Bulletin of the American Physical Society
APS March Meeting 2015
Volume 60, Number 1
Monday–Friday, March 2–6, 2015; San Antonio, Texas
Session G9: Focus Session: Materials Functionality by Design |
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Sponsoring Units: DMP Chair: Sebastien Lebegue, Universite de Lorraine Room: 006D |
Tuesday, March 3, 2015 11:15AM - 11:27AM |
G9.00001: Theory of Band Warping and its Effects on Thermoelectronic Transport Properties Nicholas Mecholsky, Lorenzo Resca, Ian Pegg, Marco Fornari Transport properties of materials depend upon features of band structures near extrema in the BZ. Such features are generally described in terms of quadratic expansions and effective masses. Such expansions, however, are permissible only under strict conditions that are sometimes violated by materials. Suggestive terms such as ``band warping'' have been used to refer to such situations and ad hoc methods have been developed to treat them. We develop a generally applicable theory, based on radial expansions, and a corresponding definition of angular effective mass which also accounts for effects of band non-parabolicity and anisotropy. Further, we develop precise procedures to evaluate band warping quantitatively and as an example we analyze the warping features of valence bands in silicon using first-principles calculations and we compare those with semi-empirical models. We use our theory to generalize derivations of transport coefficients for cases of either single or multiple electronic bands, with either quadratically expansible or warped energy surfaces. We introduce the transport-equivalent ellipsoid and illustrate the drastic effects that band warping can induce on thermoelectric properties using multi-band models. [Preview Abstract] |
Tuesday, March 3, 2015 11:27AM - 11:39AM |
G9.00002: Effective Thermal Properties and Thermal Boundary Resistances of Multiphase Composites Containing Carbon Nanotubes and Inorganic Nanoparticles Feng Gong, Dimitrios Papavassiliou, Hai Duong Monte Carlo simulations were employed to investigate the effective thermal conductivity ($K_{\mathrm{eff}}$) and thermal boundary resistances ($R_{\mathrm{bd}}$) of polymer composites containing carbon nanotubes (CNTs) and inorganic nanoparticles. By considering $R_{\mathrm{bd}}$ between any two phases and the synergistic effect of CNTs and nanoparticles, our model more accurately predicted$K_{\mathrm{eff}}$ of 3-phase composites than effective medium theories (EMTs). Complex morphology of CNTs (diameter, length) and the heat transfer at interfaces ($R_{\mathrm{bd}}$) were quantified to study their influences on $K_{\mathrm{eff}} $. By matching the simulated $K_{\mathrm{eff}}$ with the measured $K_{\mathrm{eff}}$, $R_{\mathrm{bd}}$ of polymer-CNT and polymer-nanoparticle could be estimated. The results showed that $K_{\mathrm{eff}}$ of composites increases when CNT fraction increases and when $R_{\mathrm{bd}}$ of polymer-nanofillers (CNTs and nanoparticles) decreases. CNT bundle was built to investigate its effect on $K_{\mathrm{eff}}$ of composites, which had not been considered in EMTs. It was found that when CNT bundles increase, $K_{\mathrm{eff}}$ decreases in the composites with random and parallel CNTs, whereas, $K_{\mathrm{eff}}$ increases in those with perpendicular CNTs. [Preview Abstract] |
Tuesday, March 3, 2015 11:39AM - 11:51AM |
G9.00003: Computational Materials Design (CMD$^{\textregistered}$: Realization of the Switching Mechanism in RRAM Hideaki Kasai, Susan Aspera, Yukio Tamai, Nobuyoshi Awaya, Koukou Suu, Hiro Akinaga Recent developments in computational techniques, coupled with the rapid progress in computer efficiency, make first principles-based COMPUTATIONAL MATERIALS DESIGN (CMD$^{\textregistered}$) a relevant field in the world of surface science and condensed matter physics. In this scheme, quantum mechanical calculations are performed to design promising materials and, understand the necessary mechanisms for the realization of an efficient technological device. Among the many systems our group is engaged with