YBa2Cu3O7-δ Samples Research Articles

Graphene doping effects on the magnetic and transport properties of YBa2Cu3O7-δ high temperature superconductor

In this work, bulk graphene-doped YBa2Cu3O7-δ (YBCO) high-temperature superconductor samples were prepared with composition of YBCO + x wt.% graphene nanoplatelets (G) (x = 0, 0.2, 0.4, 0.6, 0.8, 1.0). The X-ray diffraction patterns show the YBCO orthorhombic phase in all the samples. The SEM images show good grain connectivity between YBCO grains in graphene-doped samples. Furthermore, the broadening of resistivity under applied magnetic fields up to 9T and thermally activated flux creep in the mixed state were studied using Arrhenius plots. The activation energy U0 (H) increased with graphene doping results in better flux pinning and higher critical current densities. Moreover, improvement in the critical temperature (TC), upper critical field (μ0HC2) and the irreversibility field (μ0Hirr) were observed in graphene-doped samples as compared to the pure YBCO sample.

YBa2Cu3O7–δ films prepared by pulsed laser deposition in O2/Ar mixture atmosphere

The YBa2Cu3O7-δ(YBCO) superconducting films were fabricated epitaxially on STO(00 l) substrates by pulsed laser deposition method (PLD) in different O2/Ar mixture atmospheres. The surface morphology of the YBCO film is strongly dependent on the O2/Ar ratio of the ambient atmosphere. The surface particle density decreases and the particle size increases with the O2/Ar ratio decreasing. The lattice parameters and the superconducting transition temperature (Tc0) are almost independent on the O2/Ar ratio and are about the same as 1.168 nm and 90 K, respectively, which can be ascribed to the annealing process in 1 atm O2 for all the YBCO samples. Based on the above results, in O2/Ar ratio of 25:75 atmosphere, YBCO:LaAlO3 superconducting composite films with good performance were prepared by co-deposition of PLD with magnetron sputtering method. The experimental results provide a way to control the surface morphology of the YBCO films deposited by PLD method and provide valuable reference for the preparation of YBCO composite thin films by co-deposition of PLD with magnetron sputtering method in Ar/O2 mixture atmosphere.

Comparative study of thermal fluctuation induced conductivity in YBa2Cu3O7-d containing Nano-Zn0.95Mn0.05O and Nano-Al2O3 particles

In this report we presented the fluctuation induced excess conductivity in polycrystalline superconducting samples of YBa2Cu3O7-δ (for brevity YBCO or Y123) with nano-Al2O3 (20 nm) and nano- Zn0.95Mn0.05O (30 nm) particles prepared under the same conditions using the solid-state reaction route. The crystal structure and microstructure were analyzed via X-ray diffraction, scanning and transmission electron microscopies. The crystal structure of Y123 was conserved for samples added with both kinds of nanoparticles. The electrical resistivity dependence with temperature (ρ(T)) was measured and the excess conductivity in the mean field region was analyzed using the Aslamazov and Larkin approach. The fluctuation regions and the critical parameters including the coherence lengths, penetration depth and the effective layer thickness were estimated and compared for both series of samples. The critical physical quantities Bc1(0), Bc2(0) and Jc(0) were computed. Improvements in these critical physical quantities were obtained for samples sintered with 0.02 wt% nanoparticles. The nano-Al2O3 particles are more adequate than nano-Zn0.95Mn0.05O particles for enhancement of flux pinning properties of YBa2Cu3O7-δ.

Production of Sharp-Edged and Surface-Damaged Y2BaCuO5 by Ultrasound: Significant Improvement of Superconducting Performance of Infiltration Growth-Processed YBa2Cu3O7-δ Bulk Superconductors.

