arXiv subjects

Shuxiang Zhou

Publications and source records attributed to Shuxiang Zhou.

13 recordsLinked to original sources

arXiv2026

Barrierless Water Dissociation on Rare-Earth Sesquioxide Surfaces from First Principles

Water dissociation on metal oxide surfaces is a key elementary step in heterogeneous catalysis, photocatalysis, and radiation chemistry, yet its mechanistic details on rare-earth (RE) sesquioxides remain poorly understood. Here, we investigate water dissociation on the (110) surfaces of three cubic bixbyite oxides, Sc$_2$O$_3$, Y$_2$O$_3$, and Lu$_2$O$_3$, using molecular dynamics combining ab initio calculations with on-the-fly machine-learning force field acceleration. By sampling 25 independent trajectories per material, we obtain an unbiased picture of the reaction landscape inaccessible to conventional static calculations. Two distinct dissociation pathways are identified: a conventional proximal mechanism with a small but finite barrier of $\sim$0.1 eV, and a previously unreported distal mechanism that is effectively barrierless and energetically preferred at both the adsorption and dissociation stages. The low barriers are consistent with the periodic array of inherently undercoordinated RE$^{3+}$ sites in the bixbyite lattice, suggesting that ordered intrinsic coordination defects play a role analogous to stochastic oxygen vacancies in conventional oxides.

cond-mat.mtrl-sci↗

arXiv2026

Vibrational and Electronic Properties of Np2O5 from Experimental Spectroscopy and First Principles Calculations

High-valence actinide oxides are critical to understanding the behavior of 5f-electrons, yet their structural and electronic properties remain poorly understood due to challenges in synthesis and handling. We report the first Raman spectroscopic study of single-crystalline Np2O5 and the first scanning tunneling spectroscopy (STS) measurement on any neptunium-containing material. Hydrothermally synthesized crystals were structurally verified by X-ray diffraction. Raman spectra revealed sharply resolved vibrational features, including previously unreported low-frequency modes. STS measurements revealed a band gap of 1.5 eV. Density functional theory (DFT) enables vibrational mode assignments, reveals neptunium-dominated low-frequency phonons, oxygen-dominated high-frequency modes, and predicts an indirect band gap of 1.68 eV. This predicted value is in excellent agreement with the experimentally measured STS gap. This combined Raman, DFT, and STS approach provides a robust framework for correlating lattice dynamics and electronic structure in actinide materials, providing benchmark data for Np2O5, and opening new avenues for probing structure-property relationships in complex f-electron materials.

cond-mat.mtrl-sci↗

arXiv2025

The stability and topological behaviors in lanthanide antiperovskite nitrides: a high-throughput study

Antiperovskite (APV) nitrides exhibit a diverse range of electronic properties, including superconductivity, magnetic effects, and nontrivial topological behaviors. In this study, we propose a new family of APV nitrides by incorporating 4$f$-electron metals, known for strong electron correlations, localized magnetic moments, and spin-orbit coupling, to further explore the unique properties of APVs. A high-throughput density functional theory (DFT) calculation was utilized to identify stable lanthanide APV nitride compounds. To address the challenge of strong electron correlation, we developed a double-screening framework that assumes either a fully itinerant or localized nature of the $f$-electrons during calculations. Using this approach, we systematically identified 37 stable lanthanide APV nitride compounds from both thermodynamic and dynamical perspectives. Furthermore, we report nontrivial topological behaviors observed among these stable lanthanide APV nitride compounds, as computed by DFT. Notably, Dirac and semi-Dirac cones are observed near the Fermi level for Er$_3$TlN. This study opens a pathway to investigate lanthanide APVs, revealing potential novel physical properties by leveraging the rich physics of both APVs and $f$-electrons.