is on the elucidation of the switching mechanism of resistance random access memory (RRAM) devices. In this study, we propose a mechanism of resistive switching based on the change in the electronic properties of a metal-insulator-metal type of RRAM brought about by pulse voltages and presence of aligned oxygen vacancies. In this kind of RRAM, the presumed change in the electronic properties of the transition metal oxide (TMO) insulating layer is attributed to the presence of aligned oxygen vacancies with charge carrier trapping, and oxygen vacancy movement near the TMO-metal electrode interface. These results were further experimentally verified in an academe-industry joint collaboration through the NEDO project. [Preview Abstract] |
Tuesday, March 3, 2015 11:51AM - 12:27PM |
G9.00004: High-throughput computational search for new high mobility transparent (semi)conducting oxides Invited Speaker: Geoffroy Hautier Transparent conducting oxides (TCOs) are large band gap materials (to favor transparency) doped with electrons (n-type) or holes (p-type). TCOs are essential to many technologies from solar cell to transparent electronics and there is currently a large effort towards the discovery of new TCOs. I will present the results of a high-throughput computational search for new TCOs especially directed at p-type oxides. Focusing on low effective masses (leading to high mobility), large band gaps and dopability, I will show how thousands of oxides can be screened using various ab initio techniques (from density functional theory to GW) to find new potential high performance TCOs. I will discuss several unsuspected compounds with promising electronic structures and present preliminary experimental results. Beyond the description of those novel TCO candidates, I will chemically rationalize our findings, highlighting several design strategies towards the development of future high mobility TCOs. [Preview Abstract] |
Tuesday, March 3, 2015 12:27PM - 12:39PM |
G9.00005: Transparent Conductive Oxides as Near-IR Plasmonic Materials for Energy Conversion Arrigo Calzolari, Alice Ruini, Alessandra Catellani, Marco Buongiorno Nardelli Using first principles calculations, we investigate the origin of near-infrared plasmonic activity in M-doped ZnO, one of the most promising transparent conductive oxide (TCO) materials. Our results [1-2] predict realistic values for the plasma frequency and the free electron density as a function of the M-doping, in agreement with recent experimental results. Then we characterize the plasmon properties of In-doped nanowires that have been envisaged as plasmonic nanoparticles for energy conversion applications. \\[4pt] [1] A. Calzolari, et al., ACS Photonics 1, 703 (2014).\\[0pt] [2] M. Bazzani, et al., APL. 98, 121907 (2011) [Preview Abstract] |
Tuesday, March 3, 2015 12:39PM - 12:51PM |
G9.00006: Engineering the bandgap of ferroelectric ZnSnO$_3$ via sulfur substitution Brian Kolb, Alexie Kolpak Since its recent discovery, ferroelectric ZnSnO$_3$ has been investigated for utility in a number of applications. Its strong remnant polarization and good conductivity, for example, make it attractive as a photovoltaic material, but its relatively large 3 eV bandgap limits its potential usefulness. We find that the bandgap of ZnSnO$_3$ is highly sensitive to changes in lattice volume, which can be effected either with application of external strain or by substituting sulfur for oxygen. Upon forming the fully-substituted ZnSnS$_3$, the bandgap reduces to a near-optimal 1.3 eV while retaining many of the important properties of the oxide, including a strong polarization. In this talk we describe the physics governing the tunable electronic structure of ZnSnO$_3$, discuss the stability of the ZnSnS$_3$ analogue, and propose a route to its use in a photovoltaic cell by growth on a GaN substrate. [Preview Abstract] |
Tuesday, March 3, 2015 12:51PM - 1:03PM |
