Showing papers in "Physica C-superconductivity and Its Applications in 1993"
TL;DR: In this article, it was shown that there is a strong tendency for dilute holes in an antiferromagnet to phase separate, leading to high-temperature superconductivity.
Abstract: There is a strong tendency for dilute holes in an antiferromagnet to phase separate. (This is a generic feature of doping into a commensurate correlated insulating state.) We review the general and model-specific theoretical arguments that support this conclusion for neutral holes. In the presence of long-range Coulomb interactions, there is frustrated phase separation leading to large-amplitude, low-energy fluctuations in the hole density at intermediate length scales, provided the dielectric constant is sufficiently large. We describe extensive experimental evidence showing that such “clumping” of the holes is an important feature of the cuprate superconductors. We also summarize theoretical results which suggest that frustrated phase separation may account for the anomalous properties of the normal state and give rise to high-temperature superconductivity.
506 citations
TL;DR: In this paper, a theory of magnetic properties and AC-losses in superconductors with smooth current-voltage characteristics is proposed, which is applied to supercondors with a power law characteristic, E ≈ jα.
Abstract: In many high-Tc superconductors the critical current density jc is an ill-defined quantity due to the smooth current—voltage characteristic. Since jc is the basic parameter entering the critical state model, its application to such materials becomes problematic. In this paper, a theory of magnetic properties and AC-losses in superconductors with smooth current—voltage characteristics is proposed. It is applied to superconductors with a power law characteristic, E ≈ jα. The AC-losses are calculated analytically; simple scaling rules are obtained for their dependence on the frequency and the field amplitude. Moreover, it is shown that the normal ohmic conductor and the “perfect” type-II superconductor (critical state) emerge as limiting cases, α = 1 and α = ∞, from the theory.
376 citations
TL;DR: In this paper, the defect structure of HgBa 2 CuO 4+δ was investigated using neutron powder diffraction and it was concluded that the substitution of copper for about 8% of the mercury and the incorporation of additional oxygen (≈0.1 atoms per formula unit), presumably bonded to the copper defects, is the primary doping mechanism.
Abstract: We have used neutron powder diffraction to investigate the defect structure of HgBa 2 CuO 4+δ . An interstitial oxygen defect in the Hg plane is the primary doping mechanism. A superconducting transition temperature, T c onset , of 95 K is achieved when ≈0.06 oxygen atoms per formula unit are incorporated at this site by annealing the sample at 500°C in pure oxygen. Annealing in argon at 500°C lowers the oxygen content in this site to ≈0.01 and results in a T c of 59 K. The neutron powder diffraction data give evidence for a second defect in the Hg plane which we conclude involves the substitution of copper for about 8% of the mercury and the incorporation of additional oxygen (≈0.1 atoms per formula unit), presumably bonded to the copper defects. In the present samples, the concentration of this defect does not vary with synthesis conditions and its contribution to doping is, therefore, unclear. The structure of the compound is the same at room temperature and superconducting temperatures.
248 citations
TL;DR: In this article, a high transport critical current density, J c, in Ag-sheathed Bi-2223 superconducting tapes had been obtained using the oxide powder-in-tube technique.
Abstract: A high transport critical current density, J c , in Ag-sheathed Bi-2223 superconducting tapes had been obtained using the oxide powder-in-tube technique. At 77 K and self-field, the highest J c value of 69 000 A/cm 2 was measured for tapes of 80 μm thickness ( I c =35 A), while the largest critical current, I c , reached 74 A for tapes of 150 μm thickness ( J c =61 000 A/cm 2 ). A detailed investigation of the processing parameters has been carried out on the phase content and particle size of the starting powders, and on the sintering treatment and mechanical deformation of the tapes.
247 citations
TL;DR: In this paper, a pulling method using a BaO-CuO solution with the solid Y 2 BaCuO 5 (Y211) as a solute was used for continuous growth of YBa 2 Cu 3 O 7−x (Y123) crystals.
Abstract: Continuous growth of YBa 2 Cu 3 O 7− x (Y123) crystals was achieved by a pulling method using a BaO-CuO solution with the solid Y 2 BaCuO 5 (Y211) as a solute. A suitable crucible was also investigated, and an yttria crucible was found to be the best selection for this method. The growth was performed in an ambient atmosphere at about 1000°C. When a textured Sm- Ba 2 Cu 3 O 7− x (Sm123) rod was used as a seed crystal, the Y123 crystal grew epitaxially from the seed. The grown crystal contained no Y211 particles; however, it had a twin structure near the surface, which had been formed during the in situ cooling process. The temperature dependence of the resistance was metallic in both directions, along the c -axis and in the ab -plane, after appropriate oxygen annealing.
