Bi Sr Ca Research Articles

Relationship between the induced voltage of a rotor bar and the rotation characteristics of a high-temperature superconducting induction motor

Although high-temperature superconducting induction motors have a simple structure, they are distinguished by their high efficiency and high power density. However, an accurate theoretical model that defines the primary electrical characteristics controlling the motor has not been established because of the nonlinear characteristics of high-temperature superconducting squirrel-cage rotor winding. As part of establishing such a model, an experiment was conducted to analyze the relationship between the induced voltage of the rotor bar in a high-temperature superconducting squirrel-cage rotor winding and stator-side quantities (voltage and transport current), as well as its rotation characteristics. A subject was a 1.5 kW class induction motor using Bi–Sr–Ca–Cu–O high-temperature superconducting rotor bars and the experiment was performed at a temperature and a frequency of 77 K and 60 Hz, respectively. The induced voltages of the rotor bars were measured by applying a rotating magnetic field and exhibited a distorted waveform characterized by a third-order harmonic in a magnetic flux flow state. Despite the distorted voltage waveform of the rotor bar, the stator transport current responsible for driving the induction motor remained unaffected and the motor initiated rotation in a slip rotation mode. From the above results, it was experimentally clarified that a stator voltage exceeding the critical current of the rotor bar must be applied when starting the induction motor. It was also shown that the rotor bar can be regarded as a constant resistance for a constant effective value of the stator current when transitioning the motor into a slip rotation state.

Growth and characterization of Bi2Sr2Ca1–x Y x Cu2O8+δ single-crystal whiskers

Substitution of Y for Ca in the Bi2Sr2CaCu2O8+δ (Bi-2212) system is known to effectively change the hole carrier density. In this paper, we report the growth and characterization of Y-substituted Bi-2212 whisker crystals. The evaluated Y content in the whiskers increased as we increased the nominal Y-ratio in the Bi–Sr–Ca–Y–Cu–Te precursor. The X-ray diffraction patterns of whiskers aligned on a glass plate only showed (00l) Bragg peaks of the Bi-2212 phase, indicating that the grown whiskers are single crystalline. The c-axis lattice parameter showed a monotonic decrease with Y-substitution. The resistivity of Y-substituted whiskers showed a systematic decrease in superconducting transition temperature and an increase in normal resistivity, suggesting that the hole carrier density was controlled via Y-substitution. Based on these results, we propose that Bi-2212 with various carrier concentrations can be easily obtained by growing Y-substituted whiskers. Furthermore, such whiskers with controlled T c might be useful for microelectronic applications such as terahertz oscillators.

Nonlinear properties of multiphase high-temperature superconductors of the Bi–Sr–Ca–Cu–O system in the temperature range of the superconducting transition

The nonlinear characteristics of high-temperature superconductors of the Bi–Sr–Ca–Cu–O system have been experimentally investigated in the temperature range of the superconducting transition under the influence of a harmonic alternating magnetic field. The effect of the generation of odd harmonics in the signal of response to a harmonic alternating magnetic field for multiphase high-temperature superconductors containing regions with different values of the critical temperature in their bulk has been observed for the first time. The mechanism of harmonic generation in a superconductor in the resistive state, which is associated with the switch effect, i.e., with the redistribution of eddy current density between the local regions of the superconductor, has been considered.

Specifics of third-harmonic generation in Bi–Sr–Ca–Cu–O superconductors in the region of superconducting transition temperatures

The specifics of third-harmonic generation in Bi–Sr–Ca–Cu–O two-phase superconductors are studied. It is shown that the emergence of a maximum in the temperature dependence of the third-harmonic voltage in the region of superconducting transition temperatures is associated with the redistribution of the eddy current in the bulk of the semiconductor between its regions with different superconducting parameters (critical current and critical temperature).

