The ground state electron density—obtainable using Kohn-Sham Density Functional Theory(KSDFT)simulations—contains a wealth of material information,making its prediction via machine learning(ML)models ***,the computa...
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The ground state electron density—obtainable using Kohn-Sham Density Functional Theory(KSDFT)simulations—contains a wealth of material information,making its prediction via machine learning(ML)models ***,the computational expense of KS-DFT scales cubically with system size which tends to stymie training data generation,making it difficult to develop quantifiably accurate ML models that are applicable across many scales and system ***,we address this fundamental challenge by employing transfer learning to leverage the multi-scale nature of the training data,while comprehensively sampling systemconfigurations using *** ML models are less reliant on heuristics,and being based on Bayesian neural networks,enable uncertainty *** show that our models incur significantly lower data generation costs while allowing confident—and when verifiable,accurate—predictions for a wide variety of bulk systems well beyond training,including systems with defects,different alloy compositions,and at multi-million-atom ***,such predictions can be carried out using only modest computational resources.
Green hydrogen production is crucial for a sustainable future,but current catalysts for the oxygen evolution reaction(OER)suffer from slow kinetics,despite many efforts to produce optimal designs,particularly through ...
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Green hydrogen production is crucial for a sustainable future,but current catalysts for the oxygen evolution reaction(OER)suffer from slow kinetics,despite many efforts to produce optimal designs,particularly through the calculation of descriptors for *** this study,we develop a dataset of density functional theory calculations of bulk and surface perovskite oxides,and adsorption energies of OER intermediates,which includes compositions up to quaternary and facets up to(555).We demonstrate that per-site properties of perovskite oxides such as Bader charge or band center can be tuned through element substitution and faceting,and develop a machine learning model that accurately predicts these properties directly from the local chemical *** leverage these per-site properties to identify promising perovskites with high theoretical OER *** identified design principles and promising materials provide a roadmap for closing the gap between current artificial catalysts and biological enzymes such as photosystem II.
The electron microscope provides numerous insights into physics, from demonstrations of fundamental quantummechanical principles to the physics of imaging and materials. It reveals the atomic and electronic structure ...
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The electron microscope provides numerous insights into physics, from demonstrations of fundamental quantummechanical principles to the physics of imaging and materials. It reveals the atomic and electronic structure of key regionssuch as defects and interfaces. We can learn the underlying physics governing properties, and gain insight into how tosynthesize new materials with improved properties. Some recent advances and possible future directions are discussed.
Niobium(Nb)is sensitive to even minute quantities of silicon(Si)solutes,which are known to induce pronounced ***,the underlying mechanism for hardening remains elusive since the ef-fect of Si solutes on dislocation be...
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Niobium(Nb)is sensitive to even minute quantities of silicon(Si)solutes,which are known to induce pronounced ***,the underlying mechanism for hardening remains elusive since the ef-fect of Si solutes on dislocation behavior is ***,using tensile testing,in-situ microscopy and nanomechanical testing,the behavior of dislocations in dilute Nb-Si alloys,containing from 0 at.%to 0.8 at.%Si,is *** show that the hardness,strength and strain hardening rate increase from two to four times,while the uniform elongation in tension only reduces 50%as the Si content *** evolve from complex entangled patterns in Nb to parallel long-straight screw dislocation-dominated structures in Nb-Si ***-situ indentation reveals that the origins of the marked harden-ing in Nb-Si alloy are the reduction of dislocation mobility and cross-slip *** densities of dislocation debris-superjogs and loops introduced throughout the sample during warm rolling and an-nealing are found to provide active internal dislocation sources,which explain the minimal ductility loss seen in these Nb-Si *** findings can help guide the alloy design of high-performance refractory materials for extreme temperature applications.
The switching characteristics of ferroelectrics and multiferroics are influenced by the interaction of topological defects with domain *** report on the pinning of polarization due to antiphase boundaries in thin film...
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The switching characteristics of ferroelectrics and multiferroics are influenced by the interaction of topological defects with domain *** report on the pinning of polarization due to antiphase boundaries in thin films of the multiferroic hexagonal YbFeO_(3).We have directly resolved the atomic structure of a sharp antiphase boundary(APB)in YbFeO_(3) thin films using a combination of aberration-corrected scanning transmission electron microscopy(STEM)and total energy calculations based on density-functional theory(DFT).We find the presence of a layer of FeO_(6) octahedra at the APB that bridges the adjacent *** imaging shows a reversal in the direction of polarization on moving across the APB,which DFT calculations confirm is structural in nature as the polarization reversal reduces the distortion of the FeO_(6) octahedral layer at the *** APBs in hexagonal perovskites are expected to serve as domain-wall pinning sites and hinder ferroelectric switching of the domains.
In perovskite EuTiO_(3),the magnetic characteristics and magnetocaloric effect(MCE) can be flexibly regulated by converting the magnetism from antiferromagnetic to *** the present work,a series of Eu(Ti,Nb,Mn)O_(3) co...
