固态NMR中的宽带布居数反转

本文提出了一个固态NMR体系中的组合180°脉冲R_x(180°),用于宽带布居数反转。在强射频场条件下,用平均哈密顿理论对R_x(180°)进行了计算。并且在计算机模拟和实验上证实了R_x(180°)比180°单脉冲的布居数反转效果要好。     

稀土粉末Eu:Y2O3的自由感应衰减量子拍

稀土固体是重要的激光和光电子材料。目前,由于以宽带信号和太赫兹比特数据传输率为特征的信息技术的发展,稀土固体材料的相干瞬态动力学过程成为宽带与高速信息光子学的基本物理问题之一。研究了室温下稀土粉末样品Eu³⁺:Y₂O₃自由感应衰减的相干瞬态光谱,这有助于理解有效的光吸收动力学、激发态弛豫、相干能量传递和超短光脉冲在稀土固体中的传播。用一对紫外飞秒相干光脉冲作用于稀土粉末样品Eu³⁺:Y₂O₃,然后监测物质激发态的布居数随两个激发脉冲之间的延时的变化,测量到其自由感应衰减量子拍(FID),从拍频周期分析确定了其能级精细结构,能级的退相时间长达皮秒量级。理论分析和实验结果符合得很好。对稀土离子的量子干涉的研究,表明其在受激受控光放大方面具有潜在的应用前景。     

用赝势方法计算五种简单金属的Hugoniot曲线

基于本文作者在文献[1]中所导出的冷压P_x,利用德拜固体模型并考虑电子的热压,得到了金属的高温高压状态方程。在与Hugoniot方程联立后,就能算出Hugoniot曲线。本文计算了五种简单金属的Hugoniot曲线。结果表明,在现有实验数据所能达到的范围内,理论计算与实验符合都比较好。 关键词：     

优化重聚脉冲提高梯度场核磁共振信号强度

缩短射频脉冲宽度, 有助于解决脉冲电力消耗大、样品吸收率高、信噪比低等极端条件核磁共振探测的关键问题. 本文首先分析射频脉冲角度对核磁共振自旋回波信号强度的影响机理, 基于Bloch方程推导了回波信号幅度与扳转角、重聚角的关系. 在特制核磁共振分析仪上采用变脉冲角度技术, 分别在均匀磁场和梯度磁场条件下实现对扳转角和重聚角与回波信号强度关系的数值模拟和实验测量. 结果表明, 梯度场中, 扳转角为90°、重聚角为140°的射频脉冲组合获得最大首波信号强度, 比180°脉冲对应的回波幅值提高13%, 能耗降低至78%. 选用该重聚角(140°) 优化设计饱和恢复脉冲序列探测流体的纵向弛豫时间T₁特性, 准确获得 T₁分布.该结果对于低电力供应、且对信噪比有较高要求的核磁共振测量, 如随钻核磁共振测井和在线核磁共振快速检测等, 具有重要意义. 关键词： 核磁共振 信号强度 重聚脉冲角度 Bloch方程     

Nd,Gd:SrF2晶体材料在宽带放大中的光谱增益特性

光谱的增益窄化是影响超短脉冲宽带放大的关键因素之一.本文利用Nd, Gd:SrF₂晶体发射光谱的特点,开展了宽带放大中的光谱增益特性理论和实验的研究.通过数值模拟,详细研究了激光增益介质在不同的光谱增益线型及不同增益倍数下,输出光谱的演化规律. Nd, Gd:SrF₂晶体光谱增益窄化特性研究实验结果表明,输入光谱半高宽为5 nm时,在140倍的增益条件下, Nd, Gd:SrF₂晶体的输出光谱宽度未见明显窄化,实验结果与理论计算分析相符合.研究结果为氟化物晶体在宽带啁啾脉冲放大的应用奠定了基础.     

固态NMR中自旋Ⅰ=1体系的魔术回波序列

虽然组合脉冲固体回波大大地减轻了有限脉冲宽度的影响,但是它们并没有完全消除有限脉冲宽度带来的失真,而且产生另一种失真,即所谓的位相失真。本文分析了组合脉冲序列,将它用来构成魔术回波序列,这样就能消除位相失真。理论和实验的结果都证明,自旋I=1的组合脉冲魔术回波在线型的测量上优于组合脉冲固体回波序列,基本上解决了²D核核磁共振中有限脉冲宽度带来的难题。     

