National Institute Of Materials Physics - Romania

Publications

892 articles found

841. Mossbauer spectroscopy applied to radioactive waste processing

Authors: Filoti, G; Kuncser, V; Prisecaru, I; Rotaru, P; Turcanu, CN

Published: 1998, HYPERFINE INTERACTIONS, 112, 204, DOI: 10.1023/A:1011076522131

Two original evaluations of the embedding process and of the hydration promotion in cements using only Mossbauer data have been proposed. Quantitative factors connected with the Mossbauer parameters and describing the hydration degree, the quality of the precipitate bonds in the cement matrix, as well as the influence of the additional organic components on the hydration process were found.

842. Relaxation effects in the Mossbauer spectra of iron complexes with fatty acids

Authors: Filoti, G; Meriacre, VM; Mateescu, E; Kuncser, V; Turta, KI

Published: 1998, HYPERFINE INTERACTIONS, 116, 136, DOI: 10.1023/A:1012637830809

Six new mu 3-oxo trinuclear iron(III) complexes of the type [Fe3O(R-COO)(6)(H2O)(3)] . X, where X = NO3- or Cl- and R = C-5, C-7, C-8, C-9 were synthesized and investigated by Infra Red, Mossbauer Spectroscopy and magnetic measurements. The data pointed to a high spin state (S = 5/2) for iron and for antiferromagnetic interactions. The asymmetrical shape of the Mossbauer doublet and its temperature dependence was treated using the Plume relaxation model. The relaxation process is influenced by both X and R components.

843. Local effects of interstitial versus substitutional atoms in Y(2)Fe(17-x)M(x)A(y) compounds, with M=Al or Si and A=C or N

Authors: Plugaru, N; Morariu, M; Galatanu, A; Lazar, DP; Barb, D

Published: DEC 15 1997, JOURNAL OF APPLIED PHYSICS, 82, 6202, DOI: 10.1063/1.366504

Interstitial Y(2)Fe(17-x)M(x)C(y) compounds, with M=A1 or Si and x less than or equal to 2, y less than or equal to 1, were investigated by (57)Fe Mossbauer spectroscopy at room temperature. In the analysis of the spectra, the preferential occupation by Al or Si of the Fe (12k) sites in the hexagonal R(2)Fe(17) phase was taken into account. The hyperfine parameters variations are discussed on the grounds of local crystallographic details at the inequivalent iron sites, altered by the composition modifications. The low values of the isomer shifts and quadrupole interactions suggest small electronic charge redistribution in Y(2)Fe(17-x)M(x)A(y) as compared to Y(2)Fe(17). However, the isomer shift variations upon Wigner-Seitz cell volume changes evidence for screening and electron transfer effects. In order to provide a more consistent picture of the local effects of interstitial versus substitutional atoms in R(2)(Fe,M)(17)A(y) compounds, the discussion of the present results is extended to (57)Fe Mossbauer data obtained on the parent compounds and their nitrides. (C) 1997 American Institute of Physics.

844. Effect of aluminium on phase stability in the Gd3Co11(B,Al)(4) system

Authors: Galatanu, A; Kottar, A; Artigas, M; Plugaru, N; Lazar, DP

Published: NOV 14 1997, JOURNAL OF ALLOYS AND COMPOUNDS, 262, 362, DOI: 10.1016/S0925-8388(97)00408-8

In the Gd3Co11B4-xAlx alloys the ternary 3:11:4 phase with Ce3Co11B4 structure is formed with an Al content x approximate to 0.5 substituting for boron. The fraction of this phase decreases as the boron content decreases in the samples. The Al, Co and Gd in excess form Gd(Co,Al)(5) with CaCu5-type structure, and the fraction of this phase increases with increasing x. X-ray diffraction results show that these phases are not at equilibrium. A strong preference of aluminium for the 3g site in the CaCu5-type structure is determined by Rietveld refinement of the X-ray diffraction pattern of the end-series compound (x = 4). (C) 1997 Elsevier Science S.A.

845. Structural properties of amorphous and nanocrystallized Fe-Cu-Nb-Si-B and Fe-Gd-Cu-Nb-Si-B ribbons

Authors: Crisan, O; Le Breton, JM; Jianu, A; Teillet, J; Filoti, G

Published: NOV 14 1997, JOURNAL OF ALLOYS AND COMPOUNDS, 262, 389, DOI: 10.1016/S0925-8388(97)00417-9

The influence of Gd addition on the structural properties of Fe-Cu-Nb-Si-B nanocrystallized and amorphous alloys is studied. The crystallization temperature increases and the microstructure of the annealed samples changes. Gd addition induces the formation of Gd-Fe-B phases. In fully crystallized Fe-Gd-Cu-Nb-Si-B alloys the alpha-Fe(Si), Fe-Nb-B, Gd3Fe62B14 and Gd1.1Fe4B4 phases are observed. The evolution of the microstructure is followed as a function of the cumulative effects of annealing time and temperature. The results suggest the transformation of the metastable Gd3Fe62B14 phase into Gd1.1Fe4B4 and alpha-Fe. The hyperfine parameters of the Gd3Fe62B14 Mossbauer contribution are reported. (C) 1997 Elsevier Science S.A.

