A universal trend in the structural correlation with oxygen content in RBa2Cu3O x systems

It is shown that the lattice parametersa, b andc in the superconducting perovskites RBa₂Cu₃O _x are inter-related and well correlated to the total oxygen content. The correlation shows a universal trend.     

高温超导微波器件在移动通信中的应用

高温超导微波器件在移动通信基站的应用，蕴涵了巨大的商机。由高温超导滤波器、低噪声前置放大器以及微型制冷机组成的高温超导移动通信基站接收机前端子系统，将给移动通信基站的性能带来了极大的提高。目前，全球已出现一批专业化商业公司。美国已有近2000套高温超导子系统产品在基站做商业运行；欧洲和日本也已完成样机研制。中国科学院物理研究所在2001年初完成了我国第一台高温超导移动通信基站原理性样机。     

Magnetization of Gd diffused YBa2Cu3O7-x superconductor：Experiment and theory

The magnetization of Gd diffused YBa2Cu3O7-x is measured by a vibrating sample magnetometer (VSM) at selected temperatures (5, 25, 50, 77 K). The experimental results for the magnetization are analyzed in the critical state framework involving Kim-Anderson field dependence Jc(H)=Jc0/(1+|H|/H0)n of critical current density and equilibrium magnetization M eq . It is found that the inclusion of the equilibrium magnetization becomes more important at higher temperatures. At 77 K, the shape of the isothermal M-H hysteresis curve is governed by the equilibrium magnetization. Some superconducting parameters are determined by fitting the calculated curves to the experimental data.     

Electronic phase diagram of NaFelxCoxAs investigated by scanning tunneling microscopy

Our recent scanning tunneling microscopy （STM） studies of the NaFelxCoxAs phase diagram over a wide range of dopings and temperatures are reviewed. Similar to the high-Tc cuprates, the iron-based superconductors lie in close proximity to a magnetically ordered phase. Therefore, it is widely believed that magnetic interactions or fluctuations play an important role in triggering their Cooper pairings. Among the key issues regarding the electronic phase diagram are the properties of the parent spin density wave （SDW） phase and the superconducting （SC） phase, as well as the interplay between them. The NaFe l-xCoxAs is an ideal system for resolving these issues due to its rich electronic phases and the charge-neutral cleaved surface. In our recent work, we directly observed the SDW gap in the parent state, and it exhibits unconventional features that are incompatible with the simple Fermi surface nesting picture. The optimally doped sample has a single SC gap, but in the underdoped regime we directly viewed the microscopic coexistence of the SDW and SC orders, which compete with each other. In the overdoped regime we observed a novel pseudogap-like feature that coexists with supercon- ductivity in the ground state, persists well into the normal state, and shows great spatial variations. The rich electronic structures across the phase diagram of NaFel_xCoxAs revealed here shed important new light for defining microscopic models of the iron-based superconductors. In particular, we argue that both the itinerant electrons and local moments should be considered on an equal footing in a realistic model.     

Superconductivity and pseudogap states studied by microwave conductivity measurements of λ-(BEDT-TSF)2GaCl4

We have investigated the microwave response at 45 GHz in an organic superconductor λ-(BEDT-TSF)₂GaCl₄ with T_c = 4.8 K. We determine the μ₀H_c2–T phase diagram from microwave loss and find that the superconducting state is in the pure limit (l/ξ_GL  10). Although the real part of the complex conductivity (=σ₁ + iσ₂) does not show a coherence peak just below T_c, the London penetration depth completely saturates at low temperatures down to T/T_c = 0.2, which may provide an evidence for a conventional s-wave pairing. In the metallic state below about 50 K, (parallel to the c-axis) deviates downward from , while σ₂, which should be zero in a conventional metal, increases exponentially toward T_c. In spite of the fact that the Hagen–Rubens limit is well satisfied as far as the dc conductivity is concerned, a Drude model is unable to explain the large positive σ₂. In order to explain such anomalies in the metallic state, we propose a possible existence of so-called a pseudogap near a Fermi level. The anomalous increase of the positive σ₂ may be attributed to an appearance of pre-formed electron pairs in the pseudogap state. This appearance can be regarded as a precursor to the superconducting transition. Such a precursory phenomenon has been observed also in the isostructural FeCl₄ salt with the anomalous metallic states, which shows a negative σ₂ in contrast to the GaCl₄ salt. Just the opposite of ground states in between the GaCl₄ and FeCl₄ salts may result in the contrasting anomalous metallic states with different precursory phenomena with opposite signs of σ₂.     

