arXiv subjects

Shengping Shen

Publications and source records attributed to Shengping Shen.

7 recordsLinked to original sources

arXiv2026

The FAST Framework: Developing a Data-Efficient Machine Learning Potential to Decode Superionic Transition-Induced Thermophysical and Kinetic Anomalies in UO2 under Extreme Conditions

Uranium dioxide ($UO_2$) serves as the predominant nuclear fuel globally. Despite its widespread application, evaluating its mechanical, thermophysical, and species transport behaviors under extreme accident scenarios remains a formidable challenge for conventional experimental and computational methods. To address this, we develop a versatile machine learning interatomic potential (MLIP) for $UO_2$ by proposing an efficient training strategy, termed the "FAST" (Fine-tuning via Active-learning and Superionic-Targeting) framework. Our "FAST" framework integrates superionic transition-targeted sampling with active learning-enhanced exploration to efficiently construct a highly compact dataset comprising only 500 configurations for fine-tuning a foundation model. By rigorously accounting for the strong correlation of uranium 5f electrons and antiferromagnetic (AFM) ground state during DFT labeling, we train a robust DFT-level neuroevolution potential (NEP) for $UO_2$. We demonstrate that this NEP exhibits superior predictive capability for various physical properties, encompassing mechanical, defect, thermophysical, and ionic diffusion over an extensive temperature range. Moreover, this NEP accurately captures the anomalous thermophysical and kinetic behaviors triggered by superionic transition. Specifically, it reproduces both the $\lambda$-peak in linear thermal expansion coefficient (LTEC) and "non-Arrhenius" anionic diffusion. Crucially, NEP-based simulations elucidate the microscopic origins underlying these anomalies: the pre-melting of oxygen sublattice and resultant kinetic decoupling between U and O ions.

cond-mat.mtrl-sci↗

arXiv2025

Size-Dependent Tensile Behavior of Nanocrystalline HfNbTaTiZr High-Entropy Alloy: Roles of Solid-Solution and Short-Range Order

This study investigates the size-dependent mechanical behavior of the HfNbTaTiZr refractory high-entropy alloy (RHEA) under uniaxial tension, with a focus on the effects of random solid-solution (RSS) and chemical short-range order (CSRO). A machine learning framework is developed to accelerate the parameterization of interatomic force fields (FFs), enabling molecular dynamics simulations of three nanocrystalline models: (i) a meta-atom (MA) mode representing the RHEA as a hypothetical sing-element system with averaged properties, (ii) a quinary RSS model with randomly distributed constituent atoms, and (iii) a Monte Carlo (MC) model with internal CSRO. The results reveal that RSS enhances strength, while CSRO reduces flow stress level but improves strain hardening and failure resistance. A transition from Hall-Petch (HP) strengthening to inverse Hall-Petch (IHP) softening is observed, with CSRO suppressing this transition. The underlying plastic mechanisms (i.e., dislocation slip, deformation twinning, phase transformation and grain boundary movements) are analyzed from both nanostructural and energetic perspectives. Theoretical models are established to describe the size-dependent yield strength and predict the critical grain size. Additionally, the contributions of different plastic mechanisms to the overall stress response are separately quantified. These findings provide new insights into the design and performance optimization of RHEAs through nanostructural engineering.

cond-mat.mtrl-sci↗

arXiv2025

Dislocation Engineering: A New Key to Enhancing Ceramic Performances

Dislocations are line defects in crystalline solids and often exert a significant influence on the mechanical properties of metals. Recently, there has been a growing interest in using dislocations in ceramics to enhance materials performance. However, dislocation engineering has frequently been deemed uncommon in ceramics owing to the brittle nature of ceramics. Contradicting this conventional view, various approaches have been used to introduce dislocations into ceramic materials without crack formation, thereby paving the way for controlled ceramics performance. However, the influence of dislocations on functional properties is equally complicated owing to the intricate structure of ceramic materials. Furthermore, despite numerous experiments and simulations investigating dislocation-controlled properties in ceramics, comprehensive reviews summarizing the effects of dislocations on ceramics are still lacking. This review focuses on some representative dislocation-controlled properties of ceramic materials, including mechanical and some key functional properties, such as transport, ferroelectricity, thermal conductivity, and superconducting properties. A brief integration of dislocations in ceramic is anticipated to offer new insights for the advancement of dislocation engineering across various disciplines.

