High Temperature Superconductors

High temperature superconductivity, discovered by Bednorz et al. (IBM,1986) remains an active area of research worldwide, because of its high T c. The search for new superconductors has been sparked off after this discovery. High Temperature Superconductors (referred to also as HTS or high-T c superconductors) have found demonstrated application in a vast variety of applications due to its high power density and high efficiency. In areas like power electronics, HTS has been already used for prototypes of power cables, transformers, motors, and fault current limiters. HTS have found profound applications in scientific magnets and filters and in NMR and MRI techniques. However full-fledged commercialization of these applications is not yet observed. This paper briefly describes High Temperature semiconductors, current developments on it and its major applications.

The Pentagon released a 9 page report concerning UFOs and UAPs at the end of June.  Given the brevity of the unclassified version I felt the need to issue my own.

Aviation and defense related technology on our planet has advanced to the point internationally where a whole new set of considerations need to be applied to our monitoring and investigations of unexplained aerial phenomenon.  The way things are currently it looks like we'll all have to take more of a Ground Observer Corps approach to the subject while keeping up on the latest technical developments.

Now that the US Congress has recognized the importance of these issues it is hoped that these matters discussed will now be treated with the seriousness that they deserve.

Eu RoHS Directive for environmental and health concerns have resulted in significant activities to find substitutes for lead-contained solders for microelectronics. The potential candidates such as Sn-Ag 1 and Sn-Ag-Cu 1 eutectic solders with melting temperatures of 221°C and 217°C, respectively are the most prominent solders because of their excellent mechanical properties as compared with that of eutectic Sn-Pb solder2. Other candidates as drop-in replacements for eutectic Sn-Pb solder, such as Sn-In-Zn alloys, may have melting point close to 185°C, though not eutectic, and an acceptable solidification range but have received only limited attention 1. Among the many possible lead-free solder alloy candidates, three commonly used alloys to meet automotive thermal cycling requirement are Sn3.0Ag0.5Cu, Sn3.8AgO.7Cu and Sn4.0Ag0.5Cu. However, industry has found these commonly applied solder alloys to have certain level of ball drop problem which affects production yield, product quality as well as customers satisfaction. This paper reports a study which was conducted on BGA lead-free C5 solder joint system to compare SnAgNiCo solder alloy versus the conventional Sn3.8AgO.7Cu solder alloy, with the objective to strengthen the solder joint so as to eliminate ball drop encountered on the conventional Sn3.8AgO.7Cu solder alloy. This study showed that SnAgNiCo C5 solder system performed better than Sn3.8AgO.7Cu in terms of joint strength and intermetallic brittle mode failure rate. Experimental works were carried out to observe the melting properties, micro structure and elemental analysis that were obtained by Differential Scanning Calorimetry (DSC), SEM and EDX respectively. Shear and pull strength was measured by Dage which is representative of solder joint strength between the C5 solder sphere and Cu/Ni/Au pad finishing. Drop Tests were done per Tray & Packing methods to gauge solder joint performance against impact force. A comprehensive study was done to study the effect of microstructure and interface intermetallic of both solder system at ambient, high temperature storage (HTS) at 150°C for 168 hours and 504 hours, and 6× multiple reflow towards the joint integrity. Microstructure studies on SnAgNiCo solder reveals that formation of rod shape Ag 3Sn IMC distributed across the solder surface helps to act as dispersion hardening that increases the mechanical strength for the SnAgNiCo solder. Through the microstructure study with SEM, it was also found that the addition of Ni and Co into the SnAg solder alloy also helps to minimize growth of grain size and prevent increase in intermetallic thickness after thermal aging. EDX analysis confirmed that in SnAgCu solder/Ni interface, Cu-rich IMC formed on top of the Ni-rich IMC. For SnAgNiCo system, only Ni-rich IMC is found. Therefore, it is highly suspected that the presence of Cu-rich IMC posed a detrimental effect on the joint strength and tends to cause brittle joint failure. Both of the effect is then showed in ball pull result that at Time Zero after assembly and after 6× reflow, SnAgCu solder has 90% and 100% brittle mode failure, where SnAgNiCo solder has 0% and 5% for the respective read points. This result correlates with missing ball responses after packing drop tests which shows no failure for SnAgNiCo alloy. Thus, SnAgNiCo lead-free solder is a potential candidate for lead-free solder joint improvement for overall lead-free package robustness.

