arXiv subjects

Duane D. Johnson

Publications and source records attributed to Duane D. Johnson.

At least 19 recordsLinked to original sources

arXiv2026

Intrinsic Ductility from Shear Amorphization: From Pure Metals to Multi-Principal-Element Alloys

Direct links between electronic structure and intrinsic ductility remain elusive for metals. A framework is proposed that reduces the complexities of valence charge distribution, band filling, and shear strain effects into structure-property relationships describing the intrinsic ductility of metals and alloys. Rather than relying on crystal cleavage and dislocation nucleation at preexisting crack tips, we show that a lower energy fracture criterion, i.e., the activation energy density for amorphization, enables accurate predictions of both intrinsic ductility and ductile-to-brittle transition temperatures. From analytical expressions and tabulated ab-initio stiffness constants, lattice parameters, and binary interaction energies, we present a unified theory that reconciles ductile flow in pure metals and solid-solution alloys. Phase diagrams generated for the Nb-Ta-V-Ti system simultaneously explain its high strength and room-temperature tensile ductility, validating this framework as a practical one for rapid design of structural multi-principal-element alloys.

cond-mat.mtrl-sci↗

arXiv2026

Insights into hydrogen-induced vacancy stability and creep in chemically complex alloys

Hydrogen (H) content modifies the creep response of Fe-based alloys by altering thermodynamics of point-defects; here we identify the electronic-structure mechanism underlying this effect. Using spin-polarized first-principles calculations combined with a cluster dynamics formulation, we establish a general framework linking H-assisted vacancy stabilization to diffusion-mediated creep in BCC Fe, FCC Fe, and chemically complex FCC Fe-Cr-Ni alloys. H-vacancy binding analysis shows that H-stabilized vacancies form at low hydrogen content in BCC Fe but require much higher chemical potentials in FCC Fe and Fe-Cr-Ni alloys due to broader d-bands, electronic screening, and chemical disorder. Consequently, plastic deformation mediated by diffusive processes is expected to be far more strongly impacted in BCC Fe than in FCC alloys. These electronic-controlled trends determine steady-state vacancy populations and provide a symmetry-resolved microscopic basis for H-assisted creep in ferritic and austenitic steels.

cond-mat.mtrl-sci↗

arXiv2025

Machine learning driven search of hydrogen storage materials

The transition to a low-carbon economy demands efficient and sustainable energy-storage solutions, with hydrogen emerging as a promising clean-energy carrier and with metal hydrides recognized for their hydrogen-storage capacity. Here, we leverage machine learning (ML) to predict hydrogen-to-metal (H/M) ratios and solution energy by incorporating thermodynamic parameters and local lattice distortion (LLD) as key features. Our best-performing ML model provides improvements to H/M ratios and solution energies over a broad class of ternary alloys (easily extendable to multi-principal-element alloys), such as Ti-Nb-X (X = Mo, Cr, Hf, Ta, V, Zr) and Co-Ni-X (X = Al, Mg, V). Ti-Nb-Mo alloys reveal compositional effects in H-storage behavior, in particular Ti, Nb, and V enhance H-storage capacity, while Mo reduces H/M and hydrogen weight percent by 40-50%. We attributed to slow hydrogen kinetics in molybdenum rich alloys, which is validated by our pressure-composition isotherm (PCT) experiments on pure Ti and Ti5Mo95 alloys. Density functional theory (DFT) and molecular simulations also confirm that Ti and Nb promote H diffusion, whereas Mo hinders it, highlighting the interplay between electronic structure, lattice distortions, and hydrogen uptake. Notably, our Gradient Boosting Regression model identifies LLD as a critical factor in H/M predictions. To aid material selection, we present two periodic tables illustrating elemental effects on (a) H2 wt% and (b) solution energy, derived from ML, and provide a reference for identifying alloying elements that enhance hydrogen solubility and storage.

