Bi-2212 Whiskers Research Articles

Oxygen doping tuning in superconducting oxides by thermal annealing and hard X-ray irradiation

Bi2Sr2CaCu2O8+δ (Bi-2212) superconducting whiskers, owing to their microscopic size, are good candidates for the fabrication of miniaturized devices for production/sensing of THz-radiation based on their Intrinsic Josephson Junctions (IJJ) properties. With this respect, several studies demonstrated the possibility of controlling whisker IJJ parameters by modifying the oxygen content. In this paper we show that both thermal annealing and hard X-ray irradiation are effective ways to tune the oxygen doping. In particular, we monitored the effect of an annealing process at 363K and of irradiation by 17keV micro- and nano-beams on the structural and superconducting properties of selected Bi-2212 whiskers. Moreover we modeled by a finite element simulation the temperature field induced by the X-ray beam to try to clarify the origin of the measured changes.

Thermodynamic growth model of single crystal Bi-2212 whisker

In this study the growth mechanism of superconducting Bi-2212 whiskers is investigated from a thermodynamic point of view. The evolution of the free energy of the growth region in the main matrix is evaluated by estimating that of its surface energy. It is shown that the local free energy change for partial melting is the same as that of the whole structure of the sample. It is pointed out that the formation of whiskers requires a higher energy than that of plate like grains.

Fabrication of single crystalline Bi-2212 whiskers from Ga added Bi2Sr2Ca2Cu3Ox composition and their thermal, structural, electrical and magnetic properties

In this study, Bi-2212 superconducting whiskers have been fabricated by annealing a melt quenched Bi2GaSr2Ca2Cu3Ox precursor. Whiskers with 6–15μm thickness, 60–95μm width and 3–9mm length were obtained. Crystallization activation energy, Ea, was calculated to be 362kJmol−1 by using Kissinger method. Structural and/or microstructural changes as a result of different heat treatments were investigated with SEM, EDX and XRD analyses. It was found that Ga ions in the starting composition did not diffuse to the structure of whiskers and they enhanced mass transport and accelerated the whisker growth. XRD analysis showed that whiskers consisted of highly c-axis oriented single crystalline Bi2Sr2CaCu2Ox phase. From SEM analysis, it was seen that whiskers had very smooth surface without cracks and dislocations. Tc and T0 values of the whiskers were found to be 93.1K and 88.2K, respectively. Applied magnetic field dependence of the magnetization (M–H) was investigated at 10, 20 and 30K. Jc of whiskers were calculated by using Beans’ equation and found to be 2.27×106Acm−2, 1.99×106Acm−2 and 0.81×106Acm−2 at 10K, 20K and 30K, respectively.

Magnetization loops and pinning force of Bi-2212 single-crystal whiskers

Dependence of magnetization on applied magnetic field for single-crystal Bi-2212 whiskers was measured at different temperatures. Symmetric and asymmetric magnetization loops were successfully described by the extended critical state model (the extended Valkov–Khrustalev model). Pinning force of whiskers was investigated.

17 keV photon induced damage of Bi-2212 whiskers by synchrotronμ-beam exposure

Experimental data show that the normal state resistivity of superconductingBi2Sr2CaCu2O8 + δ (Bi-2212) whiskers increases after a 6 h irradiation by a synchrotronμ-beam with 17 keV photons. We analyse this result on the basis of previously reportedeffects in Bi-2212 whiskers due to ageing or heating processes. A finite element model of theexperimental setup clarifies that the heat load induced by the microbeam has to beexcluded as a possible cause for the material changes. The knock on the interstitial, looselybound, O species by secondary electrons is discussed as the most likely mechanismresponsible for this effect.