846. Current-voltage characteristics of long Bi2Sr2Ca2Cu3O10/Ag multifilamentary tapes at different bending strains

Authors: AlMosawi, MK; Crisan, A; Beduz, C; Phillips, D; Haldar, P

Published: SEP 15 1997, PHYSICA C, 289, 69, DOI: 10.1016/S0921-4534(97)01587-6

The current-voltage (I-V) characteristics of long Bi2Sr2Ca2Cu3O10/Ag (Bi:2223) multifilamentary tapes with different bending strains were measured in a large range of dissipation (10(-12)-10(-3) V/cm). The experimental data were successfully interpreted in terms of current-induced unbinding of the thermally-created vortex-antivortex pairs by taking into account the size limitation of vortex fluctuations. It was found that the shape of the I-V curves can be explained by the contributions to the dissipation of superconducting intergrain contacts having different qualities (i.e. different critical currents) and by the appearance of micro-cracks during the bending process. (C) 1997 Elsevier Science B.V.

847. The Au-substituted Al-Cu-Fe icosahedral phase: Evidence for bond hybridization

Authors: Popescu, R; Macovei, D; Manciu, M; Zavaliche, F; Fratiloiu, D; Jianu, A; Devenyi, A; Manaila, R; Xie, Y; Hu, T; Orton, BR; Cernik, RJ; Tang, CC

Published: SEP 8 1997, JOURNAL OF PHYSICS-CONDENSED MATTER, 9, 7540, DOI: 10.1088/0953-8984/9/36/003

Au-substituted Al-Cu-Fe icosahedral phases, Al62Cu25.5-xAuxFe12.5 (x less than or equal to 7) were prepared by melt spinning. EDS data showed that Cu as well as Al atoms are effectively substituted for with Au. The hypercubic lattice parameter of as-quenched samples slowly increases with x, while phonon-and phason-type disorders are not affected by Au substitution. Experimental structure factors for 'sum' lines were used to derive an average radius of the atomic hypersurfaces. Comparison of experimental versus calculated ratios of structure factors for different models yielded information about the Au distribution over the icosahedral sites. It was inferred that a fraction of the gold shapes its Al surrounding in a AuAl2-type configuration. Evidence was found for d-sp hybridization of Au-Al bonds, on the basis of the 'white-line' area at the Au L-3 absorption edge.

848. SEM studies on BSCCO superconducting ceramic produced by spray frozen, freeze drying technique

Authors: Bunescu, MC; Aldica, G; Badica, P; Vasiliu, F; Nita, P; Mandache, S

Published: AUG 1 1997, PHYSICA C, 281, 197, DOI: 10.1016/S0921-4534(97)00633-3

Scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) have been used to evidence the occurrence, morphology and microcomposition of the superconducting phases (Bi,Pb)(2)Sr2Ca2Cu3O10+delta (2223) and (Bi,Pb)(2)Sr2CaCu2O8+delta (2212), and of other non-superconducting phases, in the sintered pellets obtained from nitrate solution by spray frozen, freeze drying technique. For decomposition of the nitrate powder four different heat treatments were used. Superconducting and structure properties of the pellets have been tested by AC susceptibility measurements (610 Hz, 0.5 Oe) and X-ray diffraction analysis, respectively. A correlation between the SEM and EDS observations and the superconducting properties has been established. (C) 1997 Elsevier Science B.V.

849. Investigation of the light induced refractive index changes in Fe:PVA

Authors: Kuncser, V; Filoti, G; Avramescu, A; Podgorsek, R; Biebricher, M; Franke, H

Published: JUL 25 1997, JOURNAL OF ALLOYS AND COMPOUNDS, 257, 292, DOI: 10.1016/S0925-8388(97)00021-2

The light induced modifications in thin films of Fe:PVA were studied by optical and Mossbauer spectroscopy. Under the UV exposure both the refractive index and the absorption coefficient are changing. The real part of the refractive index is measured using m-line Spectroscopy. As a function of UV exposure, the optical absorption as well as the Mossbauer spectra were measured. A correlation between the optical and the measured Fe2+/Fe3+ ratio is discussed. (C) 1997 Elsevier Science S.A.

850. Optical and Mossbauer study of the real time holographic organometallic material Fe:PVA

Authors: Kuncser, V; Avramescu, A; Filoti, G; Rotaru, P; Podgorsek, R; Biebricher, M; Franke, H

Published: JUL 5 1997, JOURNAL OF ALLOYS AND COMPOUNDS, 256, 275, DOI: 10.1016/S0925-8388(96)03111-8

The Fe:PVA thin films were studied by optical and Mossbauer spectroscopy. Both the absorption and Mossbauer spectra are dependent on the PVA dilution and ferric chloride concentration. A strong correlation between the optical and Mossbauer results was found, indicating the major role of the iron electronic local levels in the optical phenomena. A relation between the various absorption probabilities and also indirect information about the Debye temperatures were obtained. (C) 1997 Elsevier Science S.A.