cond-mat.mtrl-sci↗

arXiv2024

Linking Order to Strength in Metals

The metallurgy and materials communities have long known and exploited fundamental links between chemical and structural ordering in metallic solids and their mechanical properties. The highest reported strength achievable through the combination of multiple metals (alloying) has rapidly climbed and given rise to new classifications of materials with extraordinary properties. Metallic glasses and high-entropy alloys are two limiting examples of how tailored order can be used to manipulate mechanical behavior. Here, we show that the complex electronic-structure mechanisms governing the peak strength of alloys and pure metals can be reduced to a few physically-meaningful parameters based on their atomic arrangements and used (with no fitting parameters) to predict the maximum strength of any metallic solid, regardless of degree of structural or chemical ordering. Predictions of maximum strength based on the activation energy for a stress-driven phase transition to an amorphous state is shown to accurately describe the breakdown in Hall-Petch behavior at the smallest crystallite sizes for pure metals, intermetallic compounds, metallic glasses, and high-entropy alloys. This activation energy is also shown to be directly proportional to interstitial (electronic) charge density, which is a good predictor of ductility, stiffness (moduli), and phase stability in high-entropy alloys, and in solid metals generally. The proposed framework suggests the possibility of coupling ordering and intrinsic strength to mechanisms like dislocation nucleation, hydrogen embrittlement, and transport properties. It additionally opens the prospect for greatly accelerated structural materials design and development to address materials challenges limiting more sustainable and efficient use of energy.

cond-mat.mtrl-sci↗

arXiv2023

A ductility metric for refractory-based multi-principal-element alloys

We propose a quantum-mechanical dimensionless metric, the local$-$lattice distortion (LLD), as a reliable predictor of ductility in refractory multi-principal-element alloys (RMPEAs). The LLD metric is based on electronegativity differences in localized chemical environments and combines atomic$-$scale displacements due to local lattice distortions with a weighted average of valence$-$electron count. To evaluate the effectiveness of this metric, we examined body$-$centered cubic (bcc) refractory alloys that exhibit ductile$-$to$-$brittle behavior. Our findings demonstrate that local$-$charge behavior can be tuned via composition to enhance ductility in RMPEAs. With finite$-$sized cell effects eliminated, the LLD metric accurately predicted the ductility of arbitrary alloys based on tensile$-$elongation experiments. To validate further, we qualitatively evaluated the ductility of two refractory RMPEAs, i.e., NbTaMoW and Mo$_{72}$W$_{13}Ta$_{10}Ti$_{2.5}Zr$_{2.5}, through the observation of crack formation under indentation, again showing excellent agreement with LLD predictions. A comparative study of three refractory alloys provides further insights into the electronic-structure origin of ductility in refractory RMPEAs. This proposed metric enables rapid and accurate assessment of ductility behavior in the vast RMPEA composition space.

cond-mat.mtrl-sci↗

arXiv2023

Accurate prediction of chemical short-range order and its effect on thermodynamic, structural, and electronic properties of disordered alloys: exemplified in Cu$_{3}$Au

Electronic-structure methods based on density-functional theory (DFT) were used to directly quantify the effect of chemical short-range order (SRO) on thermodynamic, structural, and electronic properties of archetypal face-centered-cubic (fcc) Cu$_{3}$Au alloy. We show that SRO can be tuned to alter bonding and lattice dynamics (i.e., phonons) and detail how these properties are changed with SRO. Thermodynamically favorable SRO improves phase stability of Cu$_{3}$Au from -0.0343 eV-atom$^{-1}$ to -0.0682 eV-atom$^{-1}$. We use DFT-based linear-response theory to predict SRO and its electronic origin, and accurately estimate the transition temperature, ordering instability (L1$_2$), and Warren-Cowley SRO parameters, observed in experiments. The accurate prediction of real-space SRO gives an edge over computationally and resource intensive approaches such as Monte-Carlo methods or experiments, which will enable large-scale molecular dynamic simulations by providing supercells with optimized SRO. We also analyze phonon dispersion and estimate the vibrational entropy changes in Cu$_{3}$Au (from 9k$_{B}$ at 300 K to 6$k_{B}$ at 100 K). We establish from SRO analysis that exclusion of chemical interactions may lead to a skewed view of true properties in chemically complex alloys. The first-principles methods described here are applicable to any arbitrary complex solid-solution alloys, including multi-principal-element alloys, so hold promise for designing technologically useful materials.

cond-mat.mtrl-sci↗

arXiv2023

Magnetic frustration driven by conduction carrier blocking in Nd$_2$Co$_{0.85}$Si$_{2.88}$

