YBCO Bicrystal Junctions on Sapphire: d-Wave Impact and Possible Applications

The current transport and Josephson effect have been investigated in YBCO junctions, fabricated on the sapphire bicrystal substrates. The YBCO film with thickness t150 nm was deposited by dc sputtering on the epitaxial CeO ₂ buffer layer made by rf magnetron sputtering. The junctions were characterized at dc and at mm waves. 5 m wide junctions have moderately high normal state resistance R _N = 5÷30 with critical currents I _c =50÷200 A which give I _c R _N product of order of 0.5÷2 mV. The tolerance of characteristic interface resistance (R _N S) was around 30% for the junctions on a chip. Experimental data, discussed in terms of d-wave symmetry, demonstrate possibility of design of small scale integrated Josephson microwave circuits.     

Extrinsic defect implantation in sintered YBCO slabs: Magnetic and transport properties

This paper deals with proton irradiation effects on the intragrain and intergrain magnetic and transport properties of sintered YBCO. We have irradiated slab-shaped samples with beams at different fluences and energies, aiming at checking the possibility to modify in a planned way critical currents by means of proton implantation. Magnetic characterizations show enhanced intragrain pinning. Emphasis is given to the possibility to modulate intergrain magnetic properties by irradiation, determining critical current enhancement in optimal field and temperature ranges. Resistive measurements were performed in order to investigate the complex transport phenomena in polycrystalline materials, where superconducting and normal conduction mechanisms coexist. Irradiation-induced effects on both superconducting and normal state resistivity are studied. The addition of extrinsic defects leads to enhanced transport properties, emerging especially when a magnetic field is applied.     

New Insights on the Intrinsic Anisotropy of YBCO Films

Careful investigation of the angular dependence of resistivity ρ(θ) (θ is the angle between the magnetic field and the ab-planes) and the temperature dependence of resistivity ρ(T) within the superconducting transition in an applied magnetic field B up to 1 T for a series of YBa₂Cu₃O_7−δ (YBCO) thin films revealed a large variation of intrinsic anisotropy factor γ. The series of films studied included both optimally doped and underdoped samples of different T _c , critical current density J _c , film thickness, and preparation techniques. The variation in the shape and depth of the minimum measured for ρ(θ) near θ=0° could be directly correlated to the intrinsic anisotropy of the YBCO films. The results of fitting of ρ(θ) using Bardeen–Stephen theory allowed a quantitative determination of the value of γ which varies between 7 and 230, and is independent of T _c , film thickness, or J _c . The sharper the minimum in ρ(θ) around θ=0° the larger is the anisotropy. For highly anisotropic film, ρ(θ) showed an identical behavior for B ∥ J and B ⊥ J (i.e., ρ(θ) is independent of the angle θ between B and J for this film). The large variation in γ could be attributed to the “buckling” of the CuO₂ planes.     

Thermodynamic Properties of a d-Wave Superconductor Near Zero Temperature

On the basis of Fermi liquid theory, we study the thermodynamic properties near zero temperature of a d-wave superconductor assuming the BCS pairing model. The temperature dependence of the order parameter is derived. We then obtain an analytical expression for the free energy difference between the normal and superconducting states in the vicinity of zero temperature from the coupling constant integral. New expressions for the critical field and the specific heat in the superconducting state are given as functions of temperature. We compare our expressions with previous formulas due to others.     

High Temperature Transport Properties of Dilute Nitrogen Atoms

Calculations of the transport coefficients viscosity and thermal conductivity and the diffusion collision cross section of nitrogen atoms have been carried out as a function of temperature. The dilute gas transport properties of nitrogen atoms depend only on the interactions between two nitrogen atoms along various electronic potential energy curves. The results presented here include contributions from 16 potential energy curves, four of which dissociate to two ground-state nitrogen atoms with the others also dissociating to two nitrogen atoms, at least one of which is in an excited electronic state. Thirteen of the potential energy curves are represented by the Hulburt–Hirschfeleder potential which is the best general purpose atom–atom potential. This potential depends only on the experimental spectroscopic constants and not on any adjustable parameters. Where spectroscopic constants are unavailable, fits of the Hulburt–Hirschfelder potential to ab initio quantum mechanical results are used for two states and a fit of the Morse potential is used for the other state. The results presented here should be especially useful under conditions where nitrogen atoms are at high temperatures, such as during Space Shuttle re-entry.     

Frequency and Field Dependencies of Susceptibilities of High Tc Superconductor YBCO

The temperature dependence of the first and third harmonic susceptibilities has been measured on a melt-textured YBCO for different frequencies and amplitudes of the ac magnetic field. The behavior of the experimental curves has been compared with the results obtained from the model incorporating both the concepts of Collective Creep and critical state. The predictions of the model for fundamental and third harmonic susceptibilities were consistent with the experimental data.     

Nanosheet-Doped Polymer Composites with High Intrinsic Piezoelectric Properties for Energy Harvesting

<正>Few-layer nanosheets(NSs) of hexagonal boron nitride(h-BN) and molybdenum disulfide(MoS2) display notable piezoelectric properties.Yet,their integration into polymers typically yields non-piezoelectric composites due to NSs' random distribution.We introduce a facile method for fabricating intrinsic piezoelectric composites incorporated with NSs without electric poling.Our innovative process aligns NSs within polyvinyl alcohol polymer,leveraging ice-water interfacial tension,water crystallization thrust,and directional cross-linking during freezing.     