Photoconductivity effects in mixed-phase BSCCO whiskers

We report on combined photoconductivity and annealing experiments in whisker-like crystals of the Bi–Sr–Ca–Cu–O (BSCCO) high-Tc superconductor. Both single-phase Bi2Sr2CaCu2O8+δ (Bi-2212) samples and crystals of the mixed phases Bi2Sr2Ca2Cu3O10+x (Bi-2223)/Bi-2212 have been subjected to annealing treatments at 90 °C in air in a few hours steps, up to a maximum total annealing time of 47 h. At every step, samples have been characterized by means of electrical resistance versus temperature (R versus T) and resistance versus time at fixed temperature (R versus t) measurements, both in the dark and under illumination with a UV–Vis halogen arc lamp. A careful comparison of the results from the two techniques has shown that, while for single-phase samples no effect is recorded, for mixed-phase samples an enhancement in the conductivity that increases with increasing annealing time is induced by the light at the nominal temperature T = 100 K, i.e. at an intermediate temperature between the critical temperatures of the two phases. A simple pseudo-1D model based on the Kudinov’s scheme (Kudinov et al, 1993 Phys. Rev. B 47 9017–28) has been developed to account for the observed effects, which is based on the existence of Bi-2223 filaments embedded in the Bi-2212 matrix and on the presence of electronically active defects at their interfaces. This model reproduces fairly well the photoconductive experimental results and shows that the length of the Bi-2223 filaments decreases and the number of defects increases with increasing annealing time.

Enlargement of the Field of View and Maintenance of a High Signal-to-Noise Ratio Using a Two-Element High-Tc Superconducting Array in a 3T MRI

This study examines the enlargement of the field of view (FOV) and the maintenance of a high signal-to-noise ratio (SNR) through the use of two high-temperature superconducting (HTS) resonators in a 3T MRI. Two Bi2Sr2Ca2Cu3Ox (Bi-2223) surface resonators, each of 4-cm diameter, were used in a 3T MRI. Professionally made copper resonators operate at 300 K, but each Bi-2223 resonator, operated at 77 K and demonstrated a 3.75 fold increase in SNR gain. For the same scanning time, the SNR of the images of a rat’s brain and back, obtained using two small Bi-2223 surface resonators, was higher than that obtained using a single 8-cm surface resonator.

Whole Body Screening Using High-Temperature Superconducting MR Volume Resonators: Mice Studies

High temperature superconducting (HTS) surface resonators have been used as a low loss RF receiver resonator for improving magnetic resonance imaging image quality. However, the application of HTS surface resonators is significantly limited by their filling factor. To maximize the filling factor, it is desirable to have the RF resonator wrapped around the sample so that more nuclear magnetic dipoles can contribute to the signal. In this study, a whole new Bi2Sr2Ca2Cu2O3 (Bi-2223) superconducting saddle resonator (width of 5 cm and length of 8 cm) was designed for the magnetic resonance image of a mouse's whole body in Bruker 3 T MRI system. The experiment was conducted with a professionally-made copper saddle resonator and a Bi-2223 saddle resonator to show the difference. Signal-to-noise ratio (SNR) with the HTS saddle resonator at 77 K was 2.1 and 2 folds higher than that of the copper saddle resonator at 300 K for a phantom and an in-vivo mice whole body imaging. Testing results were in accordance with predicted ones, and the difference between the predicted SNR gains and measured SNR gains were 2.4%∼2.7%. In summary, with this HTS saddle system, a mouse's whole body can be imaged in one scan and could reach a high SNR due to a 2 folds SNR gain over the professionally-made prototype of copper saddle resonator at 300 K. The use of HTS saddle resonator not only improves SNR but also enables a mouse's whole body screen in one scan.

Stoichiometric transfer by infrared pulsed laser deposition of y-doped Bi–Sr–Ca–Cu–O investigated using time-resolved optical emission spectroscopy

Pulsed laser deposition of Bi2Sr2Ca1–x YxCu2O8+δ (Bi-22Y2) with x = 0, 0.30, and 0.49 on an MgO (100) substrate was conducted using a Q-switched 1064 nm Nd:YAG laser The laser-produced plasma (LPP) emission was collected during the deposition. Time-resolved optical emission spectroscopy reveals that the plasma plume consists of neutral atoms and ions. SEM images indicate that clusters of correct stoichiometry arrive on the substrate surface. Our result confirms that IR PLD transfers material stoichiometrically.