The intermetallic compound Nd$_2$Co$_{0.85}$Si$_{2.88}$ having a triangular lattice could be synthesized in single-phase only with defect crystal structure. Investigation through different experimental techniques indicate the presence of two magnetic transitions in the system. As verified experimentally and theoretically, the high-temperature transition T$_H$ ~ 140 K is associated with the development of ferromagnetic interaction between itinerant Co moments, whereas the low-temperature transition at T$_L$ ~ 6.5 K is due to the coupling among Nd-4f and Co-3d moments, which is antiferromagnetic in nature. Detailed studies of temperature-dependent dc magnetic susceptibility, field dependence of isothermal magnetization, non-equilibrium dynamical behavior, viz. magnetic relaxation, aging effect, magnetic-memory effect, and temperature dependence of heat capacity, along with density functional theory (DFT) calculations, suggest that the ground state is magnetically frustrated spin-glass in nature, having competing magnetic interactions of equivalent energies. DFT results further reveal that the 3d/5d-conduction carriers are blocked in the system and act as a barrier for the 4f-4f RKKY interactions, resulting in spin-frustration. Presence of vacancy defects in the crystal are also conducive to the spin-frustration. This is an unique mechanism of magnetic frustration, not emphasized so far in any of the ternary R$_2$TX$_3$ (R=rare-earth, T=transition elements and X=Si, Ge, In) type compounds. Due to the competing character of the itinerant 3d and localized 4f moments, the compound exhibits anomalous field dependence of magnetic coercivity.

cond-mat.str-el↗

arXiv2022

Vacancy formation energies and migration barriers in multi-principal element alloys

Multi-principal element alloys (MPEAs) continue to garner interest as structural and plasma-facing materials due to their structure stability and increased resistance to radiation damage. Despite sensitivity of mechanical behavior to irradiation and point-defect formation, there has been scant attention on understanding vacancy stability and diffusion in refractory-based MPEAs. Using density-functional theory, we examine vacancy stability and diffusion barriers in body-centered cubic (Mo0.95W0.05)0.85Ta0.10(TiZr)0.05. The results in this MPEA show strong dependence on environment, originating from local lattice distortion associated with charge-transfer between neighboring atoms that vary with different chemical environments. We find a correlation between degree of lattice distortion and migration barrier: (Ti, Zr) with less distortion have lower barriers, while (Mo, W) with larger distortion have higher barriers, depending up local environments. Under irradiation, our findings suggest that (Ti, Zr) are significantly more likely to diffuse than (Mo, W) while Ta shows intermediate effect. As such, material degradation caused by vacancy diffusion can be controlled by tuning composition of alloying elements to enhance creep strength at extreme operating temperatures and harsh conditions.

cond-mat.mtrl-sci↗

arXiv2022

Efficient machine-learning model for fast assessment of elastic properties of high-entropy alloys

We combined descriptor-based analytical models for stiffness-matrix and elastic-moduli with mean-field methods to accelerate assessment of technologically useful properties of high-entropy alloys, such as strength and ductility. Model training for elastic properties uses Sure-Independence Screening (SIS) and Sparsifying Operator (SO) method yielding an optimal analytical model, constructed with meaningful atomic features to predict target properties. Computationally inexpensive analytical descriptors were trained using a database of the elastic properties determined from density functional theory for binary and ternary subsets of Nb-Mo-Ta-W-V refractory alloys. The optimal Elastic-SISSO models, extracted from an exponentially large feature space, give an extremely accurate prediction of target properties, similar to or better than other models, with some verified from existing experiments. We also show that electronegativity variance and elastic-moduli can directly predict trends in ductility and yield strength of refractory HEAs, and reveals promising alloy concentration regions.

cond-mat.mtrl-sci↗

arXiv2021

On the martensitic transformation in Fe$_{x}$Mn$_{80-x}$Co$_{10}$Cr$_{10}$ high-entropy alloy

High-entropy alloys (HEAs), and even medium-entropy alloys (MEAs), are an intriguing class of materials in that structure and property relations can be controlled via alloying and chemical disorder over wide ranges in the composition space. Employing density-functional theory combined with the coherent-potential approximation to average over all chemical configurations, we tune free energies between face-centered-cubic (fcc) and hexagonal-close-packed (hcp) phases in Fe$_{x}$Mn$_{80-x}$Co$_{10}$Cr$_{10}$ systems.~Within Fe-Mn-based alloys, we show that the martensitic transformation and chemical short-range order directly correlate with the fcc-hcp energy difference and stacking-fault energies, which are in quantitative agreement with recent experiments on a $x$=40~at.\% polycrystalline HEA/MEA. Our predictions are further confirmed by single-crystal measurements on a$x$=40at.\% using transmission-electron microscopy, selective-area diffraction, and electron-backscattered-diffraction mapping. The results herein offer an understanding of transformation-induced/twinning-induced plasticity (TRIP/TWIP) in this class of HEAs and a design guide for controlling the physics behind the TRIP effect at the electronic level.

