Abstract ：

The electronic structure and magnetic properties of the Ruddlesden-Popper (RP) layered perovskite Bi8Ba4Mn8O28 were investigated by using the projector augmented wave (PAW) pseudopotentials method based on the density functional theory. Due to the substitution of Ba in the A site, the rotation and tilt of the MnO6 octahedra could be approved, and their impact on the electronic structure and magnetic properties were also discussed. The generalized gradient approximation calculation with the correction of the onsite Coulomb interaction (GGA + U) showed that the ground state of Bi8Ba4Mn8O28 is a ferromagnetic half-metal with a half-metallic gap of 3. 07 eV and a total magnetic moment of 31μB. The magnetic moment of Bi8Ba4Mn8O28 is mainly contributed by the magnetic moment of Mn atoms, while the magnetic moments of Bi, Ba, and O atoms are relatively small. The half-metallicity is mainly due to the large exchange splitting between the spin-up and spin-down electrons of Mn 3d states. When the lattice constants vary in a wide range of - 10% to 14%, the half-metallicity can be maintained and the total magnetic moment of the unit cell is always kept at 31μB © 2024 Beijing University of Technology. All rights reserved.

Keyword ：

layered perovskite magnetism first-principles half-metallic electronic structure lattice deformation

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Abstract ：

Titanium alloys have shown wide application potential in the areas such as aerospace and marine because of their comprehensive properties, including high specific strength, ductility, corrosion resistance, and damage tolerance. Given the rapid development of new-generation advanced military hardware toward large scale, high-speed, light-weight, and structure-complicated titanium alloys experience increasingly harsh application environments. Thus, developing novel high-strength and high-toughness titanium alloys is an important direction in the field of titanium research. To date, the compositional design of titanium alloys is performed within the framework of some empirical rules without involving strengthening and toughening mechanisms. This kind of approach can hardly achieve an accurate and efficient material design. Based on the abovementioned background, the effect of alloying on the precipitation strengthening of the α + β dual-phase titanium alloy was studied by using the first-principles exact muffin-tin orbital method in combination with a coherent potential approximation. High-strength and high-toughness titanium alloys obtain its high strength through precipitation strengthening in the β-phase matrix with α-phase precipitates. The influence of alloying on the precipitation strengthening is crucial to the understanding and prediction of alloy strength and rational alloy design. In the present work, the elastic moduli and lattice constants of a serial binary titanium alloy Ti-xM (M = Al, V, Cr, Mn, Fe, Co, Ni, Nb, Mo, Ta, W) against the composition x were calculated using the first-principles method. Based on which, the elastic moduli of the titanium alloy with a complex composition (such as Ti-Al-V and Ti55521) were evaluated using the concept of elastic Mo equivalency. Subsequently, the precipitation strengthening of binary titanium alloys and the Ti55521 alloy was evaluated by using the elastic modulus within the framework of the modulus strengthening model. Result shows that alloying elements, such as Co, Fe, W, Mo, Ni, and Mn, have the strongest precipitation strengthening effect for the same particle size and volume fraction of α precipitates, followed by Cr, Nb, and Ta, whereas V is the weakest. The strengthening effect increases with the content of alloying element. For the Ti55521 alloy prepared by using a thermal mechanical process, subsequent short-time aging weakens the precipitation strengthening effect compared with long-time aging. © 2024 Chinese Academy of Sciences. All rights reserved.

Keyword ：

first principles titanium alloy strength precipitation strengthening elastic modulus

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Abstract ：

采用基于密度泛函理论的投影平面波方法,对Ruddlesden-Popper(RP)层状钙钛矿结构Bi8Ba4Mn8O28的电子结构和磁学性质进行了自旋极化计算.由于A位Ba的替位掺杂,造成MnO6八面体发生显著旋转、倾斜等畸变,会对电子结构与磁性产生较大影响,对此进行了充分的讨论.考虑在位库伦作用修正的广义梯度近似(GGA+U)的计算表明,Bi8Ba4Mn8O28基态为铁磁半金属,其半金属能隙3.07 eV,晶胞总磁矩为31μB.Bi8Ba4Mn8O28的晶胞磁矩主要来自Mn原子磁矩的贡献,而Bi、Ba与O原子磁矩相对较小;而半金属性则主要源于Mn 3d自旋向上与自旋向下电子间存在较大的交换劈裂所致.使晶胞承受均匀变形,当其晶格常数在-10％～14％较大范围变化时,半金属性均可得到保持,且其晶胞总磁矩可始终稳定于31μB.