G9.00007: p-type transparent conducting chalcogenides Hongliang Shi, Bayrammurad Saparov, David Singh, Athena Sefat, Mao-Hua Du Transparent conducting materials are an important component in many optoelectronic devices ranging from solar cells to transparent electronics. A good transparent conducting material must allow high optical transmittance across a wide optical spectrum, requiring a large optical band gap (\textgreater 3.0 eV), and have high conductivity. However, in materials high conductivity and large band gaps usually do not coexist. At present, only a few materials are known to be reasonably good n-type transparent conducting oxides (TCOs). The p-type TCOs are still plagued by their poor hole conductivity, usually two orders of magnitudes lower than the highest electron conductivity in the n-TCOs. Chalcogenides usually have better hole conductivity, but their band gaps are usually too small. In this study, first-principles calculations are used to design new chalcogenides with large band gaps. New ternary chalcogenides, i.e.,Cs$_{2}$Zn$_{3}$Se$_{4}$ and Cs$_{2}$Zn$_{3}$Te$_{4}$, are found by calculations to be chemically stable and have both large band gaps (\textgreater 3.0 eV) and small effective masses. These new ternary chalcogenidesare are synthesized and found to be air stable. [Preview Abstract] |
Tuesday, March 3, 2015 1:03PM - 1:15PM |
G9.00008: Comparative first principles study for Li, Na, and Mg storage at rutile, anatase, bronze, and amorphous TiO2 Konstantinos Kotsis, Fleur Legrain, Sergei Manzhos TiO2 has been studied very extensively and its applications in various fields, e.g. applications in energy storage and catalysis are well known [1, 2]. Crystalline, amorphous and amorphous/crystalline titania have emerged as anode materials for Li and post-Li batteries due to good capacity, high rates [2, 3], and safety. Which is why the electronic and atomic structures as well as the properties of various crystalline TiO2 phases have recently attracted much research interest. Amorphous TiO2 (a-TiO2) phase also looks promising based on the few available studies but is much less explored [3, 4, 5, 6]. We have previously shown that amorphization of Si improves storage energetics of Li, Na, Mg [7], and there are reasons to believe that a-TiO2 will achieve the same. At high rates of charge-discharge, capacitive contribution to the specific capacity of titania electrodes becomes significant [8, 9, 10]. Therefore, interfacial effects are critical for the performance of titania-based anodes and need to be understood. We present a comparative first principles study of Li, Na, and Mg storage at nanosheets (NS) of crystalline (anatase (101), rutile (110), and (B) (110) surfaces) and amorphous TiO2 and compare the results to Li, Na, Mg in the bulk. [Preview Abstract] |
Tuesday, March 3, 2015 1:15PM - 1:27PM |
G9.00009: Probing for cationic dopants in lanthanum manganite for solid oxide fuel cell applications Sridevi Krishnan, Vinit Sharma, Manoj K Mahapatra, Prabhakar Singh, Rampi Ramprasad Solid oxide fuel cells (SOFC) are an efficient source of clean energy. Long-term stability of SOFC cathodes is desired along with thermophysical characteristics. Sr doped LaMnO$_{\mathrm{3}}$ is one of the active material for this application. A suitable choice of the dopant has a significant influence on the stability and performance of the cathode material at elevated operating temperature. ~Using first principles computations, we compare the stability of the LaMnO$_{\mathrm{3}}$ host for a range of cationic dopants including alkali, alkaline earth metals, 3d, 4d and 5d transition metal elements in the absence and presence of an oxygen vacancy. The stability of doped LaMnO$_{\mathrm{3}}$ against decomposition to various combinations of metals and oxides is assessed using a linear programming based algorithm, and the oxygen vacancy promoters are identified. ~Properties of the dopants like the ionic radius, oxidation state, magnetic moment and Mendeleev number are correlated with their stability in the host. Employing these as feature vectors, feature selection methods are used to identify the most promising ones to be used for regression and classification problems. Using supervised learning approaches stability of the dopant in the host is predicted for test sets. [Preview Abstract] |
