Cu3 O7 Research Articles

Magnetodielectric and dielectric properties of orthorhombic HoMnO 3 thin films

Sandwich-structural multilayer films Au/HoMnO 3/YBa 2Cu 3O 7 − δ were prepared epitaxially on SrTiO 3 (001) single crystal substrates by using pulsed laser deposition technique. The HoMnO 3 films crystallized in a metastable orthorhombic structure and the Au and YBa 2Cu 3O 7 − δ were used as electrodes to investigate the dielectric and magnetodielectric properties of HoMnO 3 films. The impedance and electric modulus spectroscopic plots were used to discern the intrinsic characteristics of HoMnO 3 films or unwanted interface effects. The low-temperature (~ 2 K) dependence of the dielectric constant of HoMnO 3 films as function of frequency shows anomalies around 43 K and 22 K, which is corresponding to the Néel temperature and lock-in transition of Mn 3+ moments, respectively. The magnetodielectric effects of HoMnO 3 films were investigated at 100 kHz under a 2T applied magnetic field, and the dielectric constant was tuned resulting in a decrease of 3%. The results indicate the strong coupling between the dielectric properties and magnetic orders in orthorhombic HoMnO 3 films.

Surface planarization and masked ion-beam structuring of YBa 2Cu 3O 7 thin films

Surface planarization and masked ion-beam structuring (MIBS) of high-T c superconducting (HTS) YBa 2Cu 3O 7-δ (YBCO) thin films grown by pulsed-laser deposition (PLD) method is reported. Chemical–mechanical polishing, plasma etching, and oxygen annealing of YBCO films strongly reduce the particulate density (~ 10 –2 ×) and surface roughness (~ 10 –1 ×) of as-grown PLD layers. The resistivity, critical temperature T c ≈ 90 K and critical current density J c (77 K) > 1 MA/cm 2 of films are not deteriorated by the planarization procedure. The YBCO films are modified and patterned by irradiation with He + ions of 75 keV energy. Superconducting tracks patterned by MIBS without removal of HTS material and, for comparison, by wet-chemical etching show same T c and J c( T) values. Different micro- and nano-patterns are produced in parallel on planarized films. The size of irradiated pattern depends on the mask employed for beam shaping and features smaller than 70 nm are achieved.

Diffusion coefficient, activation energy and the effect of Ag-doping on some physical properties of silver doped Bi 1.8Pb 0.4Ca 2.2Sr 2Cu 3O x

The aim of the present study is to investigate the effect of diffusion-doped silver on some physical properties of Bi 1.8Pb 0.4Ca 2.2Sr 2Cu 3O x superconducting samples and to calculate the diffusion coefficient and the activation energy of silver. The present work consists of three parts: (a) optimization of annealing temperature, (b) the effect of Ag diffusion-doped on microstructure and superconducting properties of Bi(Pb)CaSrCuO, and (c) calculation of diffusion coefficient of silver. First, to investigate the optimum annealing temperature we prepared Bi 1.8Pb 0.4Ca 2.2Sr 2Cu 3O x ceramic superconductors annealed at 830, 835, 840, 845, and 850 °C using the solid state reaction method. The investigations consist of XRD, SEM, dc resistivity, and transport critical current density measurements. The highest T c and J c values were observed for the sample annealed at 840 °C for 48 h (B840). Large grain size, denser surface, and high volume fraction of the high- T c phase were obtained for the sample B840. The diffusion doping of Bi 1.8Pb 0.4Ca 2.2Sr 2Cu 3O x by silver increased the critical current density from 123 to 696 A/cm 2 and the transition critical temperature by about 3 K compared with the undoped sample. Ag-doping increased the amount of high- T c phase and improved the surface morphology. It also caused an increase of the lattice parameter c by an amount of 0.15%. The temperature dependence of the silver diffusion coefficient in the range 600–800 °C is described by D=2.9×10 −4exp(−1.05 eV/ k B T). Possible reasons for the observed improvement in the structural and superconducting properties of the samples due to silver diffusion are discussed.

Growth mechanism of nanorods in REBa 2Cu 3O y films (RE: rare-earth element)

Critical current density under magnetic fields has been improved by the introduction of artificial pinning centers. Nanorods in REBa 2Cu 3O y films are significantly effective as c-axis-correlated pinning centers. However, nanorods sometimes tilt from the c-axis direction of superconducting films. To understand the mechanism of nanorod tilting, ErBa 2Cu 3O y films containing Ba(Nb 0.5Er 0.5)O 3 (BNO) nanorods were deposited on a SrTiO 3 single crystal with a vicinal surface. Microstructures of the nanorods were examined by transmission electron microscopy (TEM). As a result, it was found that BNO nanorods grew diagonally from steps of the substrate surface in cross-sectional TEM images. The mechanism of the diagonal growth of nanorods can be explained by the segregation coefficient.

