Bulletin of the American Physical Society
APS March Meeting 2017
Volume 62, Number 4
Monday–Friday, March 13–17, 2017; New Orleans, Louisiana
Session Y36: Thermoelectrics: Characterization, NanostructuresFocus
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Sponsoring Units: DMP DCMP Chair: Joh Malen, University of California, Berkeley Room: 299 |
Friday, March 17, 2017 11:15AM - 11:51AM |
Y36.00001: TBD - Thermoelectric Materials and Novel Thermoelectric Phenomena Invited Speaker: Jian He |
Friday, March 17, 2017 11:51AM - 12:03PM |
Y36.00002: NMR study of partially filled skutterudites A$_{\mathrm{x}}$Co$_{\mathrm{4}}$Sb$_{\mathrm{12}}$ (A $=$ Yb, Ba, Sr, Ca) and Ba$_{\mathrm{x}}$Yb$_{\mathrm{y}}$Co$_{\mathrm{4}}$Sb$_{\mathrm{12}}$. Yefan Tian, Ali Sirusi, Joseph Ross, Sedat Ballikaya, Ctirad Uher, Yuqi Chen, Chihiro Sekine Partially filled Co-Sb skutterudites have been of considerable interest as thermoelectric materials, particularly with multiple filling for which high \textit{ZT} values can be obtained. This is due in part to control of phonon thermal conductivity, but also the change in composition leads to subtle changes in electronic behavior as well as magnetism due both to rare earth filler atoms and to native defects. We measured $^{\mathrm{59}}$Co NMR on several partially filled A$_{\mathrm{x}}$Co$_{\mathrm{4}}$Sb$_{\mathrm{12}}$ skutterudites in order to investigate such behavior. From the $T$-dependent NMR shifts along with $T_{1}$ relaxation times we can separate metallic shift contributions from those due to local moments. We compare the results to predicted band-edge behavior with multiple minima, and the estimated $g$ factors, by matching this behavior to transport measurements. Also the behavior of Yb-filled samples provides an estimate of the conduction band mediation of the magnetic response, and we also find magnetic shifts in Ba-doped skutterudite which we address in terms of Co mixed-valence behavior. [Preview Abstract] |
Friday, March 17, 2017 12:03PM - 12:15PM |
Y36.00003: Electronic Transport Properties and Band Structure of 2-D Material NaSn$_{2}$As$_{2}$ Bin He, Maxx Arguilla, Nicholas Cultrara, Joshua Goldberger, Joseph Heremans 2-D-like materials potentially have superior thermoelectric properties compared to traditional 3-D materials when the conduction mechanisms are different in the plane and along the c-axis. A classic example is that of n-type tetradymites, where the difference between electron and phonon anisotropies is exploited. Here we explore a material in which the polarity of the Hall and Seebeck signals are different. We present electrical and thermoelectric transport properties of NaSn$_{2}$As$_{2}$, a quasi-2-D system, with Na atom embedded between nearly-2D Sn-As layers. It shows typical metallic behavior with its resistance increasing linearly with temperature. Its Hall measurement shows a p-type behavior, with anomalous slope change with applied magnetic field, which varies over temperature. At the same time, its Seebeck coefficient is measured to be negative, increasing with temperature. DFT band structure calculations, confirmed ARPES measurements$^{1}$,show that this material is a 2-carrier system, which explains the discrepancy between Hall and Seebeck data. We conclude that the conduction mechanisms should be different in-plane and along the c-axis. 1. M. Arguilla, et al. ACS Nano 2016, 10, 9500−9508 [Preview Abstract] |
Friday, March 17, 2017 12:15PM - 12:27PM |
Y36.00004: Design of thermoelectrically highly efficient Heusler compounds using phase separations and nano-composites under an economic point of view Benjamin Balke Half-Heusler (HH) compounds are one of the most promising candidates for thermoelectric materials for automotive and industrial waste heat recovery applications. In this talk, I will give an overview about our recent investigations of phase separations in HH thermoelectrics, focusing on the ternary system TiNiSn-ZrNiSn-HfNiSn. I will show how we adapted this knowledge to design a p-type HH compound which exhibits a ZT that is increased by 130{\%} compared to the best published bulk p-type Heusler. I will also present how we used the phase separation to design thermoelectric highly efficient nano-composites of different single-phase materials. Since the price for Hafnium doubled within the last year, our research focused on the design of HH compounds without Hafnium. I will present a very recent calculation on ZT per Euro and efficiency per Euro for various materials followed by our latest very promising results for n-type Heusler compunds without Hafnium resulting in 20 times higher ZT/Euro values. These results strongly underline the importance of phase separations as a powerful tool for designing highly efficient materials for thermoelectric applications that fulfill the industrial demands for a thermoelectric converter. [Preview Abstract] |