http://ieeexplore.ieee.org/xpls/abs_all.jsp?arnumber=4763497&tag=1

Environmental and health concerns have resulted in significant activities to find substitutes for lead-contained solders for microelectronics. The potential candidates such as Sn-Ag1 and Sn-Ag-Cu1 eutectic solders with melting temperatures of 221°C and 217°C, respectively are the most prominent solders because of their excellent mechanical properties as compared with that of eutectic Sn-Pb solder2. Other candidates as drop in replacements for eutectic Pb-Sn solder, such as Sn-In-Zn alloys, may have melting point close to 185°C, though not eutectic, and an acceptable solidification range but have received only limited attention due to various reasons & concerns1. In semiconductor packaging industry, lead-free solders such as Sn-Ag1 and Sn-Ag-Cu1 have been widely applied in mass production of ball grid array products. Such alloys are often used for C5 solder system. However, one of the major challenges is oxidation after thermal processing such as reflow, burn-in, data retention bake and hot temperature testing. A study was conducted on BGA lead-free C5 solder joint system to assess the effect of Germanium (Ge) addition to Sn3.5Ag and Sn3.8Ag0.7Cu solder alloy. The main objective of this study is to find a way to resolve solder surface oxidation after thermal processes, while determining if there's any adverse effect on the solder joint by Ge addition. Experimental works were carried out to observe the melting properties and solder surface morphology by Differential Scanning Calorimetry (DSC) and SEM. Solder surface oxidation was measured by EDX. Shear and pull strength was measured by Dage which is representative of the intermetallic (IMC) strength between the C5 solder sphere and Cu/Ni/Au pad finishing. Solderability test was conducted per Jedec standard. Tray and Packaging Drop Tests were done to gauge solder joint performance against impact force. A comprehensive study was done to study the effect of microstructure and interface intermetallic of both solder system at ambient, high temperature storage (HTS) at 150°C for 24, 48, 96, 168, 504 and 2000 hours and multiple reflow of 1x, 2x, 3x, 6x towards the joint integrity. Overall, Ge doped alloys had significantly higher ball shear and ball pull strength. EPMA microstructure analysis after cross-sectioning on bulk solder and IMC revealed traces of Ge that contributed to the significant increase in ball shear and ball pull strength, while did not cause any bulk solder and IMC morphology changes. Solderability test passed. Drop tests had comparable performance as non Ge doped alloys. In conclusion, addition of Ge in Sn3.5Ag and Sn3.8Ag0.7Cu lead-free solder alloys is able to resolve surface oxidation problem after thermal processing, with improvement in solder joint strength for overall lead-free package robustness.

http://ieeexplore.ieee.org/xpls/abs_all.jsp?arnumber=5416568&tag=1

Hot wall technique was used to grow block single crystal films of Bi 2 Te 3 and solid solutions of Bi 0.5 Sb 1.5 Te 3 on mica (muscovite) substrates. X-ray diffraction studies demonstrated that the crystalline c-axis in the films was normal to the substrate plane. Seebeck coefficient, electrical conductivity and magnetoresistivity tensor components were measured at various orientations of magnetic and electric fields in the temperature interval 77-300 K. Scattering mechanism of charge carriers in the films was studied using temperature dependences of the degeneracy parameter and the Seebeck coefficient in terms of a many-valley model of energy spectrum. Obtained results have shown that the effective scattering parameter is considerably different from the value specific for an acoustic scattering of charge carriers in the weakly degenerate films due to an additional scattering of charge carriers on interface and interctystallite boundaries. These features of charge carrier scattering are supposed to affect electronic transport in the films and enhance figure of merit.

We construct a tool for the calculation and visualization of Moiré bands belonging to the broad family of arbitrarily stacked twisted N + M multilayer graphene. We present the underlying k • p model of twisted bilayer graphene and extend it to twisted N + M multilayer

—The ever increasing need for cost-efficient, high-density power transmission brought to the fore applied superconductivity as an alternative worth investigating. Especially , high-temperature superconducting (HTS) dc cables emerge as a promising solution for bulk power transmission and their use in the near future is expected to be increased. HTS cables have the special characteristic of varying performance under different critical conditions, especially under different operating temperatures. Therefore, detailed thermal analysis of HTS cables representing thermodynamics and heat transfer for varying length and time is of significant importance. The analytical mathematical formulation presented in this paper solves heat transfer equations for a two-dimensional axisymmetric cable model and identifies temperature distribution over length and time. The analysis is conducted on a bipolar cable suggested by the Electric Power Research Institute for long-distance HTS dc transmission, while both steady-state and transient scenarios are examined.

