National Institute Of Materials Physics - Romania

Publications

5714 articles found

2821. Morphological and optical properties of doped potassium hydrogen phthalate crystals

Authors: Enculescu, M

Published: SEP 1 2010, PHYSICA B-CONDENSED MATTER, 405, 3727, DOI: 10.1016/j.physb.2010.05.074

Potassium hydrogen phthalate (KAP) crystals doped with rhodamine 6G (Rh 6G) and polyvinylpyrrolidone (PVP) were grown by solution evaporation technique. Nucleation occurred without the use of seeds and optically transparent crystals were obtained. The grown crystals were characterized by XRD measurements performed on crystals and their powders, optical transmission and photoluminescence measurements. The influence of the dopants on the structural, morphological and optical properties of the KAP crystals was analysed. Dopants do not change the structure of the single crystals while the addition of PVP changes the morphology of crystals from pseudo-hexagonal to rhomb. Three new XRD reflections are observed in all single-crystal and powder XRD spectra and are probably (0 3 0), (0 4 0) and (0 5 0) lines. The UV cut-off and transparency of the crystals are not changed by doping. Dye-doped KAP crystals exhibit a strong emission band centred at 550 nm excited with 480 nm wavelength. For the dye-doped crystals the up-conversion was investigated and its second harmonic origins are proved using photoluminescence measurements. (C) 2010 Elsevier B.V. All rights reserved.

2822. A new ZnO photoanode for dye-sensitized solar cell

Authors: Sima, M; Secu, M; Sima, M; Vasile, E

Published: SEP 2010, OPTOELECTRONICS AND ADVANCED MATERIALS-RAPID COMMUNICATIONS, 4, 1328, DOI:

The present work reports the preparation of nanostructured ZnO nanorods in a hydrothermal-electrochemical process and preliminary attempt to fabricate a dye-sensitized solar cell using this material as photoanode. Synthesis of ZnO nanorods in solutions with and without eosin Y dye, used as nanostructuring agent, was studied. ZnO nanorod arrays were characterized by photoluminescence spectroscopy, scanning electron microscopy and X-ray diffraction analysis. Fabricated dye-sensitized solar cell comprised a photoanode prepared with nanostructured ZnO nanorods and eosin Y dye, a platinum counter electrode and an electrolyte consisting of 0.5M KI + 0.03M I-2 in acetonitrile/ethylene carbonate (v/v=1/4). Performance parameters of dye-sensitized solar cell were extracted from standard current-voltage characteristic.

2823. Flux jumps anomalous behaviour in FAST-processed MgB2 composites

Authors: Aldica, G; Badica, P; Plapcianu, C; Groza, JR; Popa, S

Published: SEP 2010, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 12, 2003, DOI:

Superconductor MgB2 has a significant potential for practical applications, but undesirable flux jumps in magnetization curves at low temperature and at moderate or intermediate magnetic fields prevent its widespread use. In the present work, we analyzed the flux-jumps tendency in MgB2 bulk doped with SiC, B4C and metallic Mg. Samples were prepared by field-assisted-sintering (FAST) as composites with up to three intercalated Fe-foils. Samples produced by FAST showed quite different phase structures clearly influencing pinning and thermo-magnetic instability features due to inhomogeneous materials structure or due to dopants. The largest flux jumps are observed in samples with high critical current density, as usually observed in conventional MgB2 bulks. However, jumps patterns are different and do not perfectly follow the jumps critical current dependence, especially for the samples with Mg-addition.

