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1.
用综合物性测量系统测试了国产Nd2Fe14B (N50M)永磁铁在低温下(10–300 K)的M-H和M-T. 获得了N50M剩磁Br和内禀矫顽力Hci在低温下的变化图, 对其取向度和三维磁化强度进行了分析研究. 结果表明, N50M在80–150 K发生强烈自旋再取向效应, Br在120–130 K出现峰值, Hci随温度下降呈线性增加. 在130 K, Br和Hci分别比常温(300 K)增加15.6%和220%, 达到1.65 T和3638 kA/m. 在150–300 K, 随温度下降, N50M宏观取向度与外磁场均匀性逐步改善, 但在80–235 K, 微观外磁场均匀性恶化.实验研究发现, 235 K附近, N50M垂直取向方向呈现“剩余磁化强度跳跃”. 研究结果为上海光源Ⅱ期低温波荡器及其他高精度低温永磁仪器与设备的物理设计提供了参考.
关键词:
低温波荡器
2Fe14B永磁铁')" href="#">Nd2Fe14B永磁铁
低温
磁特性 相似文献
2.
用嵌入原子势的分子动力学方法模拟了温度对超薄铜膜疲劳性能的影响. 通过模拟, 首先给出了超薄铜膜的总能及应力随循环周次的变化曲线; 根据叠加经验式得出的叠加量随循环周次变化曲线, 判断出各种恒定温度下超薄铜膜的疲劳寿命. 由 200–400 K温度范围内超薄铜膜的疲劳寿命-温度变化曲线, 可以发现存在两个温度区域: 在约370 K以下, 超薄铜膜的疲劳寿命随温度升高缓慢增加, 而在约370 K以上增加较快. 建立了模型并用位错演化机制解释了超薄铜膜疲劳寿命的温度依赖关系.
关键词:
分子动力学
疲劳
温度效应
位错 相似文献
3.
利用分子动力学方法建立了硬质合金基底金刚石涂层膜基界面模型, 并采用Morse势函数和Tersoff势函数相互耦合的方法来表征模型内原子间的相互作用关系, 在此基础上对不同温度(0–800 K)条件下硬质合金基底金刚石涂层膜基界面的力学性能进行了分子动力学仿真计算. 结果表明: 当温度由0 K上升到800 K的过程中, 金刚石涂层膜基界面拉伸强度呈下降趋势, 并且在0–300 K范围内下降趋势明显, 在300–800 K范围内下降趋势缓和; 体系能量随温度的变化具有相同的下降趋势. 相似文献
4.
采用自助熔剂缓冷法成功地生长出了Nd1.85Ce0. 15CuO4-δ单晶,其零场下零电阻温度约为21K. 在0—0.5T范围内分别测量了磁场平行和垂直样品表面的电阻转变曲线以及0.5T不同角度下的电阻转变曲线. 结果显示磁场平行和垂直样品表面时的转变温度Tp随磁场的变化均服从H=H0(1-Tp(h)/Tp(0))2关系. 0.5T
关键词:
1.85Ce0.15CuO4-δ单晶')" href="#">Nd1.85Ce0.15CuO4-δ单晶
输运性质 相似文献
5.
采用基于密度泛函理论第一性原理方法, 研究了对称性为Pmn21的正交结构聚阴离子型硅酸盐Li2FeSiO4及其相关脱锂相LiFeSiO4的电子结构, 并进一步采用玻尔兹曼理论对其输运性质进行计算. 电荷密度分析表明, 由于强Si–O共价键的存在使Li2FeSiO4晶体结构在嵌脱锂过程中始终保持稳定, 体积变化率只有2.7%. 能带结构与态密度计算结果表明, 费米能级附近的电子结构主要受Fe-d轨道中电子的影响, Li2FeSiO4 的带隙宽度明显小于LiFeSiO4, 说明前者的电子输运能力优于后者. 输运性质计算表明, 电导率在300–800 K时对温度的变化并不敏感, 同时也证明了Li2FeSiO4晶体的电导率大于LiFeSiO4晶体, 与能带和态密度分析结论一致. 相似文献
6.
利用射频溅射法在石英玻璃基底上制备了一系列面心立方结构的多晶TaN1-δ薄膜, 并对其晶体结构和2–350 K温度范围的电子输运性质进行了系统研究. 薄膜呈多晶结构, 并且平均晶粒尺寸随着基底温度的升高逐渐增大. 电输运测量结果表明, TaN1-δ薄膜在5 K以下表现出类似超导体-绝缘体颗粒膜的电输运性质; 随着温度的升高, 薄膜在10–30 K表现出类似金属-绝缘体颗粒膜的性质; 在70 K以上, 热涨落诱导的遂穿导电机理主导着电阻率的温度行为. 我们的结果表明: TaN1-δ多晶薄膜的类颗粒膜属性使其具有较高的电阻率和负的电阻温度系数. 相似文献
7.
