Publications of Rudi Cloots
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See detailAnisotropic field percolation and high current density in 2212 Bi-based substituted with Dy bulk magnetically textured composite ceramics
Vanderbemden, Philippe ULiege; Vanderschueren, Hyacinthe ULiege; Stassen, Sophie et al

in Matsushita, T.; Yamafuji, K. (Eds.) Proceedings of the 8th International Workshop on Critical Currents in Superconductors (1996)

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See detailMagnetic alignment in 2212 Bi-based superconducting system .1. Magnetic orientation of Bi2Sr2Ca1-x(RE)(x)Cu2O8-y [(RE)=Gd, Dy, Ho, Er] powder dispersed in epoxy resin at room temperature
Stassen, S.; Cloots, Rudi ULiege; Vanderbemden, Philippe ULiege et al

in Journal of Materials Research (1996), 11(5), 1082-1085

The magnetic anisotropy of rare-earth substituted 2212 materials (Bi(2)Sr(2)Ca(0.8)RE(0.2)Cu(2)O(x) with RE = Gd, Dy, Ho, Er) is put into evidence. Superconducting powder dispersed in epoxy resin is ... [more ▼]

The magnetic anisotropy of rare-earth substituted 2212 materials (Bi(2)Sr(2)Ca(0.8)RE(0.2)Cu(2)O(x) with RE = Gd, Dy, Ho, Er) is put into evidence. Superconducting powder dispersed in epoxy resin is oriented under an external magnetic field (4 T) in a direction that depends on the nature of the rare-earth used in the substitution. Both directions of observation (parallel or perpendicular to the field) were investigated. Splitting of (00l) peaks is neatly observed and discussed. [less ▲]

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See detailMagnetic texturing of bulk samples of the superconductor Bi2Sr2Ca0.8Dy0.2Cu2O8-y
Stassen, Sophie; Rulmont, André ULiege; Vanderbemden, Philippe ULiege et al

in Journal of Applied Physics (1996), 79(1), 553-555

The texturing process of Bi-Sr-Ca(Dy)-Cu-O (2212) is optimized by sintering under a magnetic field. The precursor crystalline powder is melted and grown under a 1.2 T magnetic field. Textured samples are ... [more ▼]

The texturing process of Bi-Sr-Ca(Dy)-Cu-O (2212) is optimized by sintering under a magnetic field. The precursor crystalline powder is melted and grown under a 1.2 T magnetic field. Textured samples are characterized by x-ray diffraction, scanning electron microscopy, electrical resistivity, and magnetic susceptibility. (C) 1996 American Institute of Physics. [less ▲]

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See detailField percolation and high current density in 80/20 DyBa2Cu3O7-x/Dy2BaCuO5 bulk magnetically textured composite ceramics
Cloots, Rudi ULiege; Dang, An; Vanderbemden, Philippe ULiege et al

in Zeitschrift Fur Physik B-Condensed Matter (1996), 100(4), 551-555

We measured the AC susceptibility of magnetically textured (123) 80%/211(20%) DyBaCuO composite in a special set-up in order to enhance the intergrain contribution. The synthesis process led to very clean ... [more ▼]

We measured the AC susceptibility of magnetically textured (123) 80%/211(20%) DyBaCuO composite in a special set-up in order to enhance the intergrain contribution. The synthesis process led to very clean ''weak links'' at grain boundaries. At the percolation threshold bulk shielding paths were such that the intergrain critical current density J(c) was above 10(5) A/cm(2). The field dependence of J(c) was understood through an analytical form indicating a distribution of currents similar to the law of clusters at fracture/percolation thresholds. [less ▲]

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See detailCopper whisker growth from inside sulfur-doped YBa2Cu307-X pellets
Cloots, Rudi ULiege; Krekels, T.; Warin, R. et al

in Journal of Solid State Chemistry (1995), 117(1), 151-156

We report on the growth of Cu whiskers (10 mu m in linear transverse size) at the surface of a YBCO pellet, in a sulfur-rich atmosphere at a high synthesis temperature. Growth arises from inside the ... [more ▼]

We report on the growth of Cu whiskers (10 mu m in linear transverse size) at the surface of a YBCO pellet, in a sulfur-rich atmosphere at a high synthesis temperature. Growth arises from inside the pellet since there is no Cu in the surrounding atmosphere. We present the experimental conditions and electron microscopic observations. We briefly propose a mechanism based on chemical considerations, in particular, a Cu reductive nucleation of the CuS phase at the surface of YBCO. Natural phenomena, laboratory findings, and computer simulation work (based on an Eden model) support this interpretation. [less ▲]