Investigation of the Transport Properties of Coated Conductors and Comparison to Those of YBCO Films Deposited on Single-Crystal Substrates

The existence of non-superconducting zones in YBa₂Cu₃O_7??? (YBCO) films below the transition temperature to the non-resistive state can limit the performances of YBCO devices, especially of coated conductors for power transportation. In this work, we present detailed measurements of the temperature dependence of the surface critical current density of commercial YBCO-coated conductors. We compare our measurements to those carried out by other authors on the same types of samples and to measurements carried out on films deposited on SrTiO₃ single crystals. The existence of a T _c gradient along the YBCO films?? c-axis, probably linked to a gradient in the oxygen content of the films, seems established for all the investigated samples.     

高频高直流迭加Mn-Zn铁氧体材料的性能

高工作频率、低损耗和高直流迭加磁芯是决定电子器件体积和性能的主要因素。在开发出DMR50材料的基础上,采用低温烧结技术,用传统的陶瓷法工艺制备了可使用至3MHz的低功耗高直流迭加Mn-Zn铁氧体材料DMR50B。在3MHz,10mT和100℃时材料的功耗在200kW/m3左右,在700kHz,30mT和100℃时只有20kW/m3左右。材料在100℃时的Bm=430 mT,HDC=100A/m。材料的截止频率fr在4MHz左右,与用斯诺克定律计算出的结果相符合,并可用晶界模型解释。材料优异的性能是由其小于单畴临界尺寸3.8μm的均匀细晶粒结构(D=2.40μm)决定的。     

FeCoSi合金磁粉磷化处理及高频电磁性能

采用快淬甩带和高能球磨工艺制备了成分为Fe70Co12Si18(合金名称中数字为原子百分数)的片状合金磁粉,并用磷酸酒精溶液对磁粉进行了磷化处理.重点研究了磷化前后及不同磷酸浓度对FeCoSi磁粉电磁参数和微波吸收性能的影响.结果 表明,随着磷酸浓度的提高,FeCoSi合金吸波材料的介电常数实部和虚部均减小,磁导率实部...     

Frequency Response of AC Susceptibility in Melt Textured YBCO Superconductors

We have reviewed the scaling relations for frequency dependent AC susceptibility proposed by Lee. et al. and other contributions. Based on vortex glass analysis, we derived a scaling equation for the peak temperature of the imaginary part and ac magnetic field frequency f. The peak temperature T_p is found to obey: T_p = Cf^1/(v(z–1))+T_g, where C is a constant, and T_g is the vortex glass temperature. The scaling relationship was applied to our melt textured YBCO superconductors, which was found in good agreement with the experimental data.     

Frequency Response of AC Susceptibility in Melt Textured YBCO Superconductors

We have reviewed the scaling relations for frequency dependent AC susceptibility proposed by Lee. et al. and other contributions. Based on vortex glass analysis, we derived a scaling equation for the peak temperature of the imaginary part and ac magnetic field frequency f. The peak temperature T_p is found to obey: T_p = Cf^1/(v(z–1))+T_g, where C is a constant, and T_g is the vortex glass temperature. The scaling relationship was applied to our melt textured YBCO superconductors, which was found in good agreement with the experimental data.     

The Infrared Hall Effect in YBCO: Temperature and Frequency Dependence of Hall Scattering

We measure the Hall angle, _H , in YBCO films in the far- and mid-infrared to determine the temperature and frequency dependence of the Hall scattering. Using novel modulation techniques we measure both the Faraday rotation and ellipticity induced by these films in high magnetic fields to deduce the complex conductivity tensor. We observe a strong temperature dependence of the mid-infrared Hall conductivity in sharp contrast to the weak dependence of the longitudinal conductivity. By fitting the frequency dependent normal state Hall angle to a Lorentzian _H () = _H /( _H – i) we find the Hall frequency, _H , is nearly independent of temperature. The Hall scattering rate, _H , is consistent with _H T ² up to 200 K and is remarkably independent of IR frequency suggesting non-Fermi liquid behavior.     

苯胺或邻苯二胺/YBCO杂化材料的性能

采用高温固相法制备钇钡铜氧(YBCO),研磨后超声分散在无水乙醇中得纳米YBCO/乙醇溶胶,再分别掺入苯胺和邻苯二胺,浓缩后真空干燥得有机物/YBCO杂化材料。采用傅里叶红外光谱(FT-IR)、X射线衍射(XRD)、X射线光电子能谱(XPS)和振动样品磁强计(VSM)研究了有机物对YBCO化学组成、物相、元素价态和磁性性能的影响。结果表明,掺入0.05%~5%(质量分数,下同)范围内的苯胺、邻苯二胺不影响YBCO的红外吸收,但显著提高了其XRD衍射峰的强度。两种杂化材料中N-Y之间的相互作用比N-Ba或N-Cu强烈,N元素含量对杂化材料中YBCO的超导转变温度T_c和磁化强度M有显著影响,N元素含量超过1%,T_c明显降低,M_min则相应提高。     