Enhancement of superconductivity in LFZ-grown BSCCO fibres by steeper axial temperature gradients

Laser floating zone (LFZ) method was employed to grow superconducting polycrystalline Bi–Sr–Ca–Cu–O fibres of 2:2:1:2 nominal composition with two different diameters (1.75 and 2.50mm). The temperature profile at the solid/liquid interface was calculated along the fibre radii from estimations of the heat transfer coefficient and thermal conductivity of the fibres. Values of temperature gradient G=3.17×105Km−1 and G=2.65×105Km−1 at the fibre centre were obtained for the thinner and the thicker fibres, respectively. Growth under a steep temperature gradient has significant consequences on the microstructure of the thinner fibres: an improved texture and the absence of the copper-free Bix(Sr,Ca)yOz secondary phase. These features lead to the superior transport properties of the thinner fibres that present a higher value of critical current density (JC=2200Acm−2) than the wider ones (JC=1400Acm−2).

Preparation of the Silver-Superconductor Composite by Deposition of the Silver Nanoparticles in the Bismuth Cuprate Superconductor

BiSCCO (Bi–Sr–Ca–Cu–O) is high temperature superconductor with a lot of possible applications. Interfaces between superconductors and metal conductors are one of the technological problems. In this work, silver-superconductor composite was prepared by using flow of silver nanoparticles suspension in DMF (N,N-dimethylformamide) through superconductor’s pore system. Silver nanoparticles were prepared by reaction of silver nitrate with DMF. Properties of prepared composite were measured by SEM charting, XRD and critical current measurements. SEM chart showed uniform distribution of silver across sample. XRD and critical current measurements validated superconducting properties of prepared composite. In the future, materials based on this method could be used as an interface between superconductors and metals or as a base for superconducting composite with much better mechanical properties.

Superconductive and Magnetic Properties of Bi2Sr2Ca2Cu3O10+δ Ceramics Doped by Pb

Among the superconducting phases of bismuth-based Bi–Sr–Ca–Cu–O, compound Bi2Sr2Ca2Cu3O10+δ (Bi-2223) is the most interesting because of its relatively high critical temperature (TC=95–110 K) and numerous applications. However, this phase is also known for its low stability and the difficulty of purifying parasites phases including the Bi-2212. To this end, the Pb used in relatively high proportions can stabilize, purify, and improve the further enhancement of TC. The influence of Pb on structural, superconducting and magnetic properties has been extensively investigated in polycrystalline Bi2−xPbxSr2Ca2Cu3O10+δ ceramics (0<x<1). For low Pb amounts, structural analysis shows that the Bi-2223 phase is difficult to achieve without the Bi-2212 phase, and for high Pb content a large fraction of secondary phases containing Pb is detected. Our results confirm that the optimal Pb content for obtaining a Bi-2223 single phase is x=0.3, 0.4.

ChemInform Abstract: Bi-Sr-Ca-Cu-O High-Tc Superconductors Produced by Using a Rapid Thermal Melt Processing Technique.

Bi–Sr–Ca–Cu–O high-Tc superconductors have been fabricated using a rapid thermal heat treatment technique. The conventionally sintered pellets were rapidly heat treated for 2 min at 1200 °C with a heating rate of 1000 °C min–1 and then annealed. The rapidly heat-treated samples exhibited non-superconducting crystalline phases which became superconducting upon annealing in air. A Tc(zero) of 105 K was obtained for the sample annealed at 861 °C for 240 h. 30% Pb was substituted for Bi in order to stabilize the high-Tc(110 K) phase. Correlations between the processing conditions and the resulting properties of sintered and rapidly heat-treated samples have been studied. Based on low-field magnetization data, the low critical field, Hc1, of heat-treated samples was estimated to be 14% higher than that of the as-sintered samples. The bulk density increased by 10% after thermal heat treatments. In the rapidly heat-treated samples, 95% of the phases was estimated to be the high Tc(2223) phase. X-Ray analysis data showed that the undesirable impurity phases were eliminated after heat treatment. Additionally, the effect of the magnetic field on the electrical resistance has been studied as a function of temperature, and Hall effect measurements have been carried out down to the superconducting state from pre-onset conditions to essentially zero resistance.

