National Institute Of Materials Physics - Romania

Ex situ spark plasma sintering was used to obtain dense MgB2 co-doped with SiC and Te. The composition (MgB2) + (SiC)(0.025) + Te-0.01 shows critical current densities J(c)(20 K, 5 T) of 3.5 x 10(2) A cm(-2) and J(c)(5 K, 9 T) of 2 x 10(3) A cm(-2). These values are higher than for pristine samples or those separately doped with Te or SiC. They are also comparable at high fields and temperatures with the best reported values for the co-doped MgB2 bulks produced by conventional in situ methods. (C) 2012 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Highly textured ZnO thin films were implanted with Co ions at fluences of 1 x 10(16) and 1 x 10(17) ions cm(-2). Although their microstructure observed by analytical high-resolution electron microscopy was very different, SQUID magnetometer measurements showed qualitatively similar magnetic properties. In the low-fluence film, only small modifications, such as a slight amorphization, planar defects or very small (<1-1.5 nm) Co clusters, were hardly observable. Implantation at a higher fluence led to important changes in the film structure: heavy amorphization and metallic Co precipitates were identified by electron diffraction, energy dispersive x-ray spectroscopy (EDS), electron energy loss spectroscopy and scanning transmission electron microscopy spectrum imaging. EDS microanalysis additionally revealed the presence of similar to 2 at% Co atoms that were likely dissolved in the ZnO lattice at the atomic level. No Co oxides or other secondary oxide phases were detected. For both implanted samples, the dimensions of Co precipitates were below the superparamagnetic limit at room temperature. Thermo-magnetization curves and magnetic hysteresis loops measured in the temperature range from 5 to 300 K indicated two superimposed magnetic regimes, one predominant above 50 K and the other below 50 K. We analysed the possible mechanisms and quantitative contributions to explain the observed magnetic behaviour at low and room temperature.

The synthesis of multifunctional magnetic nanoparticles (MF-MPs) is one of the most active research areas in advanced materials as their multifunctional surfaces allow conjugation of biological and chemical molecules, thus making it possible to achieve target-specific diagnostic in parallel to therapeutics. We report here a simple strategy to integrate in a one-step reaction several reactive sites onto the particles. The preparation of MF-MPs is based on their simultaneous modification with differently functionalized dopamine derivatives using simple solution chemistry. The formed MF-MPs show comparable magnetic properties to those of naked nanoparticles with almost unaltered particle size of around 25 nm. The different termini, amine, azide and maleimide functions, enable further functionalization of MF-MPs by the grafting-on approach. Michael addition, Cu(I) catalyzed << click >> chemistry and amidation reactions are performed on the MF-MPs integrating subsequently 6-(ferrocenyl)-hexanethiol, horseradish peroxidase (HRP) and mannose.

Ru(III)/functionalized silica-coated magnetic nanoparticles (Ru(III)-MNP) were proven to be a highly active, selective and easily recoverable catalyst for the oxidation of levulinic acid to succinic acid under green conditions.

In the last years oxide materials for electronics show significant progress. However, many details regarding technology control of the properties have to be solved. For electronics, thin films and heterestructures are important taking advantage of integration and synergetic concepts leading to new types of devices and functionalities. It is notable that, while fabrication of new devices and materials showing new phenomena are booming, the growth principles and concepts are somehow developing slowly within this general trend. This is because in many cases, growth of materials is very personalized. Understanding of the bi-directional relationship between the general and particular principles deserves attention. The immediate benefit is that knowledge on growth for one material can be transferred to another one. In our work we have analyzed such relationships for some oxide multicomponent perovskites. Materials used in our examples are Bi-Sr-Ca-Cu-O and YBa2Cu3O7, (Ca, Sr)CuO2, (Ca, Ba)CuO2 and Bi4Ti3O12. Presented thin films or heterostructures are with c-axis and non-c-axis orientations and based on these examples we discuss some of the growth principles.

The half-metallic properties of Ti2CoSn full-Heusler compound is studied within the framework of the density of states theory with the Perdew Burke Ernzerhof generalized gradient approximation (GGA). Structural optimization was performed and the calculated equilibrium lattice constant is 6.340 angstrom. The spin up band of compound has metallic character and spin down band is semiconducting with an indirect gap of 0.598 eV at equilibrium lattice constant. For the lattice parameter, ranging from 6.193 to 6.884 angstrom the compound presents 100% spin polarization and a total magnetic moment of 3 mu(B). (C) 2012 Elsevier Ltd. All rights reserved.