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See detailMagnetic kinetic growth-models
Ausloos, Marcel ULiege; Vandewalle, Nicolas ULiege; Cloots, Rudi ULiege

in Journal of Magnetism & Magnetic Materials (1995), 140(Part 3), 2185-2186

Magnetic kinetic growth models are kinetic growth model(s), like the Eden or the DLA models, but allow for the growth to have an extra degree of freedom (a 'spin') which can be coupled to an external ... [more ▼]

Magnetic kinetic growth models are kinetic growth model(s), like the Eden or the DLA models, but allow for the growth to have an extra degree of freedom (a 'spin') which can be coupled to an external field. Two-dimensional simulations show interesting morphologies and parameter dependences. [less ▲]

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See detailSimulated growth and microstructure of DyBa2Cu3O7-X with and without Dy2BaCUO5 addition
Vandewalle, Nicolas ULiege; Cloots, Rudi ULiege; Ausloos, Marcel ULiege

in Journal of Materials Research (1995), 10(2), 268-273

We present optical observations of magnetically melt-textured DyBa2Cu307-x with and without 20 wt. % excess of Dy2BaCu05. From these observations, we propose some kinetic mechanism of the growth of 123 ... [more ▼]

We present optical observations of magnetically melt-textured DyBa2Cu307-x with and without 20 wt. % excess of Dy2BaCu05. From these observations, we propose some kinetic mechanism of the growth of 123 compounds. Kinetic processes can simulated on computers. Two (very) simple models derived from the well-known Eden model are presented. They simulate the growth of the grain front. The simulated patterns agree with the observations. The microstructure of such materials cannot be explained by thermodynamic and chemical considerations alone, but explanations must include the kinetics of the growth front as well. From our observations, we conclude that the growth probability ratios g(110)/g(100)/g(001) are of the order of 10 and 50, respectively. [less ▲]

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See detailCrystallization of vitreous high-T-c superconducting oxide through laser zone melting method.
Ausloos, Marcel ULiege; Bougrine, Hassan ULiege; Cloots, Rudi ULiege et al

in Institute of Physics Conference Series (1995), 148

We synthesized Bi2Sr2CaCu2O8-y ceramics through the vitreous route. After insertion in epoxy resin, we exposed the materials to a CO2 laser beam. Various intensities and sweeping conditions were examined ... [more ▼]

We synthesized Bi2Sr2CaCu2O8-y ceramics through the vitreous route. After insertion in epoxy resin, we exposed the materials to a CO2 laser beam. Various intensities and sweeping conditions were examined. We observed the samples in high resolution polarized light microscopy and with electron scanning microscopy. Crystallization zones could be detected. A systematic analysis gave the correlation between the behavior of the material and its synthesis conditions. Electrical properties were measured through micro-electrode deposited on the surface at various locations. No superconductivity was found. The optimization of such a process and potential applications will be discussed. [less ▲]

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See detailIntragrain pinning strength depth dependence of 2223-(Bi,Pb)-based high critical Tc ceramics made by a vitreous route
Dang, An; Godelaine, P. A.; Vanderbemden, Philippe ULiege et al

in Journal of Applied Physics (1995), 77(7), 3560-3562

Campbell's method for measuring the critical current in superconductors has been used to obtain the critical current density and the pinning strength in Bi1.7Pb0.3Sr2Ca2Cu3O10−y ceramics synthesized by a ... [more ▼]

Campbell's method for measuring the critical current in superconductors has been used to obtain the critical current density and the pinning strength in Bi1.7Pb0.3Sr2Ca2Cu3O10−y ceramics synthesized by a vitreous route. The intragrain critical current is much higher than 10^5 A/cm2 at 40 K in zero dc magnetic field. A large increase of the pinning strength is observed near the grain surface. The decrease with depth is hyperbolic. The role of the precursors in the synthesis route is emphasized for introducing specific pinning centers. The analysis takes into consideration the ceramics granular nature, i.e., the existence of intergrain and intragrain currents. ©1995 American Institute of Physics. [less ▲]

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See detailSimulated growth front of 123-(RE)BCO near 211 particles
Vandewalle, Nicolas ULiege; Cloots, Rudi ULiege; Ausloos, Marcel ULiege

in Physica C: Superconductivity (1994), 235(Part 1), 427-428

The microstructural features observed on some DyBa2Cu3O7-x, samples show that kinetic considerations are as important as thermodynamic ones. In order to compute and characterize the kinetic growth front ... [more ▼]

