Search

The transparent glasses with composition 30PbO–10GeO 2 –(60−x)SiO 2 −xNb 2 O 5 (mol%) (0 ≤ x ≤ 2.5) are prepared by conventional melt quenching technique. The amorphous nature of the prepared glasses is characterized by XRD. The spectroscopic studies such as optical absorption, FTIR, Raman spectra were carried out at room temperature on these glasses. Besides this electrical properties, like dielectric constant ε ' , loss tan δ , ac conductivity σ a c etc., were also investigated over a moderately wide range of frequency (10 3 –10 6 Hz) and temperature (30–300 °C). The optical absorption spectrum of the prepared glasses has exhibited absorption bands around 325 nm and 340 nm and these are due to the triplet – singlet electronic transition of Ge 2+ state presents in the glass matrix as conversion of GeO 2 into GeO is much easier rather than SiO 2 . From FTIR spectra of as prepared glasses, it is noticed that the intensity of octahedral NbO 6 structural units is found to increase up to 2 mol% of Nb 2 O 5 there after it is observed to decrease. It is also supported by Raman shift of NbO 6 structural units observed around 650 and 930 cm −1 . The analysis of electrical studies is also revealed that the conductivity of prepared glasses is found to increase gradually up to 2 mol% of Nb 2 O 5 beyond this concentration it is observed to decrease. When the spectroscopic investigations are coupled with electrical studies it is concluded that the glass samples doped with 2 mol% of Nb 2 O 5 are found to exhibit good semiconducting nature among the prepared glasses. Such glasses are suitable for fabrication of solid state devices. [ABSTRACT FROM AUTHOR]

Abstract: The kinetic phase behavior and phase transformation paths of purified tristearoylglycerol (SSS), 3-palmitoyl-1,2-distearoyl-sn-glycerol (PSS) and 1,2-dipalmitoyl-3-stearoyl-sn-glycerol (PPS) were investigated in terms of polymorphism, crystallization and melting. The details of the phase transformation paths were obtained using the heating cycles of two sets of experiments: (a) cooling rate was varied and heating rate fixed and (b) cooling rate was fixed and heating rate varied. Kinetic effects were manifest in all measured properties, underscoring the complexity of the phase transformation paths for each TAG, and the intricate thermodynamics–molecular relationships. For the first time, XRD data obtained for SSS, PSS and PPS TAGs, cooled at rates higher than 0.5°C/min, suggested the formation of a transient structure similar to the so-called α2-phase which has been observed in mixed saturated–unsaturated TAGs quenched from the melt. The more stable phases (β′ in PSS and PPS, and β in SSS) were only observed for cooling rates lower than 1.0°C/min. The kinetic and thermodynamic differences observed in the crystallization, structure and melting of SSS, PSS and PPS are proposed to be mainly due to the disturbances introduced at the “terrace” level via methyl-end group interactions, i.e., the missing of two or four CH2 groups compared to SSS. The symmetrical SSS with a relatively flat “terrace” crystallizes preferably in the most stable β-form. Two missing CH2 groups at the sn-1 position (PSS) introduces enough structural disturbances to promote the relative prevalence and persistence of the β′-phase, and four missing CH2 groups at the sn-1 and sn-2 positions (PPS) is relatively too large of a disturbance and therefore favors the α-form. [Copyright &y& Elsevier]

Abstract: Gallium nitride (GaN) nanocrystals were synthesized by nitridation of Ga-EDTA (ethylene diamine tetra acetic acid) complexes at different temperatures starting from 600 to 900°C. X-ray diffraction analysis, Fourier transform infrared spectroscopy and Raman studies revealed that the compound synthesized at 900°C consists of single-phase GaN nanocrystals with wurtzite structure. The change in morphology of the GaN crystals at different temperatures was observed using scanning electron microscopy. The transmission electron microscopy showed the average size of the crystalline particles to be ∼20nm. The room temperature photoluminescence exhibits band-edge emission of GaN at 3.46eV for all the samples. The present study demonstrates that the nitridation of Ga-EDTA complex method has significant potential for the synthesis of GaN nanocrystals as a simple and inexpensive method. [Copyright &y& Elsevier]