Computational Thermodynamics and Kinetics: Phonons and Other Excitations/Diffusion and Kinetics
Sponsored by: TMS Functional Materials Division, TMS Materials Processing and Manufacturing Division, TMS Structural Materials Division, TMS: Chemistry and Physics of Materials Committee
Program Organizers: Vahid Attari, Texas A&M University; Sara Kadkhodaei, University of Illinois Chicago; Eva Zarkadoula, Oak Ridge National Laboratory; Damien Tourret, IMDEA Materials Institute; James Morris, Ames Laboratory
Thursday 8:30 AM
March 3, 2022
Room: 255C
Location: Anaheim Convention Center
Session Chair: Sara Kadkhodaei, University of Illinois at Chicago ; Liang Qi, University of Michigan
8:30 AM
Understanding the Role of Anharmonic Phonons in Diffusion of bcc Metal: Seyyedfaridoddin Fattahpour1; Sara Kadkhodaei1; 1University of Illinois at Chicago
Diffusion in high-temperature bcc phase of IIIB and IVB metals such as Zr or Ti is orders of magnitude higher than that of the mechanically stable bcc metals, e.g. bcc Cr, Mo, and W. The underlying reason for this anomalously higher diffusion is still poorly understood. We hypothesize that the strong anharmonicity of lattice vibrations along the soft phonon modes promotes the monovacancy diffusive jumps in these mechanically unstable but dynamically stabilized phases and is the likely reason for their anomalously higher diffusion.Here, we present a method that locates the saddle point under two scenarios: First, using a mere geometrical interpolation of the initial and final states of diffusion to locate the saddle point. Second, we implement a finite temperature stochastic sampling of the effective energy surface confined to high energy ridges. We employ this method to calculate the diffusion coefficient for bcc Ti, Zr, and dilute Zr-Sn alloys.
8:50 AM
Phonon and Thermodynamic Properties of Defected-ThO2 and (U,Th)O2: Maniesha Singh1; Tomohisa Kumagai2; Anter El-Azab1; 1Purdue University; 2Central Research Institute of Electric Power Industry
The effect of point defects with varying charge states on phonon and thermodynamics properties of nuclear oxides, ThO2 and (U,Th)O2, is investigated through the density functional theory (DFT) simulations. Firstly, two methods, zero pressure and constant volume, are used to perform DFT simulations where the results show that the vibrational entropy and formation energy of point defects in ThO2 is under- and over-estimated, respectively. Secondly, the change in volume of supercell due to point defects is studied. When the charge state of an anionic vacancy or a cationic interstitial defect is increased from neutral to its maximum, a supercell contraction is observed. On the contrary, in the case of an anionic interstitial or a cationic vacancy defect, a supercell expansion is found. Lastly, the effect of defects on the phonon dispersions and density of states is examined.
9:10 AM
Matryoshka Phonon Twinning in α-GaN: Bin Wei1; Qingan Cai2; Qiyang Sun2; Yaokun Su2; Ayman Said3; Doug Abernathy4; Jiawang Hong5; Chen Li2; 1Henan Polytechnic University; 2University of California-Riverside; 3Argonne National Laboratory; 4Oak Ridge National Laboratory; 5Beijing Institute of Technology
Understanding lattice dynamics is crucial for effective thermal management in high-power electronic devices because phonons dominate thermal transport in most semiconductors. This study utilizes complementary inelastic X-ray and neutron scattering and reports the temperature-dependent phonon dynamics of α-GaN, one of the most important third-generation power semiconductors. A prominent Matryoshka phonon dispersion is discovered with the scattering tools and confirmed by the first-principles calculations. Such Matryoshka twinning throughout the reciprocal space is demonstrated to amplify the phonon anharmonicity through creating abundant three-phonon scattering channels and cutting the phonon lifetime of affected modes by 50%. Such phonon topology effectively contributes to the reduction of the in-plane thermal transport, thus the anisotropic thermal conductivity of α-GaN. The results not only have significant implications for engineering the thermal performance and phonon-related properties of α-GaN, but also offer valuable insights on the role of anomalous phonon topology in thermal transport of other technically important semiconductors.
9:30 AM Invited
First-principles Investigations of Corrosion Mechanisms of Lightweight Metals: Liang Qi1; Mingfei Zhang1; Louis Hector Jr.2; Aditya Sundar1; Ganlin Chen1; 1University of Michigan; 2General Motors Research and Development
Lightweight metals and alloys (such as Mg and Al alloys) may have poor corrosion resistance under service conditions. Here two examples of first-principles investigations of corrosion mechanisms of Mg and Al are presented. The first example is to design Mg alloys with built-in corrosion resistance. Corrosion can result from the coupling of the anodic dissolution of Mg and cathodic hydrogen evolution reaction (HER) on Fe-rich impurities. We designed thermodynamic criteria and used high-throughput first-principles computations to search a pool of 68 elements. Our results are in qualitative accord with recent experiments. The second example is to understand the chloride (Cl)-induced initiation mechanism of localized corrosion of Al alloys by investigating the thermodynamics of the substitutional adsorption of Cl at different types of surfaces sites on hydroxylated α–Al2O3 surfaces under aqueous electrochemical conditions. The adsorbed Cl significantly increases the thermodynamic driving force to initiate localized corrosion.
10:00 AM Break
10:20 AM
Simplified and Robust Diffusion Coefficient Models for Reliable Diffusion (Atomic Mobility) Databases: Wei Zhong1; Qiaofu Zhang2; Ji-Cheng Zhao1; 1University of Maryland; 2QuesTek Innovations LLC
A simple yet general binary diffusion model was developed from a systematic assessment of the diffusion coefficients of 18 diverse binary systems that form complete solid solutions. Only one binary interaction parameter is necessary for each binary solid solution rather than 4 or more parameters that are usually used in the literature CALPHAD mobility assessments. A systematic investigation on the optimal fitting parameters for ternary solid solutions was also performed on the diffusion coefficients of fcc Ag-Au-Cu, Co-Fe-Ni, Cu-Fe-Ni, and bcc Nb-Ti-V systems. Cross-binary interaction parameters are found to be more consistent and powerful in improving the model performance than ternary interaction parameters. More than 4 fitting parameters have very limited benefits to the model performance. Recommendations are rendered based on the amount of available ternary diffusion data. The simplified yet robust diffusion models substantially reduce the number of fitting parameters while improve the reliability of the resultant diffusion/mobility databases.
10:40 AM Cancelled
Role of Electrical and Chemical Stimuli on the Electrical Responses of Resistive RAM and Neuromorphic Computing Devices: A Phase Field Study: Arijit Roy1; Pil-Ryung Cha1; 1Kookmin University
Organic and inorganic semiconducting systems are continuously being investigated to improve the performance of resistive RandomAccessMemory (ReRAM) and neuromorphic computing devices. Developing the new generation of memristor devices is challenging due to the involvement of various materials and processing issues. In memristive systems, application of electric field triggers the formation of conducting filament (CF). We use phase field model to study morphological evolution of CF. Voltage sweeping cycle mediated formation and breaking of CF leading to SET and RESET processes are simulated successfully. We could also model voltage pulse mediated growth of CF, crucial for memory and learning experience behaviors in neuromorphic computation. We further validate our numerical results with experimental observations available in the literature. We believe such correlations of operation conditions with electrical responses -- responsible for the device failure during endurance cycles and learning behavior during voltage pulsing cycles -- could shape the future of memristor research.