223 citations
TL;DR: In this paper, an exact analytical solution for current and field patterns on thin superconducting disks possessing pinning and oriented perpendicular to the external magnetic field was found for both constant and periodically varying external fields.
Abstract: Non-destructive inductance measurements of critical currents of thin superconducting YBa 2 Cu 3 O x films were carried out. In the framework of the critical state model, an exact analytical solution for current and field patterns on thin superconducting disks possessing pinning and oriented perpendicular to the external magnetic field was found. The problem was solved for both constant and periodically varying external fields. The solution allows one to describe the states of the film in weak field when there are wide regions free of vortices. The theoretical results were used to restore the temperature dependence of critical current density of HTSC films from their diamagnetic response.
213 citations
TL;DR: The second member (Hg-1212) of the recently discovered homologous series HgBa2Can−1CunO2n+2+δ has been synthesized by solid state reaction, carried out at 800°C under 60 kbar.
Abstract: The second member (Hg-1212) of the recently discovered homologous series HgBa2Can−1CunO2n+2+δ has been synthesized by solid state reaction, carried out at 800°C under 60 kbar. The X-ray diffraction powder pattern of one of the samples was refined by the Rietveld analysis. The final results clearly showed that it corresponded to the structural arrangement of the Hg-1212 compound with lattice parameters a = 3.8556 (8) A , c = 12.652 (4) A . No major impurities were observed in the X-ray pattern. AC magnetic susceptibility measurements showed that these samples undergo a paramagnetic-to-diamagnetic transition well above 120 K. The multi-transition aspect of the susceptibility curves showed that the samples contained some intergrowth. In a few samples a transition as high as 132 K was observed which might correspond to the third member of the Hg-series.
213 citations
TL;DR: The third and fourth members of the recently discovered homologous series HgBa2Can−1CunO2n+2+δ have been synthesized by solid state reaction, carried out at 950°C under 50 kbar at different annealing times.
Abstract: The third (Hg-1223) and the fourth (Hg-1234) members of the recently-discovered homologous series HgBa2Can−1CunO2n+2+δ have been synthesized by solid state reaction, carried out at 950°C under 50 kbar at different annealing times. These phases have a tetragonal cell with lattice parameters: a = 3.8532 (6) A , c = 15.818(2) A , and a = 3.8540(3) A , c = 19.006 (3) A , respectively. The c parameters are in agreement with the formula c ≌ 9.5 + 3.2 (n − 1). Electron microscopy study showed similar lattice parameters as well as the occurence of different intergrowths and stacking faults. A periodicity of 22 A has also been detected, which may be attributed to the existence of the Hg-1245 phase. EDS analysis data of several grains of Hg-1223 and Hg-1234 are in agreement with the proposed chemical formulae. AC susceptibility measurements show that an increase of the superconducting transition temperature with n in the HgBa2Can−1CunO2n+2+δ series occurs till the third member, after which a saturation seems to be achieved.
209 citations
TL;DR: In this paper, the authors proposed a new model for Bi/Pb(2223) tapes, based on the frequent small-angle c-axis grain boundaries that serve as highly conducting connections for the current between neighbouring grains, without the necessity for the supercurrent to flow perpendicularly to the CuO planes.
Abstract: Detailed analyses of the microstructure of silver-sheathed (Bi, Pb)2Sr2Ca2Cu3Ox tapes by scanning electron microscopy and X-ray diffraction, as well as measurements of the critical current density and the electrical resistivity of the isolated superconductor cores, have been performed on a series of short samples with filament thicknesses of approx 40–50 μm and jc (77 K, B=0) ≈ 15 000 A/cm2 The experimental data cannot be satisfactorily explained within the framework of the “brick wall” model for the current transport in highly textured polycrystalline high-temperature superconductors We therefore propose a new model for Bi/Pb(2223) tapes, based on the frequent small-angle c-axis grain boundaries that serve as highly conducting connections for the current between neighbouring grains, without the necessity for the supercurrent to flow perpendicularly to the CuO planes The model provides a semi-quantitative description of the field dependence of the critical current density and its anisotropy, and correlates them with characteristics microstructural features of the Bi/Pb(2223) tapes
203 citations
TL;DR: In this paper, a controlled vapor/solid reaction process for the synthesis of samples with up to 75 to 90% Hg-1212 and 65 to 75% HC-1223 by volume is presented.
