arXiv subjects

Kaveh Edalati

Publications and source records attributed to Kaveh Edalati.

At least 37 records · Page 2Linked to original sources

arXiv2025

Influence of nanostructuring through high-pressure torsion (HPT) on superconductivity of a high-entropy alloy

High-entropy alloys (HEAs) have emerged as favorable choices for different applications, including superconductors. The present work examines the impact of nanostructuring via high-pressure torsion (HPT) on the superconducting properties of the equiatomic TiZrHfNbTa HEA. Structural characterization reveals a progressive refinement of grain size and increased dislocation density, together with partial phase transformation to an ω phase with HPT processing. Magnetic susceptibility and magnetization measurements indicate a systematic enhancement in the superconducting transition temperature (from $T_c =$ 6.2 K to 7.2 K) and critical magnetic field, as well as the stabilization of the superconductivity state by HPT processing. The improvement of superconducting properties is attributed to microstructural modifications such as grain boundary density, defect generation and phase transformations, and their impact on vortex pinning, quantum confinement and electron scattering. The results suggest that nanostructuring through severe plastic deformation provides an appropriate route to optimize superconducting properties in high-entropy superconductors.

cond-mat.supr-con↗

arXiv2025

Superior electrochemical performance of zinc-ion batteries with fine-grained and textured zinc anode produced by high-pressure torsion

Zinc-ion batteries are promising alternatives to lithium-ion batteries, offering advantages in safety, cost, and environmental impact. However, their performance is often limited by the functioning of the zinc anode. This study employs severe plastic deformation via the high-pressure torsion (HPT) method to enhance the electrochemical performance of zinc anodes. HPT reduced the grain size from >1000 μm to 20 μm and introduced a (002) basal texture. The battery assembled with HPT-processed zinc demonstrated improved cycling stability, rate performance, and specific discharge capacity (>500 mAh/g at 0.5 A/g after 50 cycles), particularly at high current densities. This performance enhancement was attributed to grain-boundary and texture effects on improved ion transfer (confirmed by electrochemical impedance spectroscopy), fast redox reaction kinetics (confirmed by cyclic voltammetry), and reduced corrosion (confirmed by microscopy and potentiodynamic polarization test). This study highlights the potential of severely deformed materials with textured fine grains for advanced rechargeable battery technologies.

cond-mat.mtrl-sci↗

arXiv2025

Photocatalytic Carbon Dioxide Methanation by High-Entropy Oxides: Significance of Work Function

Methane (CH4) formation from photocatalytic carbon dioxide (CO2) conversion in water is currently of interest because methane is a fuel, and it can also be transformed into other useful hydrocarbons. However, achieving high selectivity to produce methane remains a challenge because of the large number of contributing electrons (eight) in methanation. High-entropy oxides present a new pathway to tune the catalyst selectivity by arranging various cations in the lattice. This study aims to clarify the selectivity for methane formation in high-entropy photocatalysts containing hybrid d0 + d10 orbital configuration. Several oxides are designed and synthesized which have a base of 3-4 cations with d0 orbital configuration (titanium and zirconium with a valence of 4, and niobium and tantalum with a valence of 5) and incorporate 1-2 elements with d10 orbital configuration (zinc, gallium, indium, bismuth and copper). Results demonstrate that adding elements with a d10 electronic configuration is effective for methane formation, while the selectivity toward methanation is enhanced by increasing the work function of the d10 cations. Selectivity levels over 50% are achieved using these oxides, suggesting a potential strategy for designing new catalysts for methanation.

cond-mat.mtrl-sci↗

arXiv2025

Phase and sulfur vacancy engineering in cadmium sulfide for boosting hydrogen production from catalytic plastic waste photoconversion

