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1.
在190K,220K和300K3个不同温度下测量了K3C60单晶薄膜沿[111]方向发射的同步辐射角分辨光电子谱.样品温度为190K时,能够观察到导带有规律的角散,并且带结构与已报道的温度为150K时的结果基本一样.而在220K附近,导带的许多子峰消失,色散不再存在.这两个温度的实验结果与K3C60在200K存在取向相变相符合,并且可在反铁磁Ising模型基础上得到理解.这种模型的定量分析结果还首次对K3C60在200K的相变机理作出了解释,即相变是由低温下的一维无序取向结构转变为200K以上的双取向结构畴与无序分子(约占40%)的混合.室温光电子谱与低温下的结果显著不同,对应于C60分子取向在室温附近的动态无序. 相似文献
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本文利用基于密度泛函理论(DFT)的第一性原理计算研究了它们的电子结构和光学性质.光学性质的计算结果和实验相一致.结果表明,Fe或Ag掺杂后,K2Ti6O13的带隙中出现了杂质带且其带隙值变小,因而使掺杂后的K2Ti6O13的吸收边发生红移并实现了其对可见光吸收.其中杂质带主要由Fe 3d态或Ag 4d态与Ti 3d态和O 2p态杂化而成.对于Fe掺杂的K2Ti6O13,杂质带位于带隙中间,因此可以作为电子从价带跃迁到导带的桥梁.对于Ag掺杂的K2Ti6O13,杂质带位于价带顶附近为受主能级,可以降低光生载流子的复合概率.实验和计算研究表明,通过Fe或Ag的掺杂可以实现了K2Ti6O13对可见光的吸收,这对进一步研究K2Ti6O13的光学性质具有重要意义. 相似文献
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用自洽的相对论BUU模型研究了相对论重离子碰撞的K+产生及流,研究结果表明K+集体流在相对论重离子碰撞中对核态方程(EOS)和K–N标量吸引项(∑KN)是敏感的,在对K+流中心度依赖的研究中发现在大碰撞参数时有反向流出现,可为确定∑KN值提供更为有效的信息.对K+产生的总产额及各个不同道的贡献与EOS和∑KN关系进行了细致分析,表明N△道对K+产生的贡献和影响都是最显著的; 不同道的贡献对∑KN的灵敏程度不同,其中∑KN对N△道的影响要比对πB道的大. 相似文献
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研究了一个SU(3)L×U(1)X弱电统一模型·要求M2Z1–M2W/cos2θw小于实验值,得到了MZ′的下限.再利用MZ′和MU(MV)之间的关系得到MU(MV)的下限.进而考虑了由于Z′交换引起的KL–KS质量差,并获得了更严格的Mz′和MU(MV)的下限. 相似文献
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本文用DFT计算方法研究了LiFexMn1-xPO4的热力学稳定性和嵌/脱锂电位. 结果表明,LiFexMn1-xPO4固溶体的自由能比相分离的LiFePO4/LiMnPO4混合物略高,这两种形式可能在实际LiFexMn1-xPO4材料中共存. 计算表明,LiFexMn1-xPO4固溶体的嵌/脱锂电位随锰/铁比以及过渡金属离子的空间排列而变化,并用计算结果解释了放电曲线的形状. 采用固相反应法合成了LiFexMn1-xPO4材料并研究了其电化学性质,实验中观察到附加的放电平台,其出现可能与LiFexMn1-xPO4固溶体的存在有关. 相似文献
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The dependence of the threshold parameters and the period of the electric-field-induced spatially periodic reorientation of the director in a flexoelectric nematic liquid crystal (NLC) on the anchoring conditions at the surface of a planar NLC cell has been studied. The threshold electric field and the corresponding wave-number of the periodic structure of the director field have been numerically calculated for arbitrary values of the anchoring energy. In the case of strong anchoring, the corresponding analytical expressions are obtained in a single-constant approximation. A decrease in the azimuthal anchoring energy leads to an increase in the intervals of possible values of the flexoelectric parameter ν and the ratio K2/K1 of the Frank elastic constants. A decrease in the polar anchoring energy leads to narrowing of these intervals as compared to the case of infinitely strong anchoring at the NLC cell surface. 相似文献
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J. Grupp 《Physics letters. A》1983,99(8):373-376
A twisted nematic liquid crystal (NLC) is placed between two horizontal glass discs, the upper disc being suspended by a quartz thread. The torque of the NLC is statically balanced by the torque of the twisted thread. From the measured torque the elastic constant K2 is directly determined. 相似文献
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The influences of boron addition on the phase formation, Curie temperature and magnetic entropy change of the NaZn13-type La(Fe0.9Si0.1)13 compound have been investigated. Eight boron containing La(Fe0.9Si0.1)13Bx samples were prepared with x=0, 0.03, 0.06, 0.1, 0.2, 0.3, 0.5 and 0.6, respectively. Experimental results show that a small amount of B addition in La(Fe0.9Si0.1)13 forms the solid solution NaZn13-type structure phase by substituting B for Si or doping B into interstitial position of the lattice, preserves its giant magnetocaloric effects due to their first-order structural/magnetic transition, as well as increase its Curie temperature Tc slightly. The maximum magnetic entropy changes in the magnetic field change of 0–1.6 T are around 20 J kg–1 K–1 for the samples with Boron addition less than 0.3, while improving the Curie temperatures by 2 K. 相似文献
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通过I-V特性测量,研究了横向交、直流电流对蓝青铜K0.3MoO3中电荷密度波(CDW)动力学行为的影响.实验结果表明,无论是直流还是交流,随着横向调制电流的增大,CDW滑移的阈值电场均会相应地减小;但横向交流电流的调制效应较小,可能更接近本征的效应.考察了横向交流电流的调制效应与其频率的依赖关系.