Tuesday, March 3, 2015 1:27PM - 1:39PM |
G9.00010: Designing brownmillerite SrCoO$_{2.5}$(BM-SCO) as a cathode material -- a first principles study of oxygen diffusion process in BM-SCO Chandrima Mitra, Tricia Meyer, Ho Nyung Lee, Fernando Reboredo The discovery and design of new materials for next generation energy devices are crucial steps towards addressing various energy-related issues. ABO$_{3-\delta}$ type perovskite oxides have emerged as promising candidates for cathode/electrolyte materials in solid oxide fuel cells (SOFC's). In this work, we investigate oxygen diffusion in brownmillerite oxide SrCoO$_{2.5}$ (BM-SCO), employing a first principles approach. Our calculations indicate highly anisotropic diffusion pathways, which result from its anisotropic crystal structure. The one-dimensional vacancy channels are found to provide the easiest route for diffusion. We consider transport via additional oxygen vacancies as well and find the lowest migration barrier to occur within the two dimensional plane of the octahedral coordination of Co. We further find that an important parameter that could control oxygen stoichiometry in BM-SCO, is strain. This has important implications on the migration barrier of oxygen within BM-SCO and hence on the diffusion coefficient. [Preview Abstract] |
Tuesday, March 3, 2015 1:39PM - 1:51PM |
G9.00011: A DFT study of oxygen reduction reaction on single-atom Pt nanocatalyst Youngjoo Tak, Norina A. Richter, Aloysius Soon Platinum is one of the most broadly used catalyst for many chemical reactions (e.g. oxygen reduction reaction). Although its great reactivity, platinum catalysis has not met enthusiastic reception from industry due to its high price. Pt/C catalyst is widely used to come over this problem, but still considered as an imperfect solution because of its poor stability [1,2]. Recently, platinum single-atom catalyst with TiN support has suggested and proved to be stable on the N vacancy site of TiN support under N-lean condition [3]. In this work, we present density-functional theory (DFT) study of the oxygen reduction reaction on single Pt atom embedded on the surfaces of TiN(100) and TiC(100) within the computational hydrogen model (CHE) [4]. \\[4pt] [1] Z. Peng \textit{et al}., \textit{Nano Today}\textbf{4} 143 (2009) \newline [2] B. Avasarala \textit{et al}., \textit{J. Mater. Chem.}\textbf{19 }1803 (2009) \newline [3] R. Q. Zhang \textit{et al.}, \textit{Phys. Chem. Chem. Phys}. \textbf{14} 16552 (2012) \newline [4] N{\o}rskov \textit{et al.}, \textit{J. Phys. Chem. B}\textbf{108} 17886 (2004) [Preview Abstract] |
Tuesday, March 3, 2015 1:51PM - 2:03PM |
G9.00012: Gold-doped graphene as a cost-effective, highly stable and active electrocatalyst for the oxygen reduction reaction: prediction from first principles Sergey Stolbov, Marisol Alcantara Ortigoza One of the main obstacles hindering large scale practical application of hydrogen fuel cells is a prohibited cost of the Pt (or Pt-based) catalysts for the oxygen reduction reaction (ORR) on the fuel cell cathode. In this work, we consider Au-doped graphene as an alternative to Pt for facilitating ORR. Our first-principles calculations show that Au atoms incorporated into graphene di-vacancies form a thermodynamically and electrochemically stable structure. Furthermore, calculation of the binding energies of the ORR intermediates reveals that Au-C bonding makes the C atoms neighboring to Au optimally reactive for ORR. The calculated ORR free energy diagrams suggest that the Au-graphene structures have an ORR onset potential as high as that of Pt. We also demonstrate that the linear relation among the binding energy of the reaction intermediates assumed in a number of works on computational high-throughput material screening does not hold, at least for this none purely transition-metal material. [Preview Abstract] |
Tuesday, March 3, 2015 2:03PM - 2:15PM |
G9.00013: ABSTRACT WITHDRAWN |
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