National Institute Of Materials Physics - Romania

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892 articles found

771. AC susceptibility and higher harmonics studies of heavy-ion irradiated CuBa2Ca3Cu4Oy bulk superconductor with highest irreversibility field above liquid-nitrogen temperature

Authors: Crisan, A; Iyo, A; Kito, H; Tanaka, Y; Hirai, M; Sasase, M; Okayasu, S; Ihara, H

Published: OCT 1 2002, PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS, 378, 117, DOI: 10.1016/S0921-4534(02)01393-X

A 50 mum thick slice of (Cu,C)Ba2Ca3Cu4Oy (CU:1234) bulk superconductor grown by high-pressure synthesis technique was irradiated with high-energy (240 MeV) Au15+ ions (10(11) cm(-2)). Complimentary DC magnetization measurements up to 5 T showed an increase in critical current density by two orders of magnitude. AC susceptibility studies were performed in DC magnetic fields up to 14 T and at various temperatures, using various AC field amplitudes (up to 15 Oe) and frequencies (up to 10 kHz). Critical current densities at various temperatures and fields were estimated from critical state model. Using the third harmonic response of the sample we were able to separate different contributions to the dissipation: inter-grain regions, grains without columnar defects (heavy-ions penetration depth is about one quarter of sample's thickness), and grains with columnar defects. In irradiated grains, we could observe a peak-effect in the field dependence of critical current density at high DC fields and temperatures between 85 and 105 K, suggesting the possibility of the highest irreversibility field at liquid nitrogen temperature. (C) 2002 Elsevier Science B.V. All rights reserved.

772. The influence of Tl and O content from the starting mixture on phase formation in (Cu,Tl)-1234 system

Authors: Badica, P; Crisan, A; Ihara, H

Published: OCT 1 2002, PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS, 378, 687, DOI: 10.1016/S0921-4534(02)01521-6

Superconducting samples have been synthesized from starting compositions CU0.5TlxBa2Ca3Cu4O12+y, x(Tl) = 0.35-1 in the sealed Au-tubes. Starting oxygen content was y = 0 and/or y = +/-0.225. Samples contain non-superconducting phases and only one main superconducting phase, 1234. The energy dispersive spectroscopy grain composition was Tl0.87-1.3Ba1.9-2.05Ca2.55-3.1Cu4Ox (normalized to Cu = 4). The starting Tl and oxygen content do not influence the occurrence of the phases, grain size, morphology and composition. On the other hand the phase content strongly depends on Tl content and almost does not depend on oxygen content. Both Tl and oxygen content are important for the transport properties of the superconducting grains and it seems that also of the non-superconducting matrix. T-c of the samples was in the range 119.1-111.3 K. (C) 2002 Elsevier Science B.V. All rights reserved.

773. Cum-1Bam(Sr,Ca)(n)Cun+1O2m+2n+1 superlattice thin film by layer-by-layer growth techniques

Authors: Nie, JC; Sundaresan, A; Hirai, M; Ishiura, Y; Badica, P; Crisan, A; Ihara, H

Published: OCT 1 2002, PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS, 378, 1282, DOI: 10.1016/S0921-4534(02)01690-8

Thin films of Cum-1Bam(Sr,Ca)(n)Cun+1O2m+2n+1, i.e., [BaCuO2](m)/[(Sr,Ca)CuO2](n) superlattices have been grown by layer-by-layer growth method with rf magnetron sputtering on NdGaO3(1 1 0) substrate. Two targets with the compositions BaCuO2 and (Sr,Ca)CuO2, which form the charge reservoir and superconducting layers, respectively, were used. [BaCuO2](m)/[(Sr,Ca)CuO2](n) superlattice was grown at 460-520 degreesC in a gas mixture of Ar and N2O by alternatively depositing the charge reservoir layer and superconducting layer. The superlattice modulation is close to that of high pressure synthesized bulk materials. By means of the layer-by-layer growth method, a system of Cu-based artificial lattice structures is formed. Electrical transport properties of these superlattices were also investigated. (C) 2002 Elsevier Science B.V. All rights reserved.