cond-mat.mtrl-sci↗

arXiv2025

Engineering Phonons in Compositionally Complex Carbide Ceramics

In the pursuit of advanced ceramic materials with exceptional irradiation-resistance and high-temperature tolerance for nuclear applications, compositionally complex carbides (CCCs) have emerged as a highly promising class of candidate materials for extreme environments. In such conditions, critical material properties such as thermal stability, elasticity, thermal conductivity and thermodynamics behavior are predominantly influenced by phonons. In CCCs, pronounced cation disorder can lead to significant phonon scattering due to inherent mass and force constant variations, impacting these critical properties. In this study, we used ab initio calculations to predict the phonon band structures and systematically explore the influence of mass and force constant variance on the phonon spectral function of CCCs with a rock salt structure, ranging from binary to five-metal component carbides. Our findings reveal that the selection and concentration of constituent elements can be strategically utilized to tune the phonon band structure, phonon bandgap and phonon scattering in CCCs, thereby enabling control over phonon-related properties. Additionally, we measured the thermal conductivity of some of these CCCs using the spatial-domain thermoreflectance technique. Interestingly, the measured thermal conductivity of some of these CCCs indicates that five-component ceramics exhibit higher thermal conductivity than certain ternary and binary alloys. This observation contrasts with the expectation that greater cation disorder would result in more scattering and lower thermal conductivity. This intriguing result opens up the possibility of discovering CCCs with better thermal conductivity, presenting new opportunities for their application in extreme environments.

cond-mat.mtrl-sci↗

arXiv2025

Xenon-metal pair formation in UO2 investigated using DFT+U

A recent experimental study on a spent uranium dioxide (UO2) fuel sample from Belgium Reactor 3 (BR3) identified a unique pair structure formed by the noble metal phase (NMP) and fission gas (xenon [Xe]) precipitate. However, the fundamental mechanism behind this structure remains unclear. The present study aims to provide an understanding of the interaction between five different metal precipitates (molybdenum [Mo], ruthenium [Ru], palladium [Pd], technetium [Tc], and rhodium [Rh]) and the Xe fission gas atoms in UO2, by using density functional theory (DFT) in combination with the Hubbard U correction to compute the formation energies involved. All DFT+U calculations were performed with occupation matrix control to ensure antiferromagnetic ordering of UO2. The calculated formation and binding energies of the Xe and solid fission products in the NMP reveal that these metal precipitates form stable pair structures with Xe. Notably, the formation energy of Xe-metal pairs is lower than that of the isolated single defects in all instances, with Pd and Mo showing the most favourable binding energy, likely accounting for the observed pair structure formation.

cond-mat.mtrl-sci↗

arXiv2024

Impact of dynamic Jahn-Teller effect on magnetic excitations, lattice vibration, and thermal conductivity in UxTh1-xO2 system

Vibrational and magnetic properties of single-crystal uranium-thorium dioxide (UxTh1-xO2) with a full range of 0<x<1 is investigated. Thorium dioxide is a diamagnet whose thermal properties are governed by lattice vibration. The addition of paramagnetic uranium ion leads to the emergence of magnetic effects that alter the thermophysical properties noticeably even at room temperature. The interaction of phonons with magnetic moments of uranium 5f electrons mediated by magnetoelastic coupling results in an anomalous low-temperature thermal conductivity profile. Analysis of the magnetic susceptibility measurements indicates a uranium-concentration-dependent reduction in effective magnetic moment previously associated with the dynamic Jahn-Teller (DJT) effect. The T2g Raman peak position follows a nonlinear trend as a function of uranium concentration and hints that these Raman active optical modes play a role in either DJT or mediating quadrupole-quadrupole interactions. A first principle-based thermal transport model is implemented to explain the low-temperature transport measurements, where the anomalous reduction is attributed to phonon-spin resonant scattering. The interplay between spins and phonons is also captured using high-resolution inelastic X-ray scattering (IXS) measurements of phonon linewidths. Our results provide new insights into the phonon interactions with the magnetic excitations governing DJT effect and impacting the low-temperature thermal transport processes in this material system. These findings have implications for understanding low-temperature thermal transport and magnetic properties in advanced materials for information processing and energy applications.

cond-mat.str-el↗

arXiv2024

Impacts of Point Defects on Shallow Doping in Cubic Boron Arsenide: A First Principles Study