Cadmium sulfide (CdS) is a well-known low-bandgap photocatalyst, but its efficiency is often hindered by rapid photo-generated carrier recombination and a limited number of active catalytic sites. To overcome these challenges, this study introduces an efficient CdS photocatalyst through a novel strategy combining metastable-to-stable phase transformation and sulfur vacancy generation. This strategy integrates hydrothermal treatment and a high-pressure process to create sulfur vacancies, which serve as active catalytic sites, within a thermodynamically stable wurtzite (hexagonal) phase known for its superior photocatalytic properties. The resulting CdS photocatalyst demonstrates exceptional performance in photoreforming for hydrogen production and the conversion of polyethylene terephthalate (PET) plastic into valuable materials. Compared to commercial CdS catalysts, this new material shows a 23-fold increase in both hydrogen production and plastic degradation without the need for co-catalysts. Quenching experiments reveal that holes and hydroxyl radicals play crucial roles in the photoreforming process of this vacancy-rich CdS. First-principles calculations via density functional theory (DFT) indicate that the hexagonal phase possesses a lower bandgap and it exhibits further bandgap narrowing with the introduction of sulfur vacancies. These findings not only present an innovative approach to CdS processing but also highlight the critical role of sulfur vacancies as effective defects for the catalytic photoreforming of microplastics.

cond-mat.mtrl-sci↗

arXiv2025

Mixed atomic-scale electronic configuration as a strategy to avoid cocatalyst utilization in photocatalysis by high-entropy oxides

To enhance the activity of photocatalysts for hydrogen production and CO2 conversion, noble metal cocatalysts as electron traps and/or acceptors such as platinum or gold are usually utilized. This study hypothesizes that mixing elements with heterogeneous electronic configurations and diverse electronegativities can provide both acceptor and donor sites of electrons to avoid using cocatalysts. This hypothesis was examined in high-entropy oxides (HEOs), which show high flexibility for atomic-scale compositional changes by keeping their single-or dual-phase structure. A new highentropy oxide was designed and synthesized by mixing elements with an empty d orbital (titanium, zirconium, niobium and tantalum) and a fully occupied d orbital (gallium). The oxide, synthesized by high-pressure torsion followed by calcination, had two phases (88 wt% orthorhombic (Pbcn) and 12 wt% monoclinic (I2/m)) with an overall composition of TiZrNbTaGaO10.5. It exhibited UV and visible light absorbance with a low bandgap of 2.5 eV, low radiative electron-hole recombination and oxygen vacancy generation due to mixed valences of cations. It successfully acted as a photocatalyst for CO and CH4 production from CO2 conversion and hydrogen production from water splitting without cocatalyst addition. These findings confirm that introducing heterogeneous electronic configurations and electronegativities can be considered as a design criterion to avoid the need to use cocatalysts.

cond-mat.mtrl-sci↗

arXiv2024

Developing a single-phase and nanograined refractory high-entropy alloy ZrHfNbTaW with ultrahigh hardness by phase transformation via high-pressure torsion

High-entropy alloys (HEAs) are potential candidates for applications as refractory materials. While dual-phase refractory HEAs containing an ordered phase exhibit high hardness, there is high interest in developing intermetallic-free and single-phase refractory HEAs with high hardness. In this study, a new equiatomic HEA ZrHfNbTaW with an ultrahigh hardness of 860 Hv is developed. The alloy is first synthesized with a dual-phase structure via arc melting and further homogenized to a single body-centered cubic (BCC) structure by phase transformation via high-pressure torsion (HPT), using the concept of ultra-severe plastic deformation process. The ultrahigh hardness of the alloy, which is higher than those reported for refractory alloys and single-phase HEAs, is attributed to (i) solution hardening by severe lattice distortion, (ii) Hall-Petch grain boundary hardening by the formation of nanograins with 12 nm average size, and (iii) dislocation hardening confirmed by high-resolution transmission electron microscopy.

cond-mat.mtrl-sci↗

arXiv2024

Photoreforming of plastic waste into valuable products and hydrogen using a high-entropy oxynitride with distorted atomic-scale structure