Enhancement of superconductivity by pressure-driven competition in electronic order

Finding ways to achieve higher values of the transition temperature, T(c), in superconductors remains a great challenge. The superconducting phase is often one of several competing types of electronic order, including antiferromagnetism and charge density waves. An emerging trend documented in heavy-fermion and organic conductors is that the maximum T(c) for superconductivity occurs under external conditions that cause the critical temperature for a competing order to go to zero. Recently, such competition has been found in multilayer copper oxide high-temperature superconductors (HTSCs) that possess two crystallographically inequivalent CuO(2) planes in the unit cell. However, whether the competing electronic state can be suppressed to enhance T(c) in HTSCs remains an open question. Here we show that pressure-driven phase competition leads to an unusual two-step enhancement of T(c) in optimally doped trilayer Bi(2)Sr(2)Ca(2)Cu(3)O(10+delta) (Bi2223). We find that T(c) first increases with pressure and then decreases after passing through a maximum. Unexpectedly, T(c) increases again when the pressure is further raised above a critical value of around 24 GPa, surpassing the first maximum. The presence of this critical pressure is a manifestation of the crossover from the competing order to superconductivity in the inner of the three CuO(2) planes. We suggest that the increase at higher pressures occurs as a result of competition between pairing and phase ordering in different CuO(2) planes.

Impact of addition of magnetic nanoparticles on vortex pinning and microstructure properties of Bi–Sr–Ca–Cu–O superconductor

The major limitations of polycrystalline Bi-based superconductor applications are the weak flux pinning and weak links in granular networks at relatively high temperature and applied magnetic fields. Effective flux pinning centers with various physical properties were artificially introduced into the superconducting matrix to enhance the flux pinning capability. Among these, introduction of nanoscale magnetic pinning sites into high T c superconductors is still controversial. We have investigated the effects of nanosized NiO addition on the phase formation and flux pinning of the polycrystalline ( Bi 1.8 Pb 0.4 Sr 2 Ca 2.2 Cu 3 O δ ) 1 − x ( NiO ) x with ( x = 0.000 , 0.001, 0.002, and 0.005) using XRD, SEM, AFM, and magnetization measurements. The results show that, with the increase of x , the volume fraction of the high critical temperature ( T c ) phase (2223) decreases gradually accompanied with an increase in the low T c phase (2212). However, almost no change in the T c (onset) for all samples was observed. Measurements of the temperature dependence of the remanent magnetization, M R reveal a nonmonotonic behavior with the nano-NiO addition. A clear enhancement of the pinning strength was observed for the sample with x = 0.002 at quite high temperature ( T = 90 K). These results were discussed in terms of the interaction of the magnetic nanoparticles with the superconducting matrix especially at elevated temperatures close to T c and above the depinning line. The relation between the current carrying mechanisms, phase contents, flux pinning and the microstructures of the samples were also discussed for a granular superconductor. It is believed that these magnetic nanoparticles may act as pinning sites in granular superconductors in applied magnetic field. Therefore, it is very important to carefully control all parameters involved in magnetic particles’ addition in order to balance the critical current for optimum in-field performance.

Study on resistance characteristics and operating conditions of YBCO thin-film wire for current limitation considering insulation layer

The YBCO thin-film wire has a high index value and a fast phase transition speed when a fault current is applied to it. Its critical properties are also superior to those of the existing Bi–Sr–Ca–O wire. Moreover, it can choose its stabilizing layers and control the magnitude of the resistance it generates in with the specific-resistance of the stabilizing layers. Thus, many researchers are studying the application of the Y–Ba–Cu–O(YBCO) thin-film wire to superconducting power machines. Being particularly studied are the properties of the YBCO thin-film wire as a current-limiting element material. In this study, to evaluate the basic properties of superconducting current-limiting elements that contain insulating layers, test samples were manufactured using the YBCO thin-film wire according to the absence and presence as well as the thickness of the insulating layers. Then a fault current was applied to the test samples to examine their quenching resistance trends and operational properties according to the fault angles. Towards those ends, a current was applied to various YBCO thin-film wires with different stabilizing layers to test their properties, and the YBCO thin-film wire that exhibited superior current-limiting performance was selected. Also, a fault current was applied to the selected YBCO thin-film wire with insulating layers to test their properties. Using the test results, the resistance occurrence trends were examined at the critical temperature of 90K, the perfect quenching temperature of 250K, and the middle temperature of 180K. Also, to increase the current limiters’ capacity, the element’s operational properties, such as its maximum voltage, maximum current, initial limited current, and response time were observed at 90K, 180K, and 250K according to the fault angles.