In superconducting magnetic levitation systems, interaction models between a high temperature superconductor and a permanent magnet are useful to analyze the dynamics of the levitated system. In this study, stiffness equations of a superconducting levitation system using a disk and a ring permanent are obtained using frozen image concept. The variation of the stiffness has been analyzed for vertical movements of the PMs. For engineering applications, accuracy of such models should be tested experimentally. An experimental PM-HTS setup has been built to verify the obtained models for different cooling height conditions. Levitation forces computed using the frozen image approach for the disk and ring PMs are converged to the experimental results when the cooling heights are smaller values.

Topic: Superconductors and their real life applications as a theory of knowledge
Type: Essay
Subject: Physics
Academic Level: Undergraduate 1-2
Style: MLA
Language: English (U.S)
Number of Pages: 6 (double-spaced, Times New Roman, Font 12) Number of sources: 5
Made by https://writersperhour.com

Task Details:
1) Define superconductors;
2) Discuss their properties;
3) Describe how they can be utilized to solve various real life problems.

Abstract—We explore heat transport as a thermodynamic property of mercury doped cuprate superconductors at the transition temperature. Mercury doped cuprate superconductors have higher transition temperature and hence they could be the best materials for making room temperature superconductors. It was observed that for higher critical temperatures to be achieved, the heat currents flow in these materials should be reduced since heat currents reduce the critical temperature of the superconductors. It is projected that, for the critical temperature of 300K to be achieved, the heat current flow in Hg1201, Hg1212 and Hg1223 should be 95J/s, 242J/s and 414J/s respectively. Higher values of upper critical magnetic fields promotes heat current flow in the superconductors, therefore higher critical temperatures needs low upper critical fields. At low critical temperatures the thermal diffusivity in the superconductors is very low indicating that, heat diffuses on the surface of the material very slowly. However, when the critical temperatures of the materials is increased towards the room temperature thermal diffusivity increases exponentially therefore higher critical temperature can only be achieved if thermal diffusivity in the superconducting materials is higher and the heat current is lowered.

Your article is protected by copyright and all rights are held exclusively by Springer Science +Business Media New York. This e-offprint is for personal use only and shall not be selfarchived in electronic repositories. If you wish to self-archive your article, please use the accepted manuscript version for posting on your own website. You may further deposit the accepted manuscript version in any repository, provided it is only made publicly available 12 months after official publication or later and provided acknowledgement is given to the original source of publication and a link is inserted to the published article on Springer's website. The link must be accompanied by the following text: "The final publication is available at link.springer.com".

A new, theoretical approach to macroscopic quantum coherence and superconduc-tivity in the p-type (hole doped) cuprates is proposed. The theory includes mechanisms to account for e-pair coupling in the superconducting and pseudogap phases and their inter relations observed in these materials. Electron pair coupling in the superconducting phase is facilitated by local quantum potentials created by static dopants in a mechanism which explains experimentally observed optimal doping levels and the associated peak in critical temperature. By contrast, evidence suggests that electrons contributing to the pseudogap are predominantly coupled by fractal spin waves (fractons) induced by the fractal arrangement of dopants. On another level, the theory offers new insights into the emergence of a macro-scopic quantum potential generated by a fractal distribution of dopants. This, in turn, leads to the emergence of coherent, macroscopic spin waves and a second associated macroscopic quantum potential, possibly supported by charge order. These quantum potentials play two key roles. The first involves the transition of an expected diffu-sive process (normally associated with Anderson localization) in fractal networks, into e-pair coherence. The second involves the facilitation of tunnelling between localized e-pairs. These combined effects lead to the merger of the super conducting and pseudo gap phases into a single coherent condensate at optimal doping. The underlying theory relating to the diffusion to quantum transition is supported by Coherent Random Lasing, which can be explained using an analogous approach. As a final step, an experimental program is outlined to validate the theory and suggests a new approach to increase the stability of electron pair condensates at higher temperatures.

