Intragranular Properties Research Articles

Electrical effective parameters of the grains and the Montgomery's method in $$\hbox {Bi}_{1.65}\hbox {Pb}_{0.35}\hbox {Sr}_2\hbox {Ca}_{2.5}\hbox {Cu}_{3.5}\hbox {O}_y$$ Bi 1.65 Pb 0.35 Sr 2 Ca 2.5 Cu 3.5 O y ceramics

In this paper we have applied the Montgomery’s measurement method to $$\hbox {Bi}_{1.65}\hbox {Pb}_{0.35}\hbox {Sr}_2\hbox {Ca}_{2.5}\hbox {Cu}_{3.5}\hbox {O}_y$$ ceramic samples, to study the behavior of the grains’ electrical effective parameters, such as: intrinsic effective anisotropy, $$t=\rho _c/\rho _{ab}$$ , the slope of the linear part in the temperature dependence of the ab-planes resistivity, $$A_{ab}=\varDelta \rho _{ab}/\varDelta T$$ , the weak links resistivity, $$\rho _{wl}$$ , and the orientation probability of the grains’ a-axes along a certain preferential direction, $$\gamma _{xa}$$ . Here, $$\rho _{ab}$$ , $$\rho _{c}$$ and T are the main values of the resistivitity tensor and the measurement temperature, respectively. The samples were pressed uniaxially at three different compacting pressures and extracted from the pellets by cutting an slab along the cylinder axis. Samples cut in this way, exhibit almost an isotropic behavior in the transport properties. Moreover, the sample extracted from the pellet compacted at 488 MPa exhibits the best inter and intragranular properties. The effective intrinsic anisotropy of its grains has the lowest value in the sample set. These results can be used in the fabrication of this superconducting material for certain applications.

Does the pelletization pressure modify the effective anisotropy of the grains in (Bi,Pb)2223 bulk system?

In this paper we present a new method to determine separately inter and intragranular magnitudes of polycrystalline superconducting materials, such as: intrinsic effective anisotropy, $$t=\rho _c/\rho _{ab}$$ , the slope of the linear part in the temperature dependence of the ab-planes resistivity, $$A_{ab}=\Delta \rho _{ab}/\Delta T$$ , the weak links resistivity, $$\rho _{wl}$$ , and the orientation probability of the grains’ a-axes along a certain preferential direction, $$\gamma _{xa}$$ . Here, $$\rho _{ab}$$ , $$\rho _{c}$$ and T are the main values of the resistivitity tensor and the measurement temperature, respectively. The application of the method, illustrated by two (Bi,Pb)2223 polycrystalline samples, allows comparing the parameters obtained for the grains with those reported in single crystals. Moreover, we have demonstrated that different compacting pressures in the fabrication of the pellets change not only the inter, but also the intragranular properties of the ceramics. The method could be used to follow the different steps during the synthesis of polycrystalline high $$T_{c}$$ superconductors in order to optimise the process.

Grain properties, grain-boundary interactions and their effects on the characteristics of marbles used as building stones

In this study, the effects of relationships of micro-structure, grain size and grain boundary of 15 well-known worldwide marbles on some physical and mechanical properties (dry unit weight, porosity, uniaxial compressive strength, tensile strength) and on abrasion loss value were investigated in detail, being the first in terms of elaborateness in the literature considering the mentioned features. 10 different samples were tested for each marble in each test. Microscope images were grouped as intergranular properties (shape of grains, shape of grain aggregates, grain boundary type and pressure solution), intragranular properties (twinning and alteration) and deformation. All marbles which were tested were found to be of heteroblastic texture. Nine samples were monomineralic marble while six were polymineralic. It was determined that grain characteristics and grain boundary interaction affected dry unit weight, porosity, uniaxial compressive strength, tensile strength and abrasion loss value of each marble tested.