The microstructural features observed on some DyBa2Cu3O7-x, samples show that kinetic considerations are as important as thermodynamic ones. In order to compute and characterize the kinetic growth front of 123-(RE)BCO compounds, we have introduced an anisotropic growth direction into a simple two-dimensional growth model: the Eden model defined on a square lattice. The presence of 211 particles has been also considered. The simulated patterns in the ab and ac planes agree with observations and contribute to a more comprehensive model of the kinetic of the growth front near 211 particles. [less ▲]

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See detailDyBa2Cu307-Y superconducting materials synthesized in-situ in a magnetic-field - relations between structure and properties
Cloots, Rudi ULiege; Diko, P.; Godelaine, P. A. et al

in Physica C: Superconductivity (1994), 235(Part 1), 357-358

We have synthesized c-axis oriented magnetically melt textured grown DyBa2Cu3O7-y samples at 1035 degrees C under 0.6 T magnetic induction. We discuss the crystal growth mechanism of such 123 melt ... [more ▼]

We have synthesized c-axis oriented magnetically melt textured grown DyBa2Cu3O7-y samples at 1035 degrees C under 0.6 T magnetic induction. We discuss the crystal growth mechanism of such 123 melt textured grown superconducting ceramics. A strictly tridimensional model is proposed based on Schmitz et al. model, taking into account the peculiar physical properties reported for such materials. In particular a filamentary one dimensional electron conduction path at the percolation threshold is emphasized. We have used optically polarized ligth microscopy as well as electron microscopy analysis to deduce the growth steps. [less ▲]

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See detailNONEQUILIBRIUM EFFECTS IN THE THERMAL-CONDUCTIVITY OF BI-BASED HIGH-TEMPERATURE SUPERCONDUCTORS
Bougrine, Hassan ULiege; SERGEENKOV, S.; Ausloos, Marcel ULiege et al

in Solid State Communications (1994), 91(7), 571-575

Thermal conductivity of two Bi-based high temperature superconducting ceramics, 2212 and 2223, with a markedly different microstructure have been examined. A pulse technique has been used. Depending on ... [more ▼]

Thermal conductivity of two Bi-based high temperature superconducting ceramics, 2212 and 2223, with a markedly different microstructure have been examined. A pulse technique has been used. Depending on the heating pulse duration, the more weak-links-containing 2223 sample shows either equilibrium or nonequilibrium behavior. The temperature dependence of the thermal conductivity between 110 K and 180 K is found to obey the Arrhenius law. The experimental observations are interpreted as a thermally activated heat flux motion through the polycrystalline grain boundaries with an energy barrier of nearly 10meV. It is likely due to a phase slip mechanism. An extra relaxation process due to the pore content/structure is thus emphasized in such regimes. [less ▲]

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See detailBI-BASED 2223 SUPERCONDUCTING POLYCRYSTALLINE MATERIALS PREPARED BY EITHER A SOLID-STATE ROUTE OR A GLASSY MATRIX PRECURSOR METHOD - CHEMICAL-ANALYSIS AS WELL AS ELECTRICAL AND THERMAL TRANSPORT-PROPERTIES
Cloots, Rudi ULiege; Bougrine, Hassan ULiege; HOUSSA, M. et al

in Physica C (1994), 231(3-4), 259-270

Two routes have been followed in order to prepare Bi1.7Pb0.3Sr2Ca2Cu3O(y) superconducting materials. Bi1.7Pb0.3CuO4 is always used as one of the starting basic materials. The first route involves a new ... [more ▼]

Two routes have been followed in order to prepare Bi1.7Pb0.3Sr2Ca2Cu3O(y) superconducting materials. Bi1.7Pb0.3CuO4 is always used as one of the starting basic materials. The first route involves a new experimental procedure based on the solid state synthesis of separate intermediate phases, mixed together in a two (Bi1.7Pb0.3CuO4 + 2SrCaCuO3), three (Bi1.7Pb0.3CuO4+2SrCuO2+2CaCO3) or four (Bi1.7Pb0.3CuO4+(1/12)Sr8Ca6Cu24O41 + (3/2)CaCO3 + (4/3)SrCO3) powder process. Electric resistivity versus temperature measurements are presented. Even though the T(c)(0) of each sample is above 100 K, X-ray diffraction shows that the main phase is the 2212 phase in each case. Relatively pure 2223 materials have, however, successfully been produced by the second method, which starts from a glassy intermediate phase and involves a so-called 'matrix' method. The glass precursor phase is composed of one (Bi1.7Pb0.3CuO4), two (Bi1.7Pb0.3CuO4 + 2CaCO3), and three (Bi1.7Pb0.3CuO4 + (3/2)CaCO3 + (4/3)SrCO3) components as for the solid state routes. The role of both the added alkaline earth crystalline compounds and the glass matrix precursors in this second method turns out to be very important. We propose a schematic structural model in order to explain the selectivity of the starting materials. SrCaCuO3 is found to be a good precursor of the 2212 phase, while SrCuO2 gives rise to the 2223 phase. It seems that the presence of CaCO3 in the glassy intermediate phase, thus acting as a cation reservoir, is very useful for the production of the 2223 phase. Electric resistivity, thermal conductivity and thermopower versus temperature measurements are also presented and discussed in terms of intergrowths and variations of cationic compositions in the Bi-based layers. [less ▲]

