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1.
A 19F pulsed NMR investigation of single crystals of CeF3 and CaF2-doped CeF3 has been undertaken in the temperature range 300–570K at a frequency of 14 and 60 MHz. It was found that the free-induction decay is non-linear and could be fit by a sum of exponentials using a nonlinear least square procedure to an appropriate functional form. The results of this analysis indicate that there are three distinct spin-spin relaxation times T2, which is consistent with the existence of three inequivalent fluorine sublattices. At room temperature, fluorine ions on two of the sublattices were found to be in motion, with the fastest ion specified as the F3-type in the Oftedal structure.The temperature dependence of the spin-spin relaxation time T2 for the fastest ions was found to undergo an inversion at 400 and 385K for the pure and doped samples, respectively. The inversion indicates an increase in the interchange rate of ions between two sublattices. Activation energies are 0.29 ± 0.02 eV in the low temperature region and 0.21 ± 0.01 eV in the high temperature region for the pure sample, with corresponding values of 0.24 ± 0.01 eV and 0.23 ± 0.02 eV for the doped sample.T1 was approximately the same for both samples, and essentially temperature independent, indicating an exchange-dominated spin-lattice decay mechanism.  相似文献   

2.
We have studied the phonon density of states (PDOS) in LaFeAsO(1-x)Fx with inelastic neutron scattering methods. The PDOS of the parent compound (x=0) is very similar to the PDOS of samples optimally doped with fluorine to achieve the maximum Tc (x approximately 0.1). Good agreement is found between the experimental PDOS and first-principles calculations with the exception of a small difference in Fe mode frequencies. The PDOS reported here is not consistent with conventional electron-phonon mediated superconductivity.  相似文献   

3.
GaN1-xPx三元合金的光学与结构特性   总被引:1,自引:1,他引:0  
对采用金属有机化学气相淀积(MOCVD)技术生长的GaN1-xPx三元合金进行了低温光致发光(PL)和X射线衍射(XRD)测试分析,与来自GaN层的带边发射相比,P的摩尔分数比为0.03,0.11和0.15的GaN1-xPx的光致发光峰分别呈现出了73meV,78meV和100meV的红移,文中将这种红移归因于GaN1-xPx合金具有大的带隙能量弯曲系数。X射线衍射结果表明GaN1-xPx三元合金仍为六方结构晶体,且随着P组份比的增加,GaN1-xPx合金的(0002)衍射峰逐渐向小角度方向移动,即晶格常量变大,同时,(0002)衍射峰谱线不断宽化,说明由于替位式P原子的不规则分布以及部分间隙P原子的影响造成了GaN1-xPx样品的晶格畸变。在GaN1-xPx的光致发光谱及X射线衍射谱中均未观测到相应的有关GaP的峰,表明所生长的高P含量的GaN1-xPx三元合金没有产生明显的相分离。  相似文献   

4.
李宝军  李国正  刘恩科 《光学学报》1997,17(12):1718-1723
对1.55μm波长的Si1-xGex光波导和Si1-xGex/Si多量子阱(MQW)红外探测器的集成器件结构进行了系统的分析和优化设计。优化结果为:1)对Si1-xGex光波导,Ge含量x=0.05,脊宽、高和腐蚀深度分别为8、3和2.6μm;2)对Si1-xGex/Si多量子阱红外探测器,Ge含量x=0.5,探测器由厚度为550nm、23个周期的6nmSi0.5Ge0.5+17nmSi组成,长度约2mm。结果表明,这种结构器件的内量子效率可达88%。  相似文献   