The Effect of Ag Addition on the Superconducting Properties of FeSe0.94

In this study, we examined the influence of Ag addition on the superconducting properties of polycrystalline FeSe0.94. The samples were obtained by a solid-state reaction and melting. The X-ray diffractometry (XRD) analysis showed the presence of a tetragonal phase, while the energy-dispersive X-ray analysis (EDX) analysis established an inhomogeneous Ag distribution in the grains. The superconducting properties were investigated by measuring the AC magnetic susceptibility’s fundamental and third harmonic. The intergranular critical current determined from the AC magnetic susceptibility in the Ag-doped sample was several times higher than that in the undoped one, obtained by melting at approximately the same temperatures. The irreversibility lines were obtained from the temperature dependence of the AC magnetic susceptibility’s third harmonic at different DC magnetic fields. It was found that adding Ag increases the irreversibility field in comparison with both undoped (melted and powder-sintered) samples. All results showed that the Ag addition to FeSe0.94 samples improves the following intergranular and intragranular properties: screening ability, pinning, activation energy, and critical current and increases the irreversibility field.

A nonlinear analysis of the transport Barkhausen-like noise measured in (Bi,Pb)2Sr2Ca2Cu3O10+δ superconductors

We investigated the transport Barkhausen-like noise (TBN) by using nonlinear time series analysis. TBN signals were measured in (Bi,Pb)2Sr2Ca2Cu3O10+δ ceramic samples subjected to different uniaxial compacting pressures (UCP). These samples display similar intragranular properties but different intergranular features. We found positive Lyapunov exponents in all samples, λm≥0.062, indicating the nonlinear dynamics of the experimental TBN signals. It was also observed higher values of the embedding dimension, m>9, and the Kaplan-Yorke dimension, DKY>2.9. Between samples, the behavior of λm and DKY with increasing excitation current is quite different. Such a behavior is explained in terms of changes in the microstructure associated with the UCP. In addition, determinism tests indicated that the TBN masked determinist components, as inferred by |k[over arrow]| values larger than 0.70 in most of the cases. Evidence on the existence of empirical attractors by reconstructing the phase spaces has been also found. All obtained results are useful indicators of the interplay between the uniaxial compacting pressure, differences in the microstructure of the samples, and the TBN signal dynamics.

The influence of a grain boundary on the thermal transport properties of bulk, melt-processed Y–Ba–Cu–O

We report the dependence of thermal conductivity, thermoelectric power and electrical resistivity on temperature for a bulk, large grain melt-processed Y–Ba–Cu–O (YBCO) high temperature superconductor (HTS) containing two grains separated by a well-defined grain boundary. Transport measurements at temperatures between 10 and 300 K were carried out both within one single grain (intra-granular properties) and across the grain boundary (inter-granular properties). The influence of an applied external magnetic field of up to 8 T on the measured sample properties was also investigated. The presence of the grain boundary is found to affect strongly the electrical resistivity of the melt-processed bulk sample, but has almost no effect on its thermoelectric power and thermal conductivity, within experimental error. The results of this study provide direct evidence that the heat flow in multi-granular melt-processed YBCO bulk samples should be virtually unaffected by the presence of grain boundaries in the material.

Significant Improvement in Superconductivity by Substituting Pb at Bi-site in Bi2−x Pb x Sr2CaCu2O8 with x=0.0 to 0.40

Here we report the synthesis and superconducting properties of bulk Bi2−xPbxSr2CaCu2O8 (x=0.0 to 0.4) compound. Though the superconducting transition temperature (Tc) decreases marginally, the critical current density under magnetic field Jc(H) increases with Pb content. An optimization is observed for x=0.16 with Jc(H) (7.894×103 A/cm2) that is nearly doubled in comparison to the pristine compound. It seems that controlled substitution of Pb at Bi-site in bulk Bi-2212 (Bi2Sr2CaCu2O8) system can enhance the superconducting critical parameters. These results are explained on the basis of possible improved inter- and intra-granular properties with Pb substitution in Bi2−xPbxSr2CaCu2O8 system.