Thermal conductivity of Bi–Sr–Ca–Cu–O superconductors

Using the latest approach of electron–phonon line widths for various scattering mechanisms in the relaxation time approach, the thermal conductivity of Bi–Sr–Ca–Cu–O superconductors has been analyzed successfully. The concept of electronic thermal conductivity and lattice thermal conductivity has been ruled out in the present formulation.

The study of the bolometric response of detector elements based on nanostructured HTSC-films

The bolometric response of detector elements based on nanostructured films BiSr–Ca–Cu–O is studied after 10 years of storage in natural conditions. The thermal relaxation of bolometers is measured at a low duty ratio of optical pulses in a frequency range of 1–10 kHz.

Preparation of Bi2Sr2ZnCu2Ox superconducting ceramics and investigation of their electrophysical properties

The composition of synthesized ceramic samples is investigated by x-ray phase analysis, and it is established that they are high-Tc superconducting Bi2Sr2ZnCu2Ox. It is found that the crystal structure is preserved. To investigate how the superconductivity of Bi–Sr–Ca–Cu–O is influenced by the substitution of calcium by zinc, measurements of the temperature dependence of the resistivity, thermal conductivity, and thermopower (Siebeck coefficient) are carried out. It is found that the substituted compound Bi2Sr2ZnCu2Ox retains its superconducting properties (T0=82K). It is shown that substitution of Ca by Zn leads to an increase of the thermal conductivity. While the thermopower of Bi2Sr2CaCu2Ox shows p-type conductivity in the whole range of temperatures investigated, in Bi2Sr2ZnCu2Ox the type of the conductivity is changed to n-type.

Pulling rate and current intensity competition in an electrically assisted laser floatingzone

Bi–Sr–Ca–Cu–O (BSCCO) superconducting fibres were grown using the laser floating zonetechnique assisted by a dc electrical current (electrically assisted laser floatingzone—EALFZ process). The simultaneous effect of pulling rate and applied currentintensity was evaluated on the premises of the: (i) elemental partition coefficient betweensolid and molten zone; (ii) phase development; (iii) crystal size and alignment degree of theprimary and superconducting phases; (iv) phase transformation during heat treatmentand (v) superconducting properties. The highest critical current density value (JC = 2240 A cm−2) was obtained for the fibres pulled at intermediate pulling rates (75 mm h−1) grown under a maximum dc electric current intensity (200 mA).

Magnetic field dependent critical current density of Bi–Sr–Ca–Cu–O superconductor in bulk and tape form with addition of Fe3O4 magnetic nanoparticles

The (Bi,Pb)2Sr2Ca2Cu3O10-(Fe3O4)x superconductor for x=0, 0.01, 0.03, and 0.05 were prepared. The average size of Fe3O4 used was 40 nm. The maximum critical current density (Jc) in the bulk form was observed in the x=0.01 sample. Based on this result, Ag sheathed high temperature superconductor tapes with starting compositions (Bi,Pb)2Sr2Ca2Cu3O10-(Fe3O4)0.01 were fabricated using the powder in tube method. The microstructure, phase formation, critical temperature, and transport critical current density were studied. The Jc of the nanosized Fe3O4 added tapes is 5130 A/cm2 at 77 K and 23130 A/cm2 at 30 K in zero fields. The nonadded tapes showed a lower Jc, 3090 A/cm2 at 77 K and 12 400 A/cm2 at 30 K. A sudden decrease in Jc in low magnetic fields (B&amp;lt;0.10 T) when applied parallel and perpendicular to the tapes surface was observed. By adding magnetic nanoparticles, the full vortex magnetic energy can be used to enhance Jc and thus, magnetic nanoparticles such as Fe3O4 can act as an effective flux pinning center leading to the enhancement of Jc in the bulk as well as the tape form.