Growth and physical properties of bulk REBa2Cu3O7−δ (REBCO) superconductors fabricated by the infiltration growth (IG) method strongly depend on the initial size and morphology of the RE2BaCuO5 (211) particles. The present work details the novel method we developed for producing sharp-edged and surface-damaged 211 particles to be added to the REBCO bulks. We employed high-energy ultrasonic irradiation for pretreating the 211 particles and fabricated high-performance bulk single-grain YBa2Cu3O7−δ (YBCO) superconductors via the top-seeded IG process. Increasing the ultrasound irradiation power and time duration mechanically damaged the surface of the 211 particles, producing more fine and sharp edges. Systematic investigations of the microstructural properties of the final YBCO bulks indicated that the size and content of the 211 particles gradually decreased without any additional chemical doping. The effective grain refinement and improved interfacial defect densities enhanced the critical current density by a factor of two at 77 K and self-field as compared to a YBCO sample fabricated without any pretreatment. A maximum trapped field of 0.48 T at 77 K was obtained for a sample (20 mm diameter) with 211 particles treated for 60 min and 300 W ultrasound radiation. The effectiveness of the novel method is demonstrated by the superior performance of the YBCO bulk samples prepared as compared to bulk samples fabricated with the addition of Pt and CeO2. This method is novel, cost effective, and very convenient, maintaining high sample homogeneity, and is free of chemical contaminants as compared to other methods which significantly affect the properties of all REBCO bulk products grown by sintering, melt growth, and IG methods.

Attraction and repulsion forces in melt-textured and sintered YBCO-superconductors: a comparative study

In this paper, we measure the attraction (suspension) and repulsion (levitation) forces produced by the interaction between a permanent magnet and different bulk superconductors. The measurements of the interaction force HTS-PM were carried out with a relatively simple technique developed by us, which is reproducible, reliable and low cost. The obtained results were analyzed with the Bean’s critical-state model assuming a uniform magnetic field applied to the superconductor. Two superconducting samples of YBa2Cu3O7-δ (YBCO) prepared by solid-state reaction method and by the melt-textured growth method (MTG) were used. Both samples presented a different hysteresis behaviour in the field cooling (FC) and zero field cooling (ZFC) regimes. Levitation and suspension phenomena were observed in the MTG sample; however, the sintered sample (S) with Oxygen deficiencies (δ > 0.15) displayed a slight levitation force but did not show a suspension force, the latter one attributed to a more efficient magnetic flux pinning. Additionally, the critical current density of both samples was determined from the maximum gap of the force (ΔF) in the FC regime. The obtained values were between 43.00 A/cm2 and 2,758 A/cm2 for the sintered and MTG samples, respectively. These values show a remarkable difference between sintered and MTG samples like that observed from magnetization measurements, which indicate that attraction and repulsion force measurements could provide a rapid and reliable characterization method of polycrystalline superconducting samples.

LEVITATION AND SUSPENSION FORCES MEASUREMENT SYSTEM FOR HIGH TC SUPERCONDUCTORS

The interaction forces, attraction (suspension) and repulsion (levitation) between a permanent magnet and diferent bulk Yttrium-based superconductors were carried out with an automatic system developed in our group, which is reproducible, reliable and low cost. Two superconducting samples of YBa2Cu3O7-δ (YBCO) prepared by solid-state reaction method (S) and by the melt-textured growth method (MTG) were used. Both samples were characterized by XRD technique and presented the characteristic peaks and intensity relations of the YBCO-123 superconducting phase. Oxygen deficiencies δ > 0,15 and δ < 0,10 for the S and MTG samples respectively, were observed. Both samples displayed diferent hysteresis behavior in the Force (F) vs. Distance (z) measurements when they were field cooled (FC) and zero field cooled (ZFC). This behavior agrees with hysteresis loops observed in magnetization measurements. Both levitation and suspension phenomena were observed in the MTG sample with large hysteresis loops of the force. On the contrary, the S sample with small hysteresis loops did not show a suspension force, only displayed a slight levitation force.

Contrasting effects of metal oxide dopants on the superconductivity of YBa2Cu3O7-δ ceramics

Bulk superconductor samples of YBa2Cu3O7-δ (YBCO or Y-123), with additions of 0.15 wt% MoO3, TiO2, RuO2 and two different types of Al2O3 compounds, are synthesized by a solid state reaction route. Structural, magnetic and transport properties of the samples are characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX), magnetic (M-H, M-T) and magneto-resistivity (MR-T) measurements. SEM investigations show that the addition of the Al2O3 obtained from the alumina crucible (Al2O3-cru) decreases the grain size of the sample which, in turn, degrades the transition temperatures (Tc) and magnetic critical current densities $$(J_{c}^{mag} )$$ . On the contrary, the addition of the other metal oxides enhances $$J_{c}^{mag}$$ of the samples by a few times and also increases Tc by up to 3 K. EDX analyses of the samples exhibit homogeneous distribution of additions, except for Ru-heterogeneities located around superconducting Y-123 grains. The highest Jc and Tc values obtained on the RuO2 added sample were attributed to the agglomeration of the Ru-particles, which led to the optimal porosity that supports oxygenation process and intergrain coupling of the structure. From the DC magnetization data, we estimated $$J_{c}^{mag}$$ of 3.1 × 105 A/cm2, 2.3 × 105 A/cm2, 2 × 105 A/cm2, 1.5 × 105 A/cm2, 105 A/cm2 and 5.1 × 104 A/cm2 for the RuO2, TiO2, MoO3, Al2O3, undoped and Al2O3-cru added samples at 5 K under 0.25 T, respectively.

