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9 results on '"Zhu, Ruijian"'

2. A Critical Edge Number Revealed for Phase Stabilities of Two-Dimensional Ball-Stick Polygons

Author

Zhu, Ruijian and Wang, Yanting

Subjects
Condensed Matter - Soft Condensed Matter, Condensed Matter - Statistical Mechanics
Abstract

Phase behaviors of two-dimensional (2D) systems constitute a fundamental topic in condensed matter and statistical physics. Although hard polygons and interactive point-like particles are well studied, the phase behaviors of more realistic molecular systems considering intermolecular interaction and molecular shape remain elusive. Here we investigate by molecular dynamics simulation thermal stabilities of 2D ball-stick polygons, serving as simplified models for molecular systems. Below the melting temperature $T_{m}$, we identify a critical edge number $n_{c}$, at which a waving superlattice structure emerges; when n < $n_{c}$,the triangular system stabilizes at a spin-ice-like glassy state; when n > $n_{c}$,the polygons stabilize at crystalline states, and $T_{m}$ is higher for polygons with more edges at higher pressures but exhibits a crossover for hexagon and octagon at low pressures. A theoretical framework taking into account the competition between entropy and enthalpy is proposed to provide a comprehensive understanding of our results, which is anticipated to facilitate the design of 2D materials., Comment: Version 4 is accepted by Nature Communications

Published
2023
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6. Ground-State Degeneracy Induces Spontaneous Two-Dimensional Crystalline Instability

Author

Zhu, Ruijian and Wang, Yanting

Subjects
Statistical Mechanics (cond-mat.stat-mech), Soft Condensed Matter (cond-mat.soft), FOS: Physical sciences, Condensed Matter - Soft Condensed Matter, Condensed Matter - Statistical Mechanics
Abstract

All two-dimensional hard regular polygons have stable crystalline structures above a finite phase-transition density, and adding short-range interactions is believed not to qualitatively change their thermal stabilities. By molecular dynamics simulation, however, we find that adding a short-range Lennard-Jones interaction on each vertex of the hard regular triangle leads to ground-state degeneracy of the triangular system due to the fact that the unit cell of the crystal formed by a dimer has two isotopic structures with identical potential energies, which induces spontaneous crystalline instability and allows the system to be in the glassy state at any finite temperatures before liquidizing. At a fixed finite temperature, the initial crystalline structure eventually evolves to the glassy state spontaneously through a down-hill process after it comes over a single energy barrier. This mechanism is further verified by the observation that forbidding one of the two isotopic structures of the unit cell extremely heightens the energy barrier.

Published
2023
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8. Ferroelectric nanofibers and their application in energy harvesting

Author

Zhu, Ruijian, Wang, Zengmei, Cheng, Zhenxiang, Kimura, Hideo, Zhu, Ruijian, Wang, Zengmei, Cheng, Zhenxiang, and Kimura, Hideo

Abstract

2019 Copyright All rights reserved. The brittleness of bulk ferroelectric ceramics perplexes the fabrication process for energy harvesters and reduces their durability. As one-dimensional nanostructures, ferroelectric nanofibers possess excellent performance such as decreased elastic coefficient and increased d33 with the decrease of the diameter (Ico et al., 2016; Bai et al., 2012) [1, 2], and can be easily deformed by tiny irregular mechanical vibration, therefore they are extremely useful in the fabrication of energy harvesters. We prepared KNNS-BNKZ nanofibers, BZT-BNT nanofibers, and PZT nanofibers with great ferroelectric performance, and fabricated energy harvesters based on these fibers then discussed the mechanism of energy harvesting, and realized energy collection and storage.

Published
2019

9. Poling-free energy harvesters based on robust self-poled ferroelectric fibers

Author

Zhu, Ruijian, Wang, Zeng-Mei, Ma, He, Yuan, Guo-Liang, Wang, Fengxia, Cheng, Zhenxiang, Kimura, Hideo, Zhu, Ruijian, Wang, Zeng-Mei, Ma, He, Yuan, Guo-Liang, Wang, Fengxia, Cheng, Zhenxiang, and Kimura, Hideo

Abstract

Self-poling has been found in many two-dimensional epitaxial ferroelectric nanofilms originating from epitaxial growth clamping and has become a new research focus due to its potential applications in designing new types of ferroelectric devices. However, self-poling ferroelectrics based on internal strain gradients rather than external stimuli still do not exist. Here, we demonstrate a novel and unique design for one-dimensional structures and geometries in microscale with robust upward flexoelectric self-poling created by the application of electrospun ferroelectric fibers on a patterned substrate to introduce curving structure arises from the uneven substrate and confinement by other fibers in space. The fiber textile composed of these curving structures could resist external electric field and temperature, and can be fabricated into high performance poling-free flexible nanogenerators with outputs comparable to the poled ones. These results are conducive to providing a potential solution to the depolarization problem, to simplifying the technologies for manufacturing piezoelectric nanogenerators by avoiding the application of electric field for poling, and to providing extra freedom in controlling ferroelectric polarization and designing new types of devices.

Published
2018

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