Friday, March 17, 2017 12:27PM - 12:39PM |
Y36.00005: Hopping timescales and the phonon-liquid electron-crystal picture in thermoelectric copper selenide David Voneshen, Helen Walker, Keith Refson, Jon Goff Suppression of heat transport is essential to improve the efficiency of thermoelectric devices to convert waste heat into useful power and state-of-the-art materials have achieved thermal conductivities comparable to glasses. Recently, it was suggested that sub-lattice melting in superionic Cu$_2$Se leads to a suppression of transverse phonons and dramatic further reduction in thermal conductivity to liquid-like values [H. Lui \emph{et al.} \emph{Nat. Mater.}, \textbf{11}, 422 (2012)]. The validity of this process depends critically upon relative timescales involved. Using neutron spectroscopy we have measured both the ion transport and lattice dynamics in Cu$_2$Se. We find that the hopping timescales are too slow to significantly affect lattice vibrations and that the transverse phonons persist at all temperatures. While we observe substantial changes to the phonon spectrum they occur well below the transition to the superionic phase. Instead we attribute the ultra-low thermal conductivity to anharmonicity arising from the crystal structure. [Preview Abstract] |
Friday, March 17, 2017 12:39PM - 12:51PM |
Y36.00006: Thermoelectric Measurements on InAs/GaSb double Quantum Well Fan Yu, Tingxin Li, Ruiyuan Liu, Gang Li, Ziji Xiang, Colin Tinsman, Ruirui Du, Lu Li We performed thermoelectric measurement on InAs/GaSb double quantum well, in an attempt to observe thermal power and Nernst effect contributed by the helical edge channels. A new ``Semi-AC'' method was developed to conduct thermoelectric measurements for Hall bars with a size of $\sim$20 $\mu$m, which is more reliable in terms of determining charge carrier type compared with the 2-$\omega$ method. Furthermore, we will discuss thermoelectric signals under perpendicular magnetic field, in particular under Landau level quantization. [Preview Abstract] |
Friday, March 17, 2017 12:51PM - 1:03PM |
Y36.00007: Thermoelectric properties of ultrathin films of Bi$_{2-x}$Sb$_x$Te$_{3-y}$Se$_y$ Stephane Yu Matsushita, Khuong Kim Huynh, Harukazu Yoshino, Ngoc Han Tu, Yoichi Tanabe, Katsumi Tanigaki The recent discovery of 3D-TIs showing the unconventional Dirac band on the surface provided an intriguing research platform to survey the new TE materials differently from the conventional electronic approaches. Here, we report our recent experimental studies on the thermoelectric (TE) properties of topological surface Dirac states (TSDS) in three dimensional topological insulators (3D-TIs) by employing Bi$_{2-x}$Sb$_x$Te$_{3-y}$Se$_y$ ultrathin films. We successfully obtained two nontrivial electronic surface states, a metallic TSDS (m-TSDS) and a gap-opened semiconducting TSDS (g-TSDS), in the ultrathin film limit of 8 and 4 quintuple layers, respectively. Important TE parameters (electrical conductivity ($\sigma$), thermal conductivity ($\kappa$) and thermopower ($S$)) were accurately determined. The state of m-TSDS gives $S$=-44 $\mu$VK$^{-1}$, which is more than an order of magnitude higher than those of the conventional metals and its value is enhanced to -212 $\mu$VK$^{-1}$ for g-TSDS. From the viewpoint of $\sigma$ and $\kappa$, the Wiedemann-Franz law seems to be broken due to the disordered topological surfaces, providing the future possibilities for highly efficient TE materials. [Preview Abstract] |
Friday, March 17, 2017 1:03PM - 1:15PM |
Y36.00008: Nanophononic metamaterial: Engineering local resonances in thermoelectric materials for high energy conversion performance. Mahmoud Hussein, Hossein Honarvar Engineered manipulation of phonons can yield beneficial thermal properties in semiconducting materials. One pivotal application relates to thermoelectric materials, or the concept of converting energy in the form of heat into electricity and vice-versa. The ability to use nanostructuring to reduce the thermal conductivity without negatively impacting the power factor provides a promising avenue for achieving high values of the thermoelectric energy conversion figure-of-merit, ZT. Here, we report our latest results on a novel nanostructured material configuration that seeks to achieve this goal. Termed ``nanophononic metamaterial'', the configuration is based on a freestanding silicon membrane with a periodic array, or random forest, of nanopillars erected on the surface. The nanopillars qualitatively alter the base membrane phonon spectrum due to a hybridization mechanism between their local resonances and the underlying atomic lattice dispersion. Using equilibrium molecular dynamics simulations, we predict a two orders of magnitude drop in the thermal conductivity compared to the corresponding uniform membrane value despite the fact that the nanopillars add more phonon modes to the spectrum. [Preview Abstract] |