Melt textured YBCO: High trapped fields and superconducting magnetic bearings

Bulk melt textured YBCO samples in the shape of discs were prepared by a top seeding method using Sm-123 crystals. The field distribution of the trapped field on the surface of the samples was measured at 77 K by means of a Hall probe. In single grains with diameter of 20 mm the trapped field reached maximum values up to 0.56 T at 77 K. Investigating the temperature dependence of the maximum trapped field, a value of 5.5 T at 30 K was found for the best sample. At the same temperature, degradation of the trapped field by a factor of about 10 was observed for a second sample after field cooling in a field of 7 T. This degradation is explained by damage to the sample due to magnetic stresses. At the centre of the sample a magnetic stress of 11 MPa is estimated to be responsible for this damage. Additionally YBCO material has been tested in a high speed motor with superconducting magnetic bearings (SMB) in order to demonstrate the passive stabilization properties of SMB. In first tests the shaft rotated with a speed of 12 000 rpm limited by air drag.     

The Microwave Properties of YBCO Photonic Crystal Structure Microstrip

We have fabricated three YBCO microstrip lines. One is conventional microstrip line. Two are etched periodic holes. The thickness for the microstrip lines with and without holes are 0.3 and 0.45μm, respectively. The periodic holes in the microstrip line change the microwave properties more significantly in the case of thin film than thick film. We have also fabricated YBCO photonic bandgap (PBG) microstrip circular disk filter in film with thickness 0.7,μm. The center frequency of the pass band filter is 12.23,GHz. The filter provides band width 1.6% and low insertion loss about ?0.5 d B.     

Effects of Forming Pressure on Physicochemical Properties of YBCO Ceramics

This article details the solid-state synthesis of high-temperature superconducting YBa₂Cu₃O_7?x. Tests were carried out on samples formed at different pressures (200, 400, 600 and 800 MPa) before being annealed under pure oxygen. The X-ray diffraction method showed that, regardless of the forming pressure, the samples contain about 97 wt.% of Y-123 phase. SEM images showed a polycrystalline structure of samples of similar grain size and number of pores (intergranular spaces). The values of critical temperatures (T_c0), determined from magnetoresistance measurements, are about 91.5 K for all samples, and the T_c0 temperatures do not depend on sample-forming pressure. Magnetoresistance measurements have shown that samples formed with higher pressures exhibit smaller changes in T_c0 and superconducting transition width ΔT due to the influence of the H_DC magnetic field, than the samples formed with lower pressures. Values of specific resistance determined by the use of van der Pauw method at 300 K is about 2 mΩcm for all samples. The critical temperatures (T cintra) of grains and critical current densities at 77 K were determined from AC magnetic susceptibility measurements, and they are about 91.6 K and 400 A cm^?2, respectively.     

Intrinsic Inhomogeneity: Application to the High Tc Oxides

Inhomogeneity of the doped compound leads to a possibility of observing a peculiar state that is characterized by normal resistance along with superconducting gap structure and diamagnetism. Such pseudogap state is observed in the high-T_c cuprates.     

Enhancement of Critical Current Density of MgB<Subscript>2</Subscript> by Glutaric Acid Doping: a Simultaneous Improvement on the Intrinsic and Extrinsic Properties

In this study, we report an enhancement of critical current density of bulk MgB₂ superconductors by glutaric acid (C₅H₈O₄) doping. The effects of glutaric acid doping on MgB₂ lattice resulted in a record self-field J _c of the order of 10⁶ A/cm². A simultaneous improvement in the connectivity, pinning force, and H _c2 is the major factor that determined excellent J _c performance. X-ray diffraction analysis showed that samples were single-phase MgB₂ with a minor trace of impurities. A dramatic change in grain morphology and homogeneity in grain distribution was found in the SEM images of doped samples. We observed that homogeneity in grain distribution played a crucial role in the connectivity and the upper critical field (H _c2) of the doped samples. We were able to introduce a new dopant through a two-step mixing approach which is suitable to overcome the degradation of low field and self-field J _c reported for carbon-doped MgB₂ superconductor samples.     

高频脉冲电镀制备Ni—Co／SiC复合镀层及性能研究

采用高频脉冲电源,在镍钴合金衬底上添加SiC,探索制备镍钴合金碳化硅镀层的最佳条件。较佳工艺条件为：频率80kHz,平均电流密度3A／dm^2,占空比0．24,温度为40摄氏度,添加剂为0．5g／L煮沸30min的十二烷基硫酸钠与1g／L糖精钠。通过SEM、XRD测试结果分析高频脉冲各条件对镀层性质的影响原因,研究了脉冲频率、占空比、电流密度、SiC及添加剂对镀层结构、耐腐蚀性的影响。相比相同条件下未添加SiC的镍钴合金镀层,高频脉冲镀层的孔隙率较低,表面致密均匀,耐腐蚀性较好,高频脉冲电镀Ni-Co／SiC合金镀层的耐腐蚀性随着频率的升高而显著增强。