MOCVD法在金属基体上制备YBCO超导带

本报道了用ＭＯＣＶＤ静态和动态沉积两种工艺制备ＹＢＣＯ超导带的实验结果。以Ｙ（ＴＭＨＤ）３、Ｂａ（ＴＭＨＤ）２和Ｃｕ（ＴＭＨＤ）２为挥发源，Ｏ２气为反应剂，高纯Ａｒ气为载流气体，在静止和以１０－１５ｃｍ／ｈ带速移动的金属银基体上，制出了有强烈ｃ－轴取向的ＹＢＣＯ超导带。静态沉积样品的Ｊｃ达到１．０４×１０＾４Ａ／ｃｍ＾２，动态沉积样品的Ｊｃ达到１．４×１０＾４Ａ／ｃｍ＾２（７８Ｋ，０Ｔ）。对改…     

Na6团簇2D和3D结构的竞争

在距离相关紧密结合分子动力学模型的基础上，对Ｎａ６两个最低能量异构体（一个具有Ｃ５ｖ对称性，是３Ｄ结构，另一个具有Ｄ３ｈ对称性，是２Ｄ结构）的结构性质进行了研究。通过求解Ｈｅｓｉａｎ矩阵和对距离相关紧密结合分子动力学轨道所作的速度自关联函数的福里叶变换分析，得到了这些钠原子微团簇的振动频率。尽管这两种结构的能量很接近，但它们表现出完全不同的振动性质，这反映了其几何结构的差别。     

有限温度下Na4团簇的一种新的运动模式：赝传动

在紧密结合的分子动力学基础上,对具有Ｄ２ｈ对和性的Ｎａ４团簇的势力学行为随温度的变化进行了研究。发现在Ｔ〉２００Ｋ时,Ｎａ４团簇产生一种新的运动模式－赝转动。通过研究赝转动时团簇系统热能的变化,提取了Ｎａ４发生转动的势垒为０．０２３ｅＶ。     

用新的紫外荧光光源对维生素D2的最佳光合成

介绍了维生素Ｄ２（以下简称ＶＤ２）的光化反应与光照时间的关系，即由麦角甾醇为原料，在与之转化所需的最佳匹配光谱照射下，找到ＶＤ２的最佳光转化时间。结果表明，在２８３ｎｍ波长的紫外荧光光源照射下，其转化效果最佳。在此条件下麦角甾醇转化率随照射时间的增加而逐渐上升，但同时ＶＤ２的异构体（副产物）也随之增多，因此综合以上两种因素，从而可确定１８￣２１分钟是ＶＤ２光化反应的最佳时间段。     

La2C分子的MP2及密度泛函理论研究

利用ＭＰ２及密度泛函方法（ＢＨＬＹＰ，Ｂ３Ｐ８６，Ｂ３ＬＹＰ）研究了Ｌａ２Ｃ分子的结构与稳定性，对Ｌａ２Ｃ分子共提出了两种构型，其中一种具有Ｃ２ｖ对称性，另一种为线型结构具有Ｄ∞ｈ对称性。计算结果表明，尽管对ＭＰ２和ＢＨＬＹＰ方法，线型结构较稳定，而对Ｂ３Ｐ８６及Ｂ３ＬＹＰ，Ｃ２ｖ结构较稳定，两结构在能量上很接近，表明它们具有相近的稳定性。在Ｄ∞ｈ对称性中其离子性要大于相应的Ｃ２ｖ对称性结构。     

光谱,波谱法研究铜锌超氧歧化酶与氯化钴（Ⅱ）,组氨酸钴（？…

我们首次发现的铜锌超氧歧化酶（Ｃｕ２Ｚｎ２ＳＯＤ）与氨基酸等发生直接相互作用的现象,是一种前人未研究过的重要的生化新现象。在此新发现的基础上,本文用ＩＣＰ,ＶＩＳ,ＮＭＲ和酶活性测定方法,又从不同角度拓展研究了Ｃｕ２Ｚｎ２ＳＯＤ酶与两类不同化合物,     

原子簇H4构型的稳定性

本文用多重散射Ｘα方法对Ｈ４的正方形（Ｄ４ｈ）９正四面体Ｔｄ），正三边形（Ｄ３ｈ），正三棱锥（Ｃ３ｖ），菱形（Ｄ２ｈ），矩形（Ｄ２ｈ）Ｄ２ｄ和Ｄ２等几何构型进行了研究，得到了这些构型在稳定性相对顺序，并分析了有可能成为交换反应：Ｈ２＋Ｄ２→２ＨＤ中过滤态的前五种构型，最终不能成为过滤态的原因。     