组合脉冲宽带去耦

本文在理论分析的基础上,提出了一新的用于异核宽带去耦的组合脉冲:90°(X)150°(Y)70°(-Y)150°(Y)90°(X)。理论和实验表明,由此组合脉冲组成的去耦序列:NEW-16、NEW-32,去耦谱宽比常用的去耦序列:MLEV-16、WALTZ-16的去耦谱宽增加约30%。本文还提出了一种电路,使现已提出的大多数组合脉冲去耦序列,能在Varian XL-200 NMB谱仪上实现。     

粉末样品中自旋3/2核体系中心跃迁的布居数反转

在有限脉冲宽度条件下,本文利用矢量模型与计算机模拟设计了一个组合180°脉冲:45°_x112.5°_y45°_x,可以均匀地将自旋I=3/2核体系中心跃迁的布居数反转。并且用数值计算方法对该组合180°脉冲的布居数反转效果进行了分析。实验上用Na₂SO₄粉末样品进行了验证。     

多脉冲序列可编程辅助控制器及其应用

本文描述了一种以单板机为基础的多脉冲序列可编程辅助控制器(PCMP),在常规液体NMR谱仪上实现多脉冲实验。应用PCMP获得了固体的J-耦合化学位移各向同性谱、化学位移缩窄谱,同时也可以完成时间平均旋进频率交叉极化实验以及组合脉冲宽带去耦实验,进一步开拓了常规液体谱仪的功能。     

PS/Ag球壳阵列中高Q值等离激元腔模式的激发效率研究

从理论上系统地研究了聚苯乙烯(PS)/Ag球壳阵列中银球壳的形状(球形和椭球形)和完整度(侧壁有无开口)对多阶窄线宽等离激元腔模式激发效率的影响。理论上发现，在完整的球形银壳层阵列中，基于电的等离激元腔模式(TM₂和TM₃)能够被高效激发，而基于磁的等离激元腔模式(TE₁)激发效率则非常低。通过单独地将银球壳改变为椭球形状或单独在银球壳侧壁赤道上对称构建6个小开口均能有效增大TE₁模式的激发效率。尤其是，存在一个最佳的开口(20°)可使得TE₁模式的激发效率达到最大。理论上进一步发现，TM₂、TE₁和TM₃等离激元腔模式在非完整(侧壁开口约为20°)的椭球形银壳层阵列结构中均能够同时被高效激发。在实验上，利用自支撑技术成功地制备了侧壁带有开口(约为20°)的椭球形银壳层阵列结构，实验测试的透射光谱与理论光谱非常吻合，很好地证实了理论预测结果的正确性。     

NMR Investigations of the Protonic Transport Mechanism in Composed Materials on the Basis of Cesium Acid Sulfates and Phosphates

The composite materials Cs(HSO₄)_1?x (H₂PO₄) _x were investigated by X-ray phase analysis, differential scanning calorimetry, nuclear magnetic resonance (NMR) relaxation, pulsed field gradient NMR (PFG-NMR) and impedance spectroscopy. Three composite materials types x = 0.1 ÷ 0.3 mixture CsHSO₄, α-Cs₃(HSO₄)₂(H₂PO₄), β-Cs₃(HSO₄)_2.5(H₂PO₄)_0.5—compositions of area I; x = 0.4 ÷ 0.5 mixture α-Cs₃(HSO₄)₂(H₂PO₄) and Cs₂(HSO₄)(H₂PO₄)—compositions of area II; x = 0.6 ÷ 0.9 mixture Cs₂(HSO₄)(H₂PO₄) and CsH₂PO₄—compositions of area III, were synthesized. The phase transition temperature from the low-to-high conductive phase for obtained composite materials is notably below (about 100 °C) than that for the individual components. The proton self-diffusion coefficients measured by PFG-NMR are lower than the diffusion coefficients calculated from proton conductivities data. The correlation times τ _d controlling the ³¹P–¹H magnetic dipole–dipole interaction were calculated according to data of the spin–lattice relaxation on ³¹P nuclei. The self-diffusion coefficients estimated from the Einstein equation are in good agreement with the experimental self-diffusion coefficients measured by PFG-NMR. It confirms the fact that the proton mobility is caused by the rotation of PO₄ anion tetrahedra.     

