National Institute Of Materials Physics - Romania

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892 articles found

371. COMPOSITES OF MgB2 - RARE-EARTH-OXIDES: FABRICATION BY SPARK PLASMA SINTERING AND FUNCTIONAL PROPERTIES

Authors: Batalu, D; Aldica, G; Badica, P

Published: 2015, 20TH INTERNATIONAL CONFERENCE ON COMPOSITE MATERIALS, DOI:

Dense MgB2 samples with La2O3 addition were obtained by spark plasma sintering. We used two different La2O3 raw powders showing different particle sizes and shapes. The as-obtained composite samples have significant differences in microstructure and Vickers hardness. A deposited phosphate layer was obtained by immersing the samples in PBS, and drying. Formation of phosphate needles, gathered in bouquets, show a possible bioactive behavior of MgB2.

372. GMR ON CuNiCo THIN LAYERS DEPOSITED USING TVA METHOD

Authors: Prioteasa, I; Porosnicu, C; Lungu, CP; Jepu, I; Schinteie, G; Ciupina, V; Prodan, G; Vasile, E; Dinca, P

Published: APR-JUN 2015, DIGEST JOURNAL OF NANOMATERIALS AND BIOSTRUCTURES, 10, 436, DOI:

Thermionic vacuum arc was successfully used to prepare high quality nanostructure thin films with different fields of applicability. One advantage of this deposition technique was the ability to have a controlled range of thicknesses starting from few nanometers to hundreds of nanometers. The purity of the thin films was insured by a high vacuum pressure and a lack of any kind of buffer gas inside the coating chamber. The aim of this work was to obtain significant magnetic response and to compare the MR to the structures obtained for two different granular combinatorial structures. The samples were investigated using scaning and transmision electron mycroscopy while SEM and The magnetic properties were first studied by measuring the electrical resistance behavior for a magnetic field of 0.3 T, at different values of the sample temperature and using a non-destructive optical method called Magneto-Optical Kerr Effect (MOKE). The magnetoresistive effect obtained for the studied samples varied from 0.6% to 19% in respect sample structure and temperature for a constant magnetic field.

373. SHAPE MEMORY PROPERTIES OF FeNiCoTi RIBBONS EVIDENCED BY MAGNETIC MEASUREMENTS

Authors: Tolea, F; Sofronie, M; Tolea, M; Kuncser, V; Valeanu, M

Published: APR-JUN 2015, DIGEST JOURNAL OF NANOMATERIALS AND BIOSTRUCTURES, 10, 575, DOI:

The present work addresses the shape memory and (ferro) magnetic properties of Fe52Ni29-xCo15+xTi4 (with x=0, 3 and 6) alloys. The analysed samples were prepared as ribbons by the melt spinning method and subjected to thermal treatments. X-ray diffraction, DSC, thermomagnetic measurements and Mossbauer spectroscopy were used for a complete structural and magnetic characterization. Both the preparation route and the different Co addition induce specific effects which are discussed in detail. The sample with x=0 sustains an irreversible transformation, while a partial reversible transformation and a relatively increased Curie temperature were observed for sample with x=3. However, further increasing the Co content to x= 6 leads to a loss of the martensitic transformation.

374. Qualitative comparative analysis of MgB2 powder-in-tube wires: superconductivity and X-ray cone-bean microtomography

Authors: Badica, P; Tiseanu, I; Aldica, G; Craciunescu, T; Sandu, V; Jakob, G; Rindfleisch, M

Published: NOV-DEC 2015, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 17, 1649, DOI:

Commercial wires of MgB2 with different architectures and two different heat treatments were characterized with respect to their superconducting properties (T-c, J(c), H-irr, pinning force, macro flux jumps behaviour) through magnetic measurements and were visualized by 3D x-ray micro-tomography (XRT). For a particular architecture, heat treatment conditions of 625 degrees C/3 hrs or 700 degrees C/30 min produced relatively small differences, whereas the architecture of the wires showed a strong influence on superconducting characteristics. XRT checks the integrity of the wires easily detecting in a non-invasive way 3D macro defects and shows their hidden extended shape. XRT also allows a comparative geometry analysis between similar elements (e.g. filaments or filaments-matrix interfaces) from a particular wire or from wires with different architectures. Namely, XRT shows that the geometrical perfection (defined as the degree of departure of the geometry from the designed one) of the inner MgB2 filaments from the wires with 18 elements was lower than for the outermost ones from the same wires and was also lower than for the filaments from the wires with 7 elements. It is proposed that these results of geometrical perfection correlate with better overall superconducting quality of the wires with 7 filaments (except for the stronger presence of macro flux jumps in the wires with 7 filaments).

