Characterization of high-temperature superconductors by electron microprobe analysis

In order to optimize the physical properties of HTSC small single crystals grown from a melt for basic studies of their physical properties the influence of the environment on their impurity content was investigated by EPMA. This requires quantitative analysis of all elements being present in the crystals. The accuracy of results was affected by problems with the choice and quality of standards, by contamination but also by malfunction of microprobe electronics. The HTSC materials were found to react with mills, milling balls, crucibles and the atmosphere. These problems are being discussed and some reactions being studied for Y₁Ba₂Cu₃O_6+x (0 < x < 1) HTSC in A1₂O₃ and ZrO₂ crucibles. The crystals grown contain reproducible amounts of impurities depending on boundary conditions and exhibit a zone structure in composition particularly for Y and Ba within their range of homogeneity.     

Ab Initio High Pressure Investigations of InI

The high pressure behaviour of InI is studied by DFT‐calculations and compared with experimental data. The existence of a 5s² electron pair in In⁺ represents an unfavourable bonding situation for high symmetry structures because of effective closed shell repulsion. Since cations with a ns² electron pair are highly polarizable and the electronic situation is more favourable in the low symmetry structure InI prefers a TlI‐type structure at ambient pressure. A pressure induced transition to the more densely packed high symmetry CsCl‐type structure takes place at about 19 GPa according to our calculations. At ambient pressure the interactions are predominantly ionic. However with increasing pressure the distances between In⁺ cations in the TlI‐type structure diminish drastically, mainly due to the changing space requirement of the lone electron pair. Apart from ionic interactions further bonding interactions between the In⁺ cations occur. At elevated pressure the electron localization function (ELF) as well as the band structure diagrams suggest metallic bonding between the In⁺ within the zigzag chain, i. e. increasing bonding interactions between the In⁺ cations due to the electron pair and its s‐p‐mixing. At ambient pressure In‐In interactions are rather weak and the space requirement of the lone electron pair mainly determines the characteristic arrangement of the ions. At elevated pressure the In‐In interactions become stronger and stabilise themselves additionally the specific structural arrangement.     

Nitrido-Sodalithe. II. Synthese,Struktur und Eigenschaften von M(6+(y/2)–x)H2x[P12N24]Zy mit M = Fe,Co, Ni,Mn; Z = Cl,Br, I; 0 ≤ x ≤ 4; y ≤ 2

Nitrido-Sodalites. II. Synthesis, Crystal Structure, and Properties of M_{(6+(y/2)–x)}H_2x[P₁₂N₂₄]Z_y with M = Fe, Co, Ni, Mn; Z = Cl, Br, I; 0 ≤ x ≤ 4; y ≤ 2 The nitrido sodalites M_{(6+(y/2)–x)}H_2x[P₁₂N₂₄]Z_y with M = Fe, Co, Ni, Mn; Z = Cl, Br, I; 0 ≤ x ≤ 4; y ≤ 2 are obtained by the reaction of HPN₂ or [PN(NH₂)₂]₃ with the metal halogenide MZ₂ (T = 700°C). The compounds are isotypic to Zn_(7–x)H_2x[P₁₂N₂₄]Cl₂. An increase of the ionic radii of the cations or anions results in an expansion of the lattice which is caused by an increase of the P? N? P angle. The influence of the cation is more dominant than that of the anion. By reacting [PN(NH₂)₂]₃ with metal halogenide (MZ₂) hydrogen free, X-ray amorphous products are obtained. The formation of the chloride-containing P? N-sodalite in this reaction begins at temperatures below 450°C.     

On the calculation of expectation values and transition matrix elements by coupled cluster method

Summary Finite order expressions are derived for expectation values and transition matrix elements within the framework of the coupled cluster method.     