Investigation of microhardness and superconducting parameters of CNTs blended YBCO superconductor

Here we report the effect of CNTs addition on the microhardness and superconducting properties of YBa2Cu3O7-δ (YBCO) high-temperature superconductor. All the composite samples exhibit orthorhombic structure, maintain single phase and to belong to Pmmm space group as evidence from the Rietveld refinement analysis. From FESEM micrographs, for all samples extended rods like structure is observed. The microhardness number (HV) enhances non-linearly by application of load from 0 to 3 N, beyond which the curve reaches a saturation limit. As the microhardness number gradually increases under substitution of CNTs revealed that CNTs addition has resulted significant effect on microhardness property of the YBCO superconductor. Different models like Meyer's law, Hays-Kendall approach and elastic/plastic deformation model are utilized to examine the microhardness properties of the high-temperature superconductor. Finally proportional specimen resistance model is the most efficient model to describe the microhardness properties of CNTs doped YBCO samples. The superconducting transition temperature (TC) is obtained from resistivity vs. temperature measurement and AC susceptibility measurement. From both the measurements, it is obvious that TC enhances with CNTs addition up to 0.5 wt % and then decreases. For 0.5 wt % CNTs doped YBCO sample the value of TC is nearly 96 K. As the addition of CNTs to the YBCO matrix creates artificial pinning centers inside the YBCO matrix and increases the superconducting volume fraction, hence the observed value of critical current density for all composite samples are more than that of pristine YBCO. The maximum value of Jc is observed for 0.5 wt % sample and the value is 1.8 times more than that of pure YBCO. Utilizing Zeldov model the characteristics pinning potential energy for all composite samples is calculated and the response is very similar to that of critical current density under addition of CNTs.

Magnetic Moment and its Correlation with the Critical Temperature in YBCO

Abstract: In the present work, nanoparticles were doped into superconductor samples of YBa2Cu3O7-δ (YBCO) + X, where X = 0.1, 0.2, 0.3, 0.4, and 0.5 mass-%, respectively of "nanosized metal oxides" namely Mn3O4, Co3O4, Cr2O3, CuO, and SnO2 which are synthesized by a solid-state reaction route. The phase identification and microstructure of all samples was examined by X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) techniques. The XRD patterns indicate that magnetic doping with Mn3O4, Co3O4, and Cr2O3 leads to improved orthorhombic character in the YBCO samples which is the result of a high oxygen content, and consequently may give improved superconducting properties compared to the nonmagnetic nano-oxides CuO and SnO2. The gross structure of YBCO does not change with the substitution of the three types of magnetic nanosized metal oxides with different doping levels. In addition, the results show that the critical transition temperature (Tc) decreases with increasing doping level. The Tc value for Mn3O4 was high which may be due to flux pinning from defects. The rapid suppression in Tc with increasing concentration of Mn3O4 may be due to Cooper-pair breaking and hole filling in the CuO planes. Further doping of nanomagnetic and nonmagnetic oxides affects the crystallinity and homogeneity of the YBCO samples.

Fabrication of superconducting YBCO agglomerated particles (ANPs) by electrospinning

Superconducting YBa2Cu3O7-δ (YBCO) agglomerated nanoparticle (ANPs) was fabricated by electrospinning technique and sol-gel of a homogeneous precursor of Y-Ba-Cu acetate and Poly (vinyl pyrrolidone) (PVP). The sol-gel solution of YBCO is conducted by adding 4.0 g of (Y-Ba-Cu) metal acetate according to a stoichiometric ratio of 1:2:3 molar mass and 5.0 g of PVP powder in 25.0 ml solution contains propionic acid 10 ml, acetic acid 5 ml and methanol 10 ml. By optimizing electrospinning process, sol-gel parameters and heat treatment, YBCO ANPs were obtained with a transition temperature of Tc ~90 K using the AC susceptibility. YBCO ANPs was found with high surface area 6.8310 m2/g, and not affected by high calcination temperature at 950 oC in comparison with bulk YBCO sample. XRD Characterization of YBCO was demonstrated YBCO has orthorhombic phase, FESEM images of the electrospun YBCO sample showed ANPs of size in the 200 – 400 nm range. A closer examination revealed that agglomerates contain finer particles of size ~50 nm. Electrospinning is an effective technique can produce various morphologies of YBCO superconductor at the nanoscale with unique properties for practical applications.