cond-mat.mtrl-sci↗

arXiv2025

Thermal excitation of flexoelectricity in silicon

Flexoelectricity, an electromechanical coupling between strain gradient and polarization, offers a promising dimension to enrich silicon-based devices. Although the flexoelectricity of silicon is known, some fundamental aspects remain ambiguous, such as the discrepancy between experimental results and theoretical predictions, the influence of doping concentration, and the role of the bandgap. Here, we measured the flexoelectricity of intrinsic and heavily doped Si over the temperature range of 223 -473 K. The flexoelectric coefficient is of 2.6 {\mu}C/m and barely varies with temperature in doped silicon, while in intrinsic silicon it varies by nearly two orders of magnitude from 15.2 nC/m to 1.8 {\mu}C/m as temperature increases. We show that their different temperature dependencies correspond to the temperature-insensitive donor ionization in doped silicon and the temperature-sensitive intrinsic excitation in intrinsic silicon, with the latter captured by a quantitative relationship between flexoelectricity, temperature and bandgap. Furthermore, similar experimental results on germanium (Ge) suggest the universality of this relationship in first-generation semiconductors. These findings would offer valuable reference for developing Si-based electromechanical devices, as well as understanding the strain-gradient effects on semiconductor band structures (flexoelectronics).

cond-mat.mtrl-sci↗

arXiv2024

Atomic cluster expansion interatomic potential for defects and thermodynamics of Cu-W system

The unique properties exhibited in immiscible metals, such as excellent strength, hardness, and radiation-damage tolerance, have stimulated the interest of many researchers. As a typical immiscible metal system, the Cu-W nano-multilayers combine the plasticity of copper and the strength of tungsten, making it a suitable candidate for applications in aerospace, nuclear fusion engineering, and electronic packaging etc. To understand the atomistic origin of the defects and thermodynamics of the Cu-W immiscible system, we have developed an accurate machine learning interatomic potential (ML-IAP) for Cu-W based on the atomic cluster expansion (ACE) method. The Cu-W ACE potential can faithfully reproduce the fundamental properties of Cu and W predicted by density functional theory (DFT). Moreover, the thermodynamical properties, such as the melting point, coefficient of thermal expansion, diffusion coefficient, and equation of the state curve of the Cu-W solid solution, are calculated and compared against DFT and experiments. Monte Carlo Molecular Dynamics (MC-MD) simulations performed with the Cu-W ACE potential predict the experimentally observed phase separation and uphill diffusion phenomena. Our findings not only provide an accurate ACE potential for describing the Cu-W immiscible system, but also shed light on understanding the atomistic mechanism during the Cu-W nano-multilayers formation process.

cond-mat.mtrl-sci↗

arXiv2022

Flexoelectricity and surface ferroelectricity of water ice

The phase diagram of ice is complex and contains many phases, but the most common (frozen water at ambient pressure, also known as Ih ice) is a non-polar material despite individual water molecules being polar1,2. Consequently, ice is not piezoelectric and cannot generate electricity under pressure3. On the other hand, the coupling between polarization and strain gradient (flexoelectricity) is universal4, so ice may in theory generate electricity under bending. Here we report the experimental demonstration that ice is flexoelectric, finding a coefficient of 1.14+-0.13 nC/m, comparable to that of ceramics such as SrTiO3, TiO2, or PbZrO3. Additionally, and unexpectedly, the sensitivity of flexoelectric measurements to surface boundary conditions has also revealed a ferroelectric phase transition around ~160K confined in the near-surface region of the ice slabs. The electromechanical properties of ice may find applications for low-cost transducers made in-situ in cold and remote locations. Importantly, there are also consequences for natural phenomena. In particular, we have calculated the flexoelectric charge density generated in ice-graupel collisions, and found it to be comparable to the experimental charge transferred in such events, suggesting a possible participation of ice flexoelectricity in the charging up of thunderstorms.

cond-mat.mtrl-sci↗

arXiv2018

Flexoelectret: An Electret with Tunable Flexoelectric-like Response

Because of the flexoelectric effect, dielectric materials usually polarize in response to a strain gradient. Soft materials are good candidates for developing large strain gradient because of their good deformability. However, they always suffer from lower flexoelectric coefficients compared to ceramics. In this work, a flexoelectric-like effect is introduced to enhance the effective flexoelectricity of a polydimethylsiloxane (PDMS) bar. The flexoelectric-like effect is realized by depositing a layer of net charges on the middle plane of the bar to form an electret. Experiments show that the enhancement of the flexoelectricity depends on the density of inserted net charges. It is found that a charged layer with surface potential of -5723V results in 100 times increase of the material's flexoelectric coefficient. We also show that the enhancement is proportional to the thickness of electrets. This work provides a new way of enhancing flexoelectricity in soft materials and further prompt the application of soft materials in electromechanical transducers.

cond-mat.soft↗