Determination of Stoichiometry and Superconducting Properties of Tl-1234 and (Cu0.25Tl0.75)-1234 Phases Substituted by Erbium

Superconducting samples of type TlBa₂Ca_3?y Er _y Cu₄O_11?δ and Cu_0.25Tl_0.75Ba₂Ca_3?y Er _y Cu₄O_12?δ ,y ranging from 0.0 to 0.1, have been prepared by a single step of solid-state reaction technique at normal pressure using high-purity oxide elements. The lattice parameters, for prepared samples, have been estimated from X-ray powder diffraction (XRD). The elemental stoichiometry of the prepared samples has been determined using Particle Induced X-ray Emission (PIXE), whereas the oxygen-content has been determined using elastic backscattering spectroscopy at 3 MeV proton beam. The superconducting transition temperature T _c has been determined from the electrical resistivity measurements. The data of T _c , for TlBa₂Ca_3?y Er _y Cu₄O_11?δ , show enhancement in its value from 124.5 to 128.45 K as y (Er-content) increases from 0.0 to 0.05, whereas it began to suppress with further increase in y. T _c gradually suppresses with increase of yfor Cu_0.25Tl_0.75Ba₂Ca_3?y Er _y Cu₄O_12?δ . Finally, the applied magnetic field B=0.44 T shows enlargement in the transition width. The effect of magnetic field on Tl-1234 phase is a little higher than that on (Cu_0.25Tl_0.75)-1234, indicating that the anisotropy parameter Γ for Tl-1234 is slightly higher than that for (Cu_0.25Tl_0.75)-1234.     

Effect of Ba Substitution on the Formation of (Tl,Bi)-1234 Superconducting Phase

(Tl_1−x Bi _x )(Sr_2−y Ba _y )Ca₃Cu₄O _z ((Tl,Bi)-1234) samples (x=0.1–0.3, y=0.4–1.5) were synthesized under ambient pressure by using a two-step solid-state reaction method to investigate the effect of Ba substitution on the formation and superconducting properties of the (Tl,Bi)-1234 phase. X-ray diffraction analysis shows that nearly single-phased samples are obtained for (Tl_0.8Bi_0.2)(Sr_2−y Ba _y )Ca₃Cu₄O _z (0.8≤y≤1.2), suggesting that control of the composition ratio of Sr and Ba in the bridging layer is a key to stabilizing the 1234-type structure. The critical temperature for the nearly single-phased samples remained between 106.9 K and 109.1 K and was not significantly affected by the change in the Ba content.     

Effect of Mn Addition on Structural and Superconducting Properties of (Bi, Pb)-2223 Superconducting Ceramics

This study deals with the effect of Mn addition on the structural and superconducting properties of Bi_1.8Pb_0.4Sr₂Mn _x Ca_2.2Cu_3.0O _y ceramics with x=0,0.03,0.06,0.15,0.3 and 0.6 by means of X-ray analysis (XRD), scanning electron microscopy (SEM), electron dispersive X-ray (EDX), resistivity, and transport critical current density (J _c) measurements. Zero-resistivity transition temperatures (T _c) of the samples produced via the standard solid-state reaction method are estimated from the dc resistivity measurements. Moreover, the phase fraction and lattice parameters are determined from XRD measurements while the microstructure, surface morphology and element composition analyses of the samples are investigated by SEM and EDX measurements, respectively. It is found that T _c values are obtained to decrease from 109 K to 85 K; likewise, J _c values are observed to reduce from 3200 A/cm² to 125 A/cm² with increasing Mn addition. According to the refinement of cell parameters done by considering the structural modulation, the Mn addition is confirmed by both an increase of the lattice parameter a and a decrease of the cell parameter c of the samples in comparison with that of the pure sample (Mn0). SEM measurements show that not only the surface morphology and grain connectivity are seen to degrade but the grain sizes of the samples are found to decrease with the increase of the Mn addition as well. The EDX results reveal that the elements used for the preparation of samples distribute homogeneously and the Mn atoms enter into the crystal structure by replacing Sr and Cu atoms. The possible reasons for the obtained degradation in microstructural and superconducting properties are also interpreted.     

