Computational Thermodynamics and Kinetics: Materials Physics
Sponsored by: TMS: Chemistry and Physics of Materials Committee, TMS: Computational Materials Science and Engineering Committee
Program Organizers: Niaz Abdolrahim, University of Rochester; Stephen Foiles, Sandia National Laboratories; James Morris, Oak Ridge National Laboratory; Raymundo Arroyave, Texas A & M University

Wednesday 8:30 AM
March 1, 2017
Room: 11B
Location: San Diego Convention Ctr

Session Chair: Michael Manley, Oak Ridge National Laboratory; Brent Fultz, California Institute of Technology

8:30 AM  Invited
Piezoelectric Gold - Exploiting Mechano-Chemical Coupling at Interfaces for Designing Novel Functional Materials: Charlotte Stenner1; Anja Michl1; Jörg Weissmüller1; 1Hamburg University of Technology
    The strong coupling between chemistry or electrochemistry and mechanics at interfaces may be exploited for designing materials with unexpected functional behavior. This is demonstrated by the remarkable observation that nanoporous-metal based hybrid materials behave similar to piezoe-lectric ceramics: Bodies of nanoporous gold impregnated with electrolyte emit exceptionally robust electric signals when subjected to external load. The metal-based material may thus be considered as piezoelectric, in a literal interpretation of the term. The cross-correlation between charge re-sponse to load and strain response to potential, as required by a phenomenological description of apparent piezoelectricity, is quantitatively satisfied. The local mechano-electric coupling at internal interfaces, which governs the effect, is well documented in experiment. Yet, a predictive under-standing of the quantum mechanical basis remains elusive. The talk will discuss the relevant issues in experiment and phenomenological thermodynamics, and will address the state-of-the-art in relation to density functional theory computation.

9:00 AM  
Phonon Thermodynamics of Silicon: Dennis Kim1; Olle Hellman1; Hillary Smith1; Jiao Lin2; Jane Herriman1; Jennifer Niedziela2; Douglas Abernathy2; Brent Fultz1; 1Caltech; 2Oak Ridge National Laboratory
    Phonons are the main source of total entropy, thermal expansion, and thermal transport properties of most materials, so it is essential to know the temperature-dependent lattice dynamics. We measured phonon dispersions in silicon by neutron inelastic scattering at elevated temperatures. Although the quasiharmonic model (harmonic phonons renormalized by volume) predicts the experimental entropy and thermal expansion of silicon fairly well, it does not predict correctly the temperature-dependent lattice dynamics. The necessity to include anharmonicities to describe the lattice dynamics throughout the temperature range was verified by ab-initio calculations using the temperature-dependent effective potential method. Large phonon anharmonicities manifested through shifts and broadenings go beyond the quasiharmonic model even at low temperatures. The quasiharmonic model correctly predicts the macroscopic values due to a cancelation of phonon shifts, but its validity should not be assumed because it predicts average quantities.

9:20 AM  
Vibrational Entropy from Thermally-Driven Electronic Topological Transitions: Fred (Chae-Reem) Yang1; Jorge Muñoz2; Olle Hellman1; Lisa Mauger1; Matthew Lucas3; Sally Tracy1; Brent Fultz1; 1California Institute of Technology; 2The Datum Institute; 3Air Force Research Laboratory
    A novel thermally-driven electronic topological transition was discovered in the B2-ordered intermetallic compound FeTi. Ab-initio molecular dynamics, supported by inelastic neutron scattering and nuclear resonant inelastic x-ray scattering, showed an anomalously large thermal softening of the M5 phonon mode that could not be explained by phonon-phonon interactions or electron-phonon interactions calculated at low temperatures. The softening is caused by an adiabatic electron-phonon interaction with an unusual temperature dependence. This interaction arises from the appearance of new features of the Fermi surface at elevated temperatures. This electronic topological transition (Lifshitz transition) was analyzed by electronic band unfolding, Fermi surface visualization, and enumerating the electron-phonon spanning vectors. The transition is being evaluated for vanadium and A15 vanadium-based compounds, which exhibit anomalous shifts in phonon energies caused by adiabatic electron-phonon interactions at elevated temperatures.

9:40 AM  Invited
Anharmonic Phonon Effects in Wurtzite and Zincblende GaN: Jane Herriman1; Olle Hellman1; Brent Fultz1; 1Caltech
    While a quasi harmonic model (QHM) is commonly used and sometimes sufficient to account for material thermodynamics, anharmonic phonon effects often limit its accuracy. A better understanding of the relationship between structure and phonon anharmonicity would heighten intuition for when QHMs can be trusted and when higher order approximations are necessary. We compare anharmonic effects on material thermodynamics in wurtzite and zincblende GaN using ab initio methods and the temperature dependent effective potential (TDEP) method. The polytypism of GaN makes it an excellent platform for studying structure-anharmonicity relationships as it has technologically relevant metastable phases. Preliminary results suggest that anharmonic contributions to vibrational entropy are greater in the zincblende phase of GaN than in the wurtzite phase. Such a result would suggest that the free energy gap between the zincblende and wurtzite phases decreases with increasing temperature. Results proceeding from more rigorous analysis will be presented at the meeting.