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In perovskite EuTiO_(3),the magnetic characteristics and magnetocaloric effect(MCE) can be flexibly regulated by converting the magnetism from antiferromagnetic to *** the present work,a series of Eu(Ti,Nb,Mn)O_(3) compounds,abbreviated as ETNMO for convenience of description,was fabricated and their crystallography,magnetism together with cryogenic magnetocaloric effects were systematically *** crystallographic results demonstrate the cubic perovskite structure for all the compounds,with the space group of *** magnetic phase transitions are observed in these second-order phase transition(SOPT) *** joint substitution of elements Mn and Nb can considerably manipulate the magnetic phase transition process and magnetocaloric performance of the ETNMO *** the Mn content increases,gradually widened-ΔS_(M)-T curves are obtained,and two peaks with a broad shoulder are observed in the-ΔS_(M)-T curves for Δμ_(0)H≤0-1 *** a field change of 0-5 T,the values of maximum magnetic entropy change(-ΔS_(M)^(max)) and refrigeration capacity(RC) are evaluated to be 34.7 J/(kg·K) and 364.9 J/kg for EuTi_(0.8625)Nb_(0.0625)Mn_(0.075)O_(3), 27.8 J/(kg·K) and367.6 J/kg for EuTi_(0.8375)Nb_(0.0625)Mn_(0.1)O_(3),23.2 J/(kg·K) and 369.2 J/kg for EuTi_(0.8125)Nb_(0.0625)Mn_(0.125)O_(3),17.1 J/(kg·K) and 357.6 J/kg for EuTi_(0.7875)Nb_(0.0625)Mn_(0.15)O_(3),*** co nsiderable MCE parameters make the ETNMO compounds potential candidates for cryogenic magnetic refrigeration.
Silicone rubber(SR) composites are most widely used as thermal interface materials(TIMs) for electronics heat dissipation. Thermal impedance as the main bottleneck limiting the performance of TIMs is usually neglected...
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Silicone rubber(SR) composites are most widely used as thermal interface materials(TIMs) for electronics heat dissipation. Thermal impedance as the main bottleneck limiting the performance of TIMs is usually neglected. Herein, the thermal impedance of SR composites loaded with different levels of hexagonal boron nitride(h-BN) as TIMs was elaborated for the first time by the ASTM D 5470 standard test and finite element analysis. It was found that elastic modulus and surface roughness of SR composites increased with the increase of h-BN content, indicating that the conformity was reduced. When the assembly pressure was 0.69 MPa, there existed an optimal h-BN content at which the contact resistance was minimum(0.39 K·cm^(2)·W^(-1)). Although the decreased bond line thickness(BLT) by increasing the assembly pressure was beneficial to reduce the thermal impedance, the proper assembly pressure should be selected to prevent the warpage of the contact surfaces and the increase in contact resistance, according to the compression properties of the SR composites. This study provides valuable insights into fabrication of high-performance TIMs for modern electronic device applications.
Using the Boltzmann transport equation (BTE), we study the evolution of nonequilibrium carrier distributions in simple (sp) metals, assumed to have been instantaneously excited by an ultrafast laser pulse with photon ...
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Using the Boltzmann transport equation (BTE), we study the evolution of nonequilibrium carrier distributions in simple (sp) metals, assumed to have been instantaneously excited by an ultrafast laser pulse with photon energy hν. The mathematical structure of the BTE scattering integrals reveals that hν is a natural energy scale for describing the dynamics. Normalizing all energy quantities by hν leads to a set of three unitless parameters β/δ, γ, and α that control the relaxation dynamics: β/δ is the normalized ratio of electron-phonon to electron-electron scattering strengths, γ is the normalized phonon (lattice) temperature, and α is the normalized absorbed energy density. Using this theory, we systematically investigate relaxation times for the high-energy part of the distribution (τH), energy transfer to the phonon subsystem (τE), and intracarrier thermalization (τth). In the linear region of response (valid when α is sufficiently small), we offer heuristic descriptions of each of these relaxation times as functions of β/δ and γ. Our results as a function of excitation level α show that many ultrafast experimental investigations lie in a transition region between low excitation (where the relaxation times are independent of α) and high excitation (where the two-temperature model of carrier dynamics is valid). Approximate boundaries that separate these three regions are described by simple expressions involving the normalized parameters of our model.
Numerical simulation and experimental research on Linear Friction Welding(LFW) for GH4169 superalloy were carried out. Based on the joint microstructure and mechanical properties,a suitable welding process was determi...
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Numerical simulation and experimental research on Linear Friction Welding(LFW) for GH4169 superalloy were carried out. Based on the joint microstructure and mechanical properties,a suitable welding process was determined, which provided an important theoretical basis for the manufacture and repair of aeroengine components such as the superalloy blisk. The results show that the joint strain rate gradually increases with the increase of welding frequency, and the deformation resistance of the thermoplastic metal increases in the welding process, resulting in the interface thermoplastic metal not being extruded in time to form a flash, so the joint shortening amount gradually decreases. The thermoplastic metal in the center of the welding surface is kept at high welding temperature for a long time, resulting in the decrease of the joint strength. The microhardness of the joint shows a “W” distribution perpendicular to the weld, and most of the joints break in the Thermo-mechanically Affected Zone(TMAZ) with high tensile strength and low *** the welding area is increased without changing the aspect ratio of the welding surface, the interface peak temperature increases gradually, and the joint shortening amount decreases with the increase of the welding interface size.
Stacking fault energies (SFEs) are key parameters to understand the deformation mechanisms in metals and alloys, and prior knowledge of SFEs from ab initio calculations is crucial for alloy design. Machine learning (M...
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Stacking fault energies (SFEs) are key parameters to understand the deformation mechanisms in metals and alloys, and prior knowledge of SFEs from ab initio calculations is crucial for alloy design. Machine learning (ML) algorithms used in the present work show a ∼ 80 times acceleration of generalized stacking fault energy predictions, which are otherwise computationally very expensive to get directly from density functional theory calculations, particularly for alloys. The origin of the features used for training the ML algorithms lies in the physics-based Friedel model, and the present work uncovers the connection between the physics of d electrons and the deformation behavior of transition metals and alloys. Predictions based on the ML model agree with the experimental data. Our model can be helpful in accelerated alloy design by providing a fast method of screening materials in terms of stacking fault energies.
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