Normal State Electronic Properties of Whiskers Fabricated in Bi-, Ga- and Sb-doped BSCCO System Under Applied Magnetic Fields

In this work, superconducting Bi-2212 whiskers have been fabricated by using Bi2MSr2Ca2Cu3O10+δ (where M = Bi, Ga and Sb) composition. Electronic properties of the fabricated whiskers were investigated under 0–4 T magnetic fields. The Tc value of the whiskers was found to be dependent on the applied magnetic field and doping. Normal state resistivity of the whiskers showed a nonlinear dependence on temperature. Resistivity of the whiskers deviated above a certain temperature depending on doping element and the applied magnetic field. Experimental resistivity data was fitted according to the Levenberg–Marquardt algorithm. When the fitting curve was extrapolated, it was seen that a zero resistivity value was obtained between 1.1 and 11.8 K depending on doping and the applied magnetic field.

Power Law Dependence of I–V Characteristics of Bi-2212 Whiskers at Low Magnetic Fields

In this study, BiSrCaCuO superconducting whiskers were fabricated by using a glass-ceramics process. The T c value of the whiskers fabricated was found to be 90.2 K. I–V characteristics of the whiskers were studied in the temperature range of 10–70 K under low magnetic fields. The transport critical current density of whiskers was calculated between 19 and 0.63×104 A/cm2 at 10–60 K. I–V data were fitted using the Levenberg–Marquardt technique. Results were discussed and so was their dependence on magnetic and electrical properties of the superconductors.

The single crystal superconducting Bi-2212 whiskers fabrication and their thermal transport properties

In this study, we have fabricated the superconducting single crystal whiskers using glass–ceramic BiSrCaCuO material. The crystallization kinetic studies (crystallization activation energy, E a , and the Avrami parameter, n,) were carried out using DTA data. The oxygen diffusion energy was calculated using TG data. XRD and SEM analysis of the whiskers showed Bi-2212 phase formation and the c-axis orientation. The in-plane resistivity, ρ ab, and the out-of-plane resistivity, ρ c , properties of the whiskers were investigated. The thermoelectric power, S( T), value between 10 and 300 K is found to be positive, indicating that charge carriers in the whiskers are holes. We analyzed the thermoelectric power as a function of temperature with “ Two band model with linear T-term” Linear temperature dependence in the thermal conductivity down to T c and then a sharp rise just below T c were obtained.

Synchrotron study of oxygen depletion in a Bi-2212 whisker annealed at 363 K

Direct evidence is reported of structural and electronic effects induced on a single Bi(2)Sr(2)CaCu(2)O(8+delta) (Bi-2212) whisker during a progressive annealing process. The crystal was investigated by micro X-ray diffraction (micro-XRD), micro X-ray fluorescence and electrical characterization at the European Synchrotron Radiation Facility, during a series of three in situ thermal processes at 363 K. Each step increased the sample resistivity and decreased its critical temperature, up to a semiconducting behaviour. These data correlate with micro-XRD analysis, which shows an increase of the c-axis parameter from 30.56 A to 30.75 A, indicating an oxygen depletion mechanism. Mild temperature annealing could be an effective process to modulate the intrinsic Josephson junctions' characteristics in Bi-2212 whiskers.

Control of the oxygen doping in Bi-2212 whiskers by means of their synthesisprocess

Direct evidence of oxygen doping control in single phaseBi2Sr2CaCu2O8+δ (Bi-2212) whiskers is reported, along with the changes in their structural properties obtained byvarying the growth temperature of the synthesis process in the range from 843 to872 °C. The as-grown whiskers were investigated by means of x-ray powder diffraction (XRPD),electrical transport measurements, scanning electron microscopy (SEM) and energy dispersivex-ray spectroscopy (EDS). The XRPD measurements showed that the value of thec-axis lattice parameter increases from 30.556 to 30.640 Å when increasing the growthtemperature, which indicates different oxygen doping levels spanning from the slightlyoverdoped to the nearly optimally doped regimes. Such results are also confirmed by theelectrical characterizations, which revealed a typical relationship among resistivity (ρab), superconductingcritical temperature (Tc), and c-axis value. The growth of CuO crystals has also been identifiedduring this study, with a maximum yield in the range 860–864 °C, where also a slopechange in the c-axis behavior has been found, implying a possible correlation between the two phenomena.Therefore, by changing the synthesis growth temperature, one can provide an effective wayto tune the whisker electrical transport properties.