The persistent existence of plastic waste causes serious problems for the environment, directly and indirectly affecting the health of organisms and humans. Photoreforming is a nature-friendly method that only uses solar energy to convert plastic waste into green hydrogen (H2) and valuable organic products. This study shows that a high-entropy oxynitride (HEON) photocatalyst, synthesized by the addition of nitrogen to a Ti-Zr-Hf-Nb-Ta-containing high-entropy oxide (HEO), exhibits a higher potential for the production of H2, formic acid and acetic acid from polyethylene terephthalate (PET) photoreforming compared to the relevant HEO. Examination of X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) by synchrotron light shows that, in addition to hybridization of 2p orbitals from oxygen and nitrogen, nitrogen atoms distort the structure and completely change the neighborhood of niobium and titanium (a main contributor to the conduction band), expands the atomic bonds of zirconium and tantalum, contracts the atomic bonds of hafnium and decreases the binding energy of titanium, niobium and tantalum. These electronic structure changes lead to a narrower bandgap and diminished electron-hole recombination, enhancing the photoreforming performance. This study introduces HEONs with distorted atomic bond structures as efficient low-bandgap and stable catalysts for transforming plastics into high-value organic chemicals and H2 by photocatalysis.

cond-mat.mtrl-sci↗

arXiv2024

Efficient Photocatalytic Hydrogen Production on Defective and Strained Black Bismuth (III) Oxide

Bismuth (III) oxide (Bi2O3) has been highly studied as a photocatalyst for green hydrogen production due to its low band gap, yet its efficiency requires enhancement. This study synthesizes a defective and strained black Bi2O3 by severe straining under high pressure, via a high-pressure torsion method, to improve its photocatalytic hydrogen production. The material rich in oxygen vacancies exhibits a ten-fold improvement in water splitting with excellent cycling stability. Such improvement is due to improved light absorption, narrowing band gap and reduced irradiative electron-hole recombination. Moreover, the valence band bottom energy positively increases by straining leading to a high overpotential for hydrogen production. This research highlights the potential of vacancies and lattice strain in developing dopant-free active catalysts for water splitting.

cond-mat.mtrl-sci↗

arXiv2024

Impact of high-pressure columbite phase of titanium dioxide (TiO2) on catalytic photoconversion of plastic waste and Simultaneous hydrogen (H2) production

Photoreforming is a sustainable photocatalytic process that degrades plastic waste while simultaneously producing hydrogen (H2) from water. However, this process has received limited attention due to the scarcity of effective catalysts capable of both plastic degradation and H2 production, such as titanium dioxide (TiO2). In this study, an active catalyst is developed by stabilizing the high-pressure orthorhombic phase of TiO2, known as columbite, using a high pressure torsion (HPT) method. This material effectively degrades polyethylene terephthalate (PET) plastic under light, converting it into valuable organic compounds such as formic acid, terephthalate, glycolic acid, and acetic acid. Additionally, it produces a significant amount of H2. The findings show that the high-pressure orthorhombic phase, especially in the presence of oxygen vacancies, enhances catalytic H2 production and microplastic degradation by increasing light absorption, reducing electron-hole recombination, and generating hydroxyl radicals. These results highlight the substantial potential of modified high-pressure TiO2 photocatalysts in simultaneously addressing the plastic waste crisis and the demand for H2 fuel.

cond-mat.mtrl-sci↗

arXiv2024

Efficient photoreforming of plastic waste using a high-entropy oxide catalyst

Simultaneous catalytic hydrogen (H2) production and plastic waste degradation under light, known as photoreforming, is a novel approach to green fuel production and efficient waste management. Here, we use a high-entropy oxide (HEO), a new family of catalysts with five or more principal cations in their structure, for plastic degradation and simultaneous H2 production. The HEO shows higher activity than that of P25 TiO2, a benchmark photocatalyst, for the degradation of polyethylene terephthalate (PET) plastics in water. Several valuable products are produced by photoreforming of PET bottles and microplastics including H2, terephthalate, ethylene glycol and formic acid. The high activity is attributed to the diverse existence of several cations in the HEO lattice, lattice defects, and appropriate charge carrier lifetime. These findings suggest that HEOs possess high potential as new catalysts for concurrent plastic waste conversion and clean H2 production.

cond-mat.mtrl-sci↗

arXiv2024

High-pressure torsion processing of serine and glutamic acid: Understanding mechanochemical behavior of amino acids under astronomical impacts