Keyword ：

半金属 电子结构 晶格形变 层状钙钛矿 磁性 第一性原理

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拓扑半金属,作为一种独特的拓扑电子态,近年来因其固有的拓扑特性和潜在的器件应用而备受研究关注.体-边界对应是拓扑半金属的一个关键特征,这意味着如果在体相中存在非平庸的能带拓扑,那么在表面会存在受拓扑保护导电状态,即拓扑表面态(topological surface state,TSS).这一特征使其在电催化研究领域备受关注.本文采用第一性原理计算手段研究了AlB2材料的拓扑性质,并构建(010)表面Al端面和B端面平板模型,计算得到了TSS的位置.研究了AlB2表面吸附特性,发现Al端面氢吸附吉布斯自由能(△GH*)仅为-0.031 eV,相较于商业电催化析氢(hydrogen evolution reaction,HER)催化剂Pt的-0.08 eV更接近于0,展现出了优异的HER性能.观察了 AlB2表面吸附H,OH和H2O后TSS的变化,发现当H吸附时TSS变化最显著,其次是OH吸附,H2O因其电中性和弱的表面吸附对TSS的影响很微弱.并且在吸附前后,由于受拓扑保护TSS依旧存在,仅是能量发生了改变,证实了其在环境中的稳定性.本工作研究结果为不同吸附物对AlB2的TSS的影响提供了系统的认识,为今后相关领域的理论和实验研究铺平了道路,也为拓扑材料的实际应用提供了理论支撑.

Keyword ：

拓扑表面态 表面吸附 拓扑半金属

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通过飞秒激光单脉冲实验,探究了偏振方向(0°、45°、90°、135°)对x-切铌酸锂(LN)晶体损伤阈值的影响,发现材料损伤阈值呈现明显的偏振依赖性,90°偏振方向的损伤阈值低于其他偏振方向.通过第一性原理计算,确认了飞秒激光引起的隧穿电离主要导致Nb—O键断裂.而当入射偏振角度为90°时,易导致更多的Nb—O键断裂,在该偏振方向上的损伤阈值降低.该研究有助于更深入地理解超快激光在LN晶体表面的烧蚀过程,对LN晶体表面功能性器件激光制备有重要的参考价值.

Keyword ：

第一性原理 飞秒激光 损伤阈值 偏振 铌酸锂

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本工作利用第一性原理研究了氢化效应对扶手椅型锗烯纳米带(AGeNRs)几何结构和电子结构的影响,分别计算了几何结构与稳定性、能带结构以及态密度,研究了形成能和能带结构随各种带宽度函数的变化.通过增加带的宽度,AGeNRs的带隙尺寸根据三种不同的趋势减小.基于这些趋势,可以将其分为三类,分别命名为N=3P、N=3P+1、N=3P+2,N是宽度上的锗原子数,P是整数.研究表明,裸露边缘的AGeNRs稳定性较低,氢化处理可以提高纳米带的稳定性,其中双氢化结构的稳定性最高.其次,边缘利用H原子进行修饰后,电荷密度发生转移,整个材料的电子和光学特性发生变化,说明边缘效应影响其电学和光学性质.对于裸露边缘和单氢化方式,其带隙符合N=3P+2＞N=3P＞N=3P+1;而对于双氢化处理和单氢化-双氢化的混合结构,其带隙符合N=3P＞N=3P+1＞N=3P+2.由于纳米带都是直接带隙,可以推测此类AGeNRs可能适用于光学领域,而且其电子和光学性质可以通过纳米带宽度以及氢化方式在很宽的范围内进行调节.