Abstract: The newly-discovered homologous series HgBa 2 Ca n −1 Cu n O 2 n +2+δ [Hg-12 ( n -1) n ] with n = 1, 2, 3,… possesses the highest superconducting transition-temperature ( T c ) to date. Unfortunately, because of the complexity of its compound chemistry, it remains a challenge to prepare samples with pure or nearly-pure Hg-12 ( n -1) n for both scientific and applied studies. In the present investigation, we report the successful development of a controlled vapor/solid reaction process for the synthesis of samples with up to 75 to 90% Hg-1212 and 65 to 75% Hg-1223 by volume, which display sharp superconducting transitions up to 135 K. Detailed steps of the process are presented and discussed.
183 citations
TL;DR: In this article, a microscopic theory is developed for structures S-N-N′ (S is a superconductor, N, N′ are normal metals) with potential barriers at the interfaces.
Abstract: A microscopic theory is developed for structures S-N-N′ (S is a superconductor, N, N′ are normal metals) with potential barriers at the interfaces. The length of the N layer is supposed to be shorter than the energy relaxation length but longer than the mean free path l , and the dirty case is considered ( l is shorter than the coherence length in the N-layer). The differential conductance is calculated for different values of the barrier resistances compared to the resistance of the middle layer. The conductance has an anomaly (a peak) at voltages V Δ due to an enhancement of the proximity effect at low energies (voltages). The anomaly is suppressed by pairbreaking mechanisms. It is shown that the magnetoconductance can be negative or positive depending on the ratio of the barrier resistances and on the voltage. The AC conductance (admittance) has a peak at a frequency ω Δ . At high voltages V ⪢ Δ a transition from an excess current at high barrier transparencies to a deficit current at low barrier transparencies is found in S-N-N′ (S) structures.
TL;DR: In this paper, the anomalous peak effect in a Bi 2 Sr 2 CaCu 2 O 8+ y single crystal using a specially designed Hall probe magnetometer was studied, and the authors investigated the origin of the peak effect which manifests itself in the magnetic hysteresis loop, the relaxation (10 -2 s t 4 s), and the local field imaging experiments.
Abstract: We have studied an anomalous peak effect in a Bi 2 Sr 2 CaCu 2 O 8+ y single crystal using a specially designed Hall probe magnetometer. In order to investigate the origin of the anomalous peak effect which manifests itself in the magnetic hysteresis loop, the relaxation (10 -2 s t 4 s), and the local field imaging experiments were performed. Decoupling of 2D vortices in neighboring CuO layers, namely, a dimensional crossover in the pinning mechanism, is proposed as a possible mechanism of the peak effect.
TL;DR: In this article, the authors examined the consequences of the saddle point singularity on the superconducting transition temperature, the ratio 2Δ(0)/ T c, and the isotope effect.
Abstract: Angle-resolved photoemission experiments show that the high temperature superconductors YBa 2 Cu 3 O 6.9 and YBa 2 Cu 4 O 8 have a spectral density which exhibits an “extended” saddle point singularity along the Γ-Y symmetry direction, centered on the Y point. This, in turn, leads to a van Hove singularity in the density of states with a divergence stronger than the well-known logarithmic one. We examine the consequences of this singularity in several limiting cases on the superconducting transition temperature, the ratio 2Δ(0)/ T c , and the isotope effect. We conclude that this singularity alone, although it can possibly lead to sufficiently high transition temperatures and a vanishingly small isotope effect, does not explain the ratio of 2Δ(0)/ T c ∼6 observed experimentally.
TL;DR: In this paper, the subsolidus phase relationship in the Nd-Ba-Cu-O system has been investigated at 890°C in air and the discrepancies in the published phase diagrams of this system have been clarified.
