Bulletin of the American Physical Society
APS March Meeting 2010
Volume 55, Number 2
Monday–Friday, March 15–19, 2010; Portland, Oregon
Session Y29: Focus Session: Thermoelectrics VI: Oxides, Measurements, Devices |
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Sponsoring Units: DMP FIAP GERA Chair: R Ramesh, University of California, Berkeley Room: C123 |
Friday, March 19, 2010 8:00AM - 8:12AM |
Y29.00001: High temperature thermoelectric properties of Bi$_{2}$Sr$_{2}$Co$_{2}$O$_{y}$ thin films grown by Pulsed Laser Deposition Wolter Siemons, Jayakanth Ravichandran, Herman Heijmerikx, Joseph Feser, Arun Majumdar, R. Ramesh Misfit cobaltates are strongly correlated materials showing exceptional thermoelectric properties. Sodium cobaltate is the model system for this class of materials, which show high thermopower in the limit of large carrier concentration. Even though the exact origin of enhanced thermoelectricity is debatable, there is a general consensus that strong correlation plays a huge role in this effect. In order to better understand the nature of these materials, we chose to investigate Bi$_{2}$Sr$_{2}$Co$_{2}$O$_{y}$, which is one of the least studied materials in thin film form. We grew c-axis oriented thin films of Bi$_{2}$Sr$_{2}$Co$_{2}$O$_{y}$ on c-plane sapphire substrates by Pulsed Laser Deposition method. The thermoelectric properties of the films namely thermopower, electrical and thermal conductivities were measured over a temperature range of 300-800 K. Magnetic measurements, Nuclear Magnetic Resonance (NMR) and Electron Spin Resonance (ESR) were performed to determine the valence and spin states of Cobalt and the validity of Heikes formula is checked for this compound. [Preview Abstract] |
Friday, March 19, 2010 8:12AM - 8:24AM |
Y29.00002: Thermoelectric Properties of the Chemically Doped Ca$_{3}$Co$_{4}$O$_{9 }$System: A Structural Perspective Tao Wu, Trevor Tyson, Hsin Wang, Qiang Li Cu doped and Y doped [Ca$_{2}$CoO$_{3}$][CoO$_{2}$]$_{1.61}$ (referred to as Ca$_{3}$Co$_{4}$O$_{9})$ were prepared by solid state reaction. Temperature dependent thermoelectric properties, resistivity ($\rho )$, Seeback coefficient (S) and thermal conductivity ($\kappa )$, were measured. As seen before, it is found that doping by Cu and Y significantly enhances the thermoelectric properties. In order to understand the origin of these changes in properties in terms of the atomic structure, synchrotron x-ray diffraction and x-ray absorption spectroscopy were applied to probe the change in the average structure and the location of the dopants. The details of the location and coordination of Co and Y in the host lattice and the effect on the figure of merit are discussed. This work is supported by DOE Grant DE-FG02-07ER46402. [Preview Abstract] |
Friday, March 19, 2010 8:24AM - 8:36AM |
Y29.00003: Atomic-resolution study of charge transfer and structural disorder in thermoelectric Ca$_{3}$Co$_{4}$O$_{9}$ Robert Klie Thermoelectric oxides have attracted increasing attention due to their high thermal power and temperature stability. In particular, Ca$_{3}$Co$_{4}$O$_{9}$, a misfit layered structure consisting of single layer hole-doped CoO$_{2}$ sandwiched between insulating Ca$_{2}$CoO$_{3}$ rocksalt layers, exhibits figure of merit (ZT) of $>$1 at 1000 K.$^{1 }$It was suggested that the Seebeck-coefficient can be further increased by controlling the spin- and valence-state of the Co-ions in the CoO$_{2}$ layers. This study combines aberration-corrected scanning transmission electron microscopy with electron energy loss spectroscopy (EELS) to examine the atomic and electronic structures of Ca$_{3}$Co$_{4}$O$_{9}$. Using annular dark and bright field imaging, it will be demonstrated that the CoO$_{2}$ layers are ordered, while the CoO columns in the Ca$_{2}$CoO$_{3}$ layer exhibit a modulation along (010). Atomic-column resolved EELS reveals that the Ca$_{2}$CoO$_{3}$ layers act as charge reservoirs providing mobile holes to the CoO$_{2}$ layers; the structural disorder in Ca$_{2}$CoO$_{3}$ is responsible for the low in-plane thermal conductivity. The temperature dependence of the Co-ion spin-state as the origin for the unusually high Seebeck coefficient of Ca$_{3}$O$_{4}$O$_{9}$ will be examined.$^{2}$ $^{1}$ K. Fujita, et al., \textit{Jpn. J. Appl. Phys.} \textbf{40} (2001), 4644--47$^{ }$ $^{2}$ Funded by: NSF CAREER Award DMR-0846748 [Preview Abstract] |