A summary of the current state of the art in MEM switches using high T C superconducting transmission line elements is presented. The most significant advantages of the MEM technology are the low mass and volume of the implemented devices. On the other hand one of the principal drawbacks of the room temperature MEM rf-switches are their losses. These are primarily resistive losses in the waveguide structure and contacts and are large due to the dimensions required (on the order of 100 µm wide by 3 µm thick). This places serious limitations on their use in noise/loss sensitive applications. The use of superconductors for the waveguide elements in MEM switches can reduce these losses very significantly (several orders of magnitude are not unusual in devices with identical dimensions). Adding a high dielectric constant insulator to the switch can also help shrink the necessary dimensions or extend the low frequency response of the switch. INTRODUCTION In this work, we summarize the results of our efforts to date on transitioning a rf micro-electro-mechanical (MEM) switch from normal metals to su-perconductors. The motivation of this was to reduce losses to an absolute minimum. This would enable the use of MEM switches in low noise, frequency agile , applications where low system intermodulation products and as high a third-order intermodulation intercept point (IP3) as possible are required. In order for the reader to place the work in proper perspective and benefit as much as possible from the historical body of work on these devices we have included a general background survey of the literature along with the most recent relevant results from our group on the superconducting rf MEM switch. This background section is followed by an overview of the various processing and fabrication techniques that we have used in our work to date and a discussion of the reasons for the choices made. The section on results presents the most recent results which we have obtained to date and these are discussed in terms of their impact on fabrication, yield and device performance. The final segment of this paper presents an outline of where we see this work heading and what its potential may be. BACKGROUND

The two-component model of high temperature superconductors in its real space version has been solved using Bogoliubov-de Gennes equations. The disorder in the electron and boson subsystem has been taken into account. It strongly modifies the superconducting properties and leads to local variations of the gap parameter and density of states. The assumption that the impurities mainly modify boson energies offers natural explanation of the puzzling positive correlation between the positions of impurities and the values of the order parameter found in the scanning tunnelling microscopy experiments.

In this paper contact and non-contact techniques for the measurement of transition temperature of high-Tc superconductors is described. A non contact method has been developed for measurement of transition temperature (Tc) of high-Tc superconductors. This technique is based on the measurement of change in the resonance frequency of a tank circuit with temperature. The applicability of this method in obtaining Tc of a YBCO thin film and a small piece of YBCO bulk sample is demonstrated. This technique can be effectively used for characterizing the samples of irregular shape and small dimensions where it is difficult to make proper contacts required for resistivity measurements.

Silver (Ag) nanoparticles were added into (Cu 0.5 Tl 0.5 )Ba 2 Ca 2 Cu 3 O 10Àd (CuTl-1223) high T c superconducting matrix to get (Ag) x /CuTl-1223, x ¼ 0, 0.5, 1.0, 2.0, and 4 wt. %, nanosuperconductor composites. The activation energy {U (eV)} and zero resistivity critical temperature {T c (0)} were increased with increasing contents of Ag nanoparticles in (CuTl-1223) phase up to x ¼ 2.0 wt. %. The increase of activation energy is most probably due to interaction of carriers with the metallic Ag nanoparticles present at grain boundaries of the host CuTl-1223 superconducting matrix. The systematic increase in T c (0) and gradual decrease in normal state resistivity {q 300 K (X cm)} may be due to improved inter-grains coupling by filling up the voids and pores with the inclusion of metallic Ag nanoparticles at the grain-boundaries. There are two possible mechanisms associated with the inclusion of Ag nanoparticles, one is the formation of nonsuperconducting regions causing the increase of activation energy and other (dominating) is the improved inter-grains connectivity promoting T c (0). The microscopic parameters (i.e., zero temperature coherence length along c-axis {n c (0)}, inter-layer coupling (J), inter-grain coupling (a), etc.) deduced from the fluctuation induced conductivity analysis reasonably explained the experimental findings. V C 2014 AIP Publishing LLC. [http://dx.