375. Growth and characterization by STM of BiCo222 crystal objects: whiskers and bows

Authors: Burdusel, M; Miu, L; Zhao, PH; Yan, W; Han, YL; Nie, JC; Badica, P

Published: MAR-APR 2015, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 17, 430, DOI:

Lamellar crystal objects such as straight, curved or kinked whiskers, bows and objects with missing stripes were grown in a static air atmosphere from melt-quenched substrates with starting composition Bi1.5Sr1Ca1Co0.6Oy. The average EDS composition of the objects is Bi2Sr0.75Ca1.8Co1.94Oy and the crystal structure is of the phase usually denoted in the literature as Bi-2(Sr,Ca)(2)Co2Oy (BiCO222). Objects of other phases were not found. Curvature is in the (ab)-plane. By scanning tunneling spectroscopy (STS) a semiconducting energy gap was determined at 2.41 eV.

376. Magnetocaloric effect in Ni-Fe-Ga Heusler alloys with Co and Al substitutions

Authors: Tolea, F; Sofronie, M; Crisan, AD; Tolea, M; Valeanu, M

Published: 2015, ESOMAT 2015 - 10TH EUROPEAN SYMPOSIUM ON MARTENSITIC TRANSFORMATIONS, 33, DOI: 10.1051/matecconf/20153305008

The functionality of the ferromagnetic shape memory alloys is related to the martensitic and magnetic order-disorder transformations, both of which may be tailored by doping with other elements or by suitable thermal treatments, so that alloys with concomitant (or sequential but close) structural and magnetic phase transitions may be obtained. Concerning the magnetocaloric applications, it is assumed that the thin melt-spun ribbons assure a more efficient heat transfer. In the present work we investigate the influence of Co and Al substitutions on magnetocaloric effect characteristics of NiFeGa in bulk and also in ribbons prepared by melt spinning method and subjected to different thermal treatments. X-ray diffraction, differential scanning calorimetry, magnetocaloric and magnetoresistive characterizations have been performed. The results highlight the differences between the bulk and the ribbons (both as prepared and annealed) and the role of substitutions.

377. The Influence of the Microstructure and Morphology of CeO2 Buffer Layer on the Properties of YBCO Films PLD Grown on Ni Tape

Authors: Mihalache, V; Stefan, N; Enculescu, I; Mihailescu, IN; Socol, M; Miroi, M

Published: NOV 2014, JOURNAL OF SUPERCONDUCTIVITY AND NOVEL MAGNETISM, 27, 2485, DOI: 10.1007/s10948-014-2679-9

YBa2Cu3O7-delta films were deposited on CeO2-buffered nickel substrates, with different buffer thickness. Full width at half maximum of rocking curve, Delta(omega), of CeO2 and yttrium barium copper oxide (YBCO), as well as the critical temperature, T-c, of YBCO were shown to be strongly dependent on buffer thickness. They behave similarly but not proportional to the buffer thickness increase. This and the fact that Delta(omega) vs. buffer thickness and T-c vs. buffer thickness for YBCO behave similar with RMS roughness vs. thickness of CeO2 indicates that the surface peculiarity of buffers is responsible for YBCO properties. More precisely, the surface of CeO2 films prepared by the chemical solution route based on propionic acid is prone to agglomerate (de-wet) and the degree of agglomeration depends in an intricate way on buffer thickness. We showed that nor RMS roughness neither (00l) texture degree can define alone the surface suitable for c-axis YBCO nucleation. The {111} faceted grains (even in the case of high (00l) texture) and other defects generated by agglomeration supply a low fraction of (00l) flat terminations of buffer that affect the nucleation of c-axis-oriented YBCO phase. Moreover, the thermal instability of the surface morphology of CeO2 buffers (further development of de-wetting process, {111} faceted grains, etc. during superconducting layer deposition) influence the quality of YBCO films.