Effects of CNTs blending on the superconducting parameters of YBCO superconductor

We report the structural modifications and variation of superconducting parameters of high temperature superconductor (HTSc) YBa2Cu3O7-δ (YBCO) by addition of different wt% of CNTs (0.0, 0.2, 0.4, 0.6, 0.8 & 1.0 wt%) synthesized by standard solid state reaction route. The orthorhombic structure of all the samples with Pmmm space group was confirmed from the X-ray Diffraction (XRD) analysis through Rietveld refinements. No significant variation is observed in the lattice parameters of the orthorhombic structure of YBCO superconducting matrix with increasing wt% of CNTs. The Field emission scanning electron microscope (FESEM) analysis shows better connectivity between the grains of CNTs doped samples. From the temperature dependent resistivity measurement, it is observed that there is no chemical reaction between superconducting YBCO and CNTs, rather addition of CNTs enhances the room temperature resistivity and more importantly reduces the critical temperature (TCon) for lower doped sample and then increases for higher doped sample but not for the pristine one. The paraconductivity studies reveal the 2D-3D transition in parent YBCO and the composites, with a signature of percolative behavior in the composites. Inclusion of CNTs to the YBCO enhances the value of critical current density and gives maximum value of JC which is 12 times more than that of pure YBCO sample for 0.8 wt% of YBCO.

High Temperature Superconductors (${\rm Y}_{1-x}{\rm Nd}_{x}$ )Ba2Cu3O7-δ Obtained by Acetate Method

Bulk ceramic samples with chemical composition (Y 1-x Nd x )Ba 2 Cu 3 O 7-δ , where x = 0, 0.1, 0.2, 0.5, and 1 were sintered by a proposed acetate method. The samples were then submitted to structural characterization by X-ray diffraction with crystal structure refining using the Rietveld method. AC electrical resistivity measurements from ambient temperatures down to 4.2 K were performed, as well as magnetic measurements of magnetic moment as function of temperature and magnetic hysteresis loop. Results have shown superconductivity with critical temperatures of about 91 and 60 K for pure YBa 2 Cu 3 O 7-δ (x = 0) and pure NdBa 2 Cu 3 O 7-δ (x = 1) samples, respectively. Scanning electron microscopy images were also analyzed, revealing a regular parallel-piped grain shape. The proposed method showed as an advantage to reduce the grinding time without any considerable degradation on structural or superconducting properties of pure YBa 2 Cu 3 O 7-δ (x = 0) or pure NdBa 2 Cu 3 O 7-δ ( x = 1), as related to samples prepared by a conventional solid state route.

A HIGH RETURN LOSS OF MICROWAVE BANDPASS FILTER USING SUPERCONDUCTING ELECTROSPUN YBCO NANOSTRUCTURES

A high return loss (-30 dB), small size (100 mm2) and broad bandwidth (1.5 GHz) microwave bandpass filter has been designed using finite element modelling and developed using the superconducting YBa2Cu3O7-δ (YBCO) thin films deposited on a (10 × 10 mm2) LaAlO3 substrate by spin coating. The thin films have been prepared by electrospinning and solid-state techniques. The microwave properties of filter circuits were experimentally determined using the vector network analyser (VNA) at room temperature (300 K) and in the presence of liquid nitrogen (77 K). The solid-state filter showed high return loss (i.e. -22 dB) at operating frequency of 9.7 GHz and broad bandwidth of 1.5 GHz, which is consistent with the simulation results. The insertion losses for YBCO filters are ~-2, ~-1.5 and ~-3 dB for the normal, nanoparticle and nanorod respectively. However, the electrospun filters exhibited lower performance due to the nano-structural properties of YBCO samples at nanoscale which make these sample have a large band gap compared to solid-state sample. The results indicate that the filter design and simulation result are reliable. Hence, HTS YBCO could be a potential microwave bandpass filter in industry.