Transport Properties under Magnetic Field and J c (H) Peak Effect on Single-Crystal Bi-2212 Whiskers

In this study, 50 nm–18 mm in length superconducting single-crystal Bi-2212 whiskers have been fabricated using glass-ceramic BSCCO material. The microstructure, transport and magnetic properties were characterized by XRD, SEM-EDX, R–T, I–V and M–H analysis. Highly c-axis oriented single-crystal whiskers were produced without any grain boundaries in any crystallographic direction. Tc and Tzero were obtained to be 94.8 K and 92.8 K, respectively, and decreased with increasing the magnetic field. Magnetic properties, M–H curves of the whiskers, were investigated at 3 different constant temperatures up to 5 T. Symmetric hysteresis loops for all temperature and field cases were obtained and maximum Jcmag value was calculated to be 4.58×106 A cm−2 at 10 K for 0 T but dropped to 1.61×106 A cm−2 at 30 K for 0 T.

Structural and superconducting properties of single-crystal Bi2Sr2Ca n − 1Cu n O2n + 4 + δ (n = 1–3) whiskers grown in gas-filled cavities

Using growth inside gas-filled cavities in KCl-fluxed melts, we have obtained free-standing phasepure Bi2Sr2Can − 1CunO2n + 4 + δ (n = 1–3) whiskers possessing superconducting properties in the as-grown state. Bi-2212 whiskers have been prepared in a wide range of doping levels, from underdoped (Tc = 76.5 K) to optimally doped (Tc = 84 K). The whiskers possess high structural perfection, as shown by X-ray diffraction. Annealing under optimal conditions raises the superconducting transition temperature of the underdoped Bi-2212 whiskers to Tc max = 85.5 K (ΔTc = 1.8 K), without impairing their structural perfection.

Effect of Strip Width on Low-Field Peak Effect of Critical Current Density in Bi2Sr2CaCu2O8+δ Superconducting Strips

We investigate the dependence of the critical current density J c along the crystal a -axis on the magnetic field along the c -axis at high temperatures below the superconducting transition temperature in individual Bi 2 Sr 2 CaCu 2 O 8+δ (Bi-2212) whiskers with surface barriers by electrical transport measurements. J c shows a low-field peak effect; J c increases with the magnetic field in a low-field region and shows a peak at the threshold field H peak below 100 Oe. A comparison of the low-field peak effects in whiskers of different widths shows that H peak depends on the sample width (i.e., the lateral dimension); the lateral axis is perpendicular to the magnetic field and the direction of current flow. A decrease in the sample width w shifts H peak toward a higher field. This systematic variation in H peak with w implies that the low-field peak effect observed in the Bi-2212 whiskers is associated with the effect of the finite w on dilute vortices.

Photoconductivity experiments on superconductingBi2Sr2CaCu2O8+x whiskers

In the present paper we report the results of photoconductivityexperiments carried out in nearly optimally doped, single-phaseBi2Sr2CaCu2O8+x (Bi-2212) whiskers. Samples with both straight and bent shapes have been investigated bymeans of the four-probe and two-probe configurations in dark and in illuminated conditions.Experimental data invariably show the absence of a persistent photoconductivity (PPC)effect. Such observations, combined with the very high crystal quality of the whiskers,which corresponds to the absence of defects acting as electron traps, can be explained inthe framework of the electron–hole pair excitation model (Kudinov et al 1990Phys. Lett. A 151 358). In contrast, experimental data show a reversible increase of theelectrical resistance under illumination, which is fully consistent with a local heatingeffect due to the thermal load induced by the light. Such resistance increase isespecially large for samples measured in the two-probe configuration, suggesting apossible supplementary effect due to an interaction between the light and thec-axis resistivity or the contact resistance.