Microstructural changes in epitaxial YBa 2Cu 3O 7 −δ thin films due to creation of O vacancies

Structural and transport properties of YBa 2Cu 3O 7− δ thin films subjected to different heat treatments and, consequently, having different O vacancy contents are investigated. It is observed that lattice parameters of the films follow the trend of the bulk material, indicating that either the additional stresses created in c-axis oriented films by O vacancies are negligibly small or they are relaxed at elevated temperatures. In addition, heat treatment under relatively low O 2 partial pressures, used to create O vacancies, leads to considerable reduction in local variations of lattice spacings in YBa 2Cu 3O 7− δ thin films.

Fluorine-free sol–gel preparation of YBa 2Cu 3O 7− x superconducting films by a direct annealing process

Using yttrium, barium and copper acetates as starting materials, fluorine-free YBCO precursor solution is prepared by the chemical complexation approach with diethylenetriamine, lactic acid, and α-methacrylic acid as complexing agents. Using the stable precursor solution, YBCO gel films are coated on LaAlO 3 substrate by the dip-coating method. Effect of different heat treatment processes on the phase evolution and final film properties are examined. Results indicate that, either in a dry or in a humidified atmosphere, it is difficult to obtain high-performance YBCO films by a traditional pyrolysis–annealing process, due to the formation of stable BaCO 3 phase during the pyrolysis process. On the contrary, using the fluorine-free precursor solution, epitaxial YBCO films with high Tc (>94 K) and Jc (>1 MA/cm 2) can be obtained using a direct annealing process without pyrolysis process.

Influence of Pb-rich phases of precursor powder on microstructural evolution in the silver-sheathed (Bi,Pb) 2Sr 2Ca 2Cu 3O x superconducting tapes

The influence of Pb-rich phases of precursor powder on microstructural evolution during the first heat treatment of the silver-sheathed (Bi,Pb) 2Sr 2Ca 2Cu 3O x ((Bi,Pb)-2223/Ag) superconducting tapes was studied by means of in situ synchrotron X-ray diffraction. Three monofilament tapes were fabricated using precursor powders containing different Pb-rich phases. Sintering was carried out at a fixed temperature of 830 °C in 8.5% O 2. The phase transitions, structure changes and texture evolution in (Bi,Pb)-2223/Ag tapes were carefully analyzed, and the evolution of different Pb-rich phases, such as Ca 2PbO 4 and Pb 3Sr 2.5Bi 0.5Ca 2CuO y (3321), was discussed. It was found that tapes fabricated using the precursor with the (Bi,Pb)-2212 phase exhibited higher (Bi,Pb)-2223 formation rate than tapes fabricated using the precursors with Pb-rich phases. Texture evolution indicates that texture of the (Bi,Pb)-2212 phase formed in the thermomechanical process depends strongly on the Pb-rich phases of the precursor powders, while the texture of the new formed (Bi,Pb)-2223 grains for all three tapes follows the texture of (Bi,Pb)-2212 grains, and the final (Bi,Pb)-2223 and (Bi,Pb)-2212 textures are approximately identical. A higher texture degree of (Bi,Pb)-2223 grains was achieved in tapes fabricated using the precursors with 3321 or Ca 2PbO 4 phases.

Optically induced changes and long-term relaxations of resistivity and critical temperature in He + irradiated YBa 2Cu 3O x

Thin films of YBa 2Cu 3O x with superconducting critical temperatures ( T c) ranging from 58 K to 72 K were prepared by pulsed-laser deposition and subsequent irradiation with 75 keV He + ions. Optical excitation of the films with a He-Ne laser resulted in a small resistivity reduction, when the experiment was carried out a short period of time after the ion irradiation. The value of T c was essentially unchanged by the optical treatment. Further light excitation experiments did not show a significant effect on the resistivity of the samples. We conclude that ion-irradiated metallic YBa 2Cu 3O x does not exhibit the persistent photoconductivity observed in oxygen-depleted samples with comparable critical temperatures. On the other hand we have observed a long-term relaxation of T c towards larger values that takes place even when the samples are kept in the dark. Our results indicate that T c may increase after ion irradiation to an asmptotic value about 20% over the initial value on a typical time scale of years. This observation may be important for possible applications of light-ion irradiated YBa 2Cu 3O x.