一甲基硫脲与支持电解质的阴离子在银电极上共吸附的拉曼光谱研究

本文用电化学现场表面增强拉曼散射光谱（ＳＥＲＳ）技术研究了ＭＴＵ在ＨＣｌＯ４、Ｈ２ＳＯ４和ＨＮＯ３介质中分别与一种或两种无机阴离子的共吸附行为，发现ＣｌＯ－４、ＳＯ２－４和ＮＯ－３等弱吸附无机阴离子均能被ＭＴＵ诱导物理吸附在其质子化了的氨基（ＮＨ＋３）上，这三种无机阴离子被ＭＴＵ诱导物理吸附的强弱顺序是：在电极电位位于－０．２Ｖ～－０．７Ｖ区间时，ＳＯ２－４＞ＣｌＯ－４＞ＮＯ－３，在电位位于－０．８Ｖ～－１．２Ｖ区间时，ＣｌＯ－４＞ＳＯ２－４＞ＮＯ－３。     

光谱、波谱法研究铜锌超氧歧化酶与氯化钴(Ⅱ)、组氨酸钴(Ⅱ)相互作用

我们首次发现的铜锌超氧歧化酶（Ｃｕ２Ｚｎ２ＳＯＤ）与氨基酸等发生直接相互作用的现象,是一种前人未研究过的重要的生化新现象［１］。在此新发现的基础上,本文用ＩＣＰ,ＶＩＳ,ＮＭＲ和酶活性测定等方法,又从不同角度拓展研究了Ｃｕ２Ｚｎ２ＳＯＤ酶与两类不同化合物,即无机氯化钴（ＣｏＣｌ２）、有机组氨酸钴（Ｃｏ（Ⅱ）（Ｈｉｓ）ｎ）的直接相互作用,发现酶活性中心金属离子同样与外加的这两类不同化合物发生相互作用,相应地影响了酶的催化活性。还发现Ｃｏ（Ⅱ）（Ｈｉｓ）ｎ比ＣｏＣｌ２与酶相互作用更强、更快,Ｃｏ（Ⅱ）（Ｈｉｓ）ｎ中的Ｃｏ（Ⅱ）更易进入酶中,更影响了酶的催化活性。     

用MOCVD技术在Al2O3衬底上外延GaN的光致发光研究

本文通过变温和变激发强度的光致发光研究了用ＭＯＣＶＤ在Ａｌ２Ｏ３上生长ＧａＮ单晶薄膜的带边发射，通过分峰拟合得到Ａ，Ｂ，Ｃ，Ｄ四个谱峰，其中半峰宽分别为１３．８ｍｅＶ，１０．８ｍｅＶ，１５．６ｍｅＶ，和５０ｍｅＶ。Ａ对应自由激子谱，Ｂ，Ｃ为两种束缚激子的跃迁，Ｄ与氧杂质谱有关。     

Lattice disorder and size-induced kondo behavior in CeAl2 and CePt(2+x)

When the size of CeAl2 and CePt(2+x) particles is reduced to the nanometer scale, antiferromagnetism is suppressed and Kondo behavior predominates, with the Kondo temperature T(K) either decreasing (CeAl2) or increasing (CePt(2+x)) relative to the bulk. Local structure measurements show that these nanoparticles are significantly distorted. While such distortions should strongly affect magnetic and electronic properties, we find they cannot explain the observed changes in T(K). Other size-induced changes to the electronic structure must, therefore, play a significant role.     

A study of the dynamic equilibrium between symmetrical and distorted 1,2,3-trimethylcyclohexane radical cations

Radical cations of the 1,2,3-trimethylcyclohexane isomers stabilized in various γ-irradiated solute/halocarbon matrices have been investigated by means of ESR in the temperature range 4–77K. At 4 K the ESR spectra are dominated by contributions from an asymmetrically distorted structure with the unpaired electron localized to the C1-C2 bond. On increasing the temperature a reversible change occurs in the ESR line-shape of the cations of the two symmetrical isomers. Using a two-site jump model to reproduce the temperature dependent line-shape, the phenomenon is explained in terms of an interconversion between two such distorted structures, each being the mirror image of the other. The Arrhenius plot associated with the process is markedly nonlinear towards the low temperature region. The experimental data are also modelled by postulating that another (different) electronic ground state, having higher symmetry, becomes populated with the increase of temperature. In this way, the spectral changes can be simulated using a three-site jump model which couple the thermally activated two-site jump process (E _a ca. 0.137 kcal/mol) with a dynamical equilibrium between the asymmetrical ground state and a symmetrical structure 0.058 kcal/mol higher in energy. The energy barrier to pass from the distorted to the symmetrical structure was evaluated to be 0.085 kcal/mol.     

