arXiv subjects

Xufei Fang

Publications and source records attributed to Xufei Fang.

27 records · Page 2Linked to original sources

arXiv2025

Room-temperature dislocation plasticity in ceramics: Methods, Materials, and Mechanisms

Dislocation-mediated plastic deformation in ceramic materials has sparked renewed research interest due to the technological potential of dislocations. Despite the long research history of dislocations as one-dimensional lattice defects in crystalline solids, the understanding of plastically deformable ceramics at room temperature seems lacking. The conventional view holds that ceramics are brittle, difficult to deform at room temperature and exhibit no dislocation plasticity except in small-scale testing such as nanoindentation and nano-micropillar compression. In this review, we attempt to gather the evidence and reports of room-temperature dislocation plasticity in ceramics beyond the nano-/microscale, with a focus on meso-macroscale plasticity. First, we present a mechanical deformation toolbox covering various experimental approaches for assessing the dislocation plasticity, with a focus on bulk plasticity. Second, we provide a materials toolbox listing 44 ceramic compounds that have been reported to exhibit dislocation plasticity at meso-/macroscale under ambient conditions. Finally, we discuss the mechanics of dislocations in ceramics, aiming to establish a foundation for predicting and discovering additional ceramics capable of room-temperature plastic deformation, thereby advancing the development of prospective dislocation-based technologies.

cond-mat.mtrl-sci↗

arXiv2025

Impact of dislocation densities on the microscale strength of single-crystal strontium titanate

Dislocations in ceramics at room temperature are attracting increasing research interest. Dislocations may bring a new perspective for tuning physical and mechanical properties in advanced ceramics. Here, we investigate the dislocation density dependent micromechanical properties of single-crystal SrTiO3 by tuning the dislocation densities (from ~10 to the power of 10 per square meter up to ~10 to the power of 14 per square meter). Using micropillar compression tests, we find the samples exhibit a transition from brittle fracture (if no dislocation is present in the pillars) to plastic yield (with pre-engineered dislocations in the pillars). While within the regime of plastic deformation, the yield strength and plastic flow behavior exhibit a strong dependence on the dislocation density. The yield strength first decreases and then increases with the increase of dislocation densities. Detailed examination via post-mortem transmission electron microscopy reveals a complex evolution of dislocation structure, highlighting the critical role played by dislocations in regulating the brittle/ductile behavior in SrTiO3 at room temperature. Our findings shed new light on dislocation-mediated mechanical properties in ceramics and may provide designing guidelines for the prospective dislocation-based devices.

cond-mat.mtrl-sci↗

arXiv2025

Coupled electromigration-nanoindentation study on dislocation nucleation in SrTiO3

Modern functional oxides are mainly engineered by doping, essentially by tuning the defect chemistry. Recent studies suggest that dislocations offer a new perspective for enhancing the mechanical and physical properties of ceramic oxides. This raises the question regarding the interaction between dislocations and point defects in ceramics. Here, we report the impact of defect chemistry on the mechanical response of single-crystal strontium titanate, a prototype perovskite oxide. We demonstrate that electric field-induced stoichiometry polarization alters the defect chemistry, primarily by tuning oxygen vacancies, resulting in a distinct difference in the maximum shear stresses for dislocation nucleation, as experimentally observed and corroborated by molecular dynamic simulation. The impact of indenter tip size and geometry on the dislocation nucleation behavior in samples with different point defect concentrations in ceramics is further elucidated. Similar to the electromigration findings, acceptor-doped SrTiO3 tends to promote dislocation nucleation due to the abundance of oxygen vacancies. These findings shed new light on the interaction between dislocations and point defects in oxides. They may pave the road for assessing the stability of the next-generation functional ceramics engineered by dislocations.

cond-mat.mtrl-sci↗

arXiv2025

Dislocations and plasticity of KTaO$_3$ perovskite modeled with a new interatomic potential

Potassium tantalate KTaO3 is a cubic, paraelectric perovskite ceramic that exhibits surprising ductility at room temperature as most recently reported. Much like strontium titanate (SrTiO3), plastic deformation is accommodated by dislocations gliding in {110} planes. In this work we propose a new interatomic potential for KTaO3, and apply it to model dislocations with <110> Burgers vector. We demonstrate that dislocations dissociate, and finely characterize their core structure and Peierls potential. Dislocations of edge character can carry a positive or negative electric charge, but we show that charge-neutral configurations are energetically more favorable. We also perform high-resolution electron microscopy to validate our simulation methodology. Comparing our results with other ductile perovskites, we confirm KTaO3 to be ductile, but stiffer than SrTiO3.