N.M.R. solid echoes in systems of dipolar-coupled inequivalent spins-1 or dipolar-coupled inequivalent pairs of spins-1/2

Proton solid-echo transverse relaxation functions for many thermotropic and lyotropic mesophases, mapped by measurement of the echo amplitude S_yx (t′ = τ) as a function of τ using a P_y (90°)-τ-P_x (90°)-t′ sequence, yield gaussian behaviour of the form exp [-½M ^E ₂τ²] for decays up to 20–30 per cent of the value at τ = 0. M ^E ₂, the second moment for the dipolar interactions between the spin-½ pairs, is related to the van Vleck second moment M ^VV ₂ through a factor f. Whilst experiments suggested a value of 0·70–0·72 for f = M ^E ₂/M ^VV ₂, simple models that ignored the non-equivalence of the dipolar-coupled spin-pairs had predicted f = 0·65. In this paper we derive an exact analytic expression for the spin response of a model of two dipolar-coupled inequivalent spins-1 to the pulse sequence P_y (90°)-τ-P _α(β)-t′, and show that the present model, with the quenching of the spin-flip terms of the dipolar hamiltonian, resolves the afore-mentioned discrepancy. We also reconcile the differences between the experimental and the earlier predicted values of f for deuteron N.M.R. spin echoes in perdeuterated solids.     

Phase interactions in TiN<Subscript>x</Subscript>(TiB<Subscript>x</Subscript>)-<Emphasis Type="Italic">n</Emphasis>-Si-<Emphasis Type="Italic">n</Emphasis><Superscript>+</Superscript>-Si contacts and their thermal degradation due to rapid thermal annealing

The temperature stability of TiN_x(TiB_x)-n-Si-n ⁺-Si, Au-TiN_x(TiB_x)-n-Si-n ⁺-Si, and Au-Ti(Mo)-TiN_x(TiB_x)-n-Si-n ⁺-Si Schottky-barrier contacts subjected to rapid thermal annealing in hydrogen at temperatures T=400, 600, and 800°C is studied. It is shown that structural and morphological transformations and the related degradation of electrophysical characteristics in interstitial alloys (titanium nitrides and borides) start at 600°C. Reasons for the degradation of the barrier properties of titanium borides and nitrides are discussed.     

N.M.R. solid echoes in systems of coupled pairs of spins-1/2

Proton solid echo transverse relaxation functions, mapped by measurement of the echo amplitude S _{y x} (t′ = τ) as a function of τ using a P _y (90°)-τ-P _x (90°)-t′ sequence, are reported for a variety of thermotropic mesogens and mesophases (see Table 1). The relationship of the shapes of this function to the structure and dynamics of the mesogen molecule and the mesophase structure is explored. A heuristic approach is adopted. The spin response for an alkyl chain moiety of a mesogen molecule in a uniaxial mesophase is considered to be the sum of the responses for an assembly of representative subsystems each of which consists of two equivalent pairs of spins-½. The response for the latter is calculated by introducing the effects of motional averaging into the expression obtained in Paper I and estimating an ordering matrix from deuterium quadrupole splittings measured on the corresponding deuteriated mesogen. This model, albeit physically unrealistic, qualitatively reproduces the salient features of the observed relaxation functions. The shape functions are found to be rather insensitive to the structure of the mesogen molecule and the type of mesophase involved, but distinguished by the morphological structure of the sample. In homogeneously aligned mesophases, the shape is mainly determined by the distribution in the intersegmental (CH₂) dipolar interactions, whilst in unaligned mesophases the shape is determined by the orientational distribution of the director. A value for M ₂ ^vv(inter-pair) can be obtained from the decay of the relaxation function of unaligned mesophases, but not for aligned ones. There is an exchange process which contributes to the damping of both the FID signal and solid echo relaxation function in unaligned smectic-A mesophases which is absent in the corresponding aligned mesophases. This process must be a consequence of the defect structure of the smectic-A phase and involve rapid diffusion of molecules between regions distinguished by different orientations of the mesophase director.     

The influence of annealing temperature and tellurium (Te) on electrical and dielectrical properties of Al/p-CIGSeTe/Mo Schottky diodes

p-CuIn_0.7Ga_0.3(Se_(1?x)Te_x)₂ type thin films were synthesized by thermal evaporation method on Mo coated glass substrates. To obtain Al/CuIn_0.7Ga_0.3(Se_(1?x)Te_x)₂/Mo Schottky diode structure for two compositions of x = 0.0 and 0.6, Al metal was evaporated on upper surface of CuIn_0.7Ga_0.3(Se_(1?x)Te_x)₂ as a front contact. Al/p-CuIn_0.7Ga_0.3(Se_(1?x)Te_x)₂/Mo structures were annealed temperature range from 150 °C to 300 °C for 10 min under vacuum. The electrical and dielectrical properties of Al/p-CuIn_0.7Ga_0.3(Se_(1?x)Te_x)₂ (CIGSeTe) Schottky barrier diodes (SBD) have been investigated. Capacitance–Voltage (C–V) characteristics, Conductance–Voltage (G/w–V) characteristics and interface state density were studied in order to obtain electrical and dielectrical parameters. The effects of interface state density (N_ss), series resistance (R_s), the dielectric constant (?′), dielectric loss (?″), dielectric loss tangent (tan δ), ac electrical conductivity (σ_ac) and carrier doping densities were calculated from the C–V and G/w–V measurements and plotted as a function of annealing temperature. It was observed that the values of carrier doping density N_A for annealing temperature at 150 °C decreased from 2.83 × 10⁺¹⁵ cm^?3 to 2.87 × 10⁺¹⁴ cm^?3 with increasing Te content from x = 0.0 to 0.6. The series resistance for x = 0.0 found to be between 10 and 75 Ω and between 50 and 230 Ω for x = 0.6 in the range of annealing temperature at 150–300 °C.     