774. Superconducting properties of the heavy-ions and neutron irradiated (Cu,C)Ba2Can-1CunO2n+4-delta (n-3, 4 and 5)

Authors: Kito, H; Iyo, A; Hirai, M; Crisan, A; Tokumoto, M; Okayasu, S; Sasase, M; Ihara, H

Published: OCT 1 2002, PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS, 378, 332, DOI: 10.1016/S0921-4534(02)01437-5

For further enhancement of critical currents density J(c) and irreversibility field H-irr of (Cu1-xCx) Ba2Can-1CunO2n+4-delta ((Cu,C)-(n - 1)n, n = 3, 4 and 5) family, pinning centers were introduced by ion and neutron irradiation in these compounds. The polycrystalline samples were irradiated with 3.6 x 10(17) neutrons/cm(2) or with Au15+ ions (240 MeV energy) at a fluence of 1 x 10(11) ions/cm(2). J(c) and H-irr were determined for the irradiated samples as well as unirradiated samples. The intragrain J(c) was evaluated from M-H curves using Bean's critical state model. In (Cu,C-12(n - 1) n, J(c) (77 K, 1 T) shows a remarkable increase from 3.9 x 10(4) to 9.1 x 10(5) A/cm(2) for neutron irradiated (Cu,C- 1234 and from 3.9 x 10(4) to 4.1 x 10(6) A/cm(2) for heavy-ion irradiated (Cu,C)-1234. These results indicate the possibility of further enhancement of J(c) and of achieving a very high H-irr of (Cu,C)-1234 in (Cu,C)-12(n - 1)n family. (C) 2002 Elsevier Science B.V. All rights reserved.

775. Magnetization and susceptibility studies on BaZrO3-doped YBa2Cu3O7-(x) bulk superconductors

Authors: Bradea, I; Popa, S; Aldica, G; Mihalache, V; Crisan, A

Published: AUG 2002, JOURNAL OF SUPERCONDUCTIVITY, 15, 242, DOI: 10.1023/A:1019911311340

We studied the YBa2Cu3O7-x bulk superconductor doped with BaZrO3 up to 50 wt.%, obtained by solid-state reaction powder technology. From DC magnetization loops and low frequency AC susceptibility measurements we determined the influence of the BaZrO3 doping level on the critical temperature, critical current density, field for full penetration, and intergrain lower critical field. The results show that even high content of BaZrO3 does not lead to degradation of the superconducting properties of bulk YBa2Cu3O7-x.

776. Third-harmonic susceptibility for studying dissipation in heavy ion irradiated (Cu,C)Ba2Ca3Cu4O12-y high-temperature superconductors

Authors: Crisan, A; Badica, P; Hirai, M; Kito, H; Iyo, A; Tanaka, Y

Published: AUG 2002, SUPERCONDUCTOR SCIENCE & TECHNOLOGY, 15, 1243, DOI: 10.1088/0953-2048/15/8/313

A slice of the (Cu,C)Ba2Ca3Cu4O12-y bulk superconductor grown by high-pressure synthesis was polished down to a thickness of 50 mum, and then irradiated with high-energy (240 MeV) Au15+, ions (10 11 cm(-2)). Since the length of the ion tracks was estimated to be 12.2 mum, our sample consists of two different types of grain, with and without columnar defects, having very different critical current densities. Using the third-harmonic response of the sample, we were able to separate the small dissipation in the irradiated grains from the much larger dissipation in the non-irradiated grains, in a certain experimental range of temperature, field and current density. The critical current density was estimated from critical state models. For temperatures in the range of 85-105 K, we observed a peak effect at high dc magnetic fields, suggesting the possibility of a record irreversibility field at 77.3 K.