Ion Beam Analysis and Normal-State Conduction Mechanisms for (Bi, Pb)-2223 and (Tl, Pb)/Sr-1212 Superconducting Phases Substituted by Ruthenium

Superconducting samples of type Bi_1.8Pb_0.4Sr₂Ca_2.1Cu_3−x Ru _x O_10+δ , (Bi, Pb)-2223, with 0.0≤x≤0.4 and type Tl_0.5Pb_0.5Sr_1.6Ba_0.4CaCu_2−x Ru _x O_7−δ , (Tl, Pb)/Sr-1212, with 0.0≤x≤0.525 were synthesized using the standard solid-state reaction technique. The lattice parameters and the surface morphology for these samples were determined using X-ray powder diffraction (XRD) and scanning electron microscope (SEM) measurements, respectively. All element-contents of the samples prepared were estimated from the electron dispersive X-ray (EDX) technique, and their results were compared with those obtained from particle-induced X-ray emission (PIXE). In addition, the oxygen-content was determined using elastic Rutherford backscattering spectroscopy (RBS) technique at 3 MeV proton beam. The superconducting transition temperature T _c and the hole carrier concentration P were determined from the electrical resistivity measurement. The data of both T _c and P for Bi_1.8Pb_0.4Sr₂Ca_2.1Cu_3−x Ru _x O_10+δ and Tl_0.5Pb_0.5Sr_1.6Ba_0.4CaCu_2−x Ru _x O_7−δ phases increased up to x=0.05 and 0.075, respectively and then they decreased as x increased. The superconductivity was completely destroyed around x=0.4 and 0.525 for (Bi, Pb)-2223 and (Tl, Pb)/Sr-1212 phases, respectively. The normal-state electrical resistivity data were analyzed using the two and three dimensional variable range hopping (2D-VRH and 3D-VRH) and the Coulomb gab (CG).     

Influence of Boron-Containing Dopants on Superconducting Properties of (Bi, Pb)-2223 HTS

The influence of addition of lead borate Pb(BO₂)₂ and boron oxide B₂O₃ on the phase evolution and superconducting properties of (Bi, Pb)-2223 HTSs synthesized by the solid-state reaction method in alumina crucibles has been studied. X-ray diffraction, resistivity, critical current density, and AC susceptibility measurements were performed on the prepared compounds. Obtained results have shown that boron-containing dopants lead to the drastic enhancement of the (Bi, Pb)-2223 phase formation. Boron-doped samples reveal a significant increase in both the zero resistivity temperature and transport critical current density compared to the undoped specimen. On the other hand, a high content of boron-containing dopants causes the appearance of a very low-T _c 2201 phase and leads to a deterioration of coupling between superconducting grain boundaries. Obtained results could enable us to develop a cheap and energy efficient fabrication technology for nearly single (Bi, Pb)-2223 phase superconducting materials via heat treatment of boron-incorporated precursors in an alumina crucibles.     

On the Effect of Carbon Nano-Tubes Addition on Structure and Superconducting Properties of Bi(Pb)-2223 Phase

In this work, a series of ceramic samples of Bi_1.6Pb_0.4Sr₂Ca₂Cu₃O _y (Bi(Pb)-2223) added with different amounts (0, 0.2 and 0.4 wt%) of carbon nano-tubes (CNT) are prepared from commercial powders and characterized. The study shows that the volume fraction of the Bi(Pb)-2223 phase decreases with CNT content while the grain size of the samples increases. The obtained cell parameters as well as the onset critical transition temperature are independent of this kind of addition. Also, it has been concluded that CNT addition makes the grains of the samples more connected. The measured magnetization in FC and ZFC modes indicates that CNT addition makes the grains of the samples more connected even if the irreversibility line is decreased. The variation of the residual resistivity and metalicity with CNT content suggests that the addition introduces disorder and defects into the samples. Also, the added samples present broad transitions to the superconducting state when compared to the pure one; this result may be associated to the increase of the volume fraction of the secondary phases. The activation energies, upper critical fields H _c2(0) and coherence lengths ξ(0) are extracted from the magneto-resistivity curves and their evolutions with CNT content are discussed.     