cond-mat.mtrl-sci↗

arXiv2021

Neural-networks model for force prediction in multi-principal-element alloys

Atomistic simulations can provide useful insights into the physical properties of multi-principal-element alloys. However, classical potentials mostly fail to capture key quantum (electronic-structure) effects. We present a deep 3D convolutional neural network (3D CNN) based framework combined with a voxelization technique to design interatomic potentials for chemically complex alloys. We highlight the performance of the 3D CNN model and its efficacy in computing potentials using the medium-entropy alloy TaNbMo. In order to provide insights into the effect of voxel resolution, we implemented two approaches based on the inner and outer bounding boxes. An efficient 3D CNN model, which is as accurate as the density-functional theory (DFT) approach, for calculating potentials will provide a promising schema for accurate atomistic simulations of structure and dynamics of general multi-principle element alloys.

cond-mat.mtrl-sci↗

arXiv2020

Accelerating computational modeling and design of high-entropy alloys

With huge design spaces for unique chemical and mechanical properties, we remove a roadblock to computational design of {high-entropy alloys} using a metaheuristic hybrid Cuckoo Search (CS) for "on-the-fly" construction of Super-Cell Random APproximates (SCRAPs) having targeted atomic site and pair probabilities on arbitrary crystal lattices. Our hybrid-CS schema overcomes large, discrete combinatorial optimization by ultrafast global solutions that scale linearly in system size and strongly in parallel, e.g. a 4-element, 128-atom model [a $10^{73+}$ space] is found in seconds -- a reduction of 13,000+ over current strategies. With model-generation eliminated as a bottleneck, computational alloy design can be performed that is currently impossible or impractical. We showcase the method for real alloys with varying short-range order. Being problem-agnostic, our hybrid-CS schema offers numerous applications in diverse fields.

cond-mat.mtrl-sci↗

arXiv2020

Vacancy-mediated complex phase selection in high entropy alloys

Phase selection in Ti-Zr-Hf-Al high-entropy alloys was investigated by in-situ high-energy X$-$ray diffraction, single-crystal X$-$ray diffraction, and density-functional theory based electronic-structure methods that address disorder and vacancies, predicting formation enthalpy and chemical short-range order (SRO). Samples with varying Al content were synthesized, characterized, and computationally assessed to ascertain the composition-dependent phase selection, as increased Al content often acts as a stabilizer of a body-centered-cubic structure. Equiatomic TiZrHfAl was especially interesting due to its observed bcc superstructure - a variant of $γ-$brass with 4 vacancies per cell (not 2 as in $γ-$brass). We highlight how vacancy ordering mediates selection of this variant of $γ-$brass, which is driven by vacancy-atom SRO that dramatically suppress all atomic SRO. As vacancies are inherent in processing refractory systems, we expect that similar discoveries await in other high entropy alloys or in revisiting older experimental data.

cond-mat.mtrl-sci↗

arXiv2020

Half-metallic compositional ranges for selected Heusler alloys

For a material that is a half-metal, there should exist a range of compositions for half-metallicity. This compositional range can be expressed in terms of electron count and computed. We investigate electronic and magnetic properties of doped full- and half-Heusler alloys (stoichiometry XYZ2 and XYZ, respectively) with elements X from groups 13-16 and periods 3-6 of the Periodic Table, Y={Mn, Fe}, and Z={Co, Ni}. Using spin density functional theory, we predict shifts of the Fermi energy in the doped and solid-solution alloys. These predictions can be used for band-gap engineering of multicomponent half-metals and provide the viable range of compositions, such as for a range of n=x+y+z in (Co$_{2-z}Ni_z)$(Mn$_{1-y}$Fe$_{y}$)(Sn$_{1-x}$Sb$_{x}$). This methodology for doped and chemically disordered half-metallic alloys offers a design approach to electronic-structure engineering that can accelerate development of half-metals for novel electronic and spintronic applications.

cond-mat.mtrl-sci↗

arXiv2020

Exploring the role of electronic structure on photo-catalytic behavior of carbon-nitride polymorphs

