Alloys and Compounds for Thermoelectric and Solar Cell Applications V: Student Poster Session
Sponsored by: TMS Functional Materials Division, TMS: Alloy Phases Committee
Program Organizers: Sinn-wen Chen, National Tsing Hua University; Franck Gascoin, Ensicaen University of Caen; Soon-jik Hong, Kongju National University; Philippe Jund, Université de Montpellier; Lan Li, Boise State University; Takao Mori, National Institute for Materials Science; Ce-Wen Nan, Tsinghua University; Hsin-jay Wu, National Sun Yat-Sen University

Tuesday 6:00 PM
February 28, 2017
Room: Hall B1
Location: San Diego Convention Ctr

Session Chair: Sinn-wen Chen, National Tsing Hua University

L-12: Bi0.5Sb1.5Te3 Thin Films with Bulk-like Thermoelectric Properties on Glass and Flexible Substrates: Elli Symeou1; Christiana Nicolaou1; Ioannis Giapintzakis1; 1University of Cyprus
    Localized cooling in micro- and nano-electronics as well as energy autonomy in applications such as wireless sensor networks and wearable electronics could be well served by thin film thermoelectric devices fabricated on solid and/or flexible substrates. Bi0.5Sb1.5Te3 is considered to be a state-of-the-art p-type thermoelectric material, near room temperature, due to its high power factor value. Nevertheless, the deposition of Bi0.5Sb1.5Te3 thin films with bulk-like thermoelectric properties remains a great challenge. We have grown p-type Bi0.5Sb1.5Te3 thin films onto different types of substrates such as fused silica and Kapton using pulsed laser deposition. The films were grown at room temperature and then were subjected to a post-deposition ex-situ annealing process. In this poster presentation, we will discuss how the thermoelectric properties of the obtained films are affected by the substrate type and stoichiometry. The power factor values of our post-annealed films are similar to those of the best bulk materials.

L-13: Contribution Percentages of Electromigration and Diffusion on Interfacial Reactions at Joints in Thermoelectric Modules: Jing-wei Chen1; Sinn-wen Chen1; Yi-cheng Lin1; Tao-chih Chang2; 1National Tsing Hua University; 2Industrial Technology Research Institute
    Thermoelectric modules have attracted very intensive research interests primarily due to their ability of enhancing energy usage efficiency by converting waste heat into electricity. Thermoelectric modules are usually composed of arrays of devices, and there are numerous joints in thermoelectric modules. Interfacial reactions at these joints are critical to the module’s reliability. Dissimilar materials are in contact at the joints, and the atoms diffuse at elevated temperatures as driven by chemical potential gradients. Besides diffusion, electromigration also contribute to atomic flux. The interfacial reactions of Sn-based solder joints at different temperatures and electric current densities are experimentally investigated. A one-dimensional mass transfer model was developed to describe the growth of the reaction phase layer. The contribution percentages of diffusion and electromigration upon interfacial reactions are examined. Since the electric current densities are relatively low and the working temperatures are relative high, the contribution of interfacial reactions are mostly from diffusion.

L-14: Effect of Microstructure of the Thermoelectric Properties of Al-based Intermetallic Compounds Prepared by a Melt-spinning Method: Akira Umeda1; Ken Kurosaki1; Masaya Kumagai1; Yuji Ohishi1; Hiroaki Muta1; Shinsuke Yamanaka1; 1Osaka University
    We have focused on Al-based thermoelectric (TE) materials, such as RuAl2 and VAl3, which can be candidates of low-toxicity/cost-effective TE materials. Although Al-based TE materials show high power factor, the dimensionless figure of merit zT is low, due to their relatively high lattice thermal conductivity (κlat). Since κlat is dependent on the microstructure of bulk materials, the microstructure-control is an effective way to reduce the κlat. In the present study, we prepared the bulk samples of RuAl2 and VAl3 by melt-spinning followed by spark plasma sintering, where the microstructure was controlled by mainly changing the cooling rate. The effect of microstructure, in particular the grain size, on the κlat as well as other TE properties of RuAl2 and VAl3 will be discussed.

L-15: Electronic Structure and Thermoelectric Properties of Pseudogap Intermetallic Compound Al5Co2: Masaya Kumagai1; Ken Kurosaki1; Yuji Ohishi1; Hiroaki Muta1; Shinsuke Yamanaka1; 1Osaka University
    One of the bottlenecks for widespread use of thermoelectric (TE) generators as consumer products is toxicity of currently-used TE materials. In recent years, Si-based materials (e.g. nanostructured Si, MgSi2, and FeSi2) have been extensively studied as candidates of low-toxicity high-efficiency TE materials. On the other hand, the TE properties of Al-based materials have been scarcely studied, with a few exceptions such as YbAl3 and Fe2VAl. Hence, we focused on Al5Co2 as a candidate of novel Al-based TE materials. In the present study, the electronic structure and TE properties of Al5Co2 were investigated.