5.
The crystal structure and physical properties of multiferroic polycrystalline Ca(2+)-doped BiFeO(3) samples have been investigated. The present experimental investigation suggests that Bi(1-x)Ca(x)FeO(3-x/2) (x ≤ 0.1) can be considered as a solid solution between BiFeO(3) and CaFeO(2.5). The oxidation state of Fe in these materials is + 3 and charge balance occurs through the creation of oxygen vacancies. For each composition, two structural phase transitions are revealed as anomalies in the variable-temperature in situ x-ray diffraction data which is consistent with the well-established high-temperature structural transformation in pure BiFeO(3). All compositions studied show antiferromagnetic behaviour along with a ferromagnetic component that increases with Ca(2+) doping. The resistivities of the Bi(1-x)Ca(x)FeO(3-x/2) samples at room temperature are of the order of 10(9) Ω cm and decrease with increasing Ca(2+) content. Arrhenius plots of the resistivity show two distinct linear regions with activation energies in the range of 0.4-0.7 and 0.03-0.16 eV. A correlation has been established between the critical temperatures associated with the structural phase transitions and the multiferroic properties. A composition of x = 0.085 is predicted to show maximum magneto-electric coupling.  相似文献   

6.
Low-energy spin fluctuations have been investigated in the electron-doped Pr{1-x}LaCe{x}CuO{4+delta} over a wide concentration range of 0.07相似文献   

7.
We have performed angle-resolved photoemission spectroscopy on Pb(Bi(1-x)Sb(x))2Te4, which is a member of lead-based ternary tellurides and has been theoretically proposed as a candidate for a new class of three-dimensional topological insulators. In PbBi2Te4, we found a topological surface state with a hexagonally deformed Dirac-cone band dispersion, indicating that this material is a strong topological insulator with a single topological surface state at the Brillouin-zone center. Partial replacement of Bi with Sb causes a marked change in the Dirac carrier concentration, leading to the sign change of Dirac carriers from n type to p type. The Pb(Bi(1-x)Sb(x))2Te4 system with tunable Dirac carriers thus provides a new platform for investigating exotic topological phenomena.  相似文献   

8.
An ultrasonic irradiation method was applied to the sol/gel synthesis of the single-crystal cubic barium strontium titanate Ba(1-x)Sr(x)TiO(3) (0相似文献   

9.
Lithium-excess cation disordered rock-salt materials have received much attention because of their high-capacity as a candidate for cathodes for lithium-ion batteries.The ultra-high specific capacity comes from the coordinated charge compensation of both transition metal and lattice oxygen.However,the oxygen redox at high voltage usually leads to irreversible oxygen release,thereby degrading the structure stability and electrochemical performance.Lithium-excess Li_(1.14)Ni_(0.57+0.5 x)Ti_(0.19-0.5 x)Mo_(0.10)O_(2-x)F_x(x=0,0.05,0.10,0.15,and 0.20) with different amounts of fluorine substitution were synthesized.Among them,Li_(1.14)Ni_(0.62 o)Ti_(0.140)Mo_(0.10)O_(1.85)F_(0.15)exhibits a lower capacity decline,better rate performance,and lower structure damage.The effects of fluorine substitution on the electrochemical property and structural stability were systematic studied by x-ray photoelectron spectroscopy and in situ XRD etc.Results show that fluorine substitution reduces the average valence of the anion,allowing a larger proportion of low-valent redox active transition metals,increasing the transition metal redox capacity,inhibiting irreversible oxygen release and side reaction.Fluorine substitution further improves the structural stability and suppresses lattice deformation of the material.  相似文献   

10.
We propose a general theoretical framework for ultrafast laser-induced spin dynamics in multisublattice magnets. We distinguish relaxation of relativistic and exchange origin and show that when the former dominates, nonequivalent sublattices have distinct dynamics despite their strong exchange coupling. Even more interesting, in the exchange dominated regime sublattices can show highly counterintuitive transitions between parallel and antiparallel alignment. This allows us to explain recent experiments with antiferromagnetically coupled sublattices, and predict that such transitions are possible with ferromagnetic coupling as well. In addition, we predict that exchange relaxation enhances the demagnetization speed of both sublattices only when they are antiferromagnetically coupled.  相似文献   

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