National Institute Of Materials Physics - Romania

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5781 articles found

3601. Thermally and pressure activated phase evolution in Fe-Pt-Nb-B melt spun ribbons

Authors: Crisan, AD; Nicula, R; Crisan, O; Burkel, E

Published: SEP 2007, MATERIALS SCIENCE & ENGINEERING C-BIOMIMETIC AND SUPRAMOLECULAR SYSTEMS, 27, 1282, DOI: 10.1016/j.msec.2006.06.033

The Fe-Pt-rich alloys has recently attracted a lot of interest for their potential development of the hard magnetic L1(0) (also denoted gamma(1)) FePt phase with high magnetocrystalline anisotropy. An alloy with the nominal composition Fe65Pt25Nb2B8 has been synthesised by rapid quenching of the melt. The phase evolution in the as-cast ribbons was monitored by energy dispersive X-ray diffraction of the synchrotron radiation. It is shown that the Fe65Pt25Nb2B8 alloy is completely crystallized in the as-cast state. With increasing temperature a partial disorder-order phase transformation with occurrence of hard magnetic L1(0) phase is observed. This transformation is directly related to thermal and pressure effects in the sample. With applying pressure, the phase transformation between cubic and tetragonal FePt symmetry is more pronounced and is accompanied by a strong uniaxial lattice expansion. The results are extremely promising for the direct formation from the melt of an exchange coupled hard-soft magnetic alloy with initial formation of the tetragonal hard magnetic L1(0) FePt phase. (C) 2006 Elsevier B.V. All rights reserved.

3602. Field-activated sintering of skutterudites

Authors: Kodash, VY; Groza, JR; Aldica, G; Toprak, MS; Li, S; Mamoun, M

Published: SEP 2007, SCRIPTA MATERIALIA, 57, 511, DOI: 10.1016/j.scriptamat.2007.05.032

Skutterudite (Co0.92Ni0.08)(4) Sb11.88Te0.12 powder has been consolidated under an applied electrical field using a field-assisted sintering technique (FAST). The low FAST sintering temperature and relatively high heating rate considerably reduce grain growth during sintering. (c) 2007 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

3603. Hybrid approach to the synthesis of FePt/Fe3B nanocomposite magnets

Authors: Crisan, O; Angelakeris, M; Kehagias, T; Filoti, G

Published: SEP 2007, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 9, 2737, DOI:

Exchange coupling between alternatively dispersed hard and soft magnetic phases, gives rise to exchange spring magnets with enhanced energy product (BH)(max) that are believed to represent a novel class of permanent magnets with improved properties. The synthesis of a hybrid nanocomposite system made of soft magnetic Fe3B melt spun ribbon and hard magnetic Fe-Pt thin film, obtained by e-beam co-deposition in ultrahigh vacuum onto the ribbons, is reported. Scanning electron microscopy, transmission electron microscopy and X-ray diffraction are used for structural characterization of these hybrid samples. Magnetic measurements provide observation of a drastic decrease of the saturation magnetization, compatible with the exchange coupling between hard and soft magnetic phases in the melt spun/thin film samples.

3604. Investigations of NCPM second harmonic generation and self frequency doubling in Gd1-x-yRxNdyCa4O(BO3)(3) (R = Sc or Lu) crystals

Authors: Gheorghe, L; Loiseau, P; Aka, G; Lupei, V

Published: SEP 2007, OPTICAL MATERIALS, 30, 46, DOI: 10.1016/j.optmat.2006.10.018

Pure and Nd3+ doped single crystals of Gd1-xRxCa4O(BO3)(3) (R3+ = Sc3+ or Lu3+) with large size and good quality have been grown by the Czochralski pulling technique. By changing the compositional parameter x of Gd1-xRxCa4O(BO3)(3) crystals, their optical birefringence can be controlled in order to achieve non-critical phase matching (NCPM) in the ranges of 790-824 nm along Y-axis and 920963 nm along Z-axis, during second harmonic generations. Nonlinear optical properties of these new biaxial borate crystals are reported. Preliminary investigations of self frequency doubling in NCPM condition in Gd1-x-yRxNdyCa4O(BO3)(3) crystals have been carried out. (c) 2006 Elsevier B.V. All rights reserved.

3605. Composition dependence of Pr3+ spectral characteristics in strontium lanthanum aluminate crystals

Authors: Lupei, V; Lupei, A; Gheorghe, C; Gheorghe, L; Aka, G; Vivien, D

Published: SEP 2007, OPTICAL MATERIALS, 30, 167, DOI: 10.1016/j.optmat.2006.11.018

An analysis of the high resolution spectra of the Pr3+ in strontium lanthanum aluminates, charge compensated with magnesium Sl(1-x)Pr(y)La(x-y)Mg(x)Al(12)-xO(19), (on a large composition range) is presented. The spectra are mainly dependent on the composition parameter x, and show more Pr3+ centers, two of them stable. Based on composition dependence and polarization data, structural models for the main two centers are proposed. (c) 2006 Elsevier B.V. All rights reserved.

