Investigation of Lu effect on YBa2Cu3O7−δ superconducting compounds

This study reports the effect of Lu addition on the microstructural and superconducting properties of YBa₂Lu_xCu₃O_7?δ (Y123) superconducting samples with x = 0, 0.1, 0.3, 0.5 and 0.7 by means of X-ray diffraction (XRD) analysis, scanning electron microscopy (SEM), electron dispersive X-ray (EDX), electrical resistivity and transport critical current density (J_c) measurements. The samples prepared by the liquid ammonium nitrate and derivatives are exposed to various annealing time (20, 40 and 60 h) and temperature (950, 960 and 970 °C), and the best ambient for the sample fabrication is determined to be 970 °C for 20 h. Zero resistivity transition temperatures (T_c), critical current densities (J_c), variation of transition temperatures, hole-carrier concentration, grain size, lattice parameter, surface morphology, element distribution, crystallinity and resistivity (at room temperature) values of the bulk superconducting samples prepared at 970 °C for 20 h are compared with each other. T_c and J_c values of the samples are inferred from the dc resistivity and the critical current measurements, respectively. The results show that the T_c value of the pure sample is about 90.6 K while the sample doped with 0.1 wt% Lu has the maximum T_c value (92.5 K). However, beyond x = 0.1, the T_c value is observed to decrease toward to 83.5 K with increment in the Lu addition. Similarly, the J_c values measured are found to reduce from 142 to 76 A/cm² with the addition. Moreover, XRD measurements show that both pure and Lu-doped samples exhibit the polycrystalline superconducting phase with the changing intensity of diffraction lines and contain Y123 and Y211 phase, confirming the incorporation of Lu atoms into the crystalline structure of the samples studied. At the same time, comparing of the XRD patterns of samples, the intensity ratio of the characteristic (110) and (013) peaks on the sample doped with 0.1 wt% Lu is more than that on the other samples prepared. Additionally, SEM images display that the sample doped with 0.1 wt% Lu obtains the best crystallinity, grain connectivity and largest grain size whereas the worst surface morphology is observed for the maximum doped sample (x = 0.7). Further, EDX results demonstrate that the Lu atoms doped are successfully introduced into the microstructure of the Y123 samples studied and the maximum Cu element level is observed for the sample doped with 0.1 wt%, explaining that why this sample obtains the best superconducting properties compared to others. According to all the results obtained, it is concluded that the 0.1 wt% Lu addition into the Y123 system improves the microstructural and superconducting properties of the samples studied.     

A comprehensive study on mechanical properties of Bi1.8Pb0.4Sr2MnxCa2.2Cu3.0Oy superconductors

This study manifests the crucial change in the mechanical performances of Bi_1.8Pb_0.4Sr₂Mn_xCa_2.2Cu_3.0O_y superconductor samples (x = 0, 0.03, 0.06, 0.15, 0.3 and 0.6) prepared by conventional solid-state reaction method by use of Vickers microhardness (H_v) measurements carried out at different applied loads, (0.245 N ≤ F ≤ 2.940 N). Load dependent microhardness, load independent microhardness, Young’s (elastic) modulus and yield strength values being account for the potential technological and industrial applications are evaluated from the hardness curves and compared with each other. It is found that the H_v, elastic modulus and yield strength obtained decrease (increase) with the enhancement of the applied load for the undoped (doped) samples. Surprisingly, the results of the H_v values illustrate that the samples doped with x = 0.03, 0.06, 0.15, 0.3 and 0.6 exhibit reverse indentation size effect (RISE) feature whereas the pure sample obeys indentation size effect (ISE) behavior. Furthermore, the experimental results are examined with the aid of the available methods such as Meyer’s law, proportional sample resistance model (PSR), elastic/plastic deformation (EPD), Hays–Kendall (HK) approach and indentation-induced cracking (IIC) model. The results inferred show that the hardness values calculated by PSR and EPD models are far from the values of the plateau region, meaning that these models are not adequate approaches to determine the real microhardness value of the Mn doped Bi-2223 materials. On the other hand, the HK approach is completely successful for the explanation of the ISE nature for the pure sample while the IIC model is obtained to be the best model to describe the hardness values of the doped materials exhibiting the RISE behavior. Additionally, the bulk porosity analysis for the samples reveals that the porosity increases monotonously with the increment in the Mn inclusions inserted in the Bi-2223 system, presenting the degradation of the grain connectivity.     