Friday, March 19, 2010 8:36AM - 8:48AM |
Y29.00004: Thermoelectric properties of La$_{1-y}$Sr$_{y}$Rh$_{1-x}$Co$_{x}$O$_{3}$ Soichiro Shibasaki, Koichi Noguchi, Ichiro Terasaki We have studied thermoelectric properties of the perovskite-type rhodium oxide LaRhO$_{3}$ to clarify the electronic state of La$_{1-y}$Sr$_{y}$CoO$_{3}$. We have focused on Rh oxides as a reference to Co oxide, because Rh ions are stable in the low-spin state. To reveal the difference of the thermoelectric properties between La$_{1-y}$Sr$_{y}$RhO$_{3}$ and La$_{1-y}$Sr$_{y}$CoO$_{3}$, we have measured thermoelectric properties of La$_{1-y}$Sr$_{y}$Rh$_{1-x}$Co$_{x}$O$_{3}$. XRD analysis revealed that the crystal structure of La$_{1-y}$Sr$_{y}$Rh$_{1-x}$Co$_{x}$O$_{3}$ changes from orthorhombic to rhombohedral above around x$\sim $0.75. The resistivity at 300 K decreases with the Co concentration, whereas the magnitude of the thermopower takes a maximum around x$\sim $0.25. This phenomenon clearly suggests a certain correlation between Rh and Co ions. [Preview Abstract] |
Friday, March 19, 2010 8:48AM - 9:00AM |
Y29.00005: Thermoelectric Properties of $R_{1-x}$Sr$_{x}$CoO$_{3}$ Perovskites S. Boona, B. Dabrowski, S. Kolesnik , O. Chmaissem Cobalt oxide materials have recently shown promise for use in thermoelectric applications due to enhancement of the Seebeck coefficient ($S)$ by the spin and orbital degeneracy of the Co$^{3+}$ and Co$^{4+}$ ions. We have studied Sr substituted $R$CoO$_{3}$ ($R$ = rare earth elements) perovskites that exhibit increased transition temperatures to the low-spin ground state, which is required for achieving enhanced $S$. We have found that Gd is the smallest $R$ for which the homogenous Sr substitution is possible. We will present structural and thermoelectric properties of these materials with 0 $< \quad x \quad <$ 0.5. We will describe our search for materials with optimal degeneracy ratios, which are stable within practical operating temperature ranges for thermoelectric applications. [Preview Abstract] |
Friday, March 19, 2010 9:00AM - 9:12AM |
Y29.00006: Optimization of Dimensionless Figure of Merit in Oxide Thin Film Thermoelectrics Daniel Osborne, Scott Huxtable, Ashutosh Tiwari, Jeremiah Abiade The ability of uniquely functional thermoelectric materials to convert waste heat directly into electricity is critical considering the global energy economy. Profitable, energy-efficient thermoelectrics possess thermoelectric figures of merit ZT $\ge $ 1. We examined the effect of metal nanoparticle -- oxide film interfaces on the thermal conductivity $\kappa $ and Seebeck coefficient S in bilayer and multilayer thin film oxide thermoelectrics in an effort to improve the dimensionless figure of merit ZT. Since a thermoelectric's figure of merit ZT is directly proportional to S/$\kappa $, reducing $\kappa $ and increasing S are key strategies to optimize ZT. We reduced $\kappa $ by phonon scattering due to the inclusion of metal nanoparticles in the bulk of the thermoelectric thin film, and increased S due to energy-dependent electron scattering at the metal - oxide interfaces. Doped strontium titanate (STO) thin film/Au nanoparticle composites were synthesized by alternate ablation of Au and Nb-doped STO targets during pulsed laser deposition. Characterization of the thermoelectric films involve XRD, XPS, and TEM analyses, Seebeck coefficient measurements, and also measurements of the thermal conductivity via time-domain thermoreflectance. The measured thermal conductivities and Seebeck coefficients of the thin films shows a strong dependence on the nanoscale interfaces of the films. [Preview Abstract] |
