Impact-resistant high-temperature superconductor

A method of fabricating a high-temperature superconducting ceramic is proposed and described. This method can produce a material having a higher impact strength and lower degradation in air than that obtained by other methods. Pis’ma Zh. Tekh. Fiz. 25, 23–26 (July 12, 1999)     

Microwave-band reflection coefficient of high-temperature superconductor specimens in E-plane waveguide structures

The microwave-band reflectivity of high-temperature superconductor (HTSC) specimens was measured for the first time in the E-plane waveguide structures of two types: tapered waveguide termination and E-plane corner section. The measured reflection coefficient of a textured YBa₂Cu₃O_7−δ specimen used as a tapered waveguide termination corresponds well to the theoretical curve calculated using an improved two-fluid HTSC model.     

Electrical impedance of superconductor/polymer composites

Electrical impedance measurements were carried out on high-T _c superconducting ceramic/polymer composite materials, in which superconducting particles are embedded in a polymer matrix. The results for the impedance magnitude and phase angle versus frequency (1 kHz-1 MHz), temperature (50–290 K) and volume percentage of superconductor (0–70%) are presented. The results reveal that the a.c. electrical properties of the new composite materials go through a large change at volume percentage of powder filler around 40%, which indicates that particle-particle contacts are partially formed. Far below this composition the composite is an insulator, and above this composition the composite behaves as a semiconductor. No marked transition in impedance and phase angle was observed when the material went through the superconducting transition temperature.     

Characterization of the high-temperature behaviour of a glass-filled polymer composite

The decomposition kinetics and material properties of a decomposing, expanding glass-filled polymer composite have been measured. In addition, the morphology as a function of the stage of decomposition and the decomposition-induced material damage have been monitored visually by scanning electron microscopy. The combination of these data was used to characterize the high-temperature behaviour of the material.     

Local characteristics of heat-radiation superconductor detectors based on high-temperature superconductor films

Relations are proposed for evaluating the local values of the thermal sensitivity, speed of response, and resolution of a heat radiation detector based on high-temperature superconductor films.Moscow Institute of Engineering Physics. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 62, No. 6, pp. 873–877.     

Growth of high-temperature superconductor crystals from flux

Crystallization of high-temperature superconductors was studied in La-Sr-Cu-O, Y-Ba-Cu-O and Bi-Sr-Ca-Cu-O systems. Platelet crystals YBa₂Cu₃O_6.5+x were obtained by spontaneous crystallization from homogeneous nonstoichiometric melts enriched in barium and copper oxide. La_2−x Sr _x CuO₄ was prepared by slow cooling of melts enriched in copper oxide. Bi₂(Sr,Ca) _{n + 1}Cu _n O _y , (n=1; 2) was obtained by melting zone travelling. The crystals show transition to superconducting state atT=93 K, ΔT 0.2–0.5 K (Y, Ba cuprate),T=87 K, ΔT 2K (Bi, Sr, Ca-cuprate). La, Sr-cuprate single crystals obtained by Czochralski method did not show transition to superconducting state. For flux-grown crystalsT _c was 5–26 K depending on the composition, growth and heat treatment. The short characterization of some accessory phases (Ba₃Y₂Cu₃PtO₁₀, Ca_1.75Sr_1.5Cu_0.75PtO₆, BaCuO₂, Ba₄₁Cu₄₄O₈₄Cl₂) is reported.     

Optimal perovskite-type substrates for high-temperature superconductor layers

The lattice mismatch and stereographic maps of the prevailing epitaxial relationships for HTS on perovskite-type substrates have been determined as a function of substrate orientation. The compositions and orientations of substrates for creating perfect single crystalline HTS layers are presented. The misfit may be decreased to nearly 0 for LnGaO₃ and SrLnGaO₄, where Ln is a rare-earth ion having a large ionic radius, by optimal choice of substrate orientation. For the LnAlO₃ and (Ca, Sr)LnAlO₄ families, good lattice match is lacking. The best compounds among them are LaAlO₃ and SrLaAlO₄. Because of the weak orientation dependence of the misfit for SrTiO₃ and the LnAlO₃ family, the main purpose of substrate orientation optimization is to suppress polysynthetic twinning.Paper presented at the 1st International Conference Material Science of High-Temperature Superconductors, Kharkov, Ukraine, 5–9 April 1993.     

An equation of state of high-temperature superconductor

In the present paper the expression of cohesive energy and the bulk modulus as a function of volume are formulated for high-T _c copper oxide superconductors. The model employed consists of long-range electrostatic Coulomb interaction and short-range overlap repulsion. The short-range overlap potential is considered in the Born-Landé inverse power form. The model, parameters of the Born-Landé model are calculated from the equilibrium condition and data of bulk modulus at room temperature. The computed values of pressure derivatives of bulk modulus atP=0 and the values of bulk modulus are found to be in very close agreement with experimental values for high-T _c copper oxide and their nonsuperconducting parent compounds. It is also found that the quantity ΔU/U(V _o) of these compounds increases with increasing hydrostistic pressure.     

