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Grain size effect of the flexoelectric response in BaTiO3 ceramics BaTiO3 陶瓷挠电响应的晶粒尺寸效应
IF 3.2 3区 物理与天体物理 Q2 PHYSICS, APPLIED Pub Date : 2024-01-10 DOI: 10.1063/5.0186230
Xu Yang, Baoju Xia, Xiongxin Guo, Yagang Qi, Zhen Wang, Zhenxiao Fu, Yu Chen, Ruzhong Zuo, Baojin Chu
Size effect is a fundamental phenomenon in ferroelectric materials and grain size dependence of the dielectric and piezoelectric properties of BaTiO3 (BTO) ceramics has been observed. However, the dependence of flexoelectric response on grain size has not been reported, thus far. In this work, BTO ceramics with grain sizes ranging from 0.59 to 8.90 μm were prepared by a two-step sintering method. We found that with increasing grain size, the flexoelectric coefficient of BTO ceramics increases from less than 20 μC/m (grain size 0.59–0.69 μm) to more than 300 μC/m (grain size 8.90 μm), but the grain size dependence of the flexoelectric response is different from that of the dielectric and piezoelectric properties. Observation by piezoresponse force microscopy reveals that the surface regions of BTO ceramics are spontaneously polarized. Strong inhomogeneous strain is measured by grazing incidence x-ray diffraction and the resultant flexoelectric effect is enough to polarize the surface regions. Fitting of the flexoelectric data indicates that the grain size effect of the flexoelectric response can be well explained by the polarized surface layer mechanism.
尺寸效应是铁电材料中的一个基本现象,人们已经观察到 BaTiO3(BTO)陶瓷的介电和压电特性与晶粒尺寸有关。然而,迄今为止,还没有关于挠电响应与晶粒尺寸相关性的报道。在这项研究中,我们采用两步烧结法制备了晶粒大小为 0.59 至 8.90 μm 的 BTO 陶瓷。我们发现,随着晶粒尺寸的增大,BTO 陶瓷的挠电系数从小于 20 μC/m (晶粒尺寸为 0.59-0.69 μm)增加到大于 300 μC/m(晶粒尺寸为 8.90 μm),但挠电响应的晶粒尺寸依赖性与介电和压电特性的晶粒尺寸依赖性不同。压电响应力显微镜的观察结果表明,BTO 陶瓷的表面区域是自发极化的。通过掠入射 X 射线衍射测量到了强烈的不均匀应变,由此产生的挠电效应足以使表面区域极化。挠电数据的拟合结果表明,极化表面层机制可以很好地解释挠电响应的晶粒尺寸效应。
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引用次数: 0
On the insignificance of dislocations in reverse bias degradation of lateral GaN-on-Si devices 位错在硅基氮化镓器件反向偏压衰减中的重要性
IF 3.2 3区 物理与天体物理 Q2 PHYSICS, APPLIED Pub Date : 2024-01-10 DOI: 10.1063/5.0178743
M. Stabentheiner, P. Diehle, S. Hübner, M. Lejoyeux, F. Altmann, R. Neumann, A. A. Taylor, D. Pogany, C. Ostermaier
The role of threading dislocations in the intrinsic degradation of lateral GaN devices during high reverse bias stress tests (RBSTs) is largely unknown. We now present the results on lateral p-GaN/AlGaN/2DEG heterojunctions with a width of 200 μm in GaN-on-Si. A time-dependent permanent degradation of the heterojunction under high reverse bias and elevated temperatures can be observed, ultimately leading to a hard breakdown and device destruction. By using an integrated series p-GaN resistor, the device is protected from destruction and, consequently, the influence of dislocations on the degradation mechanism could be studied. Localization by emission microscopy could show that the transient current increase during a RBST is the result of the creation of a limited amount of highly localized leakage paths along the whole device width. We could establish a 1:1 correlation of leakage sites with a structural material degradation within the AlGaN barrier for nine individual positions on two different devices by planar transmission electron microscopy analysis. To unambiguously show whether dislocations in GaN-on-Si even should be considered a potential trigger for the RBST degradation in lateral heterojunctions, a combined planar and cross-sectional lamella approach was used for the first time for larger devices. This enabled the visualization of the three-dimensional propagation path of the dislocations close to the degradation sites. It was found that there is no statistically significant link between the material degradation and pre-existing dislocations. Our findings offer new insights into the GaN-on-Si material system, upon which upcoming power technologies are built upon.