Friday, March 19, 2010 9:12AM - 9:24AM |
Y29.00007: Exact solution for the Frequency Dependent charge and heat Transport (and their sum rules) with dynamical mean-field theory Jesus Cruz, James Freericks We have calculated transport properties for the Falicov-Kimball model using the Dynamical Mean Field Theory approach. The frequency dependent electrical and thermal conductivities are evaluated within linear response at finite temperature. Other important thermal properties like the thermopower and the figure of merit are also discussed. We investigate both the optical conductivity sum rule and the thermal conductivity sum rule proposed by Shastry. In analogy to the optical conductivity, the thermal conductivity sum rule can be expressed in terms of expectation values, which can be explicitly evaluated for our model. We use a hypercubic lattice for the underlying lattice for our system and the Falicov-Kimball model because it is an exactly solvable model with a phase transition from a metallic phase to a Mott insulator with respect to the U parameter. We also examine and discuss how the frequency dependent thermopower relates to its zero frequency limit. [Preview Abstract] |
Friday, March 19, 2010 9:24AM - 9:36AM |
Y29.00008: ABSTRACT WITHDRAWN |
Friday, March 19, 2010 9:36AM - 9:48AM |
Y29.00009: ABSTRACT WITHDRAWN |
Friday, March 19, 2010 9:48AM - 10:00AM |
Y29.00010: Evaluation of the methodologies in Seebeck coefficient metrology Joshua Martin The continued development of new thermoelectric materials for high temperature power conversion applications requires reliable and accurate characterization of the electrical and thermal transport properties. The Seebeck coefficient is a useful physical property in evaluating the potential performance of these thermoelectric materials, as it is sensitive to the electronic structure. However, the deceptive simplicity of measuring the Seebeck coefficient has led to the implementation of non-ideal practices that have further complicated the inter-laboratory confirmation of reported high ZT materials. To address these challenges, we have developed an improved thermoelectric probe to evaluate and compare these different characterization methodologies and arrangements. This talk will provide an overview of our apparatus design and instrumentation, with emphasis on the techniques required to effectively manage uncertainty in high temperature Seebeck coefficient measurements. [Preview Abstract] |
Friday, March 19, 2010 10:00AM - 10:12AM |
Y29.00011: Measurements of thermoelectric properties in thin films as a function of temperature using micromachined thermal isolation platforms Rubina Sultan, Azure Avery, Dain Bassett, Barry Zink Thermoelectrics are emerging materials for practical applications such as local cooling in integrated circuits, remote power generation in space and particularly in the field of energy conversion. The dimensionless figure of merit ($ZT=\sigma {\alpha}^2 T/\textit{k}$) which defines the efficiency of a thermoelectric material depends on material's intrinsic properties (thermal conductivity, electrical conductivity and thermoelectric power) so the reliability and performance depends on the material itself. One challenge is to explore materials in thin film form by precisely measuring thermal and electrical transport properties using effective measurement techniques. A better thermoelectric material with optimized ZT combines a higher electrical power factor ($\sigma {\alpha}^2$) and lower phonon thermal conductivity. Disordered thin films and nano structures are known to have low thermal conductivity. Further, their thermal conductivity and electronic properties can be controlled by the technique of alloying. In this talk, we present our measurement technique and recent results of in plane thermal conductivity, thermopower and electrical conductivity measurements of e-beam evaporated pure amorphous Si thin films and its metal alloys in the temperature range of 77- 325 K and discuss the figure of merit. [Preview Abstract] |