Bounded perturbations of the P(ϕ)2 theory

As a perturbation to the P(?)₂ theory we consider interaction densities of the form V(?(x)), where ?(x) is a scalar hermitian boson field and V(α) is a bounded real continuous function. It is proved that the asymptotic fields exist and are equal to the asymptotic fields of the P(?)₂ theory. The connection with non-polynomial theories of rational type is indicated. Furthermore the consequences of a bounded perturbation for the S-matrix and the spectral properties are discussed.     

Influence of Zn/Co ratio on dielectric behavior of Na<Subscript>2</Subscript>Zn<Subscript>1 ‐ x</Subscript>Co<Subscript>x</Subscript>P<Subscript>2</Subscript>O<Subscript>7</Subscript> glasses

A series of zinc phosphate glass doped with cobalt Na₂Zn_(1???x)Co_xP₂O₇ (x = 0, 1, 2 and 5 mol%) was synthesized. These glasses were characterized by both infrared and large broadband dielectric spectroscopy. Infrared spectra indicate the increase of Zn/Co ratio creates defect in phosphate network due to the depolymeration of phosphate anions. The dc conductivity increases and activation energy decreases with the amount of cobalt ions in the glass network. The impedance measurements reveal that the total conductivity follows Jonscher’s power law. The dielectric constant and dielectric loss increased with the temperature and decreased with the frequency whatever the cobalt proportion.     

Phase stability,thermal, electrical and structural properties of (Bi2O3)1−x−y(Sm2O3)x(CeO2)y electrolytes for solid oxide fuel cells

In this study, (Bi₂O₃)_1?x?y(Sm₂O₃)_x(CeO₂)_y ternary system was synthesized by using solid-state reaction method. Structural, morphological, thermal and electrical properties of the samples were evaluated by means of X-ray diffraction (XRD), scanning electron microscopy, thermo gravimetry/differential thermal analyzer and four-probe method. The XRD measurement results indicated that the samples (x = 10–15, y = 5–10–15–20) had cubic δ-phase crystallographic structure. The phase stability of the samples was checked by the differential thermal analyzer measurements, which indicates most of the samples have stable δ-Bi₂O₃ phase. The electrical conductivity measurement results showed that the electrical conductivity increased with mol% CeO₂ molar ratio at a fixed molar ratio of Sm₂O₃. The highest electrical conductivity obtained for the (Bi₂O₃)_0.65(Sm₂O₃)_0.15(CeO₂)_0.20 system was 1.55 × 10^?2 (Ω.cm)^?1 at 600 °C. The activation energies were also calculated at low temperature range (350–650 °C) which vary from 1.1325 to 1.4460 eV and at high temperature (above 650 °C) which vary from 0.4813 to 1.1071 eV.     

Structure and proton conductivity of mechanochemically treated 50CsHSO4·50CsH2PO4

Mixtures of CsHSO₄ and CsH₂PO₄ were mechanochemically treated using a planetary type of ball mill. The changes in structure and proton conductivity of the solid acid compounds with the treatment have been investigated. Cs₃(HSO₄)₂(H₂PO₄) and Cs₅(HSO₄)₃(H₂PO₄)₂ were formed during milling. The mechanochemically treated composite consisting of Cs₃(HSO₄)₂(H₂PO₄) and Cs₅(HSO₄)₃(H₂PO₄)₂ showed higher conductivity than the untreated mixture. In addition, a high temperature phase of Cs₂(HSO₄)(H₂PO₄) was generated from the composite at around 100 °C on heating. Conductivity of the mechanochemically treated composite significantly increased at temperatures around 90 °C on heating. The value becomes 2 × 10^− 3 S cm^− 1 at around 180 °C. On the other hand, no steep decrease is observed on cooling. The activation energies of the mechanically milled sample with high conductivities were estimated to be about 0.3 eV for both heating and cooling processes. The relatively high proton conductivity and a low activation energy for the proton conduction should be ascribed to the presence of the high temperature phase of Cs₂(HSO₄)(H₂PO₄).