在高反向偏压应力测试 (RBST) 期间,穿线位错在侧向 GaN 器件本征退化中的作用在很大程度上是未知的。我们现在介绍的是宽度为 200 μm 的硅基氮化镓侧向 p-GaN/AlGaN/2DEG 异质结的研究结果。在高反向偏压和高温条件下,异质结会出现随时间变化的永久退化,最终导致硬击穿和器件损坏。通过使用一个集成的串联 p-GaN 电阻器,可以保护器件免受破坏,从而可以研究位错对降解机制的影响。通过发射显微镜进行定位可以发现,RBST 期间的瞬态电流增加是由于整个器件宽度上产生了数量有限的高度定位漏泄通路。通过平面透射电子显微镜分析,我们可以在两个不同器件的九个单独位置上确定漏电点与 AlGaN 势垒内部结构材料退化之间 1:1 的相关性。为了明确显示硅基氮化镓中的位错是否应被视为横向异质结中 RBST 退化的潜在触发因素,我们首次对较大型器件采用了平面和横截面薄片相结合的方法。这使得靠近降解点的位错三维传播路径可视化成为可能。研究发现,材料降解与先前存在的位错之间没有统计学意义上的显著联系。我们的研究结果为即将推出的电源技术所依赖的硅基氮化镓材料系统提供了新的见解。
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引用次数: 0
Inverse design machine learning model for metallic glasses with good glass-forming ability and properties 具有良好玻璃成型能力和性能的金属玻璃的逆向设计机器学习模型
IF 3.2 3区 物理与天体物理 Q2 PHYSICS, APPLIED Pub Date : 2024-01-10 DOI: 10.1063/5.0179854
K. Y. Li, M. Z. Li, W. H. Wang
The design of metallic glasses (MGs) with good properties is one of the long-standing bottlenecks in materials science and engineering, which has been relying mostly on far less efficient traditional trial-and-error methods. Even the currently popular machine learning-based forward designs, which use manual input to navigate high dimensional compositional space, often become inefficient with the increasing compositional complexity in MGs. Here, we developed an inverse design machine learning model, leveraging the variational autoencoder (VAE), to directly generate the MGs with good glass-forming ability (GFA). We demonstrate that our VAE with the property prediction model is not only an expressive generative model but also able to do accurate property prediction. Our model allows us to automatically generate novel MG compositions by performing simple operations in the latent space. After randomly generating 3000MG compositions using the model, a detailed analysis of four typical metallic alloys shows that unreported MG compositions with better glass-forming ability can be predicted. Moreover, our model facilitates the use of powerful optimization algorithms to efficiently guide the search for MGs with good GFA in the latent space. We believe that this is an efficient way to discover MGs with excellent properties.
设计具有良好性能的金属玻璃(MGs)是材料科学与工程领域长期存在的瓶颈问题之一,主要依赖于效率较低的传统试错法。即使是目前流行的基于机器学习的正向设计,也是通过人工输入来浏览高维成分空间,但随着 MG 成分复杂性的不断增加,这种方法的效率往往变得很低。在此,我们利用变异自动编码器(VAE)开发了一种反向设计机器学习模型,可直接生成具有良好玻璃成型能力(GFA)的 MG。我们证明,带有属性预测模型的 VAE 不仅是一个富有表现力的生成模型,还能进行准确的属性预测。我们的模型允许我们通过在潜在空间中执行简单的操作自动生成新的 MG 成分。在使用该模型随机生成 3000MG 成分后,对四种典型金属合金的详细分析表明,可以预测出未报道过的具有更好玻璃化能力的 MG 成分。此外,我们的模型还有助于使用强大的优化算法,有效地引导在潜空间中寻找具有良好 GFA 的 MG。我们相信,这是发现具有优异性能的 MG 的有效方法。
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引用次数: 0
Acoustic Bessel-like beam generation using phononic crystals 利用声子晶体产生贝塞尔样声束
IF 3.2 3区 物理与天体物理 Q2 PHYSICS, APPLIED Pub Date : 2024-01-10 DOI: 10.1063/5.0182429
Santosh Dasila, Chitti Venkata Krishnamurthy, Venkatachalam Subramanian
Diffraction-free beams with large depth-of-field have a lot of potential in the field of acoustics, such as imaging, sensing, and particle manipulation. In this study, an acoustic Bessel-like beam is produced using an axicon-sonic crystal lens. The sonic crystal is created using cylindrical glass rods arranged in a triangular shape with a centered square lattice configuration. The numerical simulation between 4 and 8 kHz indicates that the axicon-sonic crystal converts the plane acoustic wave into a Bessel-like beam. The analysis of the beam indicates that the depth of field of this beam depends on the size and periodicity (lattice parameter) of the sonic crystal. The axicon lens also displays variable focal lengths at different frequencies. A graded index layer was implemented to mitigate the reflection caused by the significant impedance mismatch. Experimental validation of acoustic Bessel-like beam formation is also reported for the working frequencies. At 8 kHz, the measured range to the 50% on-axis intensity was 34λ, while the focus width at the same frequency was measured to be 2λ. The integration of three distinct design strategies—axicon shape, sonic crystal, and graded index—expands the possibilities for sound focusing applications.
