常数d33为240 pC/N,相对介电常数rε为1 112,机械品质因数Qm为1250,机电耦合系数kp为0.52。     

Thermoelectric Properties of Polycrystalline SrZn2Sb2 Prepared by Spark Plasma Sintering

Compact polycrystalline samples of SrZn₂Sb₂ [space group $ P\overline{3} m1 $ , a = 4.503(1) Å, c = 7.721(1) Å] were prepared by spark plasma sintering. Thermoelectric performance, Hall effect, and magnetic properties were investigated in the temperature range from 2 K to 650 K. The thermoelectric figure of merit ZT was found to increase with temperature up to ZT = 0.15 at 650 K. At this temperature the material showed a high Seebeck coefficient of +230 μV K^?1, low thermal conductivity of 1.3 W m^?1 K^?1, but rather low electrical conductivity of 54 S cm^?1, together with a complex temperature behavior. SrZn₂Sb₂ is a diamagnetic p-type conductor with a carrier concentration of 5 × 10¹⁸ cm^?3 at 300 K. The electronic structure was calculated within the density-functional theory (DFT), revealing a low density of states (DOS) of 0.43 states eV^?1 cell^?1 at the Fermi level.     

Improved Thermoelectric Properties of p-Type Bismuth Antimony-Based Alloys Prepared by Spark Plasma Sintering

Bi₈₅Sb_15?x Pb _x (x = 0, 0.5, 1, 2, 3) alloys have been prepared by the mechanical alloying–spark plasma sintering (MA-SPS) method. X-ray diffraction and scanning electron microscopy were used to characterize the microstructure of the alloys. The effect of Pb content on the thermoelectric properties was investigated in the temperature range 77–300 K. The results showed that the electrical transport properties of the Bi–Sb alloys changed from n-type to p-type with substitution of Sb by Pb. The maximum power factor reached 1.6 × 10^?3 W/mK² at 190 K, a significant improvement on values reported elsewhere. This study demonstrated that high-performance p-type thermoelectric Bi–Sb materials can be obtained by spark plasma sintering.     

烧结温度对厚膜电阻的影响研究

以钌系R-2200厚膜电阻浆料作为研究对象,探讨了烧结温度、保温时间和升温速率工艺因素对其阻值及电阻温度系数(TCR)的影响。利用导电机理模型和液相烧结模型,说明了烧结工艺对钌系厚膜电阻性能的影响。实验数据与SEM表明:厚膜浆料烧结温度在875℃时,结构均匀且致密性好;烧结温度过低时,结构不稳定,功能相没有形成导电网络;而烧结温度过高时,RuO2晶粒异常长大,导电链断裂,势垒升高。     

Thermoelectric Properties of Indium-Selenium Nanocomposites Prepared by Mechanical Alloying and Spark Plasma Sintering

Indium-selenium-based compounds have received much attention as thermoelectric materials since a high thermoelectric figure of merit of 1.48 at 705?K was observed in In₄Se_2.35. In this study, four different compositions of indium-selenium compounds, In₂Se₃, InSe, In₄Se₃, and In₄Se_2.35, were prepared by mechanical alloying followed by spark plasma sintering. Their thermoelectric properties such as electrical resistivity, Seebeck coefficient, and thermal conductivity were measured in the temperature range of 300?K to 673?K. All the In-Se compounds comprised nanoscaled structures and exhibited n-type conductivity with Seebeck coefficients ranging from ?159???V?K^?1 to ?568???V?K^?1 at room temperature.     