Interaction mediated by size differences between Y 2BaCuO 5 and CeO 2 particles in melt-textured YBCO superconductors

The Refining of Y 2BaCuO 5 (Y211) is crucial in the fabrication of YBa 2Cu 3O x (Y123) bulk superconductors with a high critical current density ( J c ) for power engineering applications. In this work, the influence of an addition of Y211 and CeO 2 of different sizes on the Y211 refinement and superconducting properties of melt-textured Y123 superconductors is investigated. Nano-size Y211 and nano-size CeO 2 were prepared by attrition-milling (250 rpm and 2 h). Using mixed powders consisting of 85 wt.% Y123, 15 wt.% Y211, and 1 wt.% CeO 2, Y123 quasi-single crystals were fabricated via a top seed melt-textured growth process. The interaction between Y211 and CeO 2 of different particle sizes was examined in terms of the size, uniformity and density of the Y211 particles that existed in the melt-textured samples. The reaction between the nano-size Y211 and the nano-size CeO 2 was more violent due to the more frequent collisions compared to the other reactions (micro-size Y211/nano-size CeO 2 or micro-size Y211/micro-size CeO 2), resulting in the most effective for refinement of Y211 particles and the best J c value of 4.2 × 10 4 (A/cm 2) (at 77 K and a zero-field).

Transport Barkhausen-like noise in uniaxially pressed Bi 1.65Pb 0.35Sr 2Ca 2Cu 3O 10+ δ ceramic samples

We report on the detection of the transport Barkhausen-like noise (TBN) in polycrystalline samples of Bi 1.65Pb 0.35Sr 2Ca 2 Cu 3O 10+ δ (Bi-2223) which were subjected to different uniaxial compacting pressures. The transport Barkhausen-like noise was measured when the sample was subjected to an ac triangular-shape magnetic field ( f ∼ 1 Hz) with maximum amplitude B max ≈ 5.5 mT, in order to avoid the flux penetration within the superconducting grains. Analysis of the TBN signal, measured for several values of excitation current density, indicated that the applied magnetic field in which the noise signal first appears, B a ( t i ), is closely related to the magnetic-flux pinning capability of the material. The combined results are consistent with the existence of three different superconducting levels within the samples: (i) the superconducting grains; (ii) the superconducting clusters; and (iii) the weak-links. We finally argue that TBN measurements constitute a powerful tool for probing features of the intergranular transport properties in polycrystalline samples of high- T c superconductors.

Electronic property and structure of double-doping Y 1−2xPr xCa xBa 2Cu 3O 7−δ with 0 ⩽ x ⩽ 0.14

Equal amount Pr and Ca double-doping Y 1−2 x Pr x Ca x Ba 2Cu 3O 7− δ with 0 ⩽ x ⩽ 0.14 have been investigated by X-ray diffraction, resistivity, and X-ray photoemission spectroscopy (XPS). The deviation of the linearly decreasing of T c vs. x curve was observed when x < 0.10. The resistivity and the temperature coefficient of resistivity also exhibit abnormal behaviors around x = 0.10. It is revealed that the conductivity behavior of Y 1−2 x Pr x Ca x Ba 2Cu 3O 7− δ with low Pr content ( x < 0.10) is different from that of the relative high Pr content ( x > 0.10), which suggests a change of Pr valence with the Pr content. XPS measurement shows that the relative amount of Pr 3+ and Pr 4+ is closely related to the total Pr content x. The valence of Pr is close to +3 when x < 0.10 and increases towards +4 when x > 0.10, which implies a different mechanism for depression of superconductivity of Pr content x < 0.10 from that of Pr content x > 0.10 in Pr doping Y-123.

Effect of La 2Zr 2O 7-buffered YSZ substrate on YBa 2Cu 3O y thin films by chemical solution deposition

Epitaxial YBa 2Cu 3O y (YBCO) thin films have been fabricated by chemical solution deposition (CSD) on La 2Zr 2O 7-buffered YSZ single crystal substrate, where the buffer layer has three kinds of morphology – flat surface, rough surface and pore surface. The effect of LZO buffer layer’s roughness on the YBCO films was evaluated by X-ray diffraction, scanning electron microscopy and temperature-dependent resistivity measurements. The flat surface of LZO layer is beneficial to highly epitaxial YBCO films and high critical current density.