Abstract: The subsolidus phase relationship in the Nd-Ba-Cu-O system has been investigated at 890°C in air. In this study, the discrepancies in the published phase diagrams of this system have been clarified. For the BaO-rich region, CO2-free (CO2<3 ppm) air was necessary to synthesize equilibrium phase. Significant results include determination of the solubility limits of 0.04≤χ≤0.6 in Nd1+χBa2−χCu3O7+δ, the existence of a Nd2BaCuO10 solid solution, and discovery of a new phase, NdBa6Cu3Oy, in the BaO-rich region.
TL;DR: The two-powder process has been used to produce a superconducting bismuth-2223 phase during powder-in-tube processing as discussed by the authors, which results in a nearly pure 2223 in as little as 50 h.
Abstract: Use of a so-called two-powder process results in rapid formation of a highly pure superconducting bismuth-2223 phase during powder-in-tube processing. In this process, Sr χ Ca 1−χ CuO 2 and Bi 1.8 Pb 0.4 Sr 2−χ Ca 1+χ Cu 2 O 8 are formed as separate intermediate phases, and mixed, then processed together within a silver sheath. Mixtures with χ values of 0.0, 0.25, 0.50, 0.75, and 1.0 are studied in order to probe the relationship between 2223 formation and the melting behavior of 2212. The best results to date have been obtained with the χ=0.0 mixture containing high-melting, strontium-rich 2212 and calcium cuprate. The process is very reproducible and produces nearly pure 2223 in as little as 50 h.
TL;DR: In this article, the defect structure and superconducting propertiess of HgBa2CaCu2O6+δ were studied by neutron powder diffraction, AC susceptibility and DC resistivity.
Abstract: We have studied the defect structure and superconducting propertiess of HgBa2CaCu2O6+δ by neutron powder diffraction, AC susceptibility and DC resistivity. An as-synthesized sample has an onset Tc of 128 K, the highest yet reported for this material. The critical temperature decreases slightly (126 K) after oxygenation, and drops to 92 K after reduction in flowing argon. Neutron diffraction data give evidence that the primary doping mechanism in this material is provided by oxygen atoms in an interstitial position, similar to the case of the one-layer compound HgBa2CuO4+δ. The occupancy of this site varies from 0.08 (1) for the argon-reduced sample to 0.22 (1) for the oxygenated sample. Unlike the case of the one-layer compound, no evidence of an additional defect site was found in these samples. HgBa2CaCu2O6+δ has remarkably long copper-apical oxygen distances and almost perfectly flat CuO2 planes.
TL;DR: In this paper, the high temperature superconducting Hg-Ba-Ca-Cu-O (HBCCO) compound system reported by Schilling et al. has been reproduced with an onset transition-temperature up to ≁140 K and a main transition at ≁135 K, after proper heat-treatment.
Abstract: The high temperature superconducting Hg-Ba-Ca-Cu-O (HBCCO) compound system reported by Schilling et al. has been reproduced with an onset transition-temperature ( T c0 ) up to ≁140 K and a main transition at ≁135 K, after proper heat-treatment. We found a positive pressure-effect on T c with a rate of 0.17 to 0.18 K/kbar and an irreversibility line at temperatures higher than that in the double Bi and Tl layered high temperature superconductors (HTS's). The observation suggests that the compounds synthesized by us are underdoped and further T c enhancement (although not drastic) is possible by proper doping, and the HBCCO system appears to be a better candidate than the double Bi and Tl layered HTS's for applications based on the higher irreversibility line.
TL;DR: In this paper, a high-pressure technique was used to obtain samples with nominal compositions of Sr 0.6 Ca 0.333 CuO 2.6 A and 10.3 A along the c-axis.
Abstract: Samples with nominal compositions of Sr 0.6 Ca 0.333 CuO 2.00+ z ( z =0.00—0.20) were prepared using a high-pressure technique. The crystallographic structure of the major phase in the sample with z =0.00 was an “infinite-layer” type. With increasing z , the “infinite-layer” phase decomposed and new compounds having periodic structures of 13.6 A and 10.3 A along the c -axis appeared. The samples with z ≥0.10, which contained little of the “infinite-layer” phase, exhibited bulk superconductivity. This suggests the presence of new superconducting phases in addition to the “infinite-layer” phases in the Sr-Ca-Cu-O system.
TL;DR: In this paper, the structure and superconducting properties of the infinite-layer compound A 1− x CuO 2− z (A=Ca 1− y Sr y ) have been investigated by high-resolution electron microscopy as well as magnetization and resistivity measurements.