The pinning strength of the Ag-sheathed Bi(Pb)-Sr-Ca-Cu-O tapes with the addition of magnetic nanorod y-Fe2(\ is studied using the exponent n values obtained from power law current-electric field (I-E) characteristics. The starting composition of the y-Fe2O3 added samples is Bi1 6PbsaSr2Ca2Cu3Oi6-(7-Fe2O3)6s1. The rate of decrease of n values in applied fields for the tapes with nano-7-Fe2O3 is found lower than the tapes without nano-7-Fe2O3. This indicates that the pinning strength for the tapes with nano 7-Fe2O3 is relatively higher than the tapes prepared without nano y-Fe2O3. The results are supported by two conventional methods which are normally used to compare the pinning strength of superconductor tapes. Magnetic impurities generally suppress superconductivity. However, our study shows that magnetic nanorod y-Fe2(\ enhanced the pinning strength of Ag-sheathed Bi-Sr-Ca-Cu-O superconductor tapes. This is consistent with previous calculations on frozen flux superconductor with magnetic nanorod as pinning centers.

In this work, the effect of alumina (α-Al2O3)
nanoparticle addition on the phase formation and superconducting
properties of Bi1.6Pb0.4Sr2Ca2Cu3O10−y ((Bi,Pb)-
2223) system has been investigated. Six samples with different
alumina nanoparticle contents (0.0, 0.1, 0.2, 0.3, 0.5,
and 1 wt % of the sample’s total mass) were prepared by
conventional solid-state reaction. X-ray diffraction (XRD)
and scanning electron microscopy (SEM) methods have
been used to study phase formation and microstructure of
the prepared samples, respectively. Also, the electrical resistivity
and critical current density of the prepared samples
were measured by the four-probe technique. AC susceptibility
of the samples has been measured by an LCR meter.
XRD results showed that the addition of small amounts of
the alumina nanoparticles improve (Bi,Pb)-2223 phase
formation significantly. Temperature dependency of AC
susceptibility measurements revealed that the addition of α-
Al2O3 nanoparticles improve intergranular coupling.
The I-V measurements show that the critical current density of
samples increased from about 36 A/cm2 for the alumina
nanoparticle-free sample to about 107 A/cm2 for the sample
with 0.5 wt % α-Al2O3 nanoparticles.

Tin oxide (SnO 2) nano particle thin film has been deposited by spray pyrolysis technique using ultrasonic nebulizer of chloride solution (SnCl 2 .2H 2 O) over the glass substrate. An aqueous chloride solution was converted into a mist form of vapor using ultrasonic nebulizer and deposited over the heated substrate at temperature 300 ± 10 0 C. The XRD and SEM result shows a regular, smooth, excellent morphology and also found polycrystalline in nature which is also evident in XRD analysis. The average grain size of SnO 2 particles were found to be in the range of 25 nm to 35 nm depending on the allowed concentration of chloride solution which is calculated from XRD plot using Debye-Sherror formula. The average thickness of the as prepared film was measured of the order of 120 nm. The optical transmittance properties of the SnO 2 thin films have been also measured. The films exhibited an average transmittance value of 93% in recorded range of wavelength. Finally the ethanol gas sensing properties of the thin film (0.1 M concentration) was performed and discussed in detail.

The pressure-induced volume collapse of the Fe-based superconductor CaFe2As2 (and others) is commonly ascribed to the formation of As–As bonds with length < 3 Å. We show the situation is more complicated by applying the chemical pressure effect to CaFe2As2 through substitution of Fe with Rh and Sr with Ca. Detailed x-ray scattering and spectroscopy data reveals that adding Sr suppresses the first-order volume collapse and stabilizes magnetism even when the As–As bond length is < 3 Å. Density-functional theory calculations reveal that the volume collapse occurs only when the covalent bonding of the Fe 3d and As 4p states win out over their exchange splitting, which constricts the FeAs planes and forms As–As bonds as a byproduct.

We investigate near-field infrared spectroscopy and superfluid polariton imaging experiments on conventional and unconventional superconductors. Our modeling shows that near-field spectroscopy can measure the magnitude of the superconducting energy gap in Bardeen-Cooper-Schrieffer-like superconductors with nanoscale spatial resolution. We demonstrate how the same technique can measure the c-axis plasma frequency, and thus the c-axis superfluid density, of layered unconventional superconductors with a similar spatial resolution. Our modeling also shows that near-field techniques can image superfluid surface mode interference patterns near physical and electronic boundaries. We describe how these images can be used to extract the collective mode dispersion of anisotropic superconductors with sub-diffractional spatial resolution. arXiv:1407.6072v1 [cond-mat.supr-con]

The ever increasing need for cost-efficient, highdensity power transmission brought to the fore applied superconductivity as an alternative worth investigating. Especially, high-temperature superconducting (HTS) dc cables emerge as a promising solution for bulk power transmission and their use in the near future is expected to be increased. HTS cables have the special characteristic of varying performance under different critical conditions, especially under different operating temperatures. Therefore, detailed thermal analysis of HTS cables representing thermodynamics and heat transfer for varying length and time is of significant importance. The analytical mathematical formulation presented in this paper solves heat transfer equations for a two-dimensional axisymmetric cable model and identifies temperature distribution over length and time. The analysis is conducted on a bipolar cable suggested by the Electric Power Research Institute for long-distance HTS dc transmission, while both steady-state and transient scenarios are examined.