3606. Preparation, properties and electrical switching effects in GeSb2Te4 and (GeSb2Te4)(90)(SnSe2)(10) amorphous films

Authors: Lorinczi, A

Published: SEP 2007, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 9, 2972, DOI:

Thin films of composition GeSb2Te4 and (GeSb2Te4)(90)(SnSe2)to have been prepared by pulsed laser deposition and characterized by X-ray diffraction and scanning electron microscopy. The electrical switching was revealed in both compositions.

3607. Powder neutron diffraction of Nd3Co13-xNixB2 compounds

Authors: Plugaru, N; Rubin, J; Bartolome, J; Campo, J; Cuello, GJ; Tovar, M; Prokhnenko, O

Published: SEP 2007, JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 316, E441, DOI: 10.1016/j.jmmm.2007.02.173

We report results of a powder neutron diffraction study on the crystal structure and local magnetic moments in Nd3Co13-x NixB2 compounds with Nd3Ni13B2- type structure. The largest 3d magnetic moment resides at the 4 h sites. Nd magnetic moment is reduced with respect to the free ion value. Preferential Ni substitution for Co is also found at the 4h site. The refined magnetization direction is consistent with the T-x phase diagram derived from magnetization data. (c) 2007 Elsevier B. V. All rights reserved.

3608. Crystallization processes in Fe-Pt-Nb-B melt spun ribbons

Authors: Crisan, AD; Crisan, O; Randrianantoandro, N; Valeanu, M; Morariu, M; Burkel, E

Published: SEP 2007, MATERIALS SCIENCE & ENGINEERING C-BIOMIMETIC AND SUPRAMOLECULAR SYSTEMS, 27, 1285, DOI: 10.1016/j.msec.2006.08.031

Intermetallic Fe-Pt-Nb-B alloys with 3 different compositions have been synthesized by rapid solidification technique and their phase structure was characterized by means of X-ray diffraction and Mossbauer spectrometry. It is shown that Fe68Pt21Nb2B9 and Fe65Pt25Nb2B8 as-east samples consist mainly of A1 soft magnetic f.c.c. Fe-Pt phase, while the Fe68Pt13Nb2B17 as-cast sample exhibits topological short-range order, typical for amorphous ribbons. Crystallization processes in the amorphous sample and phase evolution with the temperature have been studied using differential scanning calorimetry (DSC). The occurrence of exothermic peaks is related to structural transformations in the alloys and the crystallization process is shown to be highly dependent upon the heating rate in the DSC process. (C) 2006 Elsevier B.V. All rights reserved.

3609. Nanostructural disorder in hydrogenated amorphous silicon

Authors: Sava, F

Published: SEP 2007, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 9, 2966, DOI:

The structure of amorphous silicon and amorphous hydrogenated silicon has been investigated starting from a large model of amorphous silicon (2052 atoms). The modifications induced in a-Si model by when hydrogen is introduced have been revealed. The diffusion of hydrogen leads to a nanostructuring effect in the continuous random network of amorphous silicon. The effect of hydrogen on the distributed distortion defects in silicon network has been modelled. The most strained bonds have been broken and hydrogen wasd attached to the dangling bonbds on silicon. A free energy relaxation process was carried out in the frame of a Monte - Carlo - Metropolis procedure. There was demonstrated that, by nanostructuring, the total free energy of the model decreases. The variation of the bond stretching and bond bending energy as a function of the number of broken bonds indicated a dominant contribution of the bond bending term. The modelling shows, undoubtedly, the disappearance of many structural defects that probably are related to the deep electronic states in the gap of amorphous silicon.

3610. Spectroscopic evidence for the bulk polymerization of N-vinyl carbazole in the presence of single-walled carbon nanotubes

Authors: Baibarac, M; Baltog, I; Lefrant, S; Gomez-Romero, P

Published: AUG 24 2007, POLYMER, 48, 5288, DOI: 10.1016/j.polymer.2007.07.008

The bulk polymerization reaction of N-vinylcarbazole (VK) at 70 degrees C in the presence of single-walled carbon nanotubes (SWNTs) leads to a new composite, whose optical properties were studied by photoluminescence (PL), surface enhanced Raman scattering (SERS) and Fourier transform infrared (FTIR) spectroscopies. A dramatic reduction of the poly(N-vinylcarbazole) (PVK) PL efficiency and a change in the vibrational structure of the PL spectrum of this polymer were observed by adding SWNTs to the synthesis mixture. Steric hindrance effects were evidenced both in SERS spectra of the VK when it interacts mechanico-chemically with SWNTs and in FTIR spectra of the un-doped PVK/SWNTs' composites. Cyclic voltammetry was used to demonstrate the doping process of PVK in PVK/SWNTs' composite. (c) 2007 Elsevier Ltd. All rights reserved.