Abstract: Microstructure and superconducting properties of the infinite-layer compound A 1− x CuO 2− z (A=Ca 1− y Sr y ) have been investigated by high-resolution electron microscopy as well as magnetization and resistivity measurements. The alkaline earth deficient samples always contain defect-layers inserted almost randomly into the parent simple structure, where we suggest that the A cation vacancies are concentrated. High-resolution electron microscopy observations reveal that oxygen deficiency can simultaneously occur within the central CuO 2 sheet of the defect layer for the sake of charge compensation for the A deficiency. p-type superconductivity with a maximum T c of 110 K is realized if the oxygen defects are filled in by application of high oxygen pressure on high-pressure synthesis ( z ∼0). On the other hand, n-type superconductivity also occurs in the same structure when oxygen deficency is increased so that z > x by a heat-treatment in a reducing atmosphere under high pressure. The fundamental relationship between structure and superconductivity is discussed on the basis of the demonstrated structural uniqueness of the title compound.
TL;DR: The crystal structure of the superconductor HgBa2Ca2Cu3O8+δ has been determined by neutron powder diffraction techniques at room temperature and at 10 K.
Abstract: The crystal structure of the superconductor HgBa2Ca2Cu3O8+δ has been determined by neutron powder diffraction techniques at room temperature and at 10 K. The compound crystallizes with the symmetry of space group P4/mmm and lattice parameters a=3.8501(1), c=15.7837(9) A . The structure is described by the sequence of layers: …[(CuO2)(Ca)(CuO2)(BaO)(HgOδ(BaO)(CuO2)(Ca)]… The compound, prepared by a solid-state reaction between HgO and the precursor Ba2Ca2Cu3Ox at a pressure of 18 kbar and 880°C, has an oxygen composition corresponding to δ=0.41 (2). This extra oxygen is located on the layer of the mercury atoms at the sites 1 2 , 1 2 , 1 2 . The superconducting transition temperature for the as-prepared sample is Tc=133 K. No evidence has been found of orthorhombic distortions, nor for substitution of some of the Hg atoms by Cu. The copper and oxygen atoms of the layers (CuO2) are coplanar for the Z=0 (CuO2 plane and almost perfectly coplanar for the others. No phase transition occurs down to 10 K.
TL;DR: In this article, a process for the preparation of superconducting films of TlxCa2Ba2Cu3Oy (0.65 10 000 A/cm2) was described.
Abstract: A process is described for the preparation of superconducting films of “1223” TlxCa2Ba2Cu3Oy (0.65 10 000 A/cm2 was measured at 60 K-2 T with the magnetic field applied parallel to the crystallographic c-axis of the film.
TL;DR: In this paper, the crystal structures of HgBa2CuO4+δ and Hg BaO2 have been refined at room temperature using neutron powder diffraction data obtained from a sample containing 44% of the first phase, 42% of second phase and 14% of Ba2Cu3O5+ Δ.
Abstract: The crystal structures of HgBa2CuO4+δ and HgBaO2 have been refined at room temperature using neutron powder diffraction data obtained from a sample containing 44% of the first phase, 42% of the second and 14% of Ba2Cu3O5+δ. the compound HgBa2CuO4+δ crystallizes with the symmetry of space group P4/mmm and lattice parameters a = 3.8829 (6), c = 9.5129 (14) A . The unit cell contains only one CuO2 layer and the material is a superconductor with a value of Tc of 94 K. The oxygen in excess of the O4 stoichiometry (δ = 0.063 in our sample) is located in interstitial positions on the HgOδ layer, and it is the only extra oxygen present in the structure. No mixing of the cations has been detected in this study. The compound HgBaO2 crystallizes with the symmetry of space group R 3 m and lattice parameters (hexagonal axes) a = 4.0991 (6), c = 19.355 (3) A . In this new polymorph of HgBaO2 the Ba atoms are octahedrally coordinated while Hg has two-fold coordination.
TL;DR: Sr-Ca-Cu-O samples which exhibited bulk superconductivity and contained phases of layer structures with long-range periodicities of (10.2+3.4m) A (where m=0, 1 and 2) were obtained using a high-pressure technique.