Friday, March 17, 2017 1:15PM - 1:27PM |
Y36.00009: Thermoelectric power factor under the effect of 1-D quantum confinement I-Ju Chen, Luna Namazi, Kimberly Dick Thelander, Heiner Linke, Claes Thelander Semiconductor nanowires hold great promises for achieving high thermoelectric efficiencies both by reducing the thermal conductivity and increasing the power factors. One way to increase the power factor is by taking advantage of the 1D quantum confinement effect. However, up to date, it is not clear whether this is feasible in nanowire structures. In this work we study experimentally the thermoelectric properties of InAs single-nanowire devices. Conductance quantization and the associated oscillations of the Seebeck coefficient are observed, indicating that the electronic transport is dominated by 1-D quantum confinement. Thermoelectric characterization is performed from the 1st up to the 4th subband. To understand quantum effects on the power factor, we investigated devices with lengths ranging from the ballistic to the diffusive regime, at temperatures between 10 and 295 K. By drawing an analogy with ballistic 1-D conductors, we analyze the maximal power factors achievable with a single 1-D subband. [Preview Abstract] |
Friday, March 17, 2017 1:27PM - 1:39PM |
Y36.00010: Low resistivity contacts to thin film thermoelectric materials Catalin D. Spataru, Yuping He, Francois L\'{e}onard, Douglas L. Medlin, Philip Barletta, Nicholas Baldasaro, Dorota Temple Thin films of telluride materials such as Bi$_{\mathrm{2}}$Te$_{\mathrm{3}}$ and Sb$_{\mathrm{2}}$Te$_{\mathrm{3}}$ have been of interest for thermoelectric applications and for devices based on their topological insulator properties. In both cases, electrical contacts play a key role in determining performance, but little is known about the detailed properties of such contacts and ways to reduce the contact resistivity. Here, we employ a combination of ab initio and macroscopic simulations to establish the basic physics of these contacts and to establish realistic limits on the contact resistivity. We show that the nature of the semiconductor material leads to unusual contact properties, such as a strong interfacial atomic dipole, that completely determine the band-bending and strong n-type doping near the interface. We predict that significant improvements over previously reported experimental data are possible, and we present new experimental data that demonstrate a 100-fold reduction in contact resistivity. Detailed analysis of the new contacts shows that additional improvement should be possible. Importantly, we show that the reduction in contact resistivity can be harnessed to improve the thermoelectric efficiency of thermoelectric modules. [Preview Abstract] |
Friday, March 17, 2017 1:39PM - 1:51PM |
Y36.00011: Investigation and Characterization of Polymer/Inorganic Bulk Composites Kaya Wei, George Nolas In the last decade polymers have been considered for thermoelectric applications primarily due to their specifically unique combination of properties that are atypical of inorganic material, including mechanical flexibility, low cost, low temperature and cost processing, and general non-toxicity. By incorporating inorganic compounds into a polymer matrix, enhanced thermoelectric properties have been achieved. As an extension of our previous work on PEDOT:PSS/Bi$_{\mathrm{0.5}}$Sb$_{\mathrm{1.5}}$Te$_{\mathrm{3}}$ polymer/inorganic bulk composites with different Bi$_{\mathrm{0.5}}$Sb$_{\mathrm{1.5}}$Te$_{\mathrm{3}}$ concentrations, we optimized the electrical conductivity by doping the polymer in order to further improve the thermoelectric properties of these composites. We will also discuss a new approach to process bulk polymer/inorganic composites. In addition, we observed better transport in dense, bulk polymers processed using spark plasma sintering compared with that of using hotpress. The transport properties were characterized in order to understand the transport in heavily-doped polymer/inorganic composites, characterized by localized charge regions, in light of the interest in polymers for thermoelectric applications. [Preview Abstract] |
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