超导型复合氧化物在苯酚羟化反应中催化作用

采用柠檬酸络合法合成了一系列含铜复合氧化物(超导体)．用化学滴定方法和 O2-TPD等技术对所合成的复合氧化物的组成和表面性质进行了测定．通过探讨催化 剂结构与活性的关系，发现含铜复合氧化物中的非化学计量氧和铜离子的平均价态 与苯酚经化活性和过氧化氢分解活性密切相关．在实验中观察到酪类化合物在苯酚 经化反应循环中具有增强电子传递功能，在此基础上提出了酮类化合物参与催化循 环的机理．     

Thermal investigations of reactive powder mixtures as precursors for melt-processing of YBa2Cu3O7−x

DTA and XRD measurements were carried out with reactive precursors taken from the YO_1.5-BaO-CuO system in order to investigate mechanisms of YBa₂Cu₃O_7–x formation. The reactions taking place depend strongly on phase composition, phase purity, powder size and heating rate. Among the examined reactive precursors a mixture of 7Y₂O₃+22BaCuO₂+10CuO turned out as the most suited for melt-processing.     

关于Bi系高T_c超导体的阳离子掺杂研究（Ⅰ）──Al－Pb，Mg－Pb和Mn－Pb二元掺杂后超导体的超导电性和结构

讨论了Ａｌ－Ｐｂ，Ｍｇ－Ｐｂ和Ｍｎ－Ｐｂ等二元阳离子掺杂对Ｂｉ系高Ｔ_ｃ超导相出现时间的影响。试验中发现，前人较少讨论的Ｍｇ~（３＋）或Ａｌ~（３＋）离子在高Ｔ_ｃ相形成时，进入到高Ｔ_ｃ超导体晶格的特定位置，它们在高Ｔ_ｃ超导相中起着各自不同的作用机制，从而影响了高Ｔ_ｃ超导相的结构和超导电性。结果表明，Ｍｇ－Ｐｂ，Ａｌ－Ｐｂ和Ｍｎ－Ｐｂ等二元阳离子的掺杂是加快高Ｔ_ｃ超导相形成和提高Ｂｉ系高Ｔ_ｃ超导相超导电性的有效途径，它们的掺杂有利于Ｂｉ系高Ｔ_ｃ相的形成。     

Structural and Mechanical Properties of Crosslinked Drawn Gelatin Films

This paper presents possible applications of thermal analysis, sorptomatic and microgravimetric methods for the study of surface adsorption and porosity properties via the programmed thermodesorption of liquid from the sample. The thermodesorption of liquids under quasi-isothermal conditions demonstrates that the adsorption layers on a high superconductor surface possess non-continuous properties. The degradation of the superconducting properties of an YBa₂Cu₃O_7–δsuperconductor sintered in a CO₂-containing atmosphere has been revealed. It is known that atmospheric contaminants such as CO₂ and H₂O can strongly influence the transition temperature, the critical current density, and the width of the superconducting transition of the YBCO superconductor. Similarly to other liquids adsorbed on solid samples, water induces changes in the physicochemical properties at the interface. A good correlation was obtained between the adsorption and porosimetric, thermal analysis and sorptometric findings. The results prove the applicability of these findings for determination of the adsorption capacity. This revised version was published online in August 2006 with corrections to the Cover Date.     

Unconventional consideration of the symmetry properties—New techniques and computer codes: Application for high‐temperature superconductors

The conventional technique for solving the equations of quantum chemistry is extended to the structures possessing certain symmetries. This proposal allows the release of unoccupied electronic states located lower than the ground‐state Fermi level of a specific system. Such states can be treated as “spectral holes.” Application of this technique, in particular, when calculating the electronic structure of the high‐temperature superconductor (HTSC) compound YBa₂Cu₃O_{7? δ} (0 ≤ δ ≤ 1) results in the following. For all versions of the examined charge distributions over a crystal lattice, spectral holes of high spatial localization are found. The “spatial spectral holes” are located mainly at the p_y‐orbitals of the apex oxygens. These orbitals overlap and form linear chains that are parallel to the known Cu(1)? O chains, disappearing when δ is close to 1. One can suppose that the linear chains of the overlapping hole states form a “superconducting channel.” Some other parameters closely related to the critical characteristics of HTSC materials are also calculated. The calculations show that the superconducting channel is broken when the oxygen chain atoms O(1) are removed (δ > 0). © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2002