arXiv subjects

Jacqueline Hidalgo-Jimenez

Publications and source records attributed to Jacqueline Hidalgo-Jimenez.

8 recordsLinked to original sources

arXiv2026

Thermal and electrical conductivity of a refractory high-entropy alloy after high-pressure torsion: Electron versus phonon contributions

The equiatomic refractory high-entropy alloy TiZrHfNbTa was processed by high-pressure torsion (HPT) to investigate the effect of nanostructuring and defect engineering on thermal and electrical transport properties. Severe plastic deformation (SPD) via the HPT treatment induces substantial accumulation of dislocations, grain refinement to the nanometer level (average: 40 nm), and partial transformation from the BCC phase to the omega phase. While hardness increases to a steady state with processing, the specific heat capacity exhibits a non-monotonic behavior: it decreases at low strains due to the suppression of low-frequency vibrational modes by dislocations, then partially recovers at high strains due to anharmonic vibrations at newly formed high-angle grain boundaries. Thermal conductivity decreases at low strains but shows a slight recovery at high strains, whereas electrical conductivity decreases monotonically to a steady state without recovery. Analysis using the Wiedemann-Franz law reveals that the electronic contribution dominates thermal transport, while the phononic contribution (limited by the scattering of phonons on defects) is only 11 to 23%, depending on the degree of straining. The contrasting evolution of thermal and electrical conductivity is ascribed to the transition from dislocation-dominated vibrations at low strains to grain boundary-dominated vibrations at high strains, which affects phonons and electrons with different efficiencies.

cond-mat.mtrl-sci↗

arXiv2026

High-Pressure Torsion-Induced Transformation of Adenosine Monophosphate: Insights into Prebiotic Chemistry of RNA by Astronomical Impacts

The origin of life is yet a compelling scientific mystery that has sometimes been attributed to high-pressure impacts by small solar system bodies such as comets, meteoroids, asteroids, and transitional objects. High-pressure torsion (HPT) is an innovative method with which to simulate the extreme conditions of astronomical impacts and offers insights relevant to prebiotic chemistry. In the present study, we investigated the polymerization and stability of adenosine monophosphate (AMP), a key precursor to ribonucleic acid (RNA), in dry and hydrated conditions (10 wt% water) under 6 GPa at ambient and boiling water temperatures. Comprehensive analyses with the use of X-ray diffraction, Raman spectroscopy, Fourier-transform infrared spectroscopy, nuclear magnetic resonance, scanning electron microscopy, and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry revealed no evidence of polymerization, while AMP partly transformed to other organic compounds such as nucleobase-derived fragments of adenine, phosphoribose fragments, dehydrated adenosine, protonated adenosine, and oxidized adenosine. The torque measurements during HPT further highlight the mechanical behavior of AMP under extreme conditions. These findings suggest that, while HPT under the conditions tested does not facilitate polymerization, the formation of various compounds from AMP confirms the significance of astronomical impacts on the prebiotic chemistry of RNA on early Earth. Keywords: Ribonucleic acid (RNA), Origin of life; Phase transformations; Chemical reactions, Small solar system bodies

cond-mat.mtrl-sci↗

arXiv2025

Active high-entropy photocatalyst designed by incorporating alkali metals to achieve d0+d10+s0 cationic configurations and wide electronegativity mismatch

Photocatalytic hydrogen (H2) production and carbon dioxide (CO2) conversion to methane (CH4) are considered promising solutions for reducing CO2 emissions. However, the development of highly active photocatalysts is essential to efficiently drive these reactions without harming the environment. In this study, we introduce a strategy that incorporates elements with both low and high electronegativities into catalysts based on transition metals, thereby enhancing both reactant adsorption and charge transfer. This strategy is implemented in a high-entropy oxide (HEO) by adding cesium, an alkali metal with very low electronegativity, and gallium, a metal with high electronegativity, to transition metals titanium, niobium and tantalum. The resulting oxide, TiNbTaGaCsO9 with a large concentration of oxygen vacancies, exhibits strong light absorption, a low bandgap and a suitable band structure for both hydrogen evolution and CO2 conversion. Compared to HEOs with only d0 or d0+d10 cationic configurations, the synthesized oxide with a wide electronegativity difference and mixed d0+d10+s0 cationic configurations shows significantly higher activity for both H2 and CH4 production, even without using a cocatalyst. These results demonstrate a design strategy for creating highly active HEOs containing alkali metals by taking advantage of the electronegativity mismatch across the periodic table.

cond-mat.mtrl-sci↗

arXiv2025

High-entropy oxide photocatalysts for green ammonia synthesis from nitrogen fixation in water

Ammonia, a critical chemical fertilizer and a potential hydrogen carrier, can be sustainably synthesized from atmospheric nitrogen and water under ambient conditions through photocatalysis. In this study, high-entropy oxides with d0 and mixed d0+d10 cationic configurations are introduced as a new group of catalysts for nitrogen fixation and photocatalytic ammonia production. The oxides exhibit impressive efficiency in ammonia production compared to binary oxides, while the efficiency is improved by using a mixed cationic configuration. It was shown that the incorporation of d10 elements, such as gallium and zinc, boosts the photocatalytic reactions by improving light absorbance, charge separation and charge lifetime. These findings demonstrate the potential of high-entropy oxides as next-generation photocatalysts for green ammonia synthesis, offering an effective alternative to conventional catalytic systems.

physics.chem-ph↗

arXiv2025

Understanding high photocatalytic activity of the TiO2 high-pressure columbite phase by experiments and first-principles calculations

The clean production of hydrogen as a zero-emission fuel can be done using photocatalysis, with TiO2 being one of the most promising photocatalysts. However, the activity of TiO2 anatase and rutile phases is still limited. In this study, an oxygen-deficient high-pressure phase of TiO2, columbite, is stabilized by a high-pressure torsion method. The phase is utilized as an active photocatalyst for hydrogen production, and the mechanism of its high activity is examined using density functional theory (DFT). The activity of columbite appears to be experimentally higher than that of the anatase phase. DFT calculations revealed that columbite does not have a narrow electronic bandgap, but its optical bandgap and light absorbance are improved by oxygen vacancies more significantly compared to anatase. Moreover, the water adsorption energy is higher and the surface activation energy for water splitting on the (101) atomic plane of columbite is lower than that for the active planes of anatase. In conclusion, although columbite is not a low-bandgap semiconductor, its large light absorbance and high surface catalytic activity make it a promising candidate for photocatalytic reactions.

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

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

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↗