具有大景深的无衍射光束在成像、传感和粒子操纵等声学领域具有很大的潜力。在这项研究中,我们使用一个声波晶体透镜(axicon-sonic crystal lens)产生了类似贝塞尔的声波光束。声波晶体由圆柱形玻璃棒制成,呈三角形排列,中心为正方形晶格结构。4 至 8 kHz 的数值模拟表明,声波晶体能将平面声波转换成贝塞尔样声束。光束分析表明,该光束的景深取决于声波晶体的尺寸和周期性(晶格参数)。此外,在不同频率下,钟形透镜的焦距也是不同的。采用分级索引层可减轻因阻抗严重失配而引起的反射。报告还对工作频率下贝塞尔样声波束的形成进行了实验验证。在频率为 8 kHz 时,测量到 50%轴上强度的范围为 34λ,而在相同频率下测量到的焦点宽度为 2λ。三种不同设计策略的整合--轴锥形、声波晶体和分级指数--拓展了声音聚焦应用的可能性。
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引用次数: 0
Applications of regime-switching in the nonlinear double-diffusivity (D-D) model 制度切换在非线性双扩散(D-D)模型中的应用
IF 3.2 3区 物理与天体物理 Q2 PHYSICS, APPLIED Pub Date : 2024-01-10 DOI: 10.1063/5.0188904
Amit K. Chattopadhyay, Elias C. Aifantis
The linear double-diffusivity (D-D) model of Aifantis, comprising two coupled Fick-type partial differential equations and a mass exchange term connecting the diffusivities, is a paradigm in modeling mass transport in inhomogeneous media, e.g., fissures or fractures. Uncoupling of these equations led to a higher order partial differential equation that reproduced the non-classical transport terms, analyzed independently through Barenblatt’s pseudoparabolic equation and the Cahn–Hilliard spinodal decomposition equation. In the present article, we study transport in a nonlinearly coupled D-D model and determine the regime-switching of the associated diffusive processes using a revised formulation of the celebrated Lux method that combines forward Fourier transform with a Laplace transform followed by an Inverse Fourier transform of the governing reaction–diffusion (R–D) equations. This new formulation has key application possibilities in a wide range of non-equilibrium biological and financial systems by approximating closed-form analytical solutions of nonlinear models.