Abstract: Sr-Ca-Cu-O samples which exhibited bulk superconductivity and contained phases of layer structures with long-range periodicities of (10.2+3.4m) A (where m=0, 1 and 2) were obtained using a high-pressure technique. Phases contained in the samples were investigated by electron diffraction, transmission electron microscopy and X-ray powder diffraction. Members with n = 2, 3 and 4 of a homologous series written as “02(n−1)n” were proposed for these new superconducting phases.
TL;DR: In this paper, the location of the irreversibility boundary H irr (T ) in the magnetic phase diagram of the material was estimated from magnetization-loop measurements and broadening of the resistive transition in external magnetic fields.
Abstract: Samples containing superconducting HgBa 2 Ca 2 Cu 3 O 8+ x (Hg-1223) (a=3.851 (3) A , c=15.847 (9) A ) as the dominant phase have been investigated by resistivity and magnetization measurements in external magnetic fields up to 50 kOe. The specimens exhibit critical temperatures T c ≈ 133 K, as measured by susceptibility and specific-heat experiments, with typical field-cooling susceptibilities χ FC > 20% of - 1/4 π at low temperatures. In zero field, the electrical resitance is zero below T = 129 K. From magnetization-loop, M ( H ), measurements and the broadening of the resistive transition in external magnetic fields, H , we estimate the location of the irreversibility boundary H irr ( T ) in the magnetic phase diagram of the material. Estimates of the critical-current densities j c in a magnetic field for T = 10 K and 75 K suggest that the intragrain critical-current densities are of comparable order of magnitude to those routinely observed in YBa 2 Cu 3 O 7 at those temperatures.
TL;DR: In this paper, the growth of perfect single-phase (2212) superconducting BSCCO whiskers with cross-sectional area S as small as 0.1 μm 2 is described.
Abstract: The growth of perfect single-phase (2212) superconducting BSCCO whiskers with cross-sectional area S as small as 0.1 μm 2 is described. Submicron cross section whiskers are shown to have perfect crystalline structure, some of them being free of dislocations. The critical current density of the whiskers J c , is shown to increase as S decreases 2 achieving 5 × 10 5 A/cm 2 for S = 0.15 μm 2 . The temperature dependence of resistivity ϱ( T ) of submicron whiskers in contrast to bulk-like single crystals exhibits a prominent deviation Δϱ down from linear temperature dependence ϱ N up to T ≈ 200 K. Δϱ is shown to be proportional to s −1 Δϱ / ϱ N S −1 exp(− T / T 0 ), T 0 =40 K K. The origin of Δϱ due to one-dimensional (1D) superconducting fluctuations is discussed.
TL;DR: In this article, a new thallium copper oxycarbonate Tl 0.5 Pb 0.824 A, c = 16.516 A was isolated by X-ray diffraction and high-resolution electron microscopy.
Abstract: A new thallium copper oxycarbonate Tl 0.5 Pb 0.5 Sr 4 Cu 2 (CO 3 )O 7 has been isolated. This new phase crystallizes in the tetragonal system with a =3.824 A, c =16.516 A. Its study by X-ray diffraction and high-resolution electron microscopy allows a structural model to be proposed which consists of the intergrowth of double rock-salt layers [(TlO) (SrO)] ∞ , with single perovskite layers [SrCuO 3 ] ∞ and layers of carbonate groups according to the general formula [(SrO)(Tl 0.5 Pb 0.5 O)] RS [(SrCuO 3 ) 2 ] P [SrCO 3 ]. In fact this structure is a derivative of a hypothetical structure “Tl 0.5 Pb 0.5 Sr 4 Cu 3 O 10 ” closely related to the 1223 structure Tl 0.5 Pb 0.5 Sr 2 Ca 2 Cu 3 O 9 . The susceptibility measurements with an AC susceptometer demonstrate that this phase is a superconductor characterized by a sharp transition with a T c of 60 K when synthesized. Moreover, the comparison with other oxycarbonates shows that this phase exhibits a much higher superconducting volume fraction which reaches 70% at 4.2 K. Annealings performed in an argon-hydrogen flow (10%H 2 ) at 290°C allows the T c to be increased up to 70 K, keeping the same superconducting volume fraction; this optimization of T c is explained in terms of hole carrier density governed by an oxygen non-stoichiometry according to the formula Tl 0.5 Pb 0.5 Sr 4 Cu 2 (CO 3 )O 7-δ . The possible synthesis of a series of superconductors with the generic formula (Tl,Pb) n Sr 4 n Cu 3 n -1 (CO 3 )O 10 n -3 is discussed.