Influence of annealing in oxygen and argon on the superconducting properties of Li-doped YBCO single-grain bulks

YBa2(Cu1-xLix)3O7-δ single-grain bulk superconductors with different Li concentrations were grown using the top-seeded melt growth process. Structural analysis of the samples and magnetisation measurements showed that substitution of the Cu atoms by the Li atoms took place in the YBa2Cu3O7-δ crystal lattice. This substitution was accompanied by the formation of effective pinning centres, which improved the pinning properties of the samples and increased the critical current density. Additional annealing and reannealing in oxygen and argon showed that the superconducting transition temperature displays substantially more suppression, when the Li-doped YBa2Cu3O7-δ samples were annealed in argon, that was associated with different distribution of the Li atoms between the CuO chains and the CuO2 planes in comparison to annealing in oxygen. Investigation of the critical current densities showed that the pinning properties of YBa2(Cu1-xLix)3O7-δ single-grain bulk superconductors did not depend on the arrangement of the Li atoms in the YBa2Cu3O7-δ crystal lattice. It was also observed that the crystal lattice parameters and the mean diameter of the non-superconducting Y2BaCuO5 particles systematically change with Li concentration.

Synthesis of Y1-xAlxBa2Cu3O7-δ via combustion route: Effects of Al2O3 nanoparticles on superconducting properties

Combustion reaction was used to synthesis Al2O3 nanoparticles embedded Y1-xAlxBa2Cu3O7-δ simultaneously. The effects of Al2O3 nanoparticles with nominal molar mass (xmol) of 0.02, 0.04, 0.06, 0.08 and 0.10 towards the critical current density JC of Y1-xAlxBa2Cu3O7-δ were verified by magnetic measurement. Resulted XRD patterns revealed that the calcined samples consist of pure Al2O3 and Y1-xAlxBa2Cu3O7-δ phases which had been confirmed by EDX results. The SEM images showed that Al2O3 nanoparticles (~10nm) were distributed in polycrystalline YBa2Cu3O7-δ grains and grain boundaries. The presence of higher concentration of Al2O3 nanoparticles has developed Al3+ rich spots which diffused within the YBa2Cu3O7-δ superconducting matrix to form Y1-xAlxBa2Cu3O7-δ and was confirmed by EDX analysis. The samples were electrically superconducting at temperature above 85K as measured by using standard four-probe technique. The magnetic field (H) dependent magnetization (M), M-H hysteresis loops measured at 77K for xmol≤0.06 samples are significantly improved attributed to the increase of trapped fluxes in the samples. Remarkable increase of magnetic JC (H) in Al2O3 nanoparticles added samples compared to the as prepared polycrystalline YBa2Cu3O7-δ sample indicating strong pinning effect. It is suggested that well-distributed Al2O3 nanoparticles in the polycrystalline YBa2Cu3O7-δ matrix achieved via auto-combustion reaction has efficiently pin the magnetic vortex. The magnetic JC was optimized to ~6 kAcm-2 in xmol=0.06 sample. On the other hand, insignificant magnetic JC improvement in xmol≥0.08 samples is probably resulted from the agglomerated Al2O3 nanoparticles in Y1-xAlxBa2Cu3O7-δ phase.

Functional behavior of the anomalous magnetic relaxation observed in melt-textured YBa2Cu3O7-δ samples showing the paramagnetic Meissner effect

We have studied the functional behavior of the field-cooled (FC) magnetic relaxation observed in melt-textured YBa2Cu3O7-δ (Y123) samples with 30 wt% of Y2Ba1Cu1O5 (Y211) phase, in order to investigate anomalous paramagnetic moments observed during the experiments. FC magnetic relaxation experiments were performed under controlled conditions, such as cooling rate and temperature. Magnetic fields up to 5T were applied parallel to the ab plane and along the c-axis. Our results are associated with the paramagnetic Meissner effect (PME), characterized by positive moments during FC experiments, and related to the magnetic flux compression into the samples. After different attempts our experimental data could be adequately fitted by an exponential decay function with different relaxation times. We discuss our results suggesting the existence of different and preferential flux dynamics governing the anomalous FC paramagnetic relaxation in different time intervals. This work is one of the first attempts to interpret this controversial effect in a simple analysis of the pinning mechanisms and flux dynamics acting during the time evolution of the magnetic moment. However, the results may be useful to develop models to explain this interesting and still misunderstood feature of the paramagnetic Meissner effect.