Effect of Second Sintering on Intragranular Structure and Mechanical Properties of 10vol%Al<sub>2</sub>O<sub>3</sub>/3Y-TZP Composites

To study the effect of second sintering on intragranular structure and mechanical properties of 10vol%Al2O3/3Y-TZP composites, the composites were prepared by ball-milling nano-γ-Al2O3 and nano-ZrO2(3mol%Y2O3), pressing unidirectionally, cold-pressing isostatically, then first sintering at 1400°C for 2h and second sintering at 1600°C for 5h in air. The composition and microstructure of the composites were examined by X-ray diffractometer and scanning electron microscope, transmission electron microscope. The results showed that the second sintering changed the microstructure and fracture mode. After second sintering, the structure of fine grains was changed into the mixed one of large grains and small grains . Many large grains contained small grains, forming intragranular stucture that could be produced by the interblending of not only Al2O3 and ZrO2 but also ZrO2 itself. The intergranular fracture after first sintering was changed into transgranular fracture and intergranular fracture after second sintering . The second sintering led to grinds growing up and intragranular forming, which enhanced the contribution of the phase transformation toughening. Although the second sintering resulted in abnormal increase of grain size, the fracture strength and the fracture toughness of the composite were 667 MPa and 12.9 MPa⋅m1/2, respectively, due to the intragranular structure and the enhanced phase transformation toughening.

Evidence for Irradiation Triggered Nonuniform Defects Distribution in Multiharmonic Magnetic Susceptibility of Neutron Irradiated YBa2Cu3O7− δ

Multiharmonic ac-magnetic susceptibility \ch11,\chi2,chi3, of neutron irradiated Li-doped YBa2Cu3O7-x has revealed a nonmonotonic dependence of all harmonics on the neutron fluence. The irradiation has a strongly depressive influence on the intergrain connection suggesting an increase of the effective thickness of the intergranular Josephson junction at aneutron fluence of 0.98x10$^{17}$ cm$_{-2}$. Less damaged are the intragrain properties. A spectacular enhancement of the superconducting intragranular properties reflected in the characteristics of all harmonics was observed at highest fluence \Phi = 9.98x10$^{17}$ cm$_{-2}$. We assume that this effect results from the development of a space inhomogeneous distribution with alternating defectless and defect rich regions.

The intergranular and intragranular properties of Ag-clamped Bi-2212 thick films melt-solidified with and without Bi2Al4O9

Two types of Ag-clamped Bi2Sr2CaCu2Ox (Bi-2212) thick films have been prepared using the screen-printing method and the melt-solidification process conducted with and without Bi2Al4O9. The melt-solidification process with Bi2Al4O9 leads to the critical-current density (JC) having a sharper dependence on the maximum sintering temperature (TM) and to the rise of the optimum TM value. We compare the microstructure and JC properties of both samples sintered at each optimum TM to investigate the influence of the bismuth vapour dispersed from Bi2Al4O9 during the melt-solidification. The results of inductively coupled plasma analysis, x-ray diffraction analysis and scanning electron microscopy studies show that the composition of the Bi-2212 layer and the precipitation of the impurities for both samples are almost the same. The intergranular coupling of the Ag-clamped sample is independent of the existence of the bismuth vapour during the melt-solidification, which is the exact opposite of the previous result obtained for a thick film with a single Ag substrate. On the other hand, it is found that the intragranular pinning of the Ag-clamped sample is damaged by the melt-solidification with Bi2Al4O9. We speculate that the degradation of the intragranular pinning is caused by the trapped oxygen between the Ag substrates at high temperatures during the melt-solidification process.

The Features of Intragranular Irreversibility Lines in Y- and Bi-Based Superconductors

The measurements of temperature dependence of AC magnetic susceptibility were used to study the influence of structural inhomogeneities on intragranular superconducting properties of YBa 2 Cu 3-X M X O Y (M = Fe, X = 0.005; Al, X = 0.01; Cr, X = 0.01), Bi 1.7 Pb 0.2 Sb 0.1 Sr 2 Ca 2 Cu 3 O γ and Bi 1.5 Pb 0.3 Sb 0.2 Sr 2 Ca 2 Cu 3 O Y ceramics. It is found that step-like regions are revealed on irreversibility lines (ILs) for superconducting granules. The steps on the temperature scale depend on sample composition as well as on the type of atoms substituted for copper. They range from 1 to 2 K for Y-based to about 5 K for Bi-based samples. Possible interpretation of the obtained results is presented.