Friday, March 19, 2010 10:12AM - 10:24AM |
Y29.00012: Heat to Electricity using Thermoacoustics Ivan Rodriguez, Orest Symko In the thermoacoustic effect, sound can be generated when heat is injected to a section of an acoustic resonator; this sound can be converted to electricity using a piezoelectric element. The driving force is the temperature gradient in the resonator. Such approach is presented here for converting heat or waste heat to electricity. The device operates at 2kHz with air at one atmosphere as working fluid. The threshold for oscillations is at a temperature difference of 90\r{ }C when heat is injected to the hot heat exchanger. For a temperature difference of 140\r{ }C, the generated electrical voltage output at the piezo open circuit is 10Vrms or higher. The device shows much promise for energy conversion with efficiency which is a sizable fraction of Carnot. [Preview Abstract] |
Friday, March 19, 2010 10:24AM - 10:36AM |
Y29.00013: Thermoelectric and Themorectification properties of quantum dot junctions David M.-T. Kuo, Yia-Chung Chang The electrical conductance, thermal conductance, thermal power and figure of merit (ZT) of semiconductor quantum dots (QDs) embedded in an insulator matrix connected with metallic electrodes are theoretically investigated in the Coulomb blockade regime. The multilevel Anderson model is used to simulate the multiple QDs junction system. The charge and heat currents in the sequence tunneling process are calculated by the Keldysh Green function technique. In the linear response regime the ZT values are still very impressive in the small tunneling rates case, although the effect of electron Coulomb interaction on ZT is significant. Considering the inelastic scattering effect arising from size fluctuations, defects and electron-phonon interactions, the reduction of ZT values is serious. In the nonlinear response regime, the nonlinear heat flow with respect to temperature is observed. When the coupling between the QDs and the electrodes is asymmetrical, we observed a thermal rectification behavior, which is also influenced by the electron Coulomb interactions and energy level differences between the two dots. [Preview Abstract] |
Friday, March 19, 2010 10:36AM - 10:48AM |
Y29.00014: The measurements of thermopower and thermal conductivity of an In$_{2}$O$_{3}$ nanowire through a general purpose template Min-Nan Ou, Ping-Chung Lee, Cheng-Lung Chen, Chien-Lin Hung, Li-Jen Chou, Yang-Yuan Chen In order to study the electron-phonon transport properties in a single nanowire for various materials, a platform of Si/Si$_{3}$N$_{4}$ for the purpose was designed to perform the measurements of thermal power and thermal conductivity simultaneously. A single In$_{2}$O$_{3}$ nanowire was placed on the platform by manipulation probes and carefully examined. A sagging structure of In$_{2}$O$_{3}$ nanowire was prepared by E-beam lithographic and reactive ion etching techniques. The In$_{2}$O$_{3}$ nanowire with length of 30 $\mu $m and diameter of 100 nm was revealed by SEM images, The resistivity measured using four-probe method indicated a semiconducting like behavior in the range temperature from 10 K to 300 K with room-temperature resistivity about 2.17 m$\Omega $-cm at 300 K. Meanwhile, the thermopower and the thermal conductivity of In$_{2}$O$_{3}$ nanowire measured by steady state and self-heating 3$\omega $ method respectively are also obtained and was discussed in details. [Preview Abstract] |
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