10:10 AM Break

10:25 AM  
Single and Poly- Crystal Elastic Constants of Nickel and Ni-Hx Alloys at Finite Temperature from Experiments and First Principles Calculations: Guillaume Hachet1; Arnaud Metsue1; Abdelali Oudriss1; Marc Huger2; Xavier Feaugas1; 1University of La Rochelle; 2University of Limoges
    The effects of H on the mechanical properties of metals have to be quantified for a better understanding of hydrogen embrittlement (HE). We have conducted experimental and numerical investigations on the elastic constants of nickel (Ni) and nickel-hydrogen alloys (Ni-Hx) since too few data can be found in the literature. Uniaxial tensile tests and ultrasonic measurements have been carried out on (001), (011) and (111) oriented single crystals Ni and Ni-Hx structure in the 300-1000K temperature range. Also, the components of the elastic constant tensor of these materials have been calculated from first principles. We have calculated the isothermal and adiabatic Cijkl up to the melting temperature from the computation of the Helmholtz free energy expressed as a sum of static, vibration and electronic excitations contributions. Finally, we have used homogenisation techniques to determine the elastic constants of polycrystals, which have been compared with additional experiments on these materials.

10:45 AM  
Thermotransport in Binary Liquid Alloys: Graeme Murch1; Tanvir Ahmed1; Ujjal Sarder1; Elena Levchenko1; Alexander Evteev1; Irina Belova1; 1The University of Newcastle
    A clear and convincing understanding of thermotransport (the coupling of mass and heat flows) is necessary for providing a satisfactory description of the properties of liquid metal alloys. This in turn will be very useful for enhancing technological progress involving these alloys. Thermotransport is generally known from the resulting segregation of the liquid components in a temperature gradient (the Soret effect), or for its contribution to heat flow in liquids (the Dufour effect). Thermotransport in liquids does not have a general theory that can both marshal the experimental facts together and provide an understanding that has predictive power. In this presentation, a new formalism for describing thermotransport in a liquid metallic alloy with examples of molecular dynamics evaluation of the thermotransport and interdiffusion and tracer diffusion parameters for a wide range of compositions in Ni-Al and Ag-Cu liquid alloys is given.

11:05 AM  
A One-Mode Phase-Field Crystal Model Quantified for Solid-Liquid Coexistence of FCC and HCP Metals: Ahmad Nourian Avval1; Ebrahim Asadi1; 1University of Memphis
    Material Properties are governed by their atomistic/micro scale structures developed during solidification or other thermo-mechanical processes. Thorough understanding of relationships between properties and processing parameters requires a model with atomistic length and diffusive time scale, the characteristic that can be fulfilled in phase-field crystal (PFC) model. Thus far, one-mode PFC model (1M-PFC) has been quantified for BCC metals while high-order PFC models were used for quantitative modeling of FCC metals (resulting in huge computational costs over 1M-PFC) and there is no PFC model quantified for HCP metals. We present a formulation of 1M-PFC by introducing two extra parameters. We show that this 1M-PFC can be quantified for different FCC metals (Ni, Cu, and Al) and HCP (Mg) as well as BCC (Fe) metals such that the prediction of elastic constants, liquid and solid densities, solid-liquid interface free energy and grain boundary free energy are in agreement with their experimental/computational counterparts.

11:25 AM  
Effects of Magnetism on the Vibrational Entropy of Iron and Cementite: Brent Fultz1; Lisa Mauger2; Jane Herriman1; Olle Hellman1; Matthew Lucas1; Sally Tracy3; 1California Institute of Technology; 2Arete Associates; 3Princeton Univ.
    Phonon spectra of bcc iron and cementite (Fe3C) were independently measured from low temperatures through their Curie temperatures to assess the effects of magnetism on vibrational entropy. The phonon spectra of both iron and cementite underwent rapid changes near the Curie temperatures (1044 K and 460 K). The change in magnetic order altered the vibrational entropy of bcc iron by approximately 0.3 kB/atom, but the effect in cementite was an order-of-magnitude smaller. Phonon dispersions and densities of states were calculated by dft methods, and were also obtained by fitting the experimental data to a Born - von Karman model with interatomic forces used as fitting parameters. In bcc iron, the largest magnetic effects were on the low transverse acoustic branch, probably owing to changes in second-nearest-neighbor interatomic forces. In cementite, the dynamics of one of the Fe sites (FeII) was more sensitive to magnetism than the other.

11:45 AM  
Heat Transport at Interface in the Metal-Organic-Frameworks MOF-5: Wenxi Huang1; Peter Greaney1; 1University of California-Riverside
    The metal-organic–framework MOF-5 is used as an adsorbent in advanced systems for vehicular hydrogen storage that are currently under development. Presently, these systems are limited by poor thermal conductivity of the adsorption bed, and thus our research addresses how the interfaces between grains of MOF-5 can be engineered to improve heat conduction. In this work we elucidate the dominant modes responsible for transmitting heat across the interface. We design 3 different types of interface for MOF-5 model achieved by changing the surface termination and simulate the interfacial heat transport across each. These results prove the basis for a set of design principles for minimizing interfacial thermal resistance in metal-organic–frameworks. The research is supported by the American Chemical Society Petroleum Research Fund.