Intragranular and intergranular superconducting properties of bulk melt-textured YBCO

We have investigated the superconducting properties of bulk melt-processed YBCO using different experimental techniques. First, single domain materials (i.e. containing no grain boundaries) have been studied. Electrical resistivity, current-voltage characteristics, M-H loops, and A.C. susceptibility have been measured for different field and current directions. The intragranular properties are characteristic of high-quality melt-processed YBCO material, with a critical current density J/sub c/(T=77 K, B=1 T//c)>10/sup 4/ A/cm/sup 2/. The anisotropy ratio J/sub c/(ab)/J/sub c/(c) is found to be close to 3. Both magnetic and transport measurements show that defects in the microstructure do not significantly impede the current flow inside the single domain. These results were compared to those measured on samples containing one "natural" single grain boundary which sometimes appears during the grain growth process. The intergranular properties show a much stronger current and magnetic field dependence than that measured within the grain and these differences are discussed.

Water dissociation and selective absorption in the Zr[V0.5Fe0.5]2 gettering alloy: An x-ray photoemission spectroscopy investigation

We report a study, based on x-ray photoemission spectroscopy, on the effects of element-specific selective absorption of the nonevaporable [Zr(V0.5Fe0.5)2] gettering alloy after massive exposure to water vapor (3×103 Pa for ≈2000 h at 400 °C). The specimens have been analyzed both after scraping and along a prolonged Ar+ sputtering in order to comparatively discriminate intergranular versus intragranular properties. Oxygen is found to diffuse into the bulk of the alloy grains giving a distribution of Zr oxides where ZrO2 is the major component. After removal of the outermost atomic layers, Fe and V show a major metallic character in the alloy volume. Traces of Zr hydroxides are also seen. The virgin (nonwater treated) [Zr(V0.5Fe0.5)2] alloy has also been comparatively measured.

AC Susceptibility Study of the Inter- and Intragranular Properties in (Bi,Pb):2223 Superconductor

The temperature and amplitude of AC field dependencies of both inter-and intragranular T p and T g temperatures of the imaginary peaks of χ′′ has been studied for a sintered single phase (Bi,Pb):2223 superconductor. The AC field dependencies for T p and T g and the relation between inter- and intragrain force densities were discussed by using Müller critical-state model. From the χ′′(T) curve, the values of intergrain magnetic critical current density J cJ was obtained via the application of Bean's critical state model. J cJ (T) dependence near T c agree with the assumption of SNS intergrain junctions.

Influence of neutron and proton irradiation on inter- and intragrain properties of BiPbCaSrCuO ceramics

The influence of irradiation by fast neutrons and protons (1.4×1014 n/cm2 and 1.6×1014 p/cm2) on the physical properties of textured Bi1.85Pb0.35Sr1.9Ca2.09Cu3.05Oy was examined. DC magnetization in low and high magnetic field are performed. No influence of irradiation on Tc and intragranular properties was observed. The decoupling of weak links with irradiation was observed in low field magnetization measurements. The magnetic behaviour was found to be anizotropic by a factor about 2.5 and this factor was not affected by irradiation.

Studies on superplastically deformed 123/Ag composites

Composites containing 25 vol% Ag were compressed at room temperature to over 110% at 850/spl deg/C in air. Measurement of the strain rate sensitivity yielded a value of 0.5, characteristic of superplastic deformation. As deformed materials had sub-micron grain size and significant c-axis texture parallel to the pressing direction. TEM examination showed that the grains were highly defected and that the grain boundaries were clean. The T/sub c/ was however low with an onset of 50 K and a width of /spl sim/10 K. Annealing studies were carried out with an aim to "fully oxygenate" the material and anneal out a minimal number of defects to obtain higher transition temperatures, at the same time retaining a significant defect density for enhanced flux-pinning. Magnetization measurements were performed after most anneals in order to evaluate intragranular and intergranular properties. Results indicate the presence of unusually high J/sub c/'s at low temperatures after the final anneal (T/sub c/ onset /spl sim/90/spl deg/K). The observations may be explained by highly superior intragranular properties coupled with increased local current loop size.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Texturation and critical currents in cerium-substituted cuprates Bi2Sr2Ca1−Ce Cu2O8 + δ

