National Institute Of Materials Physics - Romania

Publications

903 articles found

811. Superconducting properties from AC susceptibility and harmonic generation in CuBa2Ca3Cu4Oy bulk superconductors

Authors: Crisan, A; Iyo, A; Tanaka, Y; Hirai, M; Tokumoto, M; Ihara, H

Published: MAY 15 2001, PHYSICA C, 353, 240, DOI: 10.1016/S0921-4534(00)01744-5

We measured for the first time the fundamental and higher harmonic components of AC susceptibility of CuBa2Ca3Cu4Oy superconductor produced by the high-pressure technique, in various experimental conditions (temperature, DC magnetic field, AC held amplitude and frequency). The results are discussed qualitatively in the frame of the critical state and other models in the literature. By using a very simple frequency-dependent critical state model, we estimated the parameters of practical interest, critical current density and pinning potential at various DC fields and temperatures and the irreversibility field. We also extrapolated our estimations to both practical temperature of 77 K and longer time scale as of DC magnetization and transport measurements. The results appeared to be quite self-consistent. (C) 2001 Published by Elsevier Science B.V.

812. The influence of BaZrO3 on the transport properties of the (Bi,Pb)2223 superconducting system

Authors: Mihalache, V; Aldica, G; Crisan, A

Published: MAY 2001, JOURNAL OF MATERIALS SCIENCE LETTERS, 20, 891, DOI: 10.1023/A:1010912429361

813. A Mossbauer study of the new phases Th4Fe13Sn5 and ThFe0.22Sn2

Authors: Principi, G; Spataru, T; Maddalena, A; Palenzona, A; Manfrinetti, P; Blaha, P; Schwarz, K; Kuncser, V; Filoti, G

Published: APR 12 2001, JOURNAL OF ALLOYS AND COMPOUNDS, 317, 572, DOI: 10.1016/S0925-8388(00)01389-X

Two new phases Th4Fe13Sn5 and ThFe0.22Sn2 have been studied by Fe-57 and Sn-119 Mossbauer spectroscopy. The Fe-57 Mossbauer spectra of Th4Fe13Sn5, measured at room temperature and 4.2 Ii without and with applied magnetic field up to 5.5 T, exhibit four sextets. Our measurements prove that all four Ft: sub-lattices are collinear. The Sn-119 Mossbauer spectra of Th4Fe13Sn5 show two sextets with different B-eff, reflecting the influence of ferromagnetic nn iron atoms. The results obtained from full-potential linear augmented plane wave (LAPW) calculations are in agreement with the experimental data and confirm the assignment of Mossbauer spectra, The Mossbauer data for the ThFe0.22Sn compound prove the existence of two different sites both for Fe and Sn, all having icosahedral co-ordination. (C) 2001 Elsevier Science B.V, All rights reserved.

814. Crystallization of Fe75Cr5B20 amorphous alloy

Authors: Mihalca, I; Ercuta, A; Zaharie, I; Kuncser, V; Filoti, G; Jianu, A

Published: MAR 2001, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 3, 144, DOI:

815. Neutron diffraction direct observation of the decomposition processes in a Bi : Pb : Sr : Ca : Cu=1.7 : 0.3 : 2.0 : 2.5 : 3.5 nitrate freeze dried powder

Authors: Alexe, G; Badica, P; Aldica, G; Mironova, GM

Published: 2001, EPDIC 7: EUROPEAN POWDER DIFFRACTION, PTS 1 AND 2, 378-3, 345, DOI: 10.4028/www.scientific.net/MSF.378-381.340

Spray frozen, freeze dried nitrate powder with composition Bi:Pb:Sr:Ca:Cu 1.7:0.3:2.0:2.5:3.5 has been thermally decomposed (up to 870 degreesC). In situ neutron diffraction investigations during heating and cooling of the powder have been performed at DN2 instrument from the IBR2 reactor at JINR, Dubna, Russia. Phase formation and reformation and domains of stability for different phases were observed and discussed.