Imidazole Coordinated Sandwich-type Antimony Polyoxotungstates Na9[ {Na（H=O2}3{M（C3H4N2）}3（ Sb W9O33）2]·xH=O（M=Ni^Ⅱ, Co^Ⅱ, Zn^Ⅱ, Mn^Ⅱ）

The imidazole covalently coordinated sandwich-type heteropolymngstates Na9[ {Na（H=O2}3{M（C3H4N2）}3（ Sb W9O33）2]·xH=O（M=Ni^Ⅱ, Co^Ⅱ, Zn^Ⅱ, Mn^Ⅱ） were obtained by the reaction of Na2WO4·2H2O, SbCl3·6H2O, NiCl2·6H2O [MnSO4·H2O, Co（NO3）2·6H2O, ZnSO4·7H2O] and imidazole at pH≈7.5. The structure of Na9[{Na（H2O）2}3{Ni（C3H4N2）}3（SbW9O33）2]·32H2O was determined by single crystal X-ray diffraction. Polyanion [{Na（H2O）2}3{Ni（C3H4N2）}3（SbW9O33）2}3]^9- has approximate C3v symmetry, imidazole coordinated six-nuclear duster [{Na（H2O）2}3{Ni（C3H4N2）}3]^9＋ is encapsulated between two （α-SbW9O33）^9-, the three rings of imidazole in the polyanion are perpendicular to the horizontal plane formed by six metals （Na-Ni-Na-Ni-Na-Ni） in the central belt, and x-stacking interactions exist between imidazoles of neighboring polyanions with dihedral angel of 60%. The compounds were also characterized by IR, UV-Vis spectra, TG and DSC, and the thermal decomposition mechanism of the four compounds was suggested by TG curves.     

Dynamics of intramolecular processes in electronic-excited states of 2,4,5-triarylimidazole molecules

Intramolecular processes in electronic-excited states of 2,4,5-triarylimidazole molecules were studied by femtosecond laser spectroscopy. Experiments were carried out with two types of compounds, namely, those experiencing intramolecular proton transfer and two model compounds in which it is impossible. Schemes of the processes studied were proposed and the characteristic rate constants were determined. The excited-state intramolecular proton transfer (ESIPT) in the molecules with planar structure of the reaction center is a very fast process (100 fs). If the reaction center has a nonplanar structure and, hence, the intramolecular hydrogen bond is weakened, the ESIPT time is determined by the time of conformational rearrangement of the molecule.     

The rotation and the phase transition in solid C60

The interaction between C60's in solid C60 has been calculated by (exp-6-1) potential, and the cause and the controlled factor of the high rapid rotations of C60 's were discussed. In order to describe the disordered degree of C60 rotation, an equivalent M is introduced. The phase transitions at the ~260 K and at the ~90 K are studied from the viewpoint of C60 rotation. The potential barriers of the ordered rotation below the ~260 K and the disordered rotation above the ~260 K have been given, and the effect of the external pressure on the temperature of phase transition has also been given.     

The “Facilitated Transition” hypothesis as an explanation for the gemdialkyl effect

A new technique of searching the conformational space of transition states was used to explore the cause of the rate acceleration in the gem-dialkyl effect in intramolecular cyclization reactions. Several previous hypotheses were discarded and a new hypothesis was advanced based on this new data. This hypothesis, the “Facilitated Transition” hypothesis, states that increased steric hindrance reduces the overall activation energy by facilitating rotation through the transition state. The older “Reactive Rotamer” hypothesis was eliminated by generating all conformations of the starting materials using the and computer programs and demonstrating that no relationship is found between rate increase and a change in the concentration of “reactive rotamers”.     

NH_2基态和激发态的SAC－CI和量子拓扑方法研究

ＮＨ_２基态和激发态的ＳＡＣ－ＣＩ和量子拓扑方法研究郑世钧，蔡新华，宋天乐，孟令鹏，中迁博，波田雅彦（河北师范学院化学系，石家庄，０５００９１）（京都大学工程学院京都，日本）关键词ＳＡＣ－ＣＩ方法，激发态，电子密度，拓扑分析用量子拓扑学方法研究激发态...     

强冲击加载条件下的钨合金的界面研究

借助定量金相、扫描电子显微镜、透射电子显微镜等微观分析手段对钨质量分数为９３％的钨合金在１５～５０ＧＰａ冲击压力下微观结构响应性态进行了考察，发现了一些钨合金所特有的现象，即钨颗粒与粘结相交界处出现成分迁移，新相析出；并结合断口分析，探讨了钨合金在冲击作用下发生断裂的微观特征与韧脆转化间的关系及其物理本质。