A fully self-consistent density-functional theory (DFT) with improved functionals is used to provide a comprehensive account of structural, electronic, and optical properties of C$_{3}$N$_{4}$ polymorphs. Using our recently developed van Leeuwen-Baerends (vLB) corrected local-density approximation (LDA), we implemented LDA+vLB within full-potential N$^{th}$-order muffin-tin orbital (FP-NMTO) method and show that it improves structural properties and band gaps compared to semi-local functionals (LDA/GGA). We demonstrate that the LDA+vLB predicts band-structure and work-function for well-studied 2D-graphene and bulk-Si in very good agreement with experiments, and more exact hybrid functional (HSE) calculations as implemented in the Quantum-Espresso (QE) package. The structural and electronic-structure (band gap) properties of C$_{3}$N$_{4}$ polymorphs calculated using FP-NMTO-LDA+vLB is compared with more sophisticated hybrid-functional calculations. We also perform detailed investigation of photocatalytic behavior using QE-HSE method of C$_{3}$N$_{4}$ polymorphs through work-function, band (valence and conduction) position with respect to water reduction and oxidation potential. Our results show $γ$-C$_{3}$N$_{4}$ as the best candidate for photocatalysis among all the C$_{3}$N$_{4}$~polymorphs but it is dynamically unstable at `zero' pressure. We show that $γ$-C$_{3}$N$_{4}$ can be stabilized under hydrostatic-pressure, which improves its photocatalytic behavior relative to water reduction and oxidation potentials.

cond-mat.mtrl-sci↗

arXiv2020

First-principles concentration-wave approach to predict incipient order in high-entropy alloys: case of Ti$_{0.25}$CrFeNiAl$_{x}$

Multi-principal-element alloys, including high-entropy alloys, experience segregation or partially-ordering as they are cooled to lower temperatures. For Ti$_{0.25}$CrFeNiAl$_{x}$, experiments suggest a partially-ordered B2 phase, whereas CALculation of PHAse Diagrams (CALPHAD) predicts a region of L2$_{1}$+B2 coexistence. We employ first-principles density-functional theory (DFT) based electronic-structure approach to assess stability of phases of alloys with arbitrary compositions and Bravais lattices (A1/A2/A3). In addition, DFT-based linear-response theory has been utilized to predict Warren-Cowley short-range order (SRO) in these alloys, which reveals potentially competing long-range ordered phases. The resulting SRO is uniquely analyzed using concentration-waves analysis for occupation probabilities in partially-ordered states, which is then be assessed for phase stability by direct DFT calculations. Our results are in good agreement with experiments and CALPHAD in Al-poor regions ($x \le 0.75$) and with CALPHAD in Al-rich region ($0.75 \le {x} \le 1$), and they suggest more careful experiments in Al-rich region are needed. Our DFT-based electronic-structure and SRO predictions supported by concentration-wave analysis are shown to be a powerful method for fast assessment of competing phases and their stability in multi-principal-element alloys.

cond-mat.mtrl-sci↗

arXiv2019

Simple correction to bandgap in IV and III-V semiconductors: an improved first-principles local density functional theory

We report results from a fast, efficient, and first-principles full-potential N$^{th}$-order muffin-tin orbital (FP-NMTO) method combined with van Leeuwen-Baerends correction to local density exchange-correlation potential. We show that more complete and compact basis set is critical in improving the electronic and structural properties. We exemplify the self-consistent FP-NMTO calculations on group IV and III-V semiconductors. Notably, predicted bandgaps, lattice constants, and bulk moduli are in good agreement with experiments (e.g., we find for Ge $0.86~e$V, $5.57$~Å, $75$~GPa vs. measured $0.74~e$V, $5.66$~Å, $77.2$~GPa). We also showcase its application to the electronic properties of 2-dimensional $h-$BN and $h-$SiC, again finding good agreement with experiments.

cond-mat.mtrl-sci↗

arXiv2019

Reliable thermodynamic estimators for screening multicaloric materials

Reversible, diffusionless, first-order solid-solid phase transitions accompanied by caloric effects are critical for applications in the solid-state cooling and heat-pumping devices. Accelerated discovery of caloric materials requires reliable but faster estimators for predictions and high-throughput screening of system-specific dominant caloric contributions. We assess reliability of the computational methods that provide thermodynamic properties in relevant solid phases at or near a phase transition. We test the methods using the well-studied B2 FeRh alloy as a "fruit fly" in such a materials genome discovery, as it exhibits a metamagnetic transition which generates multicaloric (magneto-, elasto-, and baro-caloric) responses. For lattice entropy contributions, we find that the commonly-used linear-response and small-displacement phonon methods are invalid near instabilities that arise from the anharmonicity of atomic potentials, and we offer a more reliable and precise method for calculating lattice entropy at a fixed temperature. Then, we apply a set of reliable methods and estimators to the metamagnetic transition in FeRh (predicted $346 \pm 12$ K, observed $353 \pm 1$ K) and calculate the associated caloric properties, such as isothermal entropy and isentropic temperature changes.

cond-mat.mtrl-sci↗