378. Cobalt chromite obtained by thermal decomposition of oxalate coordination compounds

Authors: Mindru, I; Gingasu, D; Marinescu, G; Patron, L; Calderon-Moreno, JM; Bartha, C; Andronescu, C; Crisan, A

Published: NOV 2014, CERAMICS INTERNATIONAL, 40, 15258, DOI: 10.1016/j.ceramint.2014.07.009

Cobalt chromites (CoCr2O4) powders have been synthesized via thermal decomposition of oxalate precursor compounds (NH4)(4)[CoCr2(C2O4)(4)(OH)(4)]center dot 7H(2)O (I) and (Na-4)(12)[CoCr2(C2O4)(8)(OH)(4)]center dot(NH4)(2)C2O4 center dot 12H(2)O (II). The oxalate precursors have been characterized by infrared (IR) and ultraviolet visible spectroscopy (UV-vis), X-ray diffraction (XRD), scanning electron microscopy (SEM) and thermal analysis. The structure, morphology and magnetic properties of CoCr2O4 powders have been investigated by XRD, SEM, IR and Raman spectroscopy (RS), UV-vis and magnetic measurements. XRD patterns confirmed the formation of spinel-type cobalt chromite, with average crystallite sizes calculated from XRD patterns of 38 nm and 58 nm, for spinel chromites from precursors I and II, respectively. SEM micrographs revealed particle sizes between 30 and 130 nm, with a low degree of aggregation of primary nanocrystallites. Both CoCr2O4 powders presented ferrimagnetic ordering below the Currie temperature (T-c) and a phase transition at T-s similar to 20 K attributed to the onset of long-range spiral magnetic order. (C) 2014 Elsevier Ltd and Techna Group S.r.l. All rights reserved.

379. Trapped magnetic field in a (NdFeB)-(MgB2) pair-type bulk magnet

Authors: Aldica, G; Burdusel, M; Badica, P

Published: OCT 15 2014, PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS, 505, 23, DOI: 10.1016/j.physc.2014.07.001

Superconducting bulk discs, S, of 20 mm in diameter and 3.5 or 3.3 mm thickness of MgB2 (pristine or added with cubic BN, respectively) with density above 97% were prepared by Spark Plasma Sintering. Discs were combined in a pair-type sandwich-like arrangement with a permanent NdFeB axially magnetised magnet, PM (similar to 0.5 T). Measurement of the trapped field, B-tr, with temperature, time, and the reduction rate of the applied magnetic field was performed using a Hall sensor positioned at the centre between the superconductor and the permanent magnet. It is shown that the permanent magnet with certain polarity favors higher trapped field of the superconductor owing to suppression of flux jumps specific for high density MgB2 samples. The B-tr of the PM-S pair was 2.45 T (20 K) and 3.3 T (12 K). (C) 2014 Elsevier B.V. All rights reserved.

380. Evaluation of pristine and Eu2O3-added MgB2 ceramics for medical applications: hardness, corrosion resistance, cytotoxicity and antibacterial activity

Authors: Batalu, D; Stanciuc, AM; Moldovan, L; Aldica, G; Badica, P

Published: SEP 1 2014, MATERIALS SCIENCE & ENGINEERING C-MATERIALS FOR BIOLOGICAL APPLICATIONS, 42, 361, DOI: 10.1016/j.msec.2014.05.046

Nano- or micropowders of Eu2O3 were added to MgB2, resulting in a composition of (MgB2)(0.975)(EuO1.5)(0.025). Pristine and doped samples were prepared using spark plasma sintering and tested for (i) Vickers hardness, (ii) pH evolution in phosphate-buffered saline solution, (iii) corrosion resistance (Tafel polarization curves), (iv) cytotoxicity (in vitro tests), and (v) antibacterial activity. Eu2O3 addition influenced the investigated properties. Solutions of MgB2-based samples show a relatively high saturation pH of 8.5. This value is lower than that of solutions incubated with Mg or other Mg-based biodegradable alloys reported in the literature. MgB2-based samples have lower electro-corrosion rates than Mg. Their Vickers hardness is 6.8-10.2 GPa, and these values are higher than those of biodegradable Mg-based alloys. MgB2 has low in vitro biocompatibility, good antibacterial activity against Escherichia coli, and mild activity against Staphylococcus aureus. Our results suggest that MgB2-based materials deserve attention in biomedical applications, such as implants or sterile medical instruments. (C) 2014 Elsevier B.V. All rights reserved.