We were successful in synthesizing non-linear YBa(2)Cu(3)Ox whiskers, i.e. half loops or kinked shapes, which are promising candidates for solid-state devices based on the intrinsic Josephson effect and with improved electrical connections. We report on a complete characterization of their structural properties via a synchrotron nanoprobe as well as laboratory single-crystal diffraction techniques. This investigation allowed us to fully disclose the growth mechanism, which leads to the formation of curved whiskers. The superconducting properties are evaluated in comparison with their straight counterpart, revealing a strong functional analogy and confirming their potential applicability in superconducting electronic devices.

We review, based on our results, the problems and solutions for the growth of thin films and composite heterostructures emphasizing the general growth aspects and principles vs specifics for each material or heterostructure. The materials used in our examples are Bi2Sr2Ca2Cu3O10, Bi2Sr2CaCu2O8, YBa2Cu3O7, (Sr, Ca)CuO2, (Ba, Ca) CuO2, and Bi4Ti3O12. The growth method was metal organic chemical vapor deposition (MOCVD). The presented thin films or heterostructures have c- and non-c-axis orientations. We discuss the implications of the film-substrate lattice relationships, paying attention to film-substrate lattice mismatch anisotropy and to film-film lattice mismatch, which has a significant influence on the quality of the non-c-axis heterostructures. We also present growth control through the use of vicinal substrates and two-temperature (template) and interrupted growth routes allowing significant quality improvements or optimization. Other key aspects of the growth mechanism, that is, roughness, morphology, and interdiffusion, are addressed. It is concluded that the requirements for the growth of non-c-axis heterostructures are more severe than those for the c-axis ones. (C) 2012 The Japan Society of Applied Physics

Mixtures of MgB2 and metal or oxide additions with starting compositions of (MgB2)(M2O3)(x), x = 0.0025, 0.005, 0.015, and (MgB2)(M)(y), y = 0.01, M = Bi, Sb, were processed by spark plasma sintering (SPS). As-obtained samples are composites with high density exceeding 94% of the theoretical values. Secondary phases indicate similar reactions for samples with Bi- or Sb-based additions. However, samples show very different superconducting characteristics depending on the addition type and amount. A direct correlation with the melting temperature of the addition could not be revealed, although some aspects will be discussed. From the critical current density (J(c)) and irreversibility field (H-irr) enhancement viewpoints, optimum additions are oxides for x = 0.0025; 0.005. Both oxides improve Jc at high fields, but Sb2O3 is effective up to 10 K, whereas Bi2O3 is effective up to 30 K. Metal additions decrease J(c) and H-irr when compared with a pristine MgB2 sample. (C) 2012 The Japan Society of Applied Physics

Magnetite alternating copolymers divinylbenzene-maleic anhydride (DVB-MA) composites were prepared by dispersion polymerization. Because magnetite is used as a complex with oleic acid (Fe(3)O(4)OLA), the final hybrids show good dispersion of inorganic nanofillers in the polymer matrix. The obtained composites were analyzed by infrared absorption spectrometry, diffuse reflectance in visible light, thermogravimetry, X-ray fluorescence, X-ray diffraction, dynamic light scattering, scanning electron microscopy and vibrating sample magnetometry. The obtained results indicate the successful preparation of magnetite nanoparticles with an average size of about 23 nm dispersed in micrometer size copolymer spherical particles, which relative content can be controlled via the processing parameters. A relationship between the relative content of magnetite nanoparticles and the size of the polymer particles, with direct influence on the diffuse reflectance in the visible domain, was observed. A superparamagnetic behavior was evidenced at room temperature with a blocking temperature lower than as expected from the bulk anisotropy constant and the average size of the magnetite nanoparticles. Both the unexpected low blocking temperature and the observed low specific magnetizations were explained by a defected and poor crystalline structure of the magnetite nanoparticles, giving rise to spin disorder and diminished crystalline anisotropy constant. (C) 2012 Elsevier Ltd. All rights reserved.