Carpal tunnel syndrome: comparison of intraoperative structural changes with clinical and electrodiagnostic severity

The aim of this study is to grade the intraoperative findings seen in carpal tunnel syndrome (CTS) based on severity, and compare it with clinical and electrodiagnostic severity.Thirty-one hands surgically treated for CTS were graded according to the severity of clinical signs, and electrodiagnostic tests. Oedema, vascularisation, and fibrosis were graded on a scale of 1–3. Pseudoneuroma or ‘hour-glass’ formation were graded as either 0 or 1. The hands were allocated by an observer into an assumptive severity group, from grade 1 to 3. Clinical severity and electrodiagnostic severity were statistically compared with each other, and with each intraoperative severity criteria.A high statistical correlation (p<0.01) was found between clinical severity and vascularisation, fibrosis, and the assumptive intraoperative severity. No correlation could be demonstrated between electrodiagnostic severity and the intraoperative criteria.Intraoperative grading should be regarded as a supportive measure to the clinical evaluation in order to obtain a sound base for surgical intervention and internal neurolysis.     

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

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

Effect of Eu doping on structural and magneto-electrical properties of La0.7Ca0.3MnO3 manganites

We have investigated the influence of europium (Eu) doping on structural and magneto-electrical properties of La_0.7Ca_0.3MnO₃ compounds. In order to analyze the physical mechanism of a spin disorder system and study their relative evolutions, two samples of nominal compositions (La_0.7?xEu_x)Ca_0.3MnO₃ (x = 0.0 and 0.1) have been elaborated and characterized. In addition to structural changes seen by this kind of doping, the magnetoresistance (MR) and resistivity are increased while the metal–insulator transition temperature is decreased. Comparing the experimental data with the theoretical models shows that in the metal-ferromagnetic region, the electrical behaviour of both samples is quite well described by a theory based on Kondo-like spin dependent scattering, electron–electron scattering, electron–phonon and electron–magnon scatterings. For the high temperature paramagnetic insulating regime, the adiabatic small polaron hopping model is found to fit well the experimental curves.     

Fabrication and magnetoresistivit of ex-situ processed MgB<Subscript>2</Subscript>/Fe monofilament tapes without any intermediate annealing

We have fabricated MgB₂/Fe monofilament wires and tapes by a powder-in tube (PIT) technique, using an ex-situ process without any intermediate annealing. MgB₂/Fe monofilament tapes were annealed at 650–1,050°C for 60 min and 950°C for 30–240 min. We have investigated the effect of annealing temperatures and times on the formation of MgB₂ phase, activation energy, temperature dependence of irreversibility field H _irr(T) and upper critical field H _c2(T), transition temperature (T _c), lattice parameters (a and c), full width at half maximum, crystallinity, resistivity, residual resistivity ratio, active cross-sectional area fraction and critical current densities. We observed that the activation energies of the MgB₂/Fe monofilament samples increased with increasing annealing temperature up to 950°C and with increasing annealing time up to 60 min while it decreased with increasing magnetic field. For the MgB₂/Fe monofilament tape, the slope of the H _c2–T and H _irr–T curves decreased with increasing annealing temperature from 850 to 950°C as well as with increasing annealing time from 30 to 60 min. The transport and microstructure investigations show that T _c, J _c and microstructure properties are remarkably enhanced with increasing annealing temperature. The highest value of critical current density is obtained for the sample annealed at 950°C for 60 min. The J _c and T _c^offset values of the sample annealed at 950°C for 60 min were found to be 260.43 A/cm² at 20 and 38.1 K, respectively.     

Effect of diffusion-annealing time (0.5 h ≤ t ≤ 2 h) on the mechanical and superconducting properties of Cu-diffused bulk MgB2 superconductors by use of experimental and different theoretical models

This study reports the effect of different annealing time (0.5 h ≤ t ≤ 2 h) on the electrical, physical, microstructural, mechanical and superconducting properties of Cu-diffused bulk magnesium diboride (MgB₂) system by means of dc resistivity, X-ray diffraction analysis (XRD), scanning electron microscopy (SEM) and microhardness measurements (H _v ). The room temperature resistivity (at 300 K), critical transition (T _c ^offset and T _c ^onset ) temperature, variation of transition temperature, grain size, phase purity, lattice parameter, texturing, surface morphology, crystallinity and Vickers microhardness values of the samples are evaluated and compared with each other. The resistivity results obtained reveal that the (T _c ^offset and T _c ^onset ) values of the samples produced ascend with the enhancement in the annealing time up to 1 h beyond which these values start to reduce systematically and in fact the smallest T _c ^onset of 38.1 K and T _c ^offset of 36.2 K are observed for the sample annealed for 2 h. Similarly, the SEM micrographs display that the surface morphology, crystallinity and grain connectivity improve until a certain diffusion-annealing time (1 h), and after this point, all the properties obtained start to degrade with the increase of the annealing time. Furthermore, the peak intensities, grain sizes and lattice parameters deduced from the XRD measurements illustrate that a systematic elongation in the a and c axis lengths is detected with the annealing time until 1 h beyond which a regular contraction in the lattice parameters is observed for the samples. Likewise, the peak intensities belonging to MgB₂ phase enhance with the increment of the annealing time up to 1 h after which they reduce slowly; however, a new peak belonging to Mg₂Cu phase appears in the sample annealed for the duration of 2 h, confirming both the reduction of the grain size and degradation of the critical temperature. Additionally, we have focused on the microhardness measurements for the examination of the mechanical properties of the samples studied. Experimental results of microhardness measurements are estimated using the various models such as Meyer’s law, proportional sample resistance model, modified proportional sample resistance model and Hays-Kendall (HK) approach. Based on the simulation results obtained, the Hays-Kendall (HK) approach is determined as the most suitable model describing the mechanical properties of samples prepared.     