Cubic boron arsenide (BAs) stands out as a promising material for advanced electronics, thanks to its exceptional thermal conductivity and ambipolar mobility. However, effective control of p- and n-type doping in BAs poses a significant challenge, mostly as a result of the influence of defects. In the present study, we employed density functional theory (DFT) to explore the impacts of the common point defects and impurities on p-type doping of Be$_\text{B}$ and Si$_\text{As}$, and on n-type doping of Si$_\text{B}$ and Se$_\text{As}$. We found that the most favorable point defects formed by C, O, and Si are C$_\text{As}$, O$_\text{B}$O$_\text{As}$, Si$_\text{As}$, C$_\text{As}$Si$_\text{B}$, and O$_\text{B}$Si$_\text{As}$, which have formation energies of less than $1.5$ eV. While the O impurity detrimentally affects both n- and p-type dopings, C and Si impurities are harmful for n-type dopings. Interestingly, the antisite defect pair As$_\text{B}$B$_\text{As}$ benefits both p- and n-type doping. The doping limitation analysis presented in this study can potentially pave the way for strategic development in the area of BAs-based electronics.

cond-mat.mtrl-sci↗

arXiv2024

Phonon thermal transport in UO$_2$ via self-consistent perturbation theory

Computing thermal transport from first-principles in UO$_2$ is complicated due to the challenges associated with Mott physics. Here we use irreducible derivative approaches to compute the cubic and quartic phonon interactions in UO$_2$ from first-principles, and we perform enhanced thermal transport computations by evaluating the phonon Green's function via self-consistent diagrammatic perturbation theory. Our predicted phonon lifetimes at $T=600$ K agree well with our inelastic neutron scattering measurements across the entire Brillouin zone, and our thermal conductivity predictions agree well with previous measurements. Both the changes due to thermal expansion and self-consistent contributions are nontrivial at high temperatures, though the effects tend to cancel, and interband transitions yield a substantial contribution.

cond-mat.mtrl-sci↗

arXiv2024

First-principles determination of the phonon-point defect scattering and thermal transport due to fission products in ThO2

This work presents the first principles calculations of the lattice thermal conductivity degradation due to point defects in thorium dioxide using an alternative solution of the Pierels-Boltzmann transport equation. We have used the non-perturbative Green's function methodology to compute the phonon point defect scattering rates that consider the local distortion around the point defect, including the mass difference changes, interatomic force constants and structural relaxation near the point defects. The point defects considered in the work include the vacancy of thorium and oxygen, substitution of helium, krypton, zirconium, iodine, xenon, in the thorium site, and the three different configuration of the Schottky defects. The results of the phonon-defect scattering rate reveals that among the considered intrinsic defects, the thorium vacancy and helium substitution in the thorium site scatter the phonon most due to substantial changes in the force constant and structural distortions. The scattering of phonons due to the substitutional defects unveils that the zirconium atom scatters phonons the least, followed by xenon, iodine, krypton, and helium. This is contrary to the intuition that the scattering strength follows HeTh > KrTh > ZrTh > ITh > XeTh based on the mass difference. This striking difference in the zirconium phonon scattering is due to the local chemical environment changes. Zirconium is an electropositive element with valency similar to thorium and, therefore, can bond with the oxygen atoms, thus creating less force constant variance compared to iodine, an electronegative element, noble gas helium, xenon, and krypton. These results can serve as the benchmark for the analytical models and help the engineering-scale modeling effort for nuclear design.

cond-mat.mtrl-sci↗

arXiv2023

Optical pulse induced ultrafast antiferrodistortive transition in SrTiO3

The ultrafast dynamics of the antiferrodistortive (AFD) phase transition in perovskite SrTiO3 is monitored via time-domain Brillouin scattering. Using femtosecond optical pulses, we induce a thermally driven tetragonal-to-cubic structural transformation and detect notable changes in the frequency of Brillouin oscillations (BO) induced by propagating acoustic phonons. First, we establish a fingerprint frequency of different regions across the temperature phase diagram of the AFD transition characterized by tetragonal and cubic phases in the low and high temperature sides, respectively. Then, we demonstrate that in a sample nominally kept in tetragonal phase, deposition of sufficient thermal energy induces an instantaneous transformation of the heat-affected region to the cubic phase. Coupling the measured depth-resolved BO frequency with a time and depth-resolved heat diffusion model, we detect a reverse cubic-to-tetragonal phase transformation occurring on a time scale of hundreds of picoseconds. We attribute this ultrafast phase transformation in the perovskite to a structural resemblance between atomic displacements of the R-point soft optic mode of the cubic phase and the tetragonal phase, both characterized by anti-phase rotation of oxygen octahedra. Evidence of such a fast structural transition in perovskites can open up new avenues in the field of information processing and energy storage.