2824. Improvement of the critical current density of spark plasma sintered MgB2 by C-60 addition

Authors: Miu, L; Aldica, G; Badica, P; Ivan, I; Miu, D; Jakob, G

Published: SEP 2010, SUPERCONDUCTOR SCIENCE & TECHNOLOGY, 23, DOI: 10.1088/0953-2048/23/9/095002

We investigated the influence of fullerene (C-60) addition on the superconducting parameters of MgB2 bulk samples obtained by spark plasma sintering (SPS). It was found that 1.5 wt% C-60 addition leads to the reduction of the critical temperature by a few K, whereas the magnetically determined critical current density increases by approximately one order of magnitude in an applied magnetic field H = 70 kOe at temperature T = 10 K. This indicates substitution of B by C in C-60 added MgB2 processed by SPS, contrary to some data reported in the literature obtained using conventional methods. For our relatively large specimens, the occurrence of macroscale flux jumps was observed over a wide (H, T) domain. The relaxation of the irreversible magnetization suggests that the macroscale flux jumps transform into microscale flux jumps with increasing H and T

2825. Dielectric resonator antennas of ZST advanced cerramics

Authors: Ene-Dobre, M; Banciu, MG; Nedelcu, L; Ioachim, A; Alexandru, HV

Published: SEP 2010, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 12, 1929, DOI:

Investigations on dielectric on compact resonators antennas with enhanced characteristics are described in this paper. The dielectric resonators were of (Zr(0.8)Sn(0.2))TiO(4) ceramic material (ZST). It is shown that the doping with Mg reduces the sintering temperature and provides a high dielectric constant, low loss and high thermal stability in microwaves. The coupling with an extra resonator can offer a substantial bandwidth enhancement. Moreover, antenna array with four antenna elements provides a higher gain and a more directive radiation pattern.

2826. Localization of Mn2+ Ions in Mesoporous ZnS

Authors: Nistor, SV; Stefan, M; Nistor, LC; Mateescu, CD; Birjega, R

Published: SEP 2010, JOURNAL OF NANOSCIENCE AND NANOTECHNOLOGY, 10, 6205, DOI: 10.1166/jnn.2010.2599

Nanocrystalline cubic ZnS doped with 0.2% mol manganese, exhibiting a stable mesoporous structure, was synthesized at room temperature by a non toxic surfactant-assisted liquid liquid reaction. The X-ray diffraction measurements demonstrate the formation of a sponge-like mesoporous material built from cubic ZnS nanocrystals of 1.8 nm average sizes, with a tight distribution of pores of 1.8 nm mean diameter. The transmission electron microscopy images confirm the formation of the mesoporous structure with walls of 3.1 nm mean thickness built from cubic ZnS nanocrystallites of 2.1 nm average size. The resulting tight distribution of crystallites and pores yields a well resolved Electron Paramagnetic Resonance spectrum, with the narrowest reported component lines attributed to three types of isolated Mn2+ centers, called Mn2+ (I), Mn2+ (II) and Mn2+ (III). From the analysis of the spin Hamiltonian parameters it is shown that in the Mn2+ (I) centers the paramagnetic ion is situated at substitutional Zn sites in the ZnS nanocrystals, being also subjected to a small axial distortion. The relative concentration changes under thermal treatment experiments strongly suggest that in both Mn2+ (II) and Mn2+ (III) centers the Mn2+ ion is localized on the surface of the ZnS nanocrystallites, being bond to an oxygen ion in the first case and to an additional water molecule in the second case.

2827. On the bioactivity of adherent bioglass thin films synthesized by magnetron sputtering techniques

Authors: Stan, GE; Popescu, AC; Mihailescu, IN; Marcov, DA; Mustata, RC; Sima, LE; Ianculescu, A; Trusca, R; Morosanu, CO

Published: AUG 31 2010, THIN SOLID FILMS, 518, 5964, DOI: 10.1016/j.tsf.2010.05.104

We report on the synthesis of 700 nm thick bioglass thin films by magnetron sputtering from 45S5 bioglass targets in the argon atmosphere. The adhesion of films to Ti substrates increased 1 75 times when introducing an similar to 70 nm thick mixed glass-Ti buffer layer (BG(1-x)Ti(x) (x = 0-1)) with gradient of composition by co-sputtering. The morphological and structural properties of the films were studied by XRD, ETIR and microscopic techniques, showing an improvement after the two-hour thermal air treatment at 650 degrees C. We investigated in vitro the viability and proliferation of human osteoblast cells cultivated onto the surface of the films The osteoblasts spread over the surface adopting typical polyhedral shapes with numerous focal adhesion points and protrusions infiltrating deep into the films. We assigned this evolution to the improved mechanical properties and enhanced bioactivity due to the prevalent formation of combeite and wollastonite crystalline phases in the heat treated bioglass films (C) 2010 Elsevier B.V All rights reserved