The influence of texturation on the intragranular properties of bismuth cuprates was studied after partial substitution of calcium by tetravalent cerium in the 2212 ceramics (Bi 2 Sr 2 Ca 1− x Ce x Cu 2 O 8 + δ ; x ≤ 0.3). The critical temperature T c varies non-monotonically and reaches a maximum for x ∼ 0.02. The relative superconducting volume decreases due to the electrons supplied by the lanthanide. X-ray diffraction, SEM observations, ac susceptibility and magnetization show that these ceramics become easily textured by their simple compaction prior to sintering . It was found that the texturation mainly affects the intragranular properties and the initial slope of the magnetization cycles.

Magnetic characterization of hot-pressed BSCCO (2223) phase superconducting ceramic

BSCCO (2223) phase superconductor, prepared by the traditional solid-state reaction route, was densified by hot pressing, yielding high-density and textured-bulk materials. A correlation between processing parameters and inter-, intra-granular properties of the sample was performed through the evaluation of microstructural features and the study of electrical resistivity and magnetization behaviour as a function of different temperature and magnetic field.

Superconductivity in the cerium-substituted 2212 bismuth cuprate: Bi 2Sr 2Ca 1- xCe xCu 2O 8+ δ

The magnetic and superconducting properties of the 2212 bismuth cuprate have been studied after partial substitution of calcium by cerium in the Bi 2Sr 2Ca 1- x Ce x Cu 2O 8+ δ ( x≤0.3) system. Synthesis conditions show that a very small cerium doping (less than 10%) is enough to increase the domain of formation of the 2212 phase by at least 30°C. Cerium is non-magnetic in these materials and does not suppress the superconducting state of the matrix. The critical temperature T c varies non-monotonically and reaches a maximum for x∼0.02, before dropping to almost zero at the limit of solubility ( x∼0.3). Results are explained by a variation of the number of holes due to the substitution of divalent calcium by tetravalent cerium. The influence of texturation of the intragranular magnetic properties was also studied. X-ray diffraction, SEM observations, AC susceptibility and magnetization measurements clearly show that these ceramics become easily textured by their simple compaction prior to sintering. It was found that such a texturation mainly affects the intragranular properties and the initial slope of the magnetization cycles. A very slight dependence of the magnetic anisotropy as a function of the cerium concentration was noticed. Texturation is explained by simple models which take into account the size and shape of the crystallites in the decoupled regime.

Flux dynamics of YBCO/Ag composite

DC magnetization measurements have been carried out on bulk YBCO/Ag composites with silver content up to 20wt per cent. DC fields in the range 0·5 mT to 200 mT have been used to investigate the inter- and intragranular properties at 77K. The AC susceptibility as a function of temperature at different AC fields (0·026–0·30 mT) has also been studied. Under small DC fields (≈ 4 mT), depending on the Ag content andH max, the M-H loop shows a complicated behaviour. This behaviour can be explained on the basis of effect of strong field dependence of transport critical current, grain size and intragrain critical current densityJ cgm on low-field M-H loop. The estimation of intergranular critical current densityJ cjm from these loops does not remain a simple function of ΔM/d. The AC susceptibility measurements show a small increase inJ c(T) with silver content under low AC fields only, consistent with the transportJ c data; beyond thatJ c(T) decreases. This improvement inJ c(T) and transportJ c with silver can be ascribed to the improved coupling between grains but not to the pinning. Also at higher field (H max>20 mT) the addition of Ag decreases the intragrain critical current density. The upper critical field of intergranular regionH c2j and lower critical field of intragrain regionH c1g also decrease with silver content.