艾凡蒂斯的线性双扩散(D-D)模型由两个耦合的菲克型偏微分方程和连接扩散量的质量交换项组成,是非均匀介质(如裂缝或断裂)中质量输运建模的典范。通过 Barenblatt 的假抛物方程和 Cahn-Hilliard 旋转分解方程的独立分析,这些方程的解耦导致了一个高阶偏微分方程,该方程再现了非典型输运项。在本文中,我们研究了非线性耦合 D-D 模型中的输运问题,并利用著名的 Lux 方法的修订公式确定了相关扩散过程的制度转换。通过近似非线性模型的闭式分析解,这一新表述方法可广泛应用于非平衡生物和金融系统。
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引用次数: 0
Evaluation of lithium as a tritium storage medium for betavoltaics 将锂作为氚储存介质用于光伏发电的评估
IF 3.2 3区 物理与天体物理 Q2 PHYSICS, APPLIED Pub Date : 2024-01-10 DOI: 10.1063/5.0169156
Darrell Cheu, Thomas Adams, Shripad Revankar, Vilas Pol
Lithium foils were demonstrated to absorb surrogate protium for tritium-powered betavoltaics. 20 μm thick lithium foils were hole-punched from a ribbon of electrodeposited lithium on copper foil. The lithium foils were loaded with hydrogen in a custom Sievert apparatus where the pressure drop showed full hydriding at a hydrogen pressure of 2 bar and at all loading temperatures above the lithium melting point at 190, 200, 225, 250, and 300. Lithium hydride formation was confirmed with Raman spectroscopy after hydrogen loading. The kinetics of experimental hydride formation was compared to the diffusion-limited Mintz–Bloch model. While the Mintz–Bloch model showed good fit with the experimental loadings, the model overpredicted the loading kinetics starting at 250 °C and at higher temperatures. The overprediction was either caused by lithium hydride outgassing due to some reduction with some residual lithium hydroxide created from brief air exposure when sealing the lithium in the reactor or a transition from diffusion-limited hydride growth to surface or metal–hydride interface-limited hydride growth.
实验证明,锂箔可吸收代氕,用于氚动力光伏。20 μm 厚的锂箔是从铜箔上的电沉积锂带打孔而成的。锂箔在定制的 Sievert 仪器中装入氢气,压降显示在氢气压力为 2 巴时完全水合,所有装载温度均高于锂的熔点(190、200、225、250 和 300)。氢负载后,拉曼光谱证实了锂氢化物的形成。实验中氢化物形成的动力学与扩散受限的 Mintz-Bloch 模型进行了比较。虽然 Mintz-Bloch 模型与实验负载显示出良好的拟合,但该模型从 250 °C 开始以及在更高温度下对负载动力学的预测过高。造成预测过高的原因可能是锂氢化物在反应器中密封锂时与短暂暴露在空气中的残留氢氧化锂发生了还原反应而导致的放气,也可能是从扩散受限的氢化物生长过渡到表面或金属氢化物界面受限的氢化物生长。
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引用次数: 0
Large magnetic entropy change in Ni–Mn–In–Sb alloys via directional solidification and calculated by first-principles calculations 镍锰铟锑合金通过定向凝固产生的巨大磁熵变化及第一性原理计算结果
IF 3.2 3区 物理与天体物理 Q2 PHYSICS, APPLIED Pub Date : 2024-01-09 DOI: 10.1063/5.0189339
Fanghua Tian, Kaiyan Cao, Kaiyun Chen, Sen Kong, Zhiyong Dai, Qizhong Zhao, Minxia Fang, Xiaoqin Ke, Chao Zhou, Yin Zhang, Sen Yang
In this work, the magnetocaloric effect in Ni50Mn36In5Sb9 alloy was increased by more than 50% through directional solidification, and the magnetic entropy change increased to 36.2 J kg−1 K−1 under the field of 5 T. The calculated results of differential scanning calorimetry curves confirmed the enhanced entropy change, which also increased from 29.7 to 40.7 J kg−1 K−1. Moreover, first-principles calculations show that the surface formation energy along the L21 (220) plane is the lowest at room temperature, and it is easy to form and undergo martensitic transformation from the (220) crystal plane. Directional solidification causes the alloy to grow basically toward the (220) crystal plane, improve atomic ordering, reduce grain boundaries, and increase grain size. Thereby, the magnetic entropy change is enhanced.