In earlier work a capacitively shunted superconducting
MicroElectroMechanical (MEM) switch has been
designed and fabricated. The switch is composed of high temperature superconducting (HTS) YBa2Cu3O7 coplanar waveguide structure with a gold bridge membrane suspended above an area of the center conductor covered with BaTiO3 dielectric. The switch demonstrated an insertion loss of less than 0.007 dB with 30 dB isolation at 3 GHz. These switches have been shown to be viable, however, issues of the dielectric material deposition and
gold bridge release process posed limitations on the yield and switch cycling. In this work we report on the issues encountered and improvements made in the development of HTS MEMS switches for use in tunable RF devices.

Superconducting Cu0.5Tl0.5Ba2(Ca2−x Be x ) (Cu2 Ti)O10−δ (x = 0, 0.5, and 1.0) samples were synthesized using a two-step solid-state reaction method. Superconducting properties were suppressed after Be substitution at Ca sites in these samples. Variation of oxygen phonon modes after Be doping was according to the masses of Ti (47.90 amu) and Cu (63.54 amu)atoms in conducting planes. Decrease in microscopic superconducting parameters deduced from excess conductivity analysis was attributed to an-harmonic oscillations, which have reduced Cooper pairs density from a desired level for optimum superconductivity.

The theory of thermal conductivity of high temperature superconductors (HTS) based on electron and phonon line width (life times) formulation is developed with Quantum dynamical approach of Green's function. The frequency line width is observed as an extremely sensitive quantity in the transport phenomena of HTS as a collection of large number of scattering processes. The role of resonance scattering and electron-phonon interaction processes is found to be most prominent near critical temperature. The theory successfully explains the spectacular behaviour of high T c superconductors in the vicinity of transition temperature. A successful agreement between theory and experiment has been obtained by analyzing the thermal conductivity data for the sample La 1.8 Sr 0.2 Cu O 4 in the temperature range 0 − 200K . The theory is equally and successfully applicable to all other high T c superconductors.

... The Corresponding Author , Yazan Hijazi a , Mariya Brzhezinskaya a , Albert Bogozi a , Julien Noel a , Yuriy A. Vlasov a and Grover L. Larkins ... Another process enhancement is that, in order to smooth out the sharp PMGI edges after patterning, a reflow is performed using a 15 s ...

A gradiometer based on two ceramic superconducting quantum interferometers operating at liquid nitrogen temperature has been developed. The minimum gradient sensitivity is 3.1 X lo-'* T/mHz'/* in a white noise region. The minimum damping coefficient of the external disturbing factors is K = 32.

To explore the limits of layer wound (RE)Ba2Cu3O7-x (REBCO, RE = Rare Earth) coils in a high magnetic field environment &gt; 30 T, a series of small insert coils have been built and characterized in background fields. One of the coils repeatedly reached 35.4 T using a single ~100 m length of REBCO tape wet wound with epoxy and nested in a 31 T background magnet. The coil was quenched safely several times without degradation. Contributing to the success of this coil was the introduction of a thin polyester film that surrounded the conductor. This approach introduces a weak circumferential plane in the coil pack that prevents conductor delamination that has caused degradation of several epoxy impregnated coils previously made by this and other groups.

Samples of superconducting compounds were prepared by a solid-state reaction technique in a sealed quartz tube under normal pressure. The impact of the compound on the electrical properties has been studied using the electrical resistance measurements of the samples as a function of temperature. The obtained results appear that an enhancement in the phase formation, and the superconducting transition temperature T c were improved. It may be due to the decreasing of the magnetic impurities or the delocalisation of carriers which resulted in the enhancement of the density of mobile carriers in the conducting CuO 2 planes.

