National Institute Of Materials Physics - Romania

Publications

952 articles found

821. Growth by MOMBE of c-axis superconducting YBCO thin films on different substrates: In situ RHEED monitoring of the growth

Authors: Endo, K; Badica, P; Moriyasu, Y; Abe, K

Published: JUN 2003, IEEE TRANSACTIONS ON APPLIED SUPERCONDUCTIVITY, 13, 2794, DOI: 10.1109/TASC.2003.812014

Superconducting YBCO c-axis oriented thin films have been grown by MOMBE (metalorganic molecular-beam-epitaxy). Growth of the films on different substrates (100) (Y, Nd)AlO3, (100) SrTiO3 and (100) MgO has been investigated by, in situ monitoring the reflection high energy electron diffraction (RHEED). The paper discusses our results suggesting significant differences in films growth on the three presented substrates. The highest quality (high uniformity, epitaxy and low roughness) has been attained for the films prepared on SrTiO3. All films, regardless substrates, have shown values between 81 and 84 K for zero resistance critical temperature T-c0.

822. (119) Oriented Bi-2223 thin films grown on (100) NdGaO3 by MOCVD

Authors: Endo, K; Badica, P; Abe, K

Published: JUN 2003, IEEE TRANSACTIONS ON APPLIED SUPERCONDUCTIVITY, 13, 2712, DOI: 10.1109/TASC.2003.811963

Orientation control of high T-c superconductors is essential for superior device performance, because the coherence length is longer along the non c-axis directions than along c-axis direction. In this study, we report on the first successful preparation of (119) oriented Bi-2223 films by MOCVD using (100) NdGaO3 Substrates. Atomic force microscopy observations of the (119) Bi-2223 films are also reported. Our films have an in-plane aligned mountain-range-shaped surface morphology. This morphology is resulting from the epitaxial relationship between the (119) Bi-2223 film and (100) NdGaO3 substrate. Films exhibited a large in-plane anisotropy as revealed by, resistivity measurements and surface morphology observations.

823. Nanodots-induced pinning Centers in thin films: Effects on critical current density, activation energy and flux jump rate

Authors: Crisan, A; Badica, P; Fujiwara, S; Nie, JC; Sundaresan, A; Iyo, A; Tanaka, Y

Published: JUN 2003, IEEE TRANSACTIONS ON APPLIED SUPERCONDUCTIVITY, 13, 3729, DOI: 10.1109/TASC.2003.812527

By very short time rf sputtering in certain deposition conditions we have grown three-dimensional Ag nanodots on the substrate prior to the growth of TI-based superconducting films. These nanodots create pinning centers, leading to an increase in the critical current density about 10 times. From the frequency dependence of the critical current density we estimated also the, actiation energy for the flux jumps, which resulted to. be several times higher. The rate of the thermally-activated flux jumps decreases several orders of magnitude. We suggest that our method can be used for the reduction of thermal noise in high-T-c dc SQUID's.

824. Hall probe imaging of local hysteresis inversion and negative remanent fields near the edge of a YBCO thin film

Authors: Crisan, A; Pross, A; Humphreys, RG; Bending, S

Published: JUN 2003, SUPERCONDUCTOR SCIENCE & TECHNOLOGY, 16, 698, DOI: 10.1088/0953-2048/16/6/307

We report vortex imaging and local magnetometry studies near the edge of a YBCO thin film using scanning Hall probe microscopy (SHPM). Our data show some unusual features, namely local hysteresis inversion and negative remanent fields, which are semi-quantitatively explained in terms of a theoretical model of flux penetration in an infinite-long thin superconducting strip.

825. Preparation of Tl-2212 and Tl-1223 superconductor thin films and their microwave surface resistance

Authors: Sundaresan, A; Asada, H; Crisan, A; Nie, JC; Kito, H; Iyo, A; Tanaka, Y; Kusunoki, M; Ohshima, S

Published: JUN 2003, IEEE TRANSACTIONS ON APPLIED SUPERCONDUCTIVITY, 13, 2916, DOI: 10.1109/TASC.2003.812045

Epitaxial Tl2Ba2CaCu2Oy and Tl(Ba,Sr)(2)Ca-2 Cu3Oy thin films have been prepared on CeO2 buffered sapphire substrate by an ex situ process with high reproducibility. Microstructure analysis of the surface of the TI-2212 films showed well connected and smaller sized grains of 1 mum or less. In the case of TI-1223 film, plate-like crystals with pits and pin holes could be observed. The superconducting critical temperatures of both films are around 96 K. Critical current density measured by ac susceptibility technique is as high as 1 MA/cm(2) at 77 K. The microwave surface resistance of these films was measured over a wide range of temperatures by a HTS-sapphire-HTS resonator method at 38 GHz on films with area 10 mm x 10 mm. The temperature dependence of surface resistance of TI-2212 film follows very closely to that of the best YBCO films on MgO substrate, whereas the TI-1223 exhibits slightly higher values resulting from an inferior surface morphology.