TL;DR: In this paper, the authors presented analytical solutions of field and current patterns in thin film disk-shaped type-II superconductors in perpendicular time-varying periodic external magnetic fields.
Abstract: Following the procedure of Mikheenko and Kuzovlev, we present analytical solutions of field and current patterns in thin film disk-shaped type-II superconductors in perpendicular time-varying periodic external magnetic fields. We also calculate the magnetic moment and effective susceptibility. The analysis is carried out within the framework of the critical state model assuming a constant critical current. Our results are compared to that of Mikheenko and Kuzovlev; and we discuss the discrepancies.
TL;DR: In this paper, it was shown that magnetic hysteresis loop measurements are better suited to investigate fast flux-line movements than conventional flux-creep measurements, and the experimental data were well described by using an activation energy U(j)=(Uc/μ)[(jc/j)μ-1] with μ=0.74 at 16 K and 1.8 T.
Abstract: Measurements of the dependence of the magnetic hysteresis loop amplitude in a superconductor on the magnetic field sweep rate dHe/dt are shown to provide essentially the same information as magnetic relaxation experiments (flux-creep) at fixed external field He. For practical reasons, however, magnetic hysteresis loop measurements are better suited to investigate fast flux-line movements than conventional flux-creep measurements. From the general flux movement differential equation it is shown that each magnetic hysteresis loop recorded at a given dHe/dt can be labelled by an effective time t M 0 so that this experimental information can be used to extend the time window of flux-creep measurements to short times. This method is applied to the experimental data obtained on a YBa2Cu3O7 single crystal. In this way the time window is extended to less than 10-2 s which is valuable for a more precise check of existing theoretical models for the activation energy of flux motion. It is found that the experimental data are well described by using an activation energy U(j)=(Uc/μ)[(jc/j)μ-1] with μ=0.74 at 16 K and 1.8 T.
TL;DR: In this article, a combination of high-resolution Z-contrast imaging and highresolution electron energy loss spectroscopy (EELS) in the scanning transmission electron microscope (STEM) was used to study the local hole depletion and local atomic structure in the region of grain boundaries.
Abstract: Using a combination of high-resolution Z-contrast imaging and high-resolution electron energy loss spectroscopy (EELS) in the scanning transmission electron microscope (STEM), the local hole depletion and local atomic structure in the region of grain boundaries can be studied simultaneously. The atomic resolution Z-contrast image can be used to position the probe for energy loss spectroscopy, which by quantitative analysis of the pre-edge feature of the oxygen K-absorption edge can be used to measure the local hole depletion to an accuracy of approximately 5%. Additionally, as the Z-contrast technique is sensitive to the effects of damage from the specimen preparation, boundaries representative of the original material can be easily selected. Studied have been performed on both asymmetric and symmetric high-angle tilt boundaries in YBa 2 Cu 3 O 7−δ films prepared by laser ablation on yttria-stabilised-zirconia (YSZ) substrates. The symmetric boundary shows no significant hole depletion in the boundary region whereas the asymmetric boundary has significant depletion in a zone extending over a far greater region than the disordered atomic structure indicated by the image.
TL;DR: In this article, the synthesis of the HgBa2CaCu2O6+δ (Hg-1212) superconductor under various experimental conditions in sealed silica tubes is reported.
Abstract: The synthesis of the HgBa2CaCu2O6+δ (Hg-1212) superconductor under various experimental conditions in sealed silica tubes is reported. Optimization of synthesis conditions allowed the preparation of bulk superconducting Hg-1212 with Tc onset at 127 K and lattice parameters a=3.858 A , c=12.68 A . The neutron powder diffraction analysis yielded δ=0.22(4). As a result of different atmosphere annealings a relationship between the decrease of Tc and the increase of the lattice parameter a is deduced. A 300°C/10 h treatment in 99% N2/1% O2 reduces Tc to 123 K and increases the a parameter to 3.862 A. An additional 10 h reduction in a 100% N2 flow lowers Tc to 98 K while a increases to 3.865 A. Subsequent oxidation at 300°C for 10 h in O2 flow restores the lattice parameters and Tc onset to their original values. The Tc dependence on annealing conditions is shown to be reversible.