Fabrication and properties of superconducting single crystal cross-(micro)whiskers junction

Superconducting single crystal Bi-2212 (micro)whiskers have been fabricated by annealing a glass Bi 2Sr 2Ca 2Cu 3O x precursor. The T c and T zero of ∼20 mm long and 10–70 μm wide single crystal whiskers were found to be 85 K and 82 K, respectively. The critical current density J ctransport of the whiskers was calculated to be 1313 A cm −2 at 0 T and 10 K. Then, a couple of whiskers were placed cross-wise on the YSZ single crystal substrate and heat treated to form micro-scale junction. The I– V characteristics of the micro-junction at 10, 30 and 60 K were found to show a multiple branch structure and that confirms to a model based on intrinsic Josephson junction.

Influence of intergrowth Bi2223 phase on the E– J properties of Bi 2Sr 2CaCu 2O δ whiskers

In order to investigate the effect of the intergrowth Bi2223 phase on the transport properties of Bi2212 whiskers, we performed the electrical field vs. current density ( E– J) measurements for Bi2212 whiskers at various temperatures and magnetic fields. Both of the irreversibility field B irr and the critical current density J c increase with the increase of the intergrowth Bi2223 content. Although the quantitative ratio of intergrowth Bi2223 is unknown, we found the possibility of the J c improvement of Bi2212 due to the intergrowth Bi2223 phase from a detailed analysis of the E– J properties.

Growth of superconducting and non-superconducting whiskers in the Bi-Sr-Ca-Cu-O (BSCCO) system

Growth of such non-superconducting whiskers [Sr2.24Ca0.4Al2Ox, (Ca0.8–0.85Sr0.15–0.1)2CuO3,CuO, or Bi2.44Sr2Ca1.3–2Cu6.9–9.95Al0.35–0.46Ox (Cu-rich whiskers)] formed during the growth of Bi-2212 superconducting whiskers from powder or glassy substrates, is discussed. These whiskers are likely to grow from the bottom end, and there is a tight relationship with the growth of the Bi-2212 whiskers. A general reaction-path model for the whisker growth in the BSCCO system, independent of the type of the catalytic impurity and substrate, is proposed. When whiskers are grown under magnetic fields, up to 10 T, changes in the whisker size, aspect ratio, and morphology are observed.

Area-controlled growth of Bi-2212 whiskers from Bi 2+ xSr 2− xCaCu 2O y pellets

The Bi-2212 whiskers synthesized with area-controlled growth in the previous work had the behavior that the electric resistance increased as the temperature decreased below the Bi-2212 superconducting transition. In the present work, the Bi-substitution level of Bi 2+ x Sr 2− x CaCu 2O y substrates and/or the growth conditions were varied in order to improve the superconductivity of the area-controlled whiskers. Consequently, the whiskers with T c,zero = 85.5 K were grown in the case of using the substrate with x = 0.1. However the density of the whiskers decreased in comparison with the previous area-controlled whiskers with the semiconductor-like behavior.

Nucleation of Normal Phase in the Dynamic Resistive State in Submicron Bi2212 Bridges

The resistive state above the Larkin-Ovchinnikov (LO) instability current has been experimentally studied. Analysis of the stepwise I-V curves of thin superconducting bridges ≤ 1 μm wide, etched from the Bi2Sr2Ca1 Cu2 Oy (Bi2212) whiskers, reveals the following scenario of vortex dynamics: first, a pair of current-induced Abrikosov vortices enter the bridge, then they are accelerated by the current above the critical velocity of the LO instability and approach the limiting velocity of the normal phase propagation, of the order of 107 cm/s. Each vortex leaves a tail of normal phase behind itself, which is equivalent to a phase slip line. At low temperatures the tails cover the whole width of the bridge — the I-V curves between the steps become Ohmic.

Growth of High-Quality Single-Phase Bi2Sr2CaCu2Ox Whiskers by a New Growth–Melt–Regrowth Method

High-quality and large single-phase Bi2212 whiskers are grown by a new growth–melt–regrowth method. The average composition of the Bi2212 whiskers and the maximum size of single-crystal domains are Bi2.15Sr2.08Ca0.90Cu2.00Ox and 0.5 µm × 88 µm × 2 mm, respectively. The results of X-ray diffraction analysis and I–V characteristic measurement indicate that the crystallinity of the obtained Bi2212 whiskers is excellent.