在正则系综统下,温度为2000 K时,利用基于密度泛函理论的第一性原理分子动力学计算方法对Al与赤铁矿α-Fe2O3的铝热反应进行了研究. 模拟得出Fe–O键的数量随着时间的增加而减小,Al–O键和Fe–Fe键的数量随时间的增加而增大;同时Fe离子总的电荷量随时间的增加而减小,而Al离子总的电荷量随时间的增加而增大. 模拟结果表明,在Al/Fe2O3铝热反应中发生了氧化还原反应,Al被氧化,Fe离子被还原;在界面处生成Al–O键,Fe–O键发生断裂;氧化还原反应完成需约3 ps.
关键词:
铝热反应
密度泛函理论
分子动力学
正则系综 相似文献
8.
对Heusler 合金Cu2VAl多晶甩带样品进行了磁性与输运性质方面的研究. 实验 发现Cu2VAl在温度T为210K附近发生铁磁—顺磁相变,为弱铁磁体. 输运性质的 测量表 明在72K时电阻因局域杂质超导相变而发生突变,电子和声子之间的散射是主要的散射机 理. 居里温度TC以下存在侧跃导致的反常霍尔效应,并且7K附近的相变导致霍 尔电阻率发生异常.
关键词:
磁性
输运
2VAl')" href="#">Cu2VAl 相似文献
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11.
The temperature dependence of the electrical transport of an individual tin oxide nanobelt was measured in darkness from 400 to 5 K. We found four intrinsic electrical transport mechanisms through the nanobelt. It starts with thermally activated conduction between 400 K and 314 K, followed by nearest‐neighbor hopping conduction between 268 K and 115 K and variable range hopping conduction below 58 K, with a crossover from the 3D Mott to the 3D Efros–Shklovskii regime at 16 K. We claim that this sequence reveals the three‐dimensional nature of the electrical transport in the SnO2 nanobelts, even though they are expected to behave as one‐dimensional systems. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
12.
The embedded atom method is used to study the structure stability of gold nanobelt. The Au nanobelts have a rectangular cross-section with (100) orientation along the x^-,γ- and z-axes. Free surfaces are used along the x- and y-directions, and periodic boundary condition is used along z-direction. The simulation is performed at different temperatures and cross-section sizes. Our results show that the structure stability of the Au nanobelts depends on the nanobelt size, initial orientation, boundary conditions and temperature. A critical temperature exists for Au nanobelts to transform from initial (100) nanobelt to final (110) nanobelt. The mechanism of the reorientation is the slip and spread of dislocation through the nanobelt under compressive stress caused by tensile surface-stress components. 相似文献
13.
Large-scale ZnO nanobelts in aligned fashion have been prepared via a simply conducted low temperature evaporation route using the oxidization of metallic zinc plates at 450±10 °C under ambient pressure. The produced nanobelt array has been structurally characterized by powder X-ray diffraction (XRD), scanning electron microscopy, and transmission electron microscopy (TEM). The microscope images show that the nanobelts are about 120-micron long, ranging on average from 80 to 160 micron, with about 30 nm in thickness. In addition to XRD, high-resolution TEM images and electron-diffraction patterns show that the nanobelts are single crystalline with wurtzite structure and mostly grow along the [0001] direction. The photoluminescence spectra of the single nanobelts show that the nanobelts have a dominant near-band-edge emission at about 388 nm with a very weak defect emission band centered at about 514 nm. PACS 81.05.Ys; 81.15.Gh; 78.66.Jg 相似文献
14.
采用脉冲激光沉积法 (PLD), 以石英玻璃为衬底制备了钽掺杂TiO2薄膜并研究了薄膜样品的光电性质. 沉积氧气分气压从0.3 Pa变化到0.7 Pa时薄膜样品的帯隙变化范围是3.26 eV到3.49 eV. 通过测量电阻率随温度的变化关系确定了薄膜内部的主要导电机理. 在150 K到210 K温度范围内, 热激发导电机理是主要的导电机理; 而在10 K到150 K范围内; 电导率随温度的变化复合Mott的多级变程跳跃模型 (VRH); 在210 K到300 K范围内, 电阻率和exp(b/T)1/2呈正比关系.
关键词:
2')" href="#">Ta掺杂TiO2
脉冲激光沉积法
薄膜
导电机理 相似文献
15.