Astronomical impacts by small solar system bodies (meteoroids, asteroids, comets, and transitional objects) are considered a mechanism for delivering amino acids and their polymerization to proteins in early Earth conditions. High-pressure torsion (HPT) is a new methodology to simulate such impacts and clarify the behavior of biomolecules. In this study, two amino acids, crystalline L-serine and L-glutamic acid that were detected in meteorites, are processed by HPT and examined by ex situ X-ray diffraction, Raman spectroscopy, nuclear magnetic resonance, Fourier transform infrared spectroscopy, and in situ mechanical shear testing. No polymerization, chemical reactions, or phase transformations are detected after HPT, indicating that the stability and presence of these two amino acids in meteorites are quite reasonable. However, some microstructural and mechanical changes like crystal size reduction to the nanometer level, crystal defect formation, lattice expansion by vacancy formation, and shear strength enhancement to the steady state are found which are similar to the behaviors reported in metals and ceramics after HPT processing.

cond-mat.mtrl-sci↗

arXiv2024

Brookite TiO2 as an active photocatalyst for photoconversion of plastic wastes to acetic acid and simultaneous hydrogen production: Comparison with anatase and rutile

Photoreforming is a clean photocatalytic technology for simultaneous plastic waste degradation and hydrogen fuel production, but there are still limited active and stable catalysts for this process. This work introduces the brookite polymorph of TiO2 as an active photocatalyst for photoreforming with an activity higher than anatase and rutile polymorphs for both hydrogen production and plastic degradation. Commercial brookite successfully converts polyethylene terephthalate (PET) plastic to acetic acid under light. The high activity of brookite is attributed to good charge separation, slow decay and moderate electron trap energy, which lead to a higher generation of hydrogen and hydroxyl radicals and accordingly enhanced photo-oxidation of PET plastic. These results introduce brookite as a stable and active catalyst for the photoconversion of water contaminated with microplastics to value-added organic compounds and hydrogen.

cond-mat.mtrl-sci↗

arXiv2024

Impact of high-pressure torsion on hydrogen production from photodegradation of polypropylene plastic wastes

Plastic waste entering the environment through landfilling or improper disposal poses substantial risks to ecosystems and human health. Photoreforming is emerging as a clean photocatalytic technology that degrades plastic waste to organic compounds while simultaneously producing hydrogen fuel. This study introduces high-pressure torsion (HPT), a severe plastic deformation (SPD) method, as an innovative technique to enhance the photoreforming of polypropylene (PP) plastic mixed with a brookite TiO2 photocatalyst. Hydrogen production systematically increases with the number of HPT turns, accompanied by the formation of valuable small organic molecules. The enhancement in photocatalytic activity is attributed to strain-induced defect formation in both catalysts and plastics, as well as the creation of catalyst/plastic interphases that enhance charge carrier transport between inorganic and organic phases. These findings reveal a new functional application for SPD in energy conversion and sustainability.

cond-mat.mtrl-sci↗

arXiv2024

Mechanism of anatase-to-columbite TiO2 phase transformation via sheared phases: first-principles calculations and high-pressure torsion experiments

High-pressure torsion (HPT) can facilitate phase transformations in titanium dioxide (TiO2) and stabilize its high-pressure columbite phase, as an active photocatalyst, by shear straining under high pressure. This study aims to understand the mechanism underlying the acceleration of the anatase-to-columbite phase transformation by shear strain. A mechanism by considering sheared crystal structures as intermediate phases was proposed and examined using quantum mechanics in the framework of density functional theory (DFT) and HPT experiments. DFT energy and phonon calculations demonstrated the viability of the sheared structures as intermediate phases. Furthermore, the sheared structures were observed experimentally as new metastable phases using high-resolution transmission electron microscopy. These findings can explain the significant effect of shear strain on pressure-induced phase transitions, reported during severe plastic deformation of various metals and ceramics.

cond-mat.mtrl-sci↗

arXiv2024

Machine learning to explore high-entropy alloys with desired enthalpy for room-temperature hydrogen storage: Prediction of density functional theory and experimental data