Flux pinning and superconducting properties of melt-textured NEG-123 superconductor with TiO 2 addition

We studied the effect of TiO 2 doping on flux pinning and superconducting properties of a melt-grown (Nd 0.33Eu 0.33Gd 0.33) Ba 2Cu 3O y + 35 mol% Gd 2BaCuO 5 (70 nm in size) composite (NEG-123) processed in Ar–1% O 2 atmosphere. As indicated by similar, sharp superconducting transitions, the small quantities of TiO 2 used in our experiments did not deteriorate superconducting properties of the NEG material. Transmission electron microscopy (TEM) analysis found 20–50 nm Ti-based particles in the NEG-123 matrix. However, we have not observed the clouds of <10 nm sized particles in the NEG-123 matrix, as in the case of recently reported NEG-123 composites doped by Mo and Nb nanoparticles. Nevertheless, quite a good J c – B performance in the 0.1 mol% Ti-doped sample, namely 550 kA/cm 2 at the self-field and at the secondary peak field (4.5 T) was achieved at 65 K, while 320 kA/cm 2 was obtained at zero-field at 77 K, and 50 kA/cm 2 at 90.2 K. The pinning effectiveness decreased with increasing Ti content above 0.2 mol%. The analysis of the pinning force showed that higher concentration of Ti (>0.2 mol%) increased the amount of normal pins ( δl pinning), indicated by the Fp( h) peak shift from h = 0.42–0.36. The maximum pinning effect in a broad field range could be achieved by optimizing Ti content and adding sub-micron Gd-211 particles.

Magnetic field dependence of the pinning effect in [formula omitted]-doped [formula omitted] ceramic superconductor

Y Ba 2Cu 3O 7−δ(Y BCO)+BaZrO 3 composites were prepared through the solid-state route, employing nitrate precursors of BaZrO 3 (BZO), yielding submicron particles. Invoking Bean’s critical state model, an enhancement of J c in composite samples in the presence of a magnetic field at a temperature ( T ) of 40 K has been observed. The resistive broadening in the tail part is suggested to be associated with the link between the grains and to be extremely sensitive to the magnetic field. It is assumed that the global zero-resistance state in the T c 0 region of high-temperature superconductivity (HTSC) is governed by the excitations in the weak-link network.

Alumina nano-inclusions as effective flux pinning centers in Y–Ba–Cu–O superconductor fabricated by seeded infiltration and growth

The YBa 2Cu 3O 7− x (Y123) textured bulk superconductors with various amounts of nanometer alumina particles were fabricated by a seeded infiltration and growth process. The addition of nanometer alumina was found to be effective for an improvement of the superconducting properties. The critical current density ( J c) values were increased twice in self field with a slight addition amount of nanometer alumina particles (maximum J c at 0.01 wt.% alumina addition). The present work suggests that the use of insulating inclusions in the nanometer sub-scale can stabilize the flux-line lattice and greatly enhance the pinning capabilities of the infiltrated samples. No refinement of Y211 particles was observed with alumina addition. The J c improvement by nanometer alumina inclusions is likely rendered to the insulating nano-pinning centers that have been successfully embedded into superconducting Y123 matrix. On the other hand, we examined the effect of the pinning centers size on the superconducting properties of infiltrated YBCO bulk samples. To this effect insulating nano-pinning centers with two different size distributions has been successfully incorporated within YBCO matrix of bulk superconductor by slightly doping with nano-particle alumina dispersions. Two alumina nano-particle dispersions with mean size diameters of about 20 nm and 130 nm were used. It was shown that the size of the pinning centers can affect considerably the J c performances and the pinning mechanism.

Deposition of Gd 2Zr 2O 7 single buffer layers with different thickness for YBa 2Cu 3O 7−δ coated conductors on metallic substrates

A series of Gd 2Zr 2O 7 (GZO) single buffer layers with different thicknesses were epitaxially grown on highly textured Ni–5 at.% W tapes using pulsed laser deposition. These allow the subsequent growth of high-quality superconducting YBa 2Cu 3O 7−δ layers. The superconducting transition temperature T c reaches a maximum value of 92.4 K as well as a narrow transition width of 0.8 K for the optimized GZO layer thickness. The inductive measurements show the critical current density as high as 1.2 MA/cm 2 at 77 K in self-field, indicating that a GZO single buffer layer is a suitable alternative for simplifying the second generation high T c superconducting coated conductors architecture.