816. Aspects in HTS laser ablation thin film technology and characterization

Authors: Branescu, M; Gyorgy, E; Ristoscu, C; Mihailescu, IN; Jaklovsky, J; Mihalache, V

Published: 2001, 11TH INTERNATIONAL SCHOOL ON QUANTUM ELECTRONICS: LASER PHYSICS AND APPLICATIONS, 4397, 313, DOI: 10.1117/12.425154

Thin films of YBa2Cu3O7-x have been obtained on NdGaO3 substrate by pulsed laser deposition with an excimer KrF* (lambda =248 nm, tau (FWHM)greater than or equal to 20 ns) laser source from a stoichiometric target. In the present paper we report details of the technology of pulsed laser deposition of high-temperature superconductor thin films, substrates' requirements and high-temperature superconductor thin film characterisation. The study of some parameters' intercorelations for optimisation of the technology of the pulsed laser deposition of high-temperature superconductor thin films is also analysed Moreover, the contacting technology and techniques of characterisation are described.

817. Mossbauer spectroscopy study of Ti-Zr-Ni-Fe icosahedral and approximant phases

Authors: Nicula, R; Kuncser, V; Jianu, A; Filoti, G; Burkel, E

Published: DEC 15 2000, MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, 294, 541, DOI: 10.1016/S0921-5093(00)01160-6

Quaternary Ti53Zr21Ni13Fe13 alloys were prepared by melt-spinning using peripheral wheel speeds omega =19.5, 24.2 and 30m/s. The icosahedral (i-) phase formation was studied using high resolution synchrotron radiation powder diffraction. An amorphous phase component is present irrespective of the rapid solidification conditions, its volume fraction decreasing towards lower quenching speed values. The amorphous phase coexists with a b.c.c. rational approximant phase (W-phase). For omega below 20 m/s the formation of an i-phase was also noticed. Transmission Fe-57 Mossbauer spectroscopy measurements indicate that the number of asymmetrical Fe positions decreases with decreasing w in agreement with the improved structural perfection of the W-phase and with the formation of an additional i-phase. (C) 2000 Elsevier Science B.V. All rights reserved.

818. Laser ablation synthesis of Al-based icosahedral powders

Authors: Nicula, R; Jianu, A; Grigoriu, C; Barfels, T; Burkel, E

Published: DEC 15 2000, MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, 294, 89, DOI: 10.1016/S0921-5093(00)01204-1

The laser ablation (LA) synthesis of ultra-fine-grained powders with dominant icosahedral structure has been attempted using Al-Cu-Fe and Al-Pd-Mn targets. The structure of the Al-Cu-Fe LA powders was examined using synchrotron radiation diffraction experiments which revealed the presence of the icosahedral Al-Cu-Fe phase. The Al-Pd-Mn powders were studied using scanning electron microscopy (SEM) and energy dispersive synchrotron radiation diffraction. For Al-Pd-Mn, the icosahedral phase is also a constituent phase of the LA alloy powders. Our results indicate that LA may be successfully used for obtaining quasicrystalline-based ultra-fine grained powders and/or surface coatings, while also providing a basis for the powder metallurgy processing of these materials. (C) 2000 Elsevier Science B.V, All rights reserved.

819. Icosahedral phase formation in Ag-substituted Ti-Zr-Ni rapidly-quenched alloys

Authors: Nicula, R; Ponkratz, U; Jianu, A; Schick, C; Burkel, E

Published: DEC 15 2000, MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, 294, 92, DOI: 10.1016/S0921-5093(00)01205-3

The formation of icosahedral phases in Ag-substituted Ti-Zr-Ni alloys was investigated by in situ annealing diffraction experiments using synchrotron radiation. The as-quenched (Ti1-xAgx)-Zr-Ni alloys (x=2, 5, 7 and 10 at.%) are amorphous and/or in a mixed nanostructured state. Upon heating, the Ti-Zr-Ni-Ag alloys transform to either a crystalline or a quasicrystalline state, depending on the Ag content. Differential scanning calorimetry (DSC) studies were performed to identify the nature and sequence of the phase transitions. (C) 2000 Elsevier Science B.V. All rights reserved.

820. High-pressure stability of Ti-Zr-Ni quasicrystals

Authors: Nicula, R; Jianu, A; Ponkratz, U; Burkel, E

Published: OCT 1 2000, PHYSICAL REVIEW B, 62, 8848, DOI: 10.1103/PhysRevB.62.8844

The room-temperature compressibility and stability of single-phase icosahedral Ti-Zr-Ni alloys were investigated for pressures up to 30 GPa, using synchrotron radiation energy dispersive diffraction. The icosahedral Ti-Zr-Ni single phase is stable over this pressure range, no phase transition being noticed. The pressure-volume data were least-squares fitted to a Birch-Murnaghan equation of state to obtain the zero-pressure bulk modulus B-0 = (173+/-5) GPa and its pressure derivative B-0' = 2.3+/-0.5.