Preparation and Superconducting Properties of F-doped SmO_(1-x)F_xFeAs

Here we report the fabrication and superconductivity of the iron-based arsenic oxide SmO1-xFxFeAs compound.X-ray diffraction(XRD) results prove that the lattice parameters a and c decrease systematically with increasing x in between 00.35 the a and c increase with the decrease of x in the SmO1-xFxFeAs.The critical temperature(Tc) increases with increasing x in between 0.15≤x≤0.3,while x>0.3 the Tc decreases with the increase of x.It is found that at x=0.3 SmO0.7F0.3FeAs has the highest onset resistivity transition temperature of 55.5 K.The critical current density(Jc) value at 10 K for the obtained SmO0.7F0.3FeAs is 1.3×10 5 A/cm2(0T).Meanwhile one can estimates Hc2(0) from the slope of the Hc2(T) curve at T =Tc(HC2 is the upper critical field),and for the 90% normal-state resistivity(ρn) criterion(Tc=55 K),Hc2(0) is determined to be ～253 T.     

烧成及热处理工艺对钛酸锶铅基热敏材料性能及显微结构的影响

研究了烧成及热处理工艺对钛酸锶铅基热敏材料的阻温特性及显微结构的影响。通过扫描电镜（ＳＥＭ）和能量分散仪（ＥＤＡＸ）分析了材料的显微结构及不同形貌晶粒的成份。通过对组成、烧成及热处理工艺的控制，可得到具有Ｖ型ＰＴＣＲ特性的热敏材料。     

Effect of Ba Substitution on the Superconducting Properties and the Irreversibility Line of the Compounds TIPb 1223: Tl0.5Pb0.5(Sr 2−xBax)Ca2Cu3O9−δ

The superconducting properties and the irreversibility line of the Tl_0.5Pb_0.5(Sr_2?xBa_x)Ca₂Cu₃O_9?δ were studied by ac susceptibility on both ceramic and powdered samples. The samples were prepared by solid state reaction in flowing oxygen at 880°C or in sealed quartz tube at 960°C. The irreversibility lines were measured up to 4 Tesla and were determined by the maximum of the X″ peak, using the same ac field to allow comparison between them. The presence of the 1212 phase as a minor superconducting phase was clearly evidenced in all cases. The case of samples of TlPbl223 with Tl/Pb ratio different from unity was also examined.     

层板复合型TiAl基合金微层板的制备及组织性能研究

详细介绍了箔片热加工和电子束物理气相沉积(EB-PVD)在制备TiAl基合金微层板方面的特点及研究现状.重点讨论了EB-PVD制备TiAl基合金微层板的组织与性能,结果表明:TiA1基合金薄板的显微组织结构为非平直的柱状晶,亚结构为月牙形形貌;TiAl/Nb微层板中Nb层的显微组织形貌为粗大的等轴晶;TiAl/NiCoCrAl微层板中NiCo-CrA1层则主要由平直柱状晶结构的γ-Ni相组成.TiA1基合金微层板具有比TiAl基合金薄板更好的常高温力学性能,尤其是在750℃左右的高温环境中,TiAl/NiCoCrAl微层板的增韧效果最佳,伸长率高达72.2％;而TiAl/Nb微层板则表现出最好的高温综合性能,其高温抗拉强度高达443.1MPa,几乎与其室温时的抗拉强度持平.     

Anisotropic Superconducting Properties of MgB2 and Related Compounds

Anisotropic superconducting properties of inter-metallic compounds MgB₂, Y₂PdGe₃, and CaAlSi with AlB₂ structure are studied by detailed angular dependent transport measurements. MgB₂ and CaAlSi shows appreciable anisotropy of the upper critical field, H _c2, with mass anisotropy parameter =3 and 2, respectively, while Y₂PdGe₃ is almost isotropic. In-plane anisotropy of H _c2 in these hexagonal superconductors is very small, consistent with the prediction based on GL theory.     

CaTiO3对(Ba,Pb)TiO3系高温PTC材料性能和显微结构的影响

本文研究了CaTiO3含量及烧成工艺对(Ba,Pb) TiO3基PTC陶瓷材料性能和显微结构的影响.结果表明CaTiO3的最佳添加量为3mol％,室温电阻率达到最小,PTC效应最好.SEM观察表明添加CaTiO3后晶粒更均匀致密.不同烧成工艺下材料性能的比较,结果表明烧成温度越高,温度系数越大,但室温电阻率也越大；降温...     