L-16: Interfacial Reactions between Indium and Bi2Te3-based Thermoelectric Materials: Ji-min Lin1; Yohanes Hutabalian1; Shi-Ting Lu1; Jui-shen Chang1; Sinn-wen Chen1; 1National Tsing Hua University
    P-type (Bi,Sb)2Te3 and N-type Bi2(Te,Se)3 are the most commonly used alloys in thermoelectric modules. There are numerous joints in a thermoelectric module connecting these thermoelectric P-N devices to metallic plates. Indium and indium-based solders are potential joining materials for conventional soldering and transient liquid phase bonding techniques in thermoelectric modules. Although most likely barrier layers would be used, this study investigates the interfacial reactions between indium and the Bi2Te3-based thermoelectric materials to provide fundamental understanding of the interfacial reactions in the Bi2Te3-based thermoelectric modules if no barrier layers. Very significant interfacial reactions were observed in the In/Bi2Te3, In/Bi2Se3 , In/Sb2Te3, In/(Bi,Sb)2Te3 and In/Bi2(Te,Se)3 couples reacted at 250°C. The results confirm the necessity of using barrier layers. The various undetermined compounds in the Bi-Te binary system between Bi and Bi2Te3 phases are grouped together as the (Bi2)m(Bi2Te3)n compound and similarly those in the Bi-Se system are grouped as the (Bi2)m(Bi2Se3)n compound.

L-17: Micro Energy Harvesting Characteristics of Thermoelectric Thin-film Devices Fabricated Using Flip-chip Process: Jae Hwan Kim1; Tae-Yeol Lee1; Dong-Hwan Kim2; Jae-Ho Lee1; Tae-Sung Oh1; 1Hongik University; 2DGIST
    Micro energy harvesting has been extensively investigated to provide auxiliary power sources for wearable devices. Among various potential power sources, thermoelectric thin-film devices have drawn attention because they can be operated by a small temperature difference with the advantages of high power density, no moving parts, and high reliability. However, bonding of the upper electrodes in a top substrate to thermoelectric thin-films in a bottom substrate for circuit formation is difficult to limit the realization of thermoelectric thin-film devices. Flip-chip process has a strong potential to be applied for fabrication of thermoelectric devices. In this study, we fabricated thermoelectric thin-film devices consisting of n-type Bi2Te3 and p-type Sb2Te3 thin-films with flip-chip process using Sn-In solder reflow as well as anisotropic conductive adhesive and compared their power generation characteristics. Acknowledgement: This work was supported by the Basic Science Research Program of the National Research Foundation of Korea (Project No. 2014R1A1A2004630).

L-18: Rapid Synthesis of Zinc and Nickel Co-doped Tetrahedrite Thermoelectrics by Mechanical Alloying and Reactive Spark Plasma Sintering: Daniel Weller1; Donald Morelli1; 1Michigan State University
    Tetrahedrite offers advantages over other state-of-the-art thermoelectrics, such as lead telluride, because of its low cost and environmentally friendly composition. However, typical sealed-tube synthesis of tetrahedrite can require multiple days or weeks. In this study, tetrahedrite was synthesized by two different processes, mechanical alloying and reactive spark plasma sintering (SPS), that require significantly less time than the conventional furnace-ampoule method. Thermoelectric properties were measured for samples of Cu10Ni2-xZnxSb4S13 (x=0, 0.5, 1, 1.5, 2) synthesized using both techniques. Peak dimensionless figure of merit (ZT) values were obtained for Cu10Ni2Sb4S13 with ZT=0.64 and ZT=0.62 at 623 K in mechanically alloyed and SPS reacted samples, respectively.

L-19: Synthesis and Thermoelectric Properties of ZnSnSb2 with Chalcopyrite Structure: Ami Nomura1; Ken Kurosaki1; Seongho Choi1; Yuji Ohishi1; Hiroaki Muta1; Shinsuke Yamanaka1; 1Osaka University
    Our group has discovered that CuGaTe2 with chalcopyrite structure exhibits exceptionally high thermoelectric (TE) figure of merit zT = 1.4 [T. Plirdpring et al., Adv. Mater. 24, 3622 (2012).]. It has been also proved that when the tetragonal lattice parameter ratio (c/a) closet to 2, the valence bands of the chalcopyrite compounds highly degenerate at the band-edge, leading to enhancement of the power factor (PF). Actually, the c/a ratio of CuGaTe2 is close to 2. Since the c/a ratio of ZnSnSb2 with chalcopyrite structure is just 2, ZnSnSb2 is expected to show high PF. However, reports on the TE properties of ZnSnSb2 have been limited because it is hard to synthesize single-phase ZnSnSb2. In the present study, we succeeded to synthesize pure ZnSnSb2 with no impurities by using a Sn flux method. The details of the sample synthesis method and conditions and the TE properties will be presented.