Keyword ：

第一性原理 氢化效应 锗烯 电子结构

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一种质子化辅助界面电荷自调控电催化材料的制备方法和应用，属于电解水催化剂材料技术领域。通过简单便捷的电沉积法和水热法，制备得到原位生长在碳纤维上的NiP/WO3纳米复合材料。利用电化学工作站在酸性条件下将NiP/WO3质子化成NiP/HxWO3并进行电化学性能测试和利用商业vasp软件通过第一性原理模拟计算进行理论验证，从根本上阐明了NiP/WO3在酸性条件下自调控形成NiP/HxWO3的界面电荷自调控效应的机理，为设计具有显著活性的催化剂提供了一条理想的途径。

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钙钛矿超晶格材料界面的独特电子性质,在纳米器件、新型超敏传感器器件等方面具有广阔的应用前景,探索其界面独特的电子性质对理解关联电子系统中多自由度耦合和传感器器件的设计等方面具有重要的意义.本文通过构建LaAlO3/KNbO3超晶格材料,施加非均匀应变对其界面的载流子浓度等性质进行调控.计算结果表明,施加拉伸和压缩的应变梯度都可以调节界面处二维电子气性质.其中,当最大压缩应变梯度系数为12％时,界面处二维电子气浓度减小了 76.4％,并且界面磁矩消失,材料的总磁矩减小约88.44％,向无磁性材料转变;当最大拉伸型应变梯度系数为12％时,界面处电子气浓度增大约23.9％,界面磁矩明显减小,而且界面临近层出现明显的磁矩.该理论计算结果表明,应变梯度是一种新的钙钛矿界面载流子的有效调控手段,对LaAlO3/KNbO3钙钛矿超晶格材料界面电子性质的研究提升了对此类氧化物界面电子特性的认识,为探索调控氧化物界面处的高性能自旋极化载流子气开辟了新的途径.

Keyword ：

二维电子气 应变梯度 超晶格 第一性原理

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In this work, A first-principles calculation model of SmCo5 alloy with main group elements doping was established. Taking Al, Ga, In, and Sn as examples, the influence of intrinsic characteristics of doping elements, doping concentration and temperature on the phase stability and magnetic properties of SmCo5 alloy was studied. The calculation result indicate that the physical and chemical properties of doped main group elements and the size of the vacant space in the doping systems are two main factors that influence the occupation site of the doping elements. Al and Ga are beneficial to the stability of SmCo5 system. Moreover, the occupation sites probability of Al varies insignificantly with temperature, which indicates that the SmCo5 system doped with Al may be applied in applications with a wide temperature range. Regarding to the magnetic properties, the SmCo5 system doped with In has a relatively high magnetic moment, although the total magnetic moment of the SmCo5 system always decreases with the addition of the studied main group elements. The main reason is that In has a relatively large atomic radius, which may induce lattice distortion and result in the increase of magnetic moment between Co atoms. Therefore, the decrease of the total magnetic moment of the doping system can be compensated. Based on the above calculations, Al and In are selected as the candidate elements which are beneficial to the stability and magnetic properties of SmCo5 based alloys. Moreover, the optimal doping concentration ranges of Al and In were predicted. © 2022, Science Press. All right reserved.

Keyword ：

Magnetic moment First-principles calculations Element doping Sm-Co-based permanent magnetic alloy Structural stability

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二元单晶稀土六硼化物(REB6)具有丰富的物理性质,其中单晶LaB6具有优异的电子发射特性,影响二元REB6发射性能的物理机理及其他二元REB6是否具有良好的发射特性,需要进一步研究.本文采用基于密度泛函理论的第一性原理计算对典型二元单晶REB6(RE=La,Ce,Pr,Nd,Sm,Gd)的电子结构、功函数进行了理论分析,并对区熔法制备的高质量单晶REB6的热发射性能进行了测试.电子结构计算结果表明,二元REB6费米能级附近具有很高的态密度,宽域分布的稀土元素的d电子决定了REB6优异发射性能的电子态,局域分布的f轨道对发射性能不利.功函数理论计算表明具有d态价电子的二元REB6(RE=La,Ce,Gd)具有较低功函数.热发射测试结果表明,以上单晶REB6(100)晶面功函数热发射测试值与理论计算值基本相符.最终理论计算结合实验结果表明,LaB6和CeB6具有良好的热发射和场发射性能,GdB6具有良好的场发射性能.

Keyword ：

第一性原理 单晶REB6 热发射性能 功函数

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