Sn diffusion coefficient and activation energy determined by way of XRD measurement and evaluation of micromechanical properties of Sn diffused YBa2Cu3O7−x superconducting ceramics

This study manifests not only the effect of Sn diffusion on physical, electrical, mechanical, structural and superconducting properties of the bulk YBa₂Cu₃O_7?x (Y123) superconductors prepared by the conventional solid-state reaction route by use of electrical resistance, X-ray diffraction analysis (XRD), electron dispersive X-ray, scanning electron microscopy, transport critical current density (J _c ) and Vickers microhardness (H _v ) measurements but also the diffusion coefficient and the activation energy of tin (Sn) in the Y123 material for the first time. The diffusion coefficient and the activation energy of Sn are investigated in the temperature range 500–945 °C using the change of the lattice parameters extracted from the XRD patterns. The resistance (at room temperature), critical (onset and offset) temperature, variation of critical temperature, hole-carrier concentration, crystallinity, lattice parameter, texturing, surface morphology, lotgering index, element distribution, critical current density, oxygen content, load dependent microhardness, elastic modulus and yield strength values are obtained for the pure and Sn diffused samples and compared with each other. One can see that all superconducting parameters given above depend sensitively on the Sn diffusion on Y123 system. The obtained results exhibit that the room temperature resistance enhances with the Sn diffusion because of the hole filling when the onset $ (T_{c}^{onset} ) $ ( T c onset ) and offset $ (T_{c}^{offset} ) $ ( T c offset ) critical temperatures are obtained to be about 93.4 and 89.6 K for the pure sample as against 92.2 and 88.1 K for the Sn diffused sample, respectively. This may be attributed to the fact that the decrement in the critical temperatures is due to the deterioration of crystallinity and descend in the grain size. As for the critical current density measurements, J _c values are obtained to be about 125.4–65.3 A/cm², respectively, for the undiffused and Sn diffused materials. This may be led to the decrease of the flux pinning mechanism stemming from the stacking faults, planar and micro-defects. At the same time, XRD measurements display that the samples produced in this work exhibit the polycrystalline superconducting phase with the changing intensity of diffraction lines. Besides, the peak intensities belonging to major phase (Y123) decrease monotonously with Sn diffusion in the system; however, new peaks belonging to the minor (BaCuO₂) phases start to appear for Sn diffused sample confirming both the reduction of the grain size and degradation of the critical temperature. Moreover, the pure sample is confirmed by both enhancement of a and b lattice constants and the decrement of the cell parameter c of the sample in comparison with that of the Sn diffused sample. According to SEM examination, the crystallinity and grain connectivity suppress with the Sn diffusion. EDX measurements illustrate that not only do the elements used for the preparation of the Y123 superconductors with and without Sn diffusion distribute homogeneously but also the level of Cu element reduces with the Sn diffusion, presenting that the Cu²⁺ ions may partly be diffused by tetravalent tin (Sn⁴⁺) ions. Further, surprising results of the Vickers microhardness values demonstrate that the pure sample visualizes Indentation Size Effect (ISE) feature; however, the Sn diffused sample reports Reverse Indentation Size Effect (RISE) nature. Additionally, the diffusion coefficient is observed to increase from 1.11 × 10^?9 to 2.82 × 10^?8 cm² s^?1 as the diffusion-annealing temperature increases, verifying that the Sn diffusion at lower temperatures is much less significant as compared to the higher ones. Temperature dependence of the Sn diffusion coefficient and activation energy in the range of 500–945 °C is defined with the aid of the following equation: $$ D = 7.78 \times 10^{ - 6} { \exp }\left[ {\left( {( - 0.590 \pm 0.005){\raise0.7ex\hbox{${\text{eV}}$} \!\mathord{\left/ {\vphantom {{\text{eV}} {k_{B} T}}}\right.\kern-0pt} \!\lower0.7ex\hbox{${k_{B} T}$}}} \right)} \right] $$ D = 7.78 × 10 ? 6 exp [ ( ( ? 0.590 ± 0.005 ) eV / eV k B T k B T ) ] .