Synthesis and characterization of morphologically different high purity gallium oxide nanopowders

High purity gallium oxide nanopowders have been synthesized by using a simple precipitation technique with calcination at elevated temperature. From the X-ray pattern, the phase purity of the synthesized powders was confirmed as β-Ga₂O_3. Elemental quantification (stoichiometry) of Ga₂O₃ was also examined from the X-ray energy dispersive analysis (EDAX). Based on the recorded Fourier Transform Infrared (FTIR) spectrum of Ga₂O_3, the IR bands due to Ga–O bond and crystal lattice vibrations have been identified in the wavenumber range 400–4,000 cm⁻¹. From the measured SEM images, it is obvious to notice that the pH value has been playing a dominant role in obtaining morphologically different gallium oxide nanopowders. Thermogravimetric analysis reveals 8.3% of weight loss when the sample was heated to the temperature of 1,100 °C from the room temperature, which also shows a crystalline phase transformation. It is very interesting to report that a broad blue emission at 455 nm has been measured from the synthesized gallium oxide nanopowders.     

Dielectric and thermal characteristics of gel grown single crystals of ytterbium tartrate trihydrate

Dielectric and thermal characteristics of gel grown single crystals of ytterbium tartrate trihydrate have been carried out. The dielectric constant has been measured as a function of frequency in the range 2 kHz–1 MHz and temperature range 30–300 °C. The dielectric constant increases with temperature, attains a peak near 215 °C, and then decreases as the temperature exceeds 215 °C. The dielectric anomaly at 215 °C is suggested to be due to phase transition brought about in the material. The dielectric behaviour of the material is correlated with the results on thermal analysis. Thermogravimetric and differential thermal analysis have been used to study the thermal characteristics of the material. The experimental results show that the material is thermally stable up to 200 °C. The decomposition process occurs in two stages until ytterbium oxide is formed at 700 °C. The non-isothermal kinetic parameters e.g., activation energy and the frequency factor have been evaluated for each stage of thermal decomposition by using the integral method, applying the Coats–Redfern approximation.     

Vibrating Wire Thermometry in Superfluid 3He

We report systematic measurements of the response of a Vibrating Wire Resonator (VWR) in normal and superfluid liquid ³He. Special attention has been paid to the hydrodynamic regime of the superfluid B-phase, where the response parameters of the VWR do not follow a simple law. We show that a simple interpolation between the region where first order slip-corrections can be applied and the ballistic regime is insufficient. Measuring an empirical effective viscosity, we propose a temperature calibration method which allows the use of VWRs as a secondary thermometer at intermediate and high pressures in the temperature range 0.2 T _c < T < 50 mK.     

Point Contact Spectroscopy and Temperature Dependence of Resistivity of Metallic Sodium Tungsten Bronzes - Role of Optical Phonons

In this paper we report the results of electrical resistivity (1.5≤ T ≤ 300K) and point contact spectroscopy (PCS) measurements on single crystals of metallic sodium tungsten bronze with varying sodium content. We have shown that the electron-phonon coupling function as measured through PCS can explain quantitatively the large temperature dependence of resistivity ρ seen in these materials over the entire temperature range. The electron-phonon coupling function shows predominately large peaks for phonon frequency range of 30 meV ≤ ω ≤ 100 meV which match well with the calculated optical phonons for WO₆ octahedron. The integrated electron-phonon coupling constant λ from this data is ≈ 0.25-0.45, depending on the Na content. PACS numbers: 72.15.-v, 72.80.Ga     

Atomistic simulations of the solubilization of single-walled carbon nanotubes in toluene

Solubilization of the armchair, metallic (10,10) single-walled carbon nanotubes (SWCNTs) in toluene is modeled using molecular dynamics simulations. Inter- and intra-molecular atomic interactions in the SWCNT + toluene system are represented using COMPASS (Condensed-phased Optimized Molecular Potential for Atomistic Simulation Studies), the first ab initio forcefield that enables an accurate and simultaneous prediction of various gas-phase and condensed-phase properties of organic and inorganic materials.The results obtained show that due to a significant drop in the configurational entropy of toluene, the solvation Gibbs free energy for these nanotubes in toluene is small but positive suggesting that a suspension of these nanotubes in toluene is not stable and that the nanotubes would fall out of the solution. This prediction is consistent with experimental observations.     

Structural characterisation of apatite coatings

The current, most frequently employed, commercial route to produce hydroxyapatite prosthetic coatings is plasma spraying. However, this has several important limitations especially for textured surfaces. Low temperature methods of coating fabrication such as cathodic electrodeposition are attractive alternatives. However, quantitative characterisation of the phase composition of thin electrodeposited coatings can be problematic. An X-ray diffraction method, which provides quantitative compositional information without reference to external or internal standards, is introduced and validated. The method can also be applied when Bragg peaks from the supporting substrate are apparent within the data and preferred orientation can be tolerated. This method has been used to examine in detail the microstructure of electrodeposited coatings which are compared directly with those formed by a commercial plasma spraying process.We show that, unlike the plasma sprayed coatings, the electrodeposited material consists of a single crystalline phase (hydroxyapatite) and a significantly reduced amorphous phase. The electrodeposited coatings also possess significantly more microstrain and a smaller crystallite size than the corresponding plasma sprayed material.