The composition dependence of electrical switching behavior of Ge7Se93-xSbx glasses

Bulk Ge7Se93-xSbx (21 <= x <= 32) glasses are prepared by melt quenching method and electrical switching studies have been undertaken on these samples to elucidate the type of switching and the composition and thickness dependence of switching voltages. On the basis of the compressibility and atomic radii, it has been previously observed that Se-based glasses exhibit memory switching behavior. However, the present results indicate that Ge7Se93-xSbx glasses exhibit threshold type electrical switching with high switching voltages. Further, these samples are found to show fluctuations in the current-voltage (I-V) characteristics. The observed threshold behavior of Ge7Se93-xSbx glasses has been understood on the basis of larger atomic radii and lesser compressibilities of Sb and Ge. Further. the high switching voltages and fluctuations in the I-V characteristics of Ge-Se-Sb samples can be attributed to the high resistance of the samples and the difference in thermal conductivities of different structural units constituting the local structure of these glasses. The switching voltages of Ge7Se93-xSbx glasses have been found to decrease with the increase in the Sb concentration. The observed composition dependence of switching voltages has been understood on the basis of higher metallicity of the Sb additive and also in the light of the Chemically Ordered Network (CON) model. Further, the thickness dependence of switching voltages has been studied to reassert the mechanism of switching.

W physics at the ILC with polarized beams as a probe of the Littlest Higgs model

We study the possibility of using W pair production and leptonic decay of one of the W's at the ILC with polarized beams as a probe of the Littlest Higgs Model. We consider cross-sections, polarization fractions of the W's, leptonic decay energy and angular distributions, and left-right polarization asymmetry as probes of the model. With parameter values allowed by present experimental constraints detectable effects on these observables at typical ILC energies of 500 GeV and 800 GeV will be present. Beam polarization is further found to enhance the sensitivity.

Low loss and frequency (1 kHz-1 MHz) independent dielectric characteristics of 3BaO-3TiO(2)-B2O3 glasses

X-ray powder diffraction along with differential thermal analysis carried out on the as-quenched samples in the 3BaO-3TiO(2)-B2O3 system confirmed their amorphous and glassy nature, respectively. The dielectric constants in the 1 kHz-1 MHz frequency range were measured as a function of temperature (323-748 K). The dielectric constant and loss were found to be frequency independent in the 323-473 K temperature range. The temperature coefficient of dielectric constant was estimated using Havinga's formula and found to be 16 ppm K-1. The electrical relaxation was rationalized using the electric modulus formalism. The dielectric constant and loss were 17 +/- 0.5 and 0.005 +/- 0.001, respectively at 323 K in the 1 kHz-1 MHz frequency range which may be of considerable interest to capacitor industry.

Recent progress on synthesis, multi-scale structure, and properties of Y-Si-O oxides

Yttrium silicates (Y-Si-O oxides), including Y2Si2O7, Y2SiO5, and Y4·67(SiO4)3O apatite, have attracted wide attentions from material scientists and engineers, because of their extensive polymorphisms and important roles as grain boundary phases in improving the high-temperature mechanical/thermal properties of Si3N4and SiC ceramics. Recent interest in these materials has been renewed by their potential applications as high-temperature structural ceramics, oxidation protective coatings, and environmental barrier coatings (EBCs). The salient properties of Y-Si-O oxides are strongly related to their unique chemical bonds and microstructure features. An in-depth understanding on the synthesis - multi-scale structure-property relationships of the Y-Si-O oxides will shine a light on their performance and potential applications. In this review, recent progress of the synthesis, multi-scale structures, and properties of the Y-Si-O oxides are summarised. First, various methods for the synthesis of Y-Si-O ceramics in the forms of powders, bulks, and thin films/coatings are reviewed. Then, the crystal structures, chemical bonds, and atomic microstructures of the polymorphs in the Y-Si-O system are summarised. The third section focuses on the properties of Y-Si-O oxides, involving the mechanical, thermal, dielectric, and tribological properties, their environmental stability, and their structure-property relationships. The outlook for potential applications of Y-Si-O oxides is also highlighted.