Effect of Ce-Doping on Thermoelectric Properties in PbTe Alloys Prepared by Spark Plasma Sintering

Ce-doped Pb_1−x Ce _x Te alloys with x = 0, 0.005, 0.01, 0.015, 0.03, and 0.05 were prepared by induction melting, ball milling, and spark plasma sintering techniques. The structure and thermoelectric properties of the samples were investigated. X-ray diffraction (XRD) analysis indicated that the samples were of single phase with NaCl-type structure for x less than 0.03. The lattice parameter a increases with increasing Ce content. The lower Ce-doped samples (x = 0.005 and 0.01) showed p-type conduction, whereas the pure PbTe and the higher doped samples (x = 0, 0.015, 0.03, and 0.05) showed n-type conduction. The lower Ce-doped samples exhibited a much higher absolute Seebeck coefficient, but the higher electrical resistivity and higher thermal conductivity compared with pure PbTe resulted in a lower figure of merit ZT. In contrast, the higher Ce-doped samples exhibited a lower electrical resistivity, together with a lower absolute Seebeck coefficient and comparable thermal conductivity, leading to ZT comparable to that of PbTe. The lowest thermal conductivity (range from 0.99 W m⁻¹ K⁻¹ at 300 K to 0.696 W m⁻¹ K⁻¹ at 473 K) was found in the alloy Pb_0.95Ce_0.05Te due to the presence of the secondary phases, leading to a ZT higher than that of pure PbTe above 500 K. The maximum figure of merit ZT, in the alloy Pb_0.95Ce_0.05Te, was 0.88 at 673 K.     

纳米AIN粉末的制备与烧结

利用低温燃烧合成前驱物制备出平均粒度为100 nm的AlN陶瓷粉末,比较了该粉末的常压烧结和放电等离子烧结的特性。实验表明:以合成的AlN粉末为原料,添加5%(质量比)Y2O3作为烧结助剂,在常压、流动N2气氛下1600℃保温3 h,制备出平均晶粒尺寸为4~8μm、密度为3.28 g.cm-3的AlN陶瓷;将同样的粉末不加任何烧结助剂,采用SPS技术在1600℃保温4 min,得到密度为3.26 g.cm-3的AlN陶瓷,晶粒度约为1~2μm。     

电感耦合等离子体CVD制备Si薄膜的研究

电感耦合等离子体(ICP)是一种极具发展前景的低温高密度等离子体源,已经在大规模集成电路的深亚微米刻蚀和大面积均匀薄膜的淀积中得到广泛应用.采用自主设计的ICPCVD设备,在不同的衬底条件和SiH4浓度下制备了一系列的Si薄膜样品.采用多种结构分析手段对样品进行了测试,发现薄膜是非晶相、结晶相和孔隙的混合物,在较低的放电功率下即出现了相当比例的结晶相,对样品电导率和光学带隙的测试也进一步验证了这一结果.     

Thermoelectric Properties of Sn-S Bulk Materials Prepared by Mechanical Alloying and Spark Plasma Sintering

To study the possibility of SnS as an earth-abundant and environmentally friendly thermoelectric material, the electrical and thermal transport properties of bulk materials prepared by combining mechanical alloying and spark plasma sintering were investigated. It was revealed that SnS has potential as a good thermoelectric material, benefiting from its intrinsically low thermal conductivity below 1.0 W/m/K above 400 K and its high Seebeck coefficient over 500 μV/K. Although the highest ZT value was 0.16 at 823 K in the pristine sample, further enhancement can be expected through chemical doping to increase the electrical conductivity. It was also revealed that changing the stoichiometric ratio and sintering temperature had less apparent influence on the microstructure and thermoelectric properties of SnS because redundant S in the powders decomposed during the sintering process.     