L-20: Synthesis of Ge-germanide Nanocomposites by Melt-spinning Technique: Takayuki Sasaki1; Ken Kurosaki1; Yuji Ohishi1; Hiroaki Muta1; Shinsuke Yamanaka1; 1Osaka University
    Recently, Si has been considered as a promising thermoelectric (TE) material in view of its low toxicity and abundance. However, its high thermal conductivity limits enhancement of the TE properties. Owing to the high carrier mobility and low thermal conductivity, Ge is expected to show better TE properties than those of Si. Nevertheless, Ge itself and its compounds have not been well-studied. In the present study, the nanocomposites composed of Ge and various metal germanides were synthesized by melt-spinning technique, in which the size and morphology can be controlled by changing the cooling and solidification conditions. The microstructure and the TE properties of the nanocomposites will be presented.

L-21: Thermoelectric Properties of Amorphous Ti50Cu28Ni15Sn7-dispersed Bi0.4Sb1.6Te3 Nanocomposite Prepared by Mechanical Alloying and Vacuum Hot Pressing: Pee-Yew Lee1; 1National Taiwan Ocean University
    In this study, the Ti50Cu28Ni15Sn7/Bi0.4Sb1.6Te3 bulk composite samples were fabricated by mechanical alloying and vacuum hot pressing. TEM bright-field image shows that the Ti50Cu28Ni15Sn7 amorphous phase with particle size of about 50 nm were homogeneously distributed along the grain boundary of Bi0.4Sb1.6Te3 matrix with grain size around 0.5~2.0 μm. The thermoelectric properties of Ti50Cu28Ni15Sn7/Bi0.4Sb1.6Te3 samples were measured. The results indicated the values of figure of merit (ZT) for the Ti50Cu28Ni15Sn7/Bi0.4Sb1.6Te3 bulk composite samples were found to increase with temperature in the range from 298 K to 580 K. It is the first time that such specific behavior has been observed for (Bi,Sb)2Te3-based thermoelectric materials. For Ti50Cu28Ni15Sn7/Bi0.4Sb1.6Te3 specimen with 1.75 wt. % amorphous Ti50Cu28Ni15Sn7, the maximum ZT value is 1.08 at 580 K, which is the highest ZT values among the existing (Bi,Sb)2Te3-based low temperature thermoelectric materials has been measured at 580K.

L-22: Thermoelectric Properties of Bulk Al2(FeSi)3: Yasutaka Shiota1; Kunio Yamamoto1; Hiroaki Muta1; Yuji Ohishi1; Ken Kurosaki1; Shinsuke Yamanaka1; 1Osaka University
    Recently thermoelectric generation is being applied to sensing devices for sensor network, which should be composed by low toxic and environmentally friendly materials. We focused on Al2(FeSi)3 as a low toxic material, it has been found to be a semiconductor by first-principle calculations. Previous researches reveal the complex crystal structure of Al2(FeSi)3 in Al-Fe-Si alloy, however, the thermoelectric properties have not been measured yet. In the present study, single phase Al2(FeSi)3 bulk sample has been synthesized by arc melting, followed by spark plasma sintering and heat treatment. Then the electrical and thermal properties have been investigated.

L-23: Thermoelectric Properties of Nanostructured HMSs/Si Eutectic Alloy Prepared by a Melt Spinning Method: Saori Wadagaki1; Yuji Ohishi1; Hiroaki Muta1; Ken Kurosaki1; Shinsuke Yamanaka1; 1Osaka University
    Nanostructuring is one of the effective methods of reducing thermal conductivity, and that leads higher zT, which characterizes thermoelectric (TE) performance. Higher manganese silicides (HMSs, MnSi1.75-x with x=0-0.04) are considered as potentially important p-type TE materials because of their nontoxicity and abundant reserves. In this work, we fabricated nanostructured HMSs/Si eutectic alloy by a melt-spinning (MS) method. The melt spun samples had a characteristic nanostructure where Si nano-precipitates with less than 100 nm in diameter were dispersed in the HMSs matrix. On the contrary, arc-melted sample had Si precipitates with about 1 μm in diameter. To obtain bulk samples, each sample was crushed into powder followed by a spark plasma sintering (SPS). The thermal conductivity of MS+SPS sample was 4.87 W/m/K, which was approximately 13% lower than Arc+SPS sample. TE properties of these will be discussed.