cond-mat.mtrl-sci↗

arXiv2024

Damage-tolerant oxides by imprint of an ultra-high dislocation density

Dislocations in ductile ceramics offer the potential for robust mechanical performance while unlocking versatile functional properties. Previous studies have been limited by small volumes with dislocations and/or low dislocation densities in ceramics. Here, we use Brinell ball scratching to create crack-free, large plastic zones, offering a simple and effective method for dislocation engineering at room temperature. Using MgO, we tailor high dislocation densities up to ~10^15 m^-2. We characterize the plastic zones by chemical etching, electron channeling contrast imaging, and scanning transmission electron microscopy, and further demonstrate that crack initiation and propagation in the plastic zones with high-density dislocations can be completely suppressed. The residual stresses in the plastic zones were analyzed using high-resolution electron backscatter diffraction. With the residual stress being subsequently relieved via thermal annealing while retaining the high-density dislocations, we observe the cracks are no longer completely suppressed, but the pure toughening effect of the dislocations remains evident.

cond-mat.mtrl-sci↗

arXiv2024

Harvesting room-temperature plasticity in ceramics by mechanically seeded dislocations

The quest for room-temperature ductile ceramics has been repeatedly fueled by hopes for large-scale applications but so far has been not successful. Recent demonstrations of enhanced functional properties in ceramics through judicious dislocation imprint, however, have been sparking renewed interest in dislocation plasticity in brittle ceramics. Here, we propose a facile approach using room-temperature mechanically seeded mobile dislocations with a density of ~10^14/m^2 to significantly improve the room-temperature plasticity of ceramics with a large plastic strain beyond ~30%. The seeded mobile dislocations trigger profuse dislocation multiplication via cross slip and motion. Hence, they offer an avenue to suppress brittle fracture and harvest plasticity in ceramics without any additional high-temperature process. We employ both in situ nano-/micromechanical deformation and ex situ bulk deformation to bridge the length scales. This finding tackles the pressing bottleneck of dislocation engineering in ceramics for achieving ductile ceramics and harvesting both versatile mechanical and functional properties.

cond-mat.mtrl-sci↗

arXiv2024

Room-temperature bulk plasticity and tunable dislocation densities in KTaO3

We report room-temperature bulk plasticity mediated by dislocations in single-crystal cubic KTaO3, contrasting the conventional knowledge that single-crystal KTaO3 is susceptible to brittle cleavage. A mechanics-based combinatorial experimental approach using cyclic Brinell indentation, scratching, and uniaxial bulk compression consistently demonstrates room-temperature dislocation plasticity in KTaO3 from the mesoscale to the macroscale. This approach also delivers tunable dislocation densities and plastic zone sizes. Scanning transmission electron microscopy analysis underpins the activated slip system to be <110>{1-10}. Given the growing significance of KTaO3 as an emerging electronic oxide and the increasing interest in dislocations for tuning physical properties of oxides, our findings are expected to trigger synergistic research interest in KTaO3 with dislocations.

cond-mat.mtrl-sci↗

arXiv2023

Analyze Factors Influencing Drivers' Cell Phone Online Ride-hailing Software Using While driving: A Case Study in China

The road safety of traffic is greatly affected by the driving performance of online ride-hailing, which has become an increasingly popular travel option for many people. Little attention has been paid to the fact that the use of cell phone online ride-hailing software by drivers to accept orders while driving is one of the causes of traffic accidents involving online ride-hailing. This paper, adopting the extended theory of planned behavior, investigates the factors that factors influencing the behavior of Chinese online ride-hailing drivers cell phone ride-hailing software usage to accept orders while driving. Results showed that attitudes, subjective norms, and perceived behavioral control have a significant and positive effect on behavioral intentions. Behavioral intention is most strongly influenced by attitude. There is no direct and significant impact of group norms on behavioral intention. Nonetheless, group norms exert a substantial and beneficial influence on attitude, subjective norms, and perceived behavioral control. This study has discovered, through a mediating effect test, that attitude, subjective norm, and perceived behavioral control play a mediating and moderating role in the impact of group norm on behavioral intention. These findings can offer theoretical guidance to relevant departments in developing effective measures for promoting safe driving among online ride-hailing drivers.

cs.CY↗

arXiv2023

Sustainable development-oriented campus bike-sharing site evaluation model: A case study of Henan Polytechnic University

Promoting sustainable transportation options is increasingly crucial in the pursuit of environmentally friendly and efficient campus mobility systems. Among these options, bike-sharing programs have garnered substantial attention for their capacity to mitigate traffic congestion, decrease carbon emissions, and enhance overall campus sustainability. However, improper selection of bike-sharing sites has led to the growing problems of unsustainable practices in campus, including the disorderly parking and indiscriminate placement of bike-sharing. To this end, this paper proposes a novel sustainable development-oriented campus bike-sharing site evaluation model integrating the improved Delphi and fuzzy comprehensive evaluation approaches. Fourteen evaluation metrics are firstly selected from four dimensions: the user features, implementation and usage characteristics of parking spots, environmental sustainability, and social sustainability, through the combination of expert experience and the improved Delphi method. Then, the analytic hierarchy process and the entropy weight method are employed to determine the weights of the evaluation indices, ensuring a robust and objective assessment framework. The fuzzy comprehensive evaluation method is finally implemented to evaluate the quality of location selection. South Campus of Henan Polytechnic University is selected as a case study using the proposed evaluation system. This work contributes to the existing body of knowledge by presenting a comprehensive location selection evaluation system for campus bike-sharing, informed by the principles of sustainable development.

cs.CY↗