cond-mat.mtrl-sci↗

arXiv2022

Capturing the ground state of uranium dioxide from first principles: crystal distortion, magnetic structure, and phonons

Uranium dioxide (UO$_2$) remains a formidable challenge for first-principles approaches, due to the complex interplay among spin-orbit coupling, Mott physics, magnetic ordering, and crystal distortions. Here we use DFT+$U$ to explore UO$_2$ at zero temperature, incorporating all the aforementioned phenomena. The technical challenge is to navigate the many metastable electronic states produced by DFT+$U$, which is acomplished using $f$-orbital occupation matrix control to search for the ground state. We restrict our search to the high-symmetry ferromagnetic phase, including spin-orbit coupling, which produces a previously unreported occupation matrix. This newfound occupation matrix is then used as an initialization to explore the broken symmetry phases. We find the oxygen cage distortion of the 3k antiferromagnetic state to be in excellent agreement with experiments, and both the spin-orbit coupling and the Hubbard $U$ are critical ingredients. We demonstrate that only select phonon modes have a strong dependence on the Hubbard $U$, whereas magnetic ordering has only a small influence overall. We perform measurements of the phonon dispersion curves using inelastic neutron scattering, and our calculations show good agreement when using reasonable values of $U$. The quantitative success of DFT+$U$ warrants exploration of thermal transport and other observables within this level of theory.

cond-mat.mtrl-sci↗

arXiv2022

Parameterizing empirical interatomic potentials for predicting thermophysical properties via an irreducible derivative approach: the case of ThO$_2$ and UO$_2$

The accuracy of classical physical property predictions using molecular dynamics simulations is determined by the quality of the interatomic potentials. Here we introduce a training approach for empirical interatomic potentials (EIPs) which is well suited for capturing phonons and phonon-related properties. Our approach is based on direct comparisons of the second- and third-order irreducible derivatives between an EIP and the Born-Oppenheimer potential within density functional theory (DFT) calculations. Irreducible derivatives fully exploit space group symmetry and allow for training without redundant information. We demonstrate the fidelity of our approach in the context of ThO$_2$ and UO$_2$, where we optimize parameters of an embedded-atom method potential in addition to core-shell interactions. Our EIPs provide thermophysical properties in good agreement with DFT and outperform widely utilized EIPs for phonon dispersion and thermal conductivity predictions. Reasonable estimates of thermal expansion and formation energies of Frenkel pairs are also obtained.

cond-mat.mtrl-sci↗

arXiv2018

Combined ab initio and empirical model of the thermal conductivity of uranium, uranium-zirconium, and uranium-molybdenum

In this work we developed a practical and general modeling approach for thermal conductivity of metals and metal alloys that integrates ab initio and semiempirical physics-based models to maximize the strengths of both techniques. The approach supports creation of highly accurate, mechanistic, and extensible thermal conductivity modeling of alloys. The model was demonstrated on α-U and U-rich U-Zr and U-Mo alloys, which are potential fuels for advanced nuclear reactors. The safe use of U-based fuels requires quantitative understanding of thermal transport characteristics of the fuel. The model incorporated both phonon and electron contributions, displayed good agreement with experimental data over a wide temperature range, and provided insight into the different physical factors that govern the thermal conductivity under different temperatures. This model is general enough to incorporate more complex effects like additional alloying species, defects, transmutation products, and noble gas bubbles to predict the behavior of complex metallic alloys like U-alloy fuel systems under burnup.

cond-mat.mtrl-sci↗