Localized state conduction through a variable-range hopping mechanism in the low-temperature region (~180–270 K) and thermally activated phonon-assisted tunneling in the higher-temperature region (~270–320 K) has been observed in a polycrystalline Sb35Se65 sample. 相似文献
16.
The electrical conductivity, structural and optical properties of ZnO nanostructured semiconductor thin film prepared by sol-gel spin coating method have been investigated. The X-ray diffraction result indicates that the ZnO film has the polycrystalline nature with average grain size of 28 nm. The optical transmittance spectrum indicates the average transmittance higher than 90% in visible region. The optical band gap, Urbach energy and optical constants (refractive index, extinction coefficient, real and imaginary parts of the dielectric constant) of the film were determined. The electrical conductivity of the film dependence of temperature was measured to identify the dominant conductivity mechanism. The conductivity mechanism of the film is the thermally activated band conduction. The electrical conductivity and optical results revealed that the ZnO film is an n-type nanostructured semiconductor with a direct band gap of about 3.30 eV at room temperature. 相似文献
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18.
This paper reports that the large-scale single crystalline boron carbide nanobelts have been fabricated through a simple carbothermal reduction method with B/B2O3/C/Fe powder as precursors at 1100℃. Transmission electron microscopy and selected area electron diffraction characterizations show that the boron carbide nanobelt has a B4C rhomb-centred hexagonal structure with good crystallization. Electron energy loss spectroscopy analysis indicates that the nanobelt contains only B and C, and the atomic ratio of B to C is close to 4:1. High resolution transmission electron microscopy results show that the preferential growth direction of the nanobelt is [101]. A possible growth mechanism is also discussed. 相似文献
19.
Single-crystalline wurtzite ZnS nanobelts are synthesized by the vapor phase transport (VPT) process. When oxidized, a single-crystalline ZnS nanobelt turns into a ZnO nanotwin belt containing two twinning parts with a sharp and clear edge, which is a (0001) twinning plane parallel to and running through the length direction. The two twinning parts in a ZnO nanotwin belt have the same crystalline direction, [0001], along their width, and the and crystalline directions along the length direction. On some ZnO nanobelts, nanovoids appear along the twinning planes and when those nanovoids connect with each other, one original ZnS nanobelt can divide into two single-crystalline ZnO nanobelts with quite clear edges. 相似文献
20.
Liao Yi-min Yan Yin-zhou Wang Qiang Yang Li-xue Pan Yong-man Xing Cheng Jiang Yi-jian 《光谱学与光谱分析》2022,(10):3000-3005
ZnO is third-generation semiconductors which can be used as the carrier of ultraviolet photoluminescence and multiresonance mode laser. In recent years, ZnO microcrystals prepared by optical vapor supersaturation precipitation (OVSP) have shown important advantages in photocatalysis, efficient multi-color light source and efficient electroluminescence. However, the high preparation cost and low production efficiency hinder the development of the large-scale device. In this work, we designed and built a set of growth devices with a working wavelength of 1 080 nm and a power of 18% (@2 500 W) laser heating. The height of the raw material rod was 6. 5 mm, and the diameter was 8 mm. The results show that the morphology, structure, and luminescence properties of the products prepared by this device are very close to those prepared by the OVSP method, and the production efficiency is greatly improved (similar to 500 %). The growth device successfully prepared acceptor-rich ZnO single crystal micro rods with complete hexagonal cross-section morphology. The diameter and length of ZnO micro rods are about 3. 8 and 10 similar to 20 mu m, respectively. Raman spectra show that the Raman peaks of ZnO micro rods are sharp, and the Raman mode at 437 cm(-1) indicates that the ZnO micro rods are hexagonal wurtzite structures with good crystallinity. By analysing the PL spectra of ZnO micro rods, it was found that the ZnO microtubes prepared by the OVSP method had a similar ultraviolet bimodal structure, indicating that there exists an abundant zinc-vacancies acceptor. In the 80 similar to 280 K range, with the increase of temperature, the fluorescence intensity of ZnO microrods appears "thermal quenching-negative thermal quenching-thermal quenching" behavior. The negative thermal quenching behavior in the range of 166 similar to 200 K is related to the intermediate state energy level (trap center) at 477 meV below the conduction band bottom, and the thermal quenching phenomenon in the range of 200 similar to 280 K is related to the non-radiative recombination center at 600 meV below the conduction band bottom. The appearance of both is related to the prepared ZnO microrod oxygen vacancy (V-o) defect. The laser growth device developed in this paper has high feasibility and practicability. This preparation method lays a technical foundation for the rapid batch growth of ZnO single crystal micro rods with rich acceptors and is also of great significance for its application in optoelectronic devices. 相似文献