Keywords: (Cu 0.5 Tl 0.5)Ba 2 Ca 2 (Cu 3Àx Ti x)O 10Àd superconductors Transition metals doping Increased T c Suppressed density of phonons a b s t r a c t Ti-doped (Cu 0.5 Tl 0.5)Ba 2 Ca 2 (Cu 3Àx Ti x)O 10Àd (x = 0, 0.25, 0.50, 0.75) samples have been synthesized at 860°C by following two step solid state reaction methods and studied their superconducting properties by X-ray diffraction, resistivity, ac-susceptibility, FTIR absorption measurements. Ti-doped samples have shown orthorhombic crystal structure and the cell parameters increase with the increase of Ti-contents. The T c (R = 0) and onset of diamagnetism increases with increase Ti-doping in the final compound. The magnitude of superconductivity, however, increases for Ti-doping of y = 0.25, 0.75. The numbers of carriers in the conducting planes have been optimized by carrying out post-annealing of the samples in oxygen atmosphere. After the post-annealing the T c (R = 0) is improved in un-doped samples whereas it is suppressed in all Ti-doped samples. After post annealing in oxygen atmosphere, the magnitude of super-conductivity (measured in emu/gm.Os) remains unchanged in un-doped samples whereas it is suppressed in all Ti-doped samples. In FTIR absorption measurements, the CuO 2 /TiO 2 planar oxygen modes are slightly hardened in Ti-doped samples. The most likely reason for the hardening of the planar oxygen modes is decrease in the mass of Ti (47.90 amu) in comparison with Cu (63.54 amu) atoms; the atoms with lighter-mass vibrate at higher frequency. It is most likely that the existence of atoms of different masses in CuO 2 /TiO 2 planes may suppress the density of phonon population due to setting-in of an-harmonic oscillations. The phonons of harmonic oscillation with wave vector q interact with q 0 of an-harmonic oscillation and produce a new phonon with wave vector Q. The phonons with wave vector Q do not contribute in the Cooper-pair formation. It is most likely that a decrease in the population of desired phonons required for higher T c occurs that in turn suppress the density of the Cooper-pair which in turn promote a decrease in the magnitude of superconductivity. These studies indicate the essential role of electron-phonons-interactions in the mechanism of high T c superconductivity.

—Superconducting dc systems present a promising alternative for power transmission. Advantages of dc transmission , such as enhanced controllability combined with the loss-less characteristic of superconductivity result in an advantageous mixture, especially for bulk power transmission. This paper presents alternative concepts for integration of superconducting dc links within conventional ac or dc grids. Focus is given on how a superconducting dc link could coexist with conventional transmission systems in order its advantages to be exploited, while its operation is secured. Appropriate system configurations, cable models, advantages of superconducting transmission, such as reduction of transmission losses as well as modeling feasibility are analytically discussed. A selection of the grid integration scenarios is tested under both steady-state as well as fault conditions.

—Applications of superconductivity in power systems, especially in transmission systems, is a subject of study since 1970s. Superconductors' advantage of providing an almost loss-less transmission system, due to the non-existence of joule losses, has been highlighted during the last decades. However, the absence of resistance and its ability to damp oscillatory phenomena, which in case of a superconducting transmission system can be long-lasting, can result in a system prone to instability. Therefore, persisting oscillations that can be attributable to a variety of reasons (ac or dc faults, voltage sags, rapid load changes, switching actions etc.) need to be damped by applying other methods. This paper introduces a method to provide damping in a superconducting two-terminal voltage-source converter (VSC) transmission system by incorporating suitably-dimensioned snub-ber circuits. The method is generally used in other types of application but, in this paper, its suitability is tested on a specific case reference model built in MATLAB/Simulink R , as well as under different oscillation causes, i.e. dc and ac faults.

We report on the fabrication of ribbon-like thin films on flat sputter-deposited Ag films whose surface smoothness remained within the order of tens of nm. It was found that the addition of Pb to the starting material improves the wettability of molten phase and facilitates the growth of Bi-2212 ribbon-like thin films on a flat Ag substrate, and that the increase of Ca and Cu in starting material suppresses the intergrowth of the Bi-2201 phase in ribbon-like thin films. By using (Bi,Pb)-2246 powders, with nominal composition of Bi 1:6 Pb 0:4 Sr 1:6 Ca 3:2 Cu 4:8 O y , as the starting material, the superconducting Bi-2212 ribbon-like thin films with an onset T c at 74 K on a very flat Ag substrate were successfully synthesized. Additionally, the growth mechanism of ribbon-like thin films on flat Ag substrate was investigated by in situ high temperature microscope observation.