Theoretical Study on the Stable Structures and Aromaticities for Pnictogen Dianionic Sb42-, Bi42-, and (SbBi)22- Clusters

运用密度泛函方法(B3LYP)和后Hartree-Fock (post-HF：MP2、CCSD(T)),对三个新的磷属二价阴离子团簇Sb42-、Bi42-和(SbBi)22-的几个可能的同分异构体进行结构优化、振动频率和原子化能的理论计算．计算结果表明Sb42-和Bi42-团簇有三种稳定的结构：正方形(D4h)、屋顶型(roof,C2v-1)和C2v-2结构,其中正方形结构是基态．由异原子组成的(SbBi)22-团簇也有三种稳定结构：菱形(D4h)、屋顶型(roof,C1)和C2v结构,其中菱形结构是基态．计算显示Sb42-、Bi42-和(SbBi)22-团簇的所有屋顶型(roof)结构的核独立化学位移(NICS)全部为负值,从而说明这些屋顶型结构拥有芳香性;平面环结构(正方形或菱形)的核独立化学位移值全部为正值,说明这三种平面环结构具有反芳香性．用分子轨道分析对这两类屋顶型和平面环结构的芳香性和反芳香性作了解释和讨论．     

Magnetic, structural, and thermal properties of CoV?O?

In this paper, we investigate the electric, magnetic, structural, and thermal properties of spinel CoV(2)O(4). The temperature dependence of magnetization shows that, in addition to the paramagnetic-to-ferrimagnetic transition at T(C) = 142 K, two magnetic anomalies exist at 100 K, T(1) = 59 K. Consistent with the anomalies, the thermal conductivity presents two valleys at 100 K and T(1). At the temperature T(1), the heat capacity shows one peak, which cannot be attributed to the structural transition as revealed by the x-ray diffraction patterns for CoV(2)O(4). Below the transition temperature T(1), the ac susceptibility displays the characteristics of a glass. The series of phenomena at T(1) and the orbital state on V(3+) sites are discussed.     

Large inverse and normal magnetocaloric effects in HoBi compound with nonhysteretic first-order phase transition

HoBi single crystal and polycrystalline compounds with NaCl-type structure are successfully obtained, and their magnetic and magnetocaloric properties are studied in detail. With temperature increasing, HoBi compound undergoes two magnetic transitions at 3.7 K and 6 K, respectively. The transition temperature at 6 K is recognized as an antiferromagnetic-to-paramagnetic (AFM-PM) transition, which belongs to the first-order magnetic phase transition (FOMT). It is interesting that the HoBi compound with FOMT exhibits good thermal and magnetic reversibility. Furthermore, a large inverse and normal magnetocaloric effect (MCE) is found in HoBi single crystal in the $H|| [100]$ direction, and the positive $\Delta S_{\rm M}$ peak reaches 13.1 J/kg$\cdot$K under a low field change of 2 T and the negative $\Delta S_{\rm M}$ peak arrives at $-18 $ J/kg$\cdot$K under a field change of 5 T. These excellent properties are expected to be applied to some magnetic refrigerators with special designs and functions.     

几何结构对Na8团簇熔化过程的影响

运用距离相关紧密结合的分子动力学模型,对金属原子团簇Na8的两种不同的异构体进行了数值模拟.根据零温下基态结构中不同原子到质心的不同距离,把Na8的两种异构体分为多个子系统.分别提取各个子系统在不同温度下的围绕质心的径向分布、无单位键长涨落、平均位移、扩散系数,发现尽管两个异构体的基态能量很接近,但他们的稳定性、熔化过程的热力学性质等有着很大的差别,这也反映了它们在几何结构上的差别.     