在这项工作中,通过定向凝固,Ni50Mn36In5Sb9 合金中的磁致效应增加了 50%以上,在 5 T 磁场下,磁熵增大到 36.2 J kg-1 K-1;差示扫描量热曲线的计算结果证实了熵变的增强,也从 29.7 J kg-1 K-1 增加到 40.7 J kg-1 K-1。此外,第一性原理计算表明,在室温下,沿 L21(220)面的表面形成能最低,容易从(220)晶面形成并发生马氏体转变。定向凝固使合金基本上向(220)晶面生长,改善了原子有序性,减少了晶界,增大了晶粒尺寸。因此,磁熵变化得到了增强。
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引用次数: 0
Understanding electronic structure tunability by metal dopants for promoting MgB2 hydrogenation 了解金属掺杂剂在促进 MgB2 加氢过程中的电子结构可调性
IF 3.2 3区 物理与天体物理 Q2 PHYSICS, APPLIED Pub Date : 2024-01-09 DOI: 10.1063/5.0175546
H. M. Lefcochilos-Fogelquist, L. F. Wan, A. J. E. Rowberg, S. Kang, V. Stavila, L. E. Klebanoff, M. D. Allendorf, B. C. Wood
Hydrogen is a promising energy carrier, but its onboard application is limited by the need for compact, low-pressure storage solutions. Solid-state complex metal hydride systems, such as MgB2/Mg(BH4)2, offer high storage capacities but suffer from sluggish kinetics and poor reversibility. One avenue for improving reactivity is to introduce metal dopants to alter electronic and atomic properties, but the role of these chemical additives remains poorly understood, particularly for the hydrogenation reaction. In this work, we used density functional theory calculations on model MgB2 systems to rationalize the potential role of metal dopants in destabilizing B–B bonding within the MgB2 lattice. We carried out detailed electronic structure analyses for 28 different metal dopant adatoms to identify properties that contribute to a dopant’s efficacy. Based on the simulation results, we propose that an intermediate ionic and covalent character of the bonds between adatoms and B atoms is desirable for facilitating charge redistribution, disrupting the B–B bond network, and promoting H2 dissociation and H atom chemisorption on MgB2.
氢是一种前景广阔的能源载体,但由于需要紧凑、低压的存储解决方案,氢在车载设备上的应用受到了限制。固态复合金属氢化物系统(如 MgB2/Mg(BH4)2)具有很高的存储容量,但存在动力学缓慢和可逆性差的问题。改善反应性的一个途径是引入金属掺杂剂来改变电子和原子特性,但人们对这些化学添加剂的作用仍然知之甚少,尤其是在氢化反应中。在这项研究中,我们利用密度泛函理论对模型 MgB2 系统进行了计算,以合理解释金属掺杂物在 MgB2 晶格内破坏 B-B 键稳定性的潜在作用。我们对 28 种不同的金属掺杂原子进行了详细的电子结构分析,以确定有助于提高掺杂剂功效的特性。根据模拟结果,我们提出,掺杂原子与 B 原子间的键最好具有离子和共价的中间特性,以促进电荷再分配、破坏 B-B 键网络、促进 MgB2 上的 H2 解离和 H 原子化学吸附。
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引用次数: 0
Erratum: “Design principles for achieving red emission in Eu2+/Eu3+ doped inorganic solids” [J. Appl. Phys. 129, 200903 (2021)] 更正:"在掺杂 Eu2+/Eu3+ 的无机固体中实现红色发射的设计原则" [J. Appl.
IF 3.2 3区 物理与天体物理 Q2 PHYSICS, APPLIED Pub Date : 2024-01-09 DOI: 10.1063/5.0194774
Jianwei Qiao, Zhiguo Xia
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引用次数: 0
Numerical simulations of a magnonic reservoir computer 磁性水库计算机的数值模拟
IF 3.2 3区 物理与天体物理 Q2 PHYSICS, APPLIED Pub Date : 2024-01-09 DOI: 10.1063/5.0184848
Stuart Watt, Mikhail Kostylev
A numerical model for a spin wave delay-line active ring resonator is presented. Spin wave dynamics along a one-dimensional strip of magnetic material are modeled using the nonlinear Schrödinger equation. The equation is solved numerically in Fourier space using the fourth-order Runge–Kutta method and yields qualitative agreement with experimental measurements of spin wave dynamics in two different regimes. The model provides a useful tool for performing experiments based on neuromorphic computing and logic gates in traveling spin wave devices.
本文介绍了自旋波延迟线有源环形谐振器的数值模型。利用非线性薛定谔方程对沿一维磁性材料带的自旋波动力学进行建模。利用四阶 Runge-Kutta 方法在傅里叶空间对该方程进行了数值求解,结果与两种不同状态下的自旋波动力学实验测量结果基本一致。该模型为在行进自旋波设备中进行基于神经形态计算和逻辑门的实验提供了有用的工具。
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引用次数: 0
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Journal of Applied Physics
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