Superconducting Cu 0.5 Tl 0.5 Ba 2 (Ca 2−x Be x )(Cu 2 Ti) O 10−δ (x = 0, 0.5, and 1.0) samples were synthesized using a two-step solid-state reaction method. Superconducting properties were suppressed after Be substitution at Ca sites in these samples. Variation of oxygen phonon modes after Be doping was according to the masses of Ti (47.90 amu) and Cu (63.54 amu)atoms in conducting planes. Decrease in microscopic superconducting parameters deduced from excess conductivity analysis was attributed to an-harmonic oscillations, which have reduced Cooper pairs density from a desired level for optimum superconductivity.

High performance high T c superconductor based series micro electromechanical system (MEMs) switches have been utilized to switch between a bandpass hairpin filter, center frequency f 0 = 2.5 GHz, and BW of 250 MHz, and a through transmission line. This was accomplished with four switches actuated in pairs, one pair at a time. When the first pair is actuated, the through transmission line is capacitively connected between the input and output ports; accordingly, the system behaves as a throughline. When the second pair of switches is actuated, the bandpass filter is coupled to the input and output ports; thus a corresponding bandpass response is obtained. The design is implemented on a YBa 2 Cu 3 O 7 thin film deposited on a 15 mm · 15 mm LaAlO 3 substrate by pulsed laser deposition. BaTiO 3 deposited by RF magnetron sputtering is utilized as the insulation layer at the switching points of contact. The advantages and issues of this structure and its fabrication details are discussed along with simulations and experimental data.

The high-T c superconducting (HTS) dynamo is a promising device that can inject large DC supercurrents into a closed superconducting circuit. This is particularly attractive to energise HTS coils in NMR/MRI magnets and superconducting rotating machines without the need for connection to a power supply via current leads. It is only very recently that quantitatively accurate, predictive models have been developed which are capable of analysing HTS dynamos and explain their underlying physical mechanism. In this work, we propose to use the HTS dynamo as a new benchmark problem for the HTS modelling community. The benchmark geometry consists of a permanent magnet rotating past a stationary HTS coated-conductor wire in the open-circuit configuration, assuming for simplicity the 2D (infinitely long) case. Despite this geometric simplicity the solution is complex, comprising time-varying spatially-inhomogeneous currents and fields throughout the superconducting volume. In this work, this b...

Current-voltage (I-V) characteristics of Tl2Ba2CaCu2O8 thin films in zero magnetic field are measured and analyzed with the conventional Kosterlitz-Thouless-Berezinskii (KTB) approach, dynamic scaling approach and finite-size scaling approach, respectively. It is found from these results that the I-V relation is determined by the vortex-unbinding mechanism with the KTB dynamic critical exponent z = 2. On the other hand, the evidence of finite-size effect is also found, which blurs the feature of a phase transition.

The effect of partial replacement of R = KMnO 4 in Tl 2 Ba 2 Ca(Cu 1-x R x) 2 O δ+6 (TBCCO or Tl-2212) superconductor samples with x = 0.0, 0.05 and 0.1 was investigated. The samples were prepared by standard solid-state reaction methods in a sealed quartz tube under normal pressure. The investigation consisted of X-ray diffraction (XRD) and DC electrical resistance measurements under fixed magnetic field. Transport measurements indicated that the superconducting transition temperature values of the samples depend on the amount of the added KMnO 4. The values of T c and T o of the samples decreased with increasing KMnO 4 content. The possible reasons for the observed degradation in the superconducting and microstructure properties of Tl-2212 due to the addition of KMnO 4 were discussed.

In earlier work a capacitively shunted superconducting MicroElectroMechanical (MEM) switch has been designed and fabricated. The switch is composed of high temperature superconducting (HTS) YBa 2 Cu 3 O 7 coplanar waveguide structure with a gold bridge membrane suspended above an area of the center conductor covered with BaTiO 3 dielectric. The switch demonstrated an insertion loss of less than 0.007 dB with 30 dB isolation at 3 GHz. These switches have been shown to be viable, however, issues of the dielectric material deposition and gold bridge release process posed limitations on the yield and switch cycling. In this work we report on the issues encountered and improvements made in the development of HTS MEMS switches for use in tunable RF devices.