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See detailMagnetic Eden model
Ausloos, Marcel ULiege; Vandewalle, Nicolas ULiege; Cloots, Rudi ULiege

in Europhysics Letters [=EPL] (1993), 24(8), 629-634

We introduce the <<Magnetic Eden Model(s)>>. It consists in the usual Eden growth model(s), but allowing for the elements of the growth to have an extra degree of freedom (a <<spin>>). The growth is ... [more ▼]

We introduce the <<Magnetic Eden Model(s)>>. It consists in the usual Eden growth model(s), but allowing for the elements of the growth to have an extra degree of freedom (a <<spin>>). The growth is controlled by a condition depending on the <<magnetic state>> of the perimeter (through some <<spin coupling>>) and an external parameter, the <<magnetic field>>. Even though these words seem to refer to some <<energetic condition>> the growth model is of purely kinetic origin. This is demonstrated by exactly solving the 1-dimensional growth model for a semi-open chain, and, e.g. finding the correlation functions. In two-dimensions, simulations of clusters lead us to show that the perimeter growth exponent is coupling dependent. We show the morphologies of growth clusters on a <<phase diagram>> and indicate the <<physical origin>> and transition(s) between compact and lacunar clusters. [less ▲]

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See detailSTUDY OF THE CRYSTALLIZATION PROCESS IN BI2-XPBXSR2CA2CU3O10-Y GLASS SYSTEMS - OPTICAL POLARIZED-LIGHT MICROSCOPY, ELECTRICAL AND MAGNETIC-PROPERTIES
Cloots, Rudi ULiege; Romain, Anne-Claude ULiege; Rulmont, André ULiege et al

in Superconductor Science & Technology (1993), 6(12), 850-857

Synthesis of Bi2-xPbxSr2Ca2Cu3O10-y (x = 0 and x = 0.3) has been performed using the glass recrystallization route technique. After splat quenching, the samples were annealed at 820, 850 or 870-degrees-C ... [more ▼]

Synthesis of Bi2-xPbxSr2Ca2Cu3O10-y (x = 0 and x = 0.3) has been performed using the glass recrystallization route technique. After splat quenching, the samples were annealed at 820, 850 or 870-degrees-C for 96 or 144 h (with one intermediary grinding). High-resolution polarization micrographs and electrical (and magnetic susceptibility) measurements have been taken. Various growth mechanisms can thus be checked, and the physical properties are studied in relation to the microstructure. It is found that the 2223 phase does not crystallize directly from the amorphous one but results from a dissolution-reprecipitation process. The stability of the 2212 phase is emphasized. The 2201 phase precipitates at high temperature and rapidly reacts with the melt to form the 2223 phase. The kinetics of the lead-substituted sample seems to be controlled by the Ca2PbO4 phase. which acts as a flux. [less ▲]

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See detailSuperconductivity fluctuations in Bi(Pb) based granular ceramics superconductors: evidence for fractal behavior
Ausloos, Marcel ULiege; Laurent, Christian; Patapis, S. K. et al

in Zeitschrift für Physik. B, Condensed Matter (1991), 83(3), 355-359

We report precise measurements of the electrical resistivity in three different Bi(Pb) based granular ceramics superconductors. We show that a single critical exponent (5/6) describes the ... [more ▼]

We report precise measurements of the electrical resistivity in three different Bi(Pb) based granular ceramics superconductors. We show that a single critical exponent (5/6) describes the superconductivity fluctuations. Such a critical exponent indicates a fractal behavior of the superconducting path. Our results thus indicate a strict two dimensional fluctuation percolation set (below the superconductivity onset temperature 195 K down to T(c)), and provide some proof for Tarascon et al. "shell conductivity path" hypothesis. We estimate the shell thickness to be of the order of 10 angstrom. [less ▲]

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