关键词:
0.3MoO3单晶')" href="#">K0.3MoO3单晶
电荷密度波
横向电流调制效应 相似文献
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Magnetic and spectroscopic properties of the planar antiferromagnet K2FeF4 are determined by the Fe2+ ions at tetragonal sites. The two-dimensional easy-plane anisotropy exhibited by K2FeF4 is due to the zero field splitting (ZFS) terms arising from the orbital singlet ground state of Fe2+ ions with the spin S=2. To provide insight into the single-ion magnetic anisotropy of K2FeF4, the crystal field theory and the microscopic spin Hamiltonian (MSH) approach based on the tensor method is adopted. Survey of available experimental data on the crystal field energy levels and free-ion parameters for Fe2+ ions in K2FeF4 and related compounds is carried out to provide input for microscopic modeling of the ZFS parameters and the Zeeman electronic ones. The ZFS parameters are expressed in the extended Stevens notation and include contributions up to the fourth-order using as perturbation the spin-orbit and electronic spin-spin couplings within the tetragonal crystal field states of the ground 5D multiplet. Modeling of the ZFS parameters and the Zeeman electronic ones is carried out. Variation of these parameters is studied taking into account reasonable ranges of the microscopic ones, i.e. the spin-orbit and spin-spin coupling constants, and the energy level splittings, suitable for Fe2+ ions in K2FeF4 and Fe2+:K2ZnF4. Conversions between the ZFS parameters in the extended Stevens notation and the conventional ones are considered to enable comparison with the data of others. Comparative analysis of the MSH formulas derived earlier and our more complete ones indicates the importance of terms omitted earlier as well as the fourth-order ZFS parameters and the spin-spin coupling related contributions. The results may be useful also for Fe2+ ions at axial symmetry sites in related systems, i.e. Fe:K2MnF4, Rb2Co1−xFexF4, Fe2+:Rb2CrCl4, and Fe2+:Rb2ZnCl4. 相似文献
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The layered perovskite type oxides, K2La2Ti3O10 and zinc(Zn)-doped K2La2Ti3O10 were prepared by sol-gel method and were characterized by power X-ray diffraction, UV-vis diffuse reflectance and X-ray photoelectron spectroscopy. The photocatalytic activity for water splitting of the catalyst powders was investigated with I− as electron donor under ultraviolet and visible light irradiation respectively. The electronic structure of the powders has been analyzed by the first principles calculation, which reveals the photo responses in the visible region and the improvement of the photocatalytic activity of K2La2Ti3O10. Conclusions were made that zinc(Zn)-doped K2La2Ti3O10 exhibited higher reactivity for hydrogen production. When I− was used as electron donor, the optimum doping concentration of zinc(Zn) was found to be 0.015:1 (nZn:nTi). The average hydrogen production rates were 126.6 μmol/(gcat h) under ultraviolet irradiation and 55.5 μmol/(gcat h) under visible light irradiation which were raised by 131% and 251% compared with undoped K2La2Ti3O10 photocatalyst, respectively. 相似文献
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Jing Chen Qiao-yan Dong Li-gang Zhang Bao-gen Shen 《Journal of magnetism and magnetic materials》2009,321(19):3217-3220
In NaZn13-type LaFe11.4Al1.6C0.02 compound, a signature of weak ferromagnetism is observed at ∼100 K under a low field by ac magnetic-susceptibility and electrical-resistivity measurements, implying the coexistence of ferromagnetic (FM) and antiferromagnetic (AFM) phases. The hysteresis in isofield magnetization curves and large magnetic relaxation demonstrate the metastability of the magnetic state in the AFM-FM transition region. The variations of magnetization with temperature, time and field show distinct step-like behaviors, which is probably attributed to the discontinuous growth of ferromagnetic cluster in antiferromagnetic matrix. 相似文献
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