High-Field Paramagnetic Meissner Effect in Ga-Implanted Single Crystal

We report on dc magnetization data collected from a modified superficial pinning potential YBa 2 Cu 3 O 7-δ single crystal with the goal of checking the majority contribution of the magnetic flux compression scenario to the high-field paramagnetic Meissner effect (HFPME). The additional superficial pinning centers were introduced at the YBa 2 Cu 3 O 7-δ [YBCO(Ga)] single crystal surface by Ga ion beam bombardment. The field-cooled warming (M FCW (T)), field-cooled cooling (M FCC (T)), and zero-field-cooled (M ZFC (T)) dc magnetizations were recorded, while magnetic fields H up to 50 kOe were applied parallel to the single crystal c-axis. M FCW (T) and M FCC (T) data show the usual superconductor diamagnetic response to H <;5 kOe. In contrast, when 5 kOe ≤ H ≤ 50 kOe was applied, M FCW (T) and M FCC (T), particularly for T≪T irr (H) (magnetic irreversibility temperature), become paramagnetic. The magnetic-field-dependent paramagnetic behavior of M FCW (T) and M FCC (T) is the physical signature of HFPME in superconductor materials. We contrast the HFPME observed to the YBCO(Ga) sample with that observed to a not irradiated YBa 2 Cu 3 O 7-δ (YBCO) single crystal. We suggest that the enhancement of superficial pinning potential collaborates definitely to the strengthening of the magnetic flux compression scenario and consequently to the reinforcement of the HPME in YBa 2 Cu 3 O 7-δ single crystals.

High-field paramagnetic Meissner effect up to 14 T in melt-textured YBa2Cu3O7–δ

We have performed magnetization experiments in a melt-textured YBa2Cu3O7-δ (Y123) sample with Y2BaCuO5 (Y211) inclusions, under magnetic fields up to 14T applied parallel or perpendicular to the ab plane. Magnetic anisotropy and paramagnetic moments were observed in both FC (field-cooling) and FCW (field-cooled warming) procedures and these features correspond to the so-called High-Field Paramagnetic Meissner Effect (HFPME). The HFPME effect increases monotonically as the magnetic field rises and a strong paramagnetic relaxation, toward increasing paramagnetic moment was additionally observed as a function of time. Microscopy analysis revealed a complex and correlated microstructure of the Y211 particles. These correlated defects are well known to cause strong flux pinning. Our results suggest a scenario of strong flux compression within weak or non-superconducting regions of the samples, developed as a consequence of the Meissner effect and assisted by strong flux pinning by the Y211 particles. This scenario is observed up to 14T and clearly persists beyond.

An improved top seeded infiltration growth method for the fabrication of Y–Ba–Cu–O bulk superconductors

Buffer-aided top seeded infiltration and growth (TSIG) with a suitable liquid phase reservoir has been compared with the top seeded melt growth (TSMG) process and applied successfully to fabricate single grain YBa2Cu3O7-δ​(YBCO) bulk superconductors. A Yb-based liquid phase has been observed to yield the homogeneous, high density YBCO single grains by the TSIG technique. Sintering the Y2BaCuO5(Y-211) preform prior to TSIG has been found to be critical in retaining the shape of the sample during the infiltration and growth process. A number of advantages of the TSIG process have been demonstrated, including a dramatic reduction in sample shrinkage and a general improvement in bulk microstructure. TSIG processed samples also exhibit a fine and even distribution of unreacted, embedded Y-211 inclusions that play a key role in flux pinning in the fully processed bulk material. A YBCO sample of diameter 25mm fabricated by the optimised buffer-aided TSIG process was able to trap a field of 0.63T at 77K, which is the highest value of trapped field ever reported for a YBCO sample fabricated by the TSIG process. The technique reported here has the potential to improve further the microstructural and superconducting properties of single grain bulk YBCO, which enhances further the applications potential of these materials.

Effect of pressure on the critical temperature of single-crystal Y0.95Pr0.05Ba2Cu3O7–δwith a specified planar defect geometry

The effect of high hydrostatic pressures up to 17 kbar on the conductivity in the basal ab-plane of single crystal samples of Y1–xPrxBa2Cu3O7–δ with a system of unidirectional twin boundaries and lightly doped with praseodymium (x = 0.05) is studied. It is found that, in contrast with undoped YBa2Cu3O7-δ samples with an optimum oxygen content, high pressure leads to a double increase in the pressure derivative dTc/dP. Possible mechanisms for the effect of high pressure on Tc are discussed taking the existence of singularities in the carrier electronic spectrum into account.