Safe and high-density storage of hydrogen, for a clean-fuel economy, can be realized by hydride-forming materials, but these materials should be able to store hydrogen at room temperature. Some high-entropy alloys (HEAs) have recently been shown to reversibly store hydrogen at room temperature, but the design of HEAs with appropriate thermodynamics is still challenging. To explore HEAs with appropriate hydride formation enthalpy, this study employs machine learning (ML), in particular, Gaussian process regression (GPR) using four different kernels by training with 420 datum points collected from literature and curated here. The developed ML models are used to predict the formation enthalpy of hydrides for the TixZr2-xCrMnFeNi (x = 0.5, 1.0 and 1.5) system, which is not in the training set. The predicted values by ML are consistent with data from experiments and density functional theory (DFT). The present study thus introduces ML as a rapid and reliable approach for the design of HEAs with hydride formation enthalpies of -25 to -39 kJ/mol for hydrogen storage at room temperature.

cond-mat.mtrl-sci↗

arXiv2024

Investigation of a high-entropy oxide photocatalyst for hydrogen generation by first-principles calculations coupled with experiments: Significance of electronegativity

High-entropy oxides (HEOs), containing at least five principal cations, have recently emerged as promising photocatalysts for hydrogen production via water splitting. Despite their high potential, the impact of the cation mixtures on photocatalytic activity remains poorly understood. This study investigates the high-entropy photocatalyst TiZrHfNbTaO11 using first-principles calculations combined with experimental methods to elucidate the effects of various elements on electronic structure and water splitting performance. The results indicate that the HEO exhibits a bandgap comparable to TiO2 polymorphs rutile, brookite and anatase. Cations with lower electronegativity, such as hafnium and zirconium, provide the strongest water adsorption energy, serving as active sites for water adsorption. Additionally, the co-presence of highly electronegative cations like niobium and tantalum adjacent to hafnium and zirconium enhances charge transfer to water molecules, improving splitting efficiency. These findings suggest novel strategies for designing high-entropy photocatalysts by synergistic incorporating cations with different electronegativities.

cond-mat.mtrl-sci↗

arXiv2024

AB-Type Dual-Phase High-Entropy Alloys as Negative Electrode of Ni-MH Batteries: Impact of Interphases on Electrochemical Performance

High-entropy alloys (HEAs) and their corresponding high-entropy hydrides are new potential candidates for negative electrode materials of nickel-metal hydride (Ni-MH) batteries. This study investigates the cyclic electrochemical hydrogen storage performance of two AB-type HEAs (A: hydride-forming elements, B: non-hydride-forming elements) in Ni-MH batteries. TiV2ZrCrMnFeNi with a dual-phase structure shows a fast activation and a low charge transfer impedance with a discharge capacity of 150 mAhg-1, while TiV1.5Zr1.5CrMnFeNi with a single phase shows a slow activation and a capacity of only 60 mAhg-1. The better electrochemical performance of TiV2ZrCrMnFeNi was attributed to its higher vanadium/zirconium ratio and abundant interphase boundaries, which act as hydrogen paths and heterogeneous hydride nucleation sites. These results suggest the high potential of dual-phase HEAs as new active electrode materials for Ni-MH batteries.

cond-mat.mtrl-sci↗

arXiv2024

Black brookite rich in oxygen vacancies as an active photocatalyst for CO2 conversion: experiments and first-principles calculations

Photocatalytic CO2 conversion is a clean technology to deal with CO2 emissions, and titanium oxide (TiO2) polymorphs are the most investigated photocatalysts for such an application. In this study, black TiO2 brookite is produced by a high-pressure torsion (HPT) method and employed as an active photocatalyst for CO2 conversion. Black brookite with a large concentration of lattice defects (vacancies, dislocations and grain boundaries) showed enhanced light absorbance, narrowed optical bandgap and diminished recombination rate of electrons and holes. The photocatalytic activity of the black oxide for CO2 conversion was higher compared to commercial brookite and benchmark P25 catalyst powders. First-principles calculations suggested that the presence of oxygen vacancies in black brookite is effective not only for reducing optical bandgap but also for providing active sites for the adsorption of CO2 on the surface of TiO2.

cond-mat.mtrl-sci↗