Long, highly-ordered high-temperature superconductor nanowire arrays

The preparation and electrical properties of high-temperature superconductor nanowire arrays are reported for the first time. YBa2Cu3O(7-delta) nanowires with widths as small as 10 nm (much smaller than the magnetic penetration depth) and lengths up to 200 microm are studied by four-point electrical measurements. All nanowires exhibit a superconducting transition above liquid nitrogen temperature and a transition temperature width that depends strongly upon the nanowire dimensions. Nanowire size effects are systematically studied, and the results are modeled satisfactorily using phase-slip theories that generate reasonable parameters. These nanowires can function as superconducting nanoelectronic components over much wider temperature ranges as compared to conventional superconductor nanowires.     

氮化铝/聚合物复合导热塑料研究进展

导热塑料由于具有质轻、耐化学腐蚀、易加工成型、力学性能优异等性能而成为了人们研究的热点。本文分析了氮化铝复合材料的导热机理,综述了氮化铝/聚合物型导热塑料的研究进展,并详细阐述了填料(粒径、用量、表面处理、复配)和复合工艺等对导热塑料导热、绝缘和力学性能的影响。最后,对导热塑料今后的研究方向进行了展望。     

Three-dimensionality of field-induced magnetism in a high-temperature superconductor

Many physical properties of high-temperature superconductors are two-dimensional phenomena derived from their square-planar CuO2 building blocks. This is especially true of the magnetism from the copper ions. As mobile charge carriers enter the CuO2 layers, the antiferromagnetism of the parent insulators, where each copper spin is antiparallel to its nearest neighbours, evolves into a fluctuating state where the spins show tendencies towards magnetic order of a longer periodicity. For certain charge-carrier densities, quantum fluctuations are sufficiently suppressed to yield static long-period order, and external magnetic fields also induce such order. Here we show that, in contrast to the chemically controlled order in superconducting samples, the field-induced order in these same samples is actually three-dimensional, implying significant magnetic linkage between the CuO2 planes. The results are important because they show that there are three-dimensional magnetic couplings that survive into the superconducting state, and coexist with the crucial inter-layer couplings responsible for three-dimensional superconductivity. Both types of coupling will straighten the vortex lines, implying that we have finally established a direct link between technical superconductivity, which requires zero electrical resistance in an applied magnetic field and depends on vortex dynamics, and the underlying antiferromagnetism of the cuprates.     

Silver hexacyanoferrate/conducting polymer composite

In this work, we present an alternative route to prepare silver hexacyanoferrate(II)/polyaniline (PANI) composites thin films and compare these results with the conventional chemical synthetic route, and with the electrochemical process deposited in platinum electrodes. Differently from the electrochemical method, used to synthesize the conducting polymer film on a electrode surface, this new chemical route make use of dialysis membrane as a solid support to synthesize the silver hexacyanoferrate(III) compound, and subsequently uses this composite membrane as oxidant to polymerize the aniline monomer. The spectroscopic (UV-Vis. and IR region) and electrochemical characterization (cyclic voltammetry) indicate that the polymeric composite remains optically active and conductive. The X-ray analysis show that the composite has an amorphous and a crystalline structure assigned to the conducting polymer and to the Ag₄[Fe^II(CN)₆] structure respectively.     

纳米碳管/聚合物功能复合材料

纳米碳管(Carbonnanotubes,CNT)具有π π共轭电子结构,可与结构相似的聚合物(Polymer)通过范德华力结合形成复合材料。导电聚合物(Electricallyconductingpolymer,ECP)包覆多壁纳米碳管(Multi walledcarbonnanotubes,MWNT)后,可用于诸如超级电容器等电子器件。共轭发光聚合物修饰纳米碳管形成的CNT polymer复合材料,具有很强的发光性能,有望用于电子接收器和光电器件。通过连结氨基聚合物,可使多壁纳米碳管溶解和功能化,从而将纳米碳管引入生物学系统中。研究结果表明,CNT polymer复合物有许多潜在的应用,有待进一步发展。     

Properties of the microwave absorption in high-temperature superconductor Y-Ba-Cu-O

It is shown that the measurement of the properties of the low-magnetic field microwave absorption using an EPR spectrometer needs to be corrected for instrumental effects, which can be accomplished by using a low-field calibration resonance from Cr³⁺ in ruby. The results show the existence of a hysteresis in intensity and field position, but the latter is somewhat smaller than previously reported. The temperature dependence of the intensity of the absorption is accounted for in terms of the temperature dependence of the current in a Josephson junction assuming a mean field temperature dependence for the superconducting gap.     

纳米羟基磷灰石/聚合物多孔复合支架材料

为提高骨组织工程支架材料的力学性能,改善其生物活性,综合天然与合成高分子的优点,采用溶液共混相分离法制备出聚己内酯(PCL)-壳聚糖(CS)多孔支架材料, 并进一步采用离心注浆法填充具有生物活性的纳米羟基磷灰石(HA)-聚乙烯醇(PVA)复合浆料, 制备了n-HA-PVA/PCL-CS复合多孔支架材料, 改善了PCL-CS支架材料力学性能。采用扫描电子显微镜、红外光谱、元素分析、孔隙率和抗压强度试验对材料进行了表征。结果表明, PCL-CS支架材料的内部具有蜂窝状的相互贯通的孔隙结构,孔隙率可以达到60%～80%。CS含量越大,孔隙率越大,而抗压强度越小。填充后的n-HA-PVA/PCL-CS复合多孔支架材料,孔隙率有所下降,但仍大于60%,而其弹性模量可提高至25.71 MPa。