777. (Cu,Tl)Ba2Ca3Cu4Ox compositions: II. Heating rate applied to synthesis of superconducting ceramics

Authors: Badica, P; Iyo, A; Crisan, A; Ihara, H

Published: JUN 2002, SUPERCONDUCTOR SCIENCE & TECHNOLOGY, 15, 982, DOI: 10.1088/0953-2048/15/6/324

Superconducting samples with a starting composition Cu0.5TlxBa2Ca3Cu4O12 (x = 1-0.35) were prepared in Au tubes from oxides by using different heating rates. The optimum heating rate was 0.11 degreesC min(-1) applied between 860 and 880 degreesC. These samples show the highest content of 1234 phase and the lowest of Ba-Cu-O phases as well as the highest critical temperatures. The highest values were T-c = 119.2 K and T-c0 = 115.1 K. All samples show J(c) values around 6 x 10(5) A cm(-2), at 60 K and 0.5 T. In the rest of the samples, heated by using lower or higher heating rates, a high concentration of 1223 and/or 1245 phases is detected. The content of the 1234 phase and of Ba(Ca.Tl)-Cu-O residual liquid phase, in the samples synthesized for the optimum heating rate, depends on the Tl content in the starting mixture. The influence of the oxygen content in the starting mixture on phase composition is not as strong as of Tl, but it has a major role in establishing the superconducting behaviour of the 1234 grains. Some arguments that suggest the dependence of the transport properties of the non-superconducting matrix on oxygen content will be discussed. In our technological arrangement the determined optimum heating rate can be applied to the synthesis of other single-layered superconducting phases, e.g. 1212 phase from a Cu0.25Tl0.75Ba2CaCu2O8.115 starting composition.

778. High temperature magnetic behaviour of iron-based nanocrystalline alloys

Authors: Randrianantoandro, N; Labaye, I; Berger, L; Crisan, O; Grafoute, M; Calvayrac, F; Greneche, JM

Published: JUN 2002, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 4, 198, DOI:

After a presentation of structural aspects of iron-based nanocrystalline alloys, the magnetic behaviours of those two-phase magnetic structures are conceptually discussed at high temperatures as a function of the crystalline volumetric fraction, on the basis of the magnetic correlation length compared to the distances between crystalline grains. In addition, some results predicted by an approach based on Monte-Carlo simulation are then briefly presented: they show a qualitative agreement with experimental results.

779. (Cu,Tl)Ba2Ca3Cu4Ox compositions: I. The influence of synthesis time and temperature on the phase formation and evaporation-condensation mechanism

Authors: Badica, P; Iyo, A; Crisan, A; Ishiura, Y; Sundaresan, A; Ihara, H

Published: JUN 2002, SUPERCONDUCTOR SCIENCE & TECHNOLOGY, 15, 974, DOI: 10.1088/0953-2048/15/6/323

Temperature and time dependence of the phase formation in the (Cu-0.5,Tl-0.5)-1234 composition have been studied. The liquid-vapour deposition mechanism for the formation of 12(n - 1)n superconducting phases is presented. XRD, SEM, EDS and weight loss data are discussed. Samples were superconducting with maximum T-c and J(c) (at 60 K and 0.5 T), determined from M(H) loops of 118 K and 4 x 10(5) A cm(-2), respectively.

780. TlSr2CaCu2Oy template for the growth of superconducting Tl(Ba, Sr)(2)Ca2Cu3Oy thin films on CeO2 buffered sapphire

Authors: Sundaresan, A; Crisan, A; Nie, JC; Hirai, M; Asada, H; Kito, H; Tanaka, Y; Ihara, H

Published: JUN 2002, SUPERCONDUCTOR SCIENCE & TECHNOLOGY, 15, 963, DOI: 10.1088/0953-2048/15/6/322

Thin films of Tl(Ba, Sr)(2)Ca2Cu3Oy superconductor have been grown on CeO2 buffered r-cut sapphire substrate with the use of a template TlSr2CaCu2Oy by the amorphous phase epitaxy method. By using this template containing Sr, we have overcome the problem of chemical reactions between Ba and Cc present in the superconducting and buffer layers, respectively, at the normal processing temperatures of 840-890 degreesC. Films grown by this method have an excellent c-axis orientation as well as in-plane alignment with the TlSr2CaCu2Oy template, which in turn is aligned with the CeO2 layers. These films have superconducting critical temperature values up to 104 K and critical current density values as high as 1 MA cm(-2) at 77.3 K and 0 T.