826. Intensification of synthesis and examination of technological parameters influence on the properties and structure of Bi-(Pb)-Sr-Cu-Ca-O ceramics (vol 384, pg 111, 2003)

Authors: Yurchenko, IA; Alekseev, AF; Yurchenko, DO; Badica, P; Gridasova, TY; Morozov, VV; Nemirovsky, AV; Peklun, VF

Published: MAY 15 2003, PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS, 387, 420, DOI: 10.1016/S0921-4534(03)00703-2

827. Intra- and inter-grain critical current density in (Cu,C): 1234 superconductors

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

Published: MAY 2003, PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS, 388, 422, DOI: 10.1016/S0921-4534(02)02550-9

From DC magnetization studies in fields up to 14 T and temperatures between 20 and 100 K, we estimated the intra-and inter-grain critical current density J(c) of (Cu,C): 1234 high-T-c superconductors, in the frame of critical state models. The inter-grain J(c) was determined by comparing the magnetization loops of as-grown sample and of the ground sample. Finally, short comments on J(c) resulted from AC susceptibility measurements and of the impressive increase of intra-grain J(c) due to heavy-ion and neutron irradiation are presented. (C) 2003 Elsevier Science B.V. All rights reserved.

828. Electron-doped superconductivity in Sr1-xCaxCuO2-delta infinite-layer thin films

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

Published: MAY 2003, PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS, 388, 442, DOI: 10.1016/S0921-4534(02)02568-6

Thin films of infinite-layer compound Sr1-xCaxCuO2-delta have been prepared by rf magnetron sputtering. For an optimum level of oxygen vacancy superconductivities were observed (T-c (onset) = 42 and 50 K, T-c(rho=0) = 11 and 20 K). Structural and transport data suggest that the doping mechanism is electron-type. The superconducting transitions were also confirmed by ac susceptibility. Further increase of doping showed to destroy superconductivity. (C) 2003 Elsevier Science B.V. All rights reserved.

829. Preparation of Tl-2212 and -1223 superconductor thin films and their microwave properties

Authors: Sundaresan, A; Asada, H; Crisan, A; Nie, JC; Kito, H; Iyo, A; Tanaka, Y; Kusunoki, M; Ohshima, S

Published: MAY 2003, PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS, 388, 474, DOI: 10.1016/S0921-4534(02)02585-6

Tl2Ba2CaCu2Oy (Tl-2212) and Tl(Ba,Sr)(2)Ca2Cu3Oy (Tl-1223) superconductor thin films have been prepared on CeO2 buffered sapphire substrate by an ex situ process namely, amorphous phase epitaxy (APE) method. In the case of Tl-1223, an amorphous layer of TlSr2CaCu2Oy (TlSr-1212) was deposited on top Of CeO2 layer to avoid chemical reaction between Tl-1223, containing Ba, and CeO2 layers. All films are epitaxial with smooth surface and excellent crystallinity. Superconducting transition temperatures (T-c) of Tl-2212 and 1223 are around 95 and 104 K, respectively. Critical current density (J(c)) at 77 K measured on 5 x 5 mm. films by inductive technique is as high as 2 MA/cm(2). Surface resistance R-s of Tl-2212 films measured by a dielectric resonator technique at 38 GHz is comparable to the best YBCO films. (C) 2003 Elsevier Science B.V. All rights reserved.

830. LiF addition to (Cu,C) Ba2Ca3Cu4Oy superconductor

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

Published: MAY 2003, PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS, 388, 396, DOI: 10.1016/S0921-4534(02)02535-2

Samples of (Cu0.6C0.4)Ba2Ca3Cu4Oy ((Cu,C)-1234) with addition of 0.1 mol LiF have been synthesized by high pressure technique. It was found that LiF promotes' the formation of superconducting phases with n higher than 4 of the (Cu,C)Ba2Can-1CunOy series. In order to obtain single-phase samples, for the same synthesis conditions, the oxygen content in the starting mixture (supplied by AgO) should be increased from 0.45 to 0.73 mol AgO, when using LiF. Samples with LiF have shown a certain morphology suggesting an enhanced 2D and suppressed 3D type of growth assisted by a liquid phase. T-c decreased from 116.5 to 113 K for the sample with LiF, but at the same time the transition width also decreased and J(c) has shown a fish-tail effect. (C) 2003 Elsevier Science B.V. All rights reserved.