2828. Interfacial atomic diffusion in AF/Fe/Cu/Fe (AF=Fe50Mn50 and Ir50Mn50) multilayer systems

Authors: Kuncser, V; Keune, W; von Hoersten, U; Schinteie, G; Stefan, N; Palade, P; Filoti, G

Published: AUG 31 2010, THIN SOLID FILMS, 518, 5985, DOI: 10.1016/j.tsf.2010.05.100

Spin valve like AF/Fe/Cu/Fe (AF = Fe50Mn50 and Ir50Mn50) multilayer systems have been prepared by molecular beam epitaxy. Thin tracer layers enriched in the Fe-57 isotope were artificially grown at the AF/Fe and Fe/Cu interfaces and the interfacial atomic diffusion was observed via Fe-57 conversion electron Mossbauer spectroscopy. The results show that the atomic interdiffusion at all involved interfaces is lower in the IrMn based structures as compared to the FeMn based ones. (C) 2010 Elsevier B.V. All rights reserved

2829. Application of spark plasma sintering to processing of dense Ba(Ti1-xSnx)O-3 (x=0.13) ceramic

Authors: Aldica, G; Cernea, M; Radu, R; Trusca, R

Published: AUG 27 2010, JOURNAL OF ALLOYS AND COMPOUNDS, 505, 277, DOI: 10.1016/j.jallcom.2010.06.044

Short time spark plasma sintering at 1200 degrees C for 10 min and under a uniaxial pressure of 95 MPa followed by annealing at 1100 degrees C for 5 h is proposed for synthesis of high density (99%) Ba(Ti0.87Sn0.13)O-3 ceramic. Starting powder of 450 nm was obtained by co-precipitation, while the average grain size in the sintered ceramic was of 580 nm. X-ray diffraction analysis of the as prepared Ba(Ti0.87Sn0.13)O-3 samples indicated the presence of single phase BaTi0.87Sn0.13O3 developed in the BaTiO3 cubic structure. Samples have high relative dielectric constant of 5680 and low dissipation factor (tan delta = 0.009) at Curie temperature of 57 degrees C and 1 kHz, good tunability and ferroelectric properties. Remarkable is that these results are from some points of view different than for the conventionally processed samples with similar stoichiometry. Some ideas in this regard are presented and this suggests that SPS can be useful for expanded possibilities in the control of the properties. (C) 2010 Elsevier B.V. All rights reserved.

2830. Thermodynamic destabilization of Li-N-H system by Si addition

Authors: Palade, P; Lungu, GA; Husanu, AM

Published: AUG 27 2010, JOURNAL OF ALLOYS AND COMPOUNDS, 505, DOI: 10.1016/j.jallcom.2010.03.249

Li-N-H and Li-Si-N-H composites have been synthesized by ball milling starting from lithium amide, lithium hydride and silicon powders. Hydrogen sorption behaviour was investigated for the Si-containing composites and a Li-N-H reference sample. The as-milled Si-containing sample showed the presence of the constituent powders but after few absorption-desorption cycles an important amount of Li(2)SiN(2) appeared in both de-hydrogenated and re-hydrogenated composites. This phase was present in higher amount in the de-hydrogenated sample than in the re-hydrogenated one. The presence of this phase was also confirmed by XPS measurements. Li-N-H and Li-Si-N-H composites in de-hydrogenated state also contained lithium imide. X-ray diffraction data indicated a reversible hydrogen generating reaction between lithium amide, lithium hydride and silicon to produce Li(2)SiN(2). lithium imide and hydrogen. The plateau pressure of Li-N-Si-H system is twice the one for Li-N-H at the same temperature (about 265 degrees C), as shown by pressure-composition isotherms in desorption mode. For the first time it has been observed a thermodynamic destabilization of Li-N-H by mixing it with Si. (C) 2010 Elsevier B.V. All rights reserved.