Magnetic structure of CuCrO?: a single crystal neutron diffraction study

This paper presents results of a recent study of multiferroic CuCrO(2) by means of single crystal neutron diffraction. This system has two close magnetic phase transitions at T(N) = 24.2 K and T(mf) = 23.6 K. The low temperature magnetic structure below T(mf) is unambiguously determined to be a fully three-dimensional proper screw. Between T(N) and T(mf) antiferromagnetic order is found that is essentially two-dimensional. In this narrow temperature range, magnetic near neighbor correlations are still long range in the (H,K) plane, whereas nearest neighbors along the L direction are uncorrelated. Thus, the multiferroic state is realized only in the low temperature three-dimensional state and not in the two-dimensional state.     

The interplay between the lattice and magnetism in La(Fe_11.4Al_1.6)C_0.02 studied by powder neutron diffraction

The crystallographic structure and magnetic properties of La(Fe 11.4 Al 1.6 )C 0.02 are studied by magnetic measure- ment and powder neutron diffraction with temperature and applied magnetic field. Rietveld refinement shows that La(Fe 11.4 Al 1.6 )C 0.02 crystallizes into the cubic NaZn 13 -type with two different Fe sites: Fe I (8b) and Fe II (96i), and that Al atoms preferentially occupy the Fe II site. A ferromagnetic state can be induced at a medial temperature of 39 K–139 K by an external magnetic field of 0.7 T, and a large lattice is correspondingly found at 100 K and 0.7 T. In all other conditions, La(Fe 11.4 Al 1.6 )C 0.02 has no net magnetization in the paramagnetic (T > T N = 182 K) or antifer- romagnetic states, and thus keeps its small lattice. Analysis of the Fe–Fe bond length indicates that the ferromagnetic state prefers longer Fe–Fe distances.     

Multiple magnetic transitions in single crystals of Ce_(12)Fe_(57.5)As_(41) and La_(12)Fe_(57.5)As_(41)

Measurements of magnetic and transport properties were performed on needle-shaped single crystals of Ce_(12)Fe_(57.5)As_(41)and La_(12)Fe_(57.5)As_(41).The availability of a complete set of data enabled a side-by-side comparison between these two rare earth compounds.Both compounds exhibited multiple magnetic orders within 2-300 K and metamagnetic transitions at various fields.Ferromagnetic transitions with Curie temperatures of 100 and 125 K were found for Ce_(12)Fe_(57.5)As_(41)and La_(12)Fe_(57.5)As_(41),respectively,followed by antiferromagnetic type spin reorientations near Curie temperatures.The magnetic properties underwent complex evolution in the magnetic field for both compounds.An antiferromagnetic phase transition at about 60 K and 0.2 T was observed merely for Ce_(12)Fe_(57.5)As_(41).The field-induced magnetic phase transition occurred from antiferromagnetic to ferromagnetic structure.A strong magnetocrystalline anisotropy was evident from magnetization measurements of Ce_(12)Fe_(57.5)As_(41).A temperature-field phase diagram was present for these two rare earth systems.In addition,a logarithmic temperature dependence of electrical resistivity was observed in the two compounds within a large temperature range of 150-300 K,which is rarely found in 3D-based compounds.It may be related to Kondo scattering described by independent localized Fe 3d moments interacting with conduction electrons.     

Anharmonic transitions in nearly dry L-cysteine I

Two special dynamical transitions of universal character have recently been observed in macromolecules (lysozyme, myoglobin, bacteriorhodopsin, DNA and RNA) at T* ~100-150 K and T(D) ~180-220 K. The underlying mechanisms governing these transitions have been the subject of debate. In the present work, a survey is reported on the temperature dependence of structural, vibrational and thermodynamical properties of a nearly anhydrous amino acid (orthorhombic polymorph of the amino acid l-cysteine at a hydration level of 3.5%). The temperature dependence of x-ray powder diffraction patterns, Raman spectra and specific heat revealed these two transitions at T* = 70 K and T(D) = 230 K for this sample. The data were analyzed considering amino acid-amino acid, amino acid-water, water-water phonon-phonon interactions and molecular rotor activation. Our results indicated that the two referred temperatures define the triggering of very simple and particular events that govern all the interactions of the biomolecular: activation of CH(2) rigid rotors (T < T* ), phonon-phonon interactions between specific amino acid and water dimer vibrational modes (T* < T < T(D)), and water rotational barriers surpassing (T > T(D)).