镧钛酸铅铁电薄膜成膜机理探讨

采用快速热处理和传统热处理工艺对金属有机物热分解法制备的镧钛酸铅（ＰＬＴ）铁电薄膜进行了热处理，用扫描电镜对不同热处理工艺和不同厚度的ＰＬＴ薄膜的形貌进行了分析。结果表明，快速热处理工艺有利于活性高，较薄膜层的结晶和致密化反应；ＰＬＴ薄膜在传统和快速热处理过程中的形成过程与蒸发和溅射薄膜的核生长型薄膜的形成过程相似，薄膜的形成经历了岛状－网状－连续的过程，即随层数的增加，薄膜逐渐从不连续转变为连续，而热处理工艺只影响形成连续薄膜的厚度。     

sol-gel法制备多孔纳米SiO2薄膜

以 NH_3·H_2O 为催化剂,用正硅酸乙酯(TEOS)溶胶–凝胶工艺制备纳米多孔二氧化硅薄膜。强碱催化使二氧化硅胶粒溶解度增大并增大了体系的离子强度;丙三醇的加入,与水解中间体结合,有效抑制了二氧化硅溶胶胶粒的长大;PVA(聚乙烯醇)对二氧化硅胶粒有强的吸附作用,使胶粒聚联成大的网络结构,增加了成膜性能。通过改变反应物的剂量,调节添加剂的用量,可以制得折射率 1.18~1.42,对应孔率 60.50%~7.75%并且孔径小于 100 nm 的纳米多孔二氧化硅薄膜,。单层薄膜厚度在 3 μm 以内精确可控。     

沉积温度对电子束蒸发HfO2薄膜残余应力的影响

采用电子束蒸发沉积方法在BK7玻璃基底和熔融石英基底上沉积了HfO2薄膜,研究了不同沉积温度下的应力变化规律。利用ZYGO干涉仪测量了基片镀膜前后曲率半径的变化,计算了薄膜应力。结果发现在所考察的实验条件下HfO2薄膜的残余应力均为张应力,应力值随沉积温度的升高先增大后减小。两种基底上薄膜的残余应力的主要产生机制不同。对于BK7玻璃基底HfO2薄膜的残余应力起决定作用的是内应力,熔融石英基底上HfO2薄膜的残余应力在较低沉积温度下制备的薄膜起决定作用的是热应力,在沉积温度进一步升高后内应力开始起决定作用。通过对样品的X射线衍射(XRD)测试,发现在所考察的温度范围内,HfO2薄膜的结构发生了晶态转换,这一结构转变与薄膜残余应力的变化相对应。两种基底上薄膜微结构的演变及基底性能差异是两种基底上薄膜应力不同的主要原因。     

金刚石厚膜热残余应力三维模拟及失效分析

运用ANSYS软件建立了三维轴对称有限元模型,对金刚石厚膜(φ40mm×1mm)内部和膜/钼基体界面处的热残余应力各个分量的分布作了全面的模拟,讨论了热残余应力对金刚石厚膜失效的影响.结果表明,金刚石厚膜内的热残余应力各个分量并非均匀分布,离界面越近,其值越大;界面处大的轴向拉应力和剪应力对于厚膜从基体上脱落有重要影响;在膜的上表面靠近外边缘局部区域内存在较大的径向拉应力和轴向拉应力,是造成膜开裂失效的原因;本文的三维有限元模型比以往的一维解析模型更全面,且能更合理地解释金刚石膜的失效现象.     

射频磁控溅射法在柔性聚酰亚胺衬底上制备ZnS薄膜及其特性研究

为使Ⅱ-Ⅵ族化合物ZnS薄膜具有可弯曲性,选用柔性的聚酰亚胺作为衬底材料,用射频磁控溅射法沉积ZnS薄膜,对所制备薄膜的结晶结构、组分和光学特性进行分析.实验结果表明,所制备薄膜为结晶态的闪锌矿ZnS结构,择优取向为(111)晶面,晶粒尺寸为25.6 nm.薄膜组分接近化学计量比,并具有少量的S损失.薄膜在可见光区和近红外光区的平均透射率分别为82.0％和90.5％,透光特性良好.作为对比,在钠钙玻璃衬底上溅射的ZnS薄膜的结晶度高于聚酰亚胺衬底薄膜,但其透射率略低于柔性ZnS薄膜.实验结果表明了用磁控溅射法在柔性聚酰亚胺衬底上制备ZnS薄膜的可行性.