SnO_2基陶瓷的制备及其性能研究

以纳米SnO2粉末为原料制备导电陶瓷,研究了所制备的SnO2-Sb2O3-CuO三元系SnO2基陶瓷的烧结性能和导电性能。用光学显微镜、扫描电镜和X射线能谱仪等对陶瓷基体的相组成和微观组织进行了分析。结果表明,纳米SnO2粉末在加入一定量的Sb2O3和CuO添加剂后,烧结活性有所提高;加入烧结助剂CuO可明显促进SnO2的烧结;在最佳CuO-Sb2O3配比下,制备的SnO2基陶瓷的综合性能良好。     

Influence of Nano-Ag Addition on the Mechanical Properties of (Cu0.5Tl0.5)-1223 Superconducting Phase

Superconducting samples of type (nano-Ag) _x Cu_0.5Tl_0.5Ba₂Ca₂Cu₃O_10?δ , x=0.0,0.5,1.0,1.5,2.0, and 3.0 wt.% of the total sample’s mass were prepared by a single step solid-state reaction technique. The prepared samples were characterized using X-ray powder diffraction (XRD) and a scanning electron microscope (SEM). The electrical properties of the prepared samples were investigated using the electrical resistivity and I–V measurements. The Vickers microhardness (H _v ) was measured at different applied loads (0.25–3.0 N) for studying the mechanical performance of the prepared samples. All prepared samples exhibited normal indentation size effect (normal ISE) and the H _v number was load dependent. H _v number increases as nano-Ag addition increased. The experimental data of H _v was analyzed using different models; Mayer’s law, Hays–Kendall (H–K) approach, elastic/plastic deformation (EPD) model, proportional specimen resistance (PSR) model, and indentation induced cracking (IIC) model. In addition, the true microhardness (H _o ) values were evaluated through different models. The obtained data has good agreement with the PSR model. Also, Young’s modulus (E), yield strength (Y), fracture toughness (K _f ), and brittle index (B _i ) were calculated.     

Influence of Nano-Ag Addition on Phase Formation and Electrical Properties of (Cu0.5Tl0.5)-1223 Superconducting Phase

Superconducting samples of type (nano-Ag) _x Cu_0.5Tl_0.5Ba₂Ca₂Cu₃O_10?δ , x=0.0, 0.5, 1.0, 1.5, 2.0 and 3.0 wt.%, were prepared under ambient pressure via a single step solid-state reaction technique at 850 °C. The prepared samples were characterized by means of X-ray powder diffraction (XRD), scanning electron microscope (SEM), energy dispersive X-ray (EDX) and differential scanning calorimetry (DSC). The electrical properties of the prepared samples were investigated using the electrical resistivity and I–V measurements. The low addition of nano-Ag up to x=1.5 wt.% enhanced the phase formation and improved the superconducting transition temperature T _c , critical current density J _c , and melting temperature. For x>1.5 wt.%, a reverse trend was observed.     

Preparation, Stability Regions, and Properties of M2TeI6 (M = Rb, Cs, Tl) Crystals

The stability regions of Rb₂TeI₆, Cs₂TeI₆, and Tl₂TeI₆ were mapped out using quantitative thermal analysis and microhardness measurements on annealed and quenched samples. The congruently melting compositions of the three compounds were shown to coincide with their stoichiometric compositions. A procedure was developed for growing Rb₂TeI₆, Cs₂TeI₆, and Tl₂TeI₆ single crystals, and some properties of the grown crystals were investigated.     

微-介孔分级结构MIL-101(Cr)的制备及其性能

为简化合成工艺、降低样品损耗,以丙酸作为添加剂,通过改变丙酸与九水硝酸铬浓度比,合成含有微-介孔分级结构的MIL-101(Cr)。利用X射线衍射仪、全自动比表面及孔隙度分析仪及扫描电子显微镜等表征手段对不同浓度比的MIL-101(Cr)的粒径、BET比表面积、孔体积、N_2吸附性能和微观结构进行研究。结果表明:选择适量的丙酸可以合成含有微-介孔分级结构的MIL-101(Cr),其具有更强的吸附性能。在该反应体系中,丙酸的浓度可以改变MIL-101(Cr)的结构,且合成方式简易方便,为拓展MIL-101(Cr)的应用提供可行的方案。