Novel synthesis of superparamagnetic Ni-Co-B nanoparticles and their effect on superconductor properties of MgB2

A new procedure for the preparation of amorphous Ni-Co-B nanoparticles is reported, with a detailed investigation of their morphology by X-ray diffraction and transmission electron microscopy, as well as their magnetic properties. Many factors, such as chemical composition, anisotropy, size and shape of the particles, were controlled through chemical synthesis, resulting in the control of morphological and magnetic properties of the nanoparticles. Controlling pH values with ethylenediamine and using sodium dodecyl sulfate surfactant lowered the size of the nanoparticles to below 10 nm. Such a small structure and chemical disorder in nanocrystalline materials lead to magnetic properties that are different from those in their bulk-sized counterparts. The obtained nanoparticles can be used for different purposes, from pharmaceutical applications to implementations in different materials technology. The focus of this research is the synthesis of Ni-Co-B nanoparticles in a new way and studying the reaction of Ni-Co-B nanoparticles with Mg and B precursors and their effect on MgB2 properties. New nanostructures are formed in the reaction of Ni-Co-B nanoparticles with Mg: Mg2Ni, Co2Mg and possibly Mg2Co.

Effect of LiYO2 on the synthesis and pressureless sintering of Y2SiO5

Y2SiO5 has potential applications as a high-temperature structural ceramic and environmental/thermal barrier coating. In this work, we synthesized single-phase Y2SiO5 powders utilizing a solid-liquid reaction method with LiYO2 as an additive. The reaction path of the Y2O3/SiO2/LiYO2 mixture with variation in temperatures and the role of the LiYO2 additive on preparation process were investigated in detail. The powders obtained by this method have good sinterability. Through a pressureless sintering process, almost fully dense Y2SiO5 bulk material was achieved with a very high density of 99.7% theoretical.

Mechanical properties and damage tolerance of Y2SiO5

Y2SiO5 has potential applications as functional-structural ceramic and environmental/thermal barrier coating material. As an important grain-boundary phase in the sintered Si3N4, it also influences the mechanical and dielectric performances of the host material. In this paper, we present the mechanical properties of Y2SiO5 including elastic moduli, hardness, strength and fracture toughness, and try to understand the mechanical features from the viewpoint of crystal structure. Y2SiO5 has low shear modulus, low hardness, as well as high capacity for dispersing mechanical damage energy and for resisting crack penetration. Particularly, it can be machined by cemented carbides tools. The crystal structure characteristics of Y2SiO5 suggest the low-energy weakly bonded atomic planes crossed only by the easily breaking Y-O bonds as well as the rotatable rigid SiO4 tetrahedra are the origins of low shear deformation, good damage tolerance and good machinability of this material. TEM observations also demonstrate that the mechanical damage energy was dispersed in the form of the micro-cleavages, stacking faults and twins along these weakly bonded atomic planes, which allows the "microscale-plasticity" for Y2SiO5.

Kinetics and mechanism of hot corrosion of γ-Y 2Si 2O 7 in thin-film Na 2SO 4 molten salt

γ-Y 2Si 2O 7 is a promising candidate material both for hightemperature structural applications and as an environmental/thermal barrier coating material due to its unique properties such as high melting point, machinability, thermal stability, low linear thermal expansion coefficient (3.9×10 -6/K, 200°-1300°C), and low thermal conductivity (<3.0 W/ṁK above 300°C). The hot corrosion behavior of γ-Y 2Si 2O 7 in thin-film molten Na 2SO 4 at 850°-1000°C for 20 h in flowing air was investigated using a thermogravimetric analyzer (TGA) and a mass spectrometer (MS). γ-Y 2Si 2O 7 exhibited good resistance against Na 2SO 4 molten salt. The kinetic curves were well fitted by a paralinear equation: the linear part was caused by the evaporation of Na2SO4 and the parabolic part came from gas products evolved from the hotcorrosion reaction. A thin silica film formed under the corrosion scale was the key factor for retarding the hot corrosion. The apparent activation energy for the corrosion of γ-Y 2Si 2O 7 in Na 2SO 4 molten salt with flowing air was evaluated to be 255 kJ/mol.