Recovery of valuable elements from spent YBa 2Cu 3O 7– x/Ag composite superconductor bulks

Silver as a highly conductive metal is usually doped in YBa 2Cu 3O 7– x superconductor bulks to improve critical current density of YBa 2Cu 3O 7– x superconductor. The valuable metal elements silver, yttrium, barium and copper in waste YBa 2Cu 3O 7– x /Ag composite superconductor bulks were recovered, respectively. Silver was recovered with process at first, the waste was dissolved by nitric acid and silver chloride was precipitated by adding chloride acid, then silver pig was obtained by melting silver chloride together with sodium carbonate at 1 000 °C. The effective factors on recovery ratio and purity of silver were studied. The chemical analysis proves that the purity of silver ingot is 95.86%. The recovery ratio of silver is calculated to be 92.56%. The loss of silver may be due to the loss of silver chloride during filtering and the volatilization of silver when silver chloride and sodium carbonate are smelted at high temperature. For other three metal elements, Y 3+, Ba 2+ and Cu 2+, in the surplus waste liquid after recovering silver, they were separated with the sequence of barium, copper and then yttrium step by step. First, sulfate acid was used to precipitate barium sulfate. Then, sodium sulfide was added to the surplus solution so that copper could be separated as copper sulfide. During this separation procedure, it was important to control the pH value to be 1–2. After that, oxalic acid was added into the surplus solution to obtain yttrium oxalate. Finally, yttrium oxide was formed by burning yttrium oxalate. The XRD results indicate that the final products are all single-phase compounds as BaSO 4, CuS and Y 2O 3, respectively.

Study of magnetic field effect on the specific heat and entropy in DyBa 2Cu 3O 7− x

The change in the specific heat by the application of magnetic field up to 16 T for high temperature superconductor system for DyBa 2Cu 3O 7− x by Revaz et al. [23] is examined through the phenomenological Ginzburg–Landau(G–L) theory of anisotropic Type-II superconductors. The observed specific heat anomaly near T c with magnetic field is explained qualitatively through the expression 〈Δ C〉=( B a / T c ) t/(1− t) (αΘ( γ)/ λ 2 m (0)), which is the anisotropic formulation of the G–L theory in the London limit developed by Kogan and coworkers; relating to the change in specific heat Δ C for the variation of applied magnetic field for different orientations with c-axis. The analysis of this equation explains satisfactorily the specific heat anomaly near T c and determines the anisotropic ratio γ as 5.608, which is close to the experimental value 5.3±0.5 given in the paper of Revaz et al. for this system.

Optimization of the properties of codoped single-domain Y–Ba–Cu–O bulk superconductors

The intrinsic effects of nanoscopic MnO 2 powders addition combined with Fe cation substitutions for copper sites on the microstructure and superconductive properties of YBa 2Cu 3O 7− δ (Y123) melt-solidified bulks have been investigated. On the one hand, an increase in Y 2BaCuO 5 (Y211) particle pushing, leading to an inhomogeneous bulk microstructure, is caused by increasing MnO 2 content due to increased net interfacial energy, Δ σ 0; and, on the other hand, an addition of MnO 2 powders is effective in enhancing both the δT c- type and δl-type pinning. It also shows that the Fe addition helps to optimize the high magnetic field performance and Y211 particle distribution in textured pellets. Further, this experiment suggests that a combination of the element substitution and the nanoscopic particle is a beneficial way to optimize the microstructure and superconductive properties of single-domain bulk superconductors.

The doping dependence of the irreversibility line in grain-aligned Sm 1− xEu xBa 2Cu 3O 7−δ high- Tc superconductor

The irreversible properties of a rare-earth high- T c superconductor are investigated using grain-aligned Sm 1- x Eu x Ba 2Cu 3O 7−δ ( x = 0.0, 0.3, 0.5, 0.7, and 0.9) samples. The samples were synthesized using the usual solid–state reaction method. It is found that the transition temperature T c and the critical current density J c calculated by the Bean model are significantly improved in the optimally doped samples ( x = 0.5 and 0.7). Furthermore, the double logarithmic graph of the irreversibility line B irr in the grain-aligned series samples obeys approximately a power law dependence ( 1 − T / T c ) n . Results show that in the case of optimally doped samples with x = 0.5 and 0.7 the graph of B irr is fitted well with the relation ( 1 − T / T c ) n with the model-dependent parameter n ∼1.5 without any crossover in the entire temperature range, while in samples with x = 0.0, 0.3, and 0.9 B irr does show a prominent crossover and can be characterized with n ∼1.5 only near T c, above which B irr varies more rapidly. Finally, it is suggested that B irr is strongly dependent on the extrinsic properties of our grain-aligned samples.