TDPAC studies of Hf doped YBCO

Time differential perturbed angular correlation measurements of the 133–482 keVγ-γ cascade of¹⁸¹Ta in Hf-doped YBa₂Cu₃O_7−x are presented. The¹⁸¹Hf precurser nuclei are incorporated into the sample by thermal neutron irradiation. Two quadrupole interaction frequencies are observed in the as-irradiated sample:v _Q1=161±10 MHz with intensityf ₁=75%, asymmetry parameterη ₁=0.32 and damping parameter Λ₁=0.42, andv _Q2=1108±40 MHz withf ₂=25%,η ₂=0.62, and Λ₂=0.60. On annealing the sample in air at various temperaturesT _a and quenching to room temperature,f ₁ remained nearly constant forT _a<600°C andv _Q1 for all annealing temperatures indicating that these are insensitive to oxygen stoichiometry. This frequency is interpreted to be due to¹⁸¹Hf substitutingY sites. BeyondT _a=600°C,f ₁ increased and reached a constant value of 90% forT _a=800°C. The value ofv _Q2 showed a slight variation between 1086 and 1160 MHz, whilef ₂ remained nearly constant at 25% forT _a<600°C. This component is identified to be due to¹⁸¹Hf substituting Cu 1 sites in the Cu-O chains of YBCO. Above 600°Cv _Q2 decreased and reached a value of 808 MHz beyond 750°C.     

Dislocation driven chromium precipitation in Fe-9Cr binary alloy: a positron lifetime study

The influence of initial heat treatment on anomalous Cr precipitation within high temperature solubility region of the Fe–9Cr alloy has been investigated using positron lifetime studies. Air-quenched samples with pre-existing dislocations exhibited a distinct annealing stage in positron lifetime between 800 and 1100?K corresponding to Cr-precipitation. During this stage, Transmission Electron Microscopy showed fine precipitates of average size 4 nm, dispersed throughout the sample and from Energy-dispersive X-ray spectroscopy (EDS) analysis they are found to be Cr-enriched. The presence of dislocations is found to be responsible for Cr precipitation.     

Greener synthetic approach for the preparation of substituted flexible dimeric pyridinium salts and its importance

We have prepared substituted flexible dimeric pyridinium bromide using conventional and greener approach. Solvent-free solid phase (greener) approach is superior than the conventional owing to nontoxic, easy workup procedure, and 20 times lesser reaction time. Toxic organic solvents and column chromatography are avoided. Aldol condensation reaction is studied with various substituted aromatic aldehyde and compared with available recent literatures. Synthesized substituted flexible dimeric pyridinium salts acted as potential catalysts because of their better performance even in low concentration, recyclability, and activation of two molecules of aldehydes at the same time for aldol condensation reaction.     

Synthesis,characterization, and anti-cancer activity of chalcone derivatives as-potent anaplastic lymphoma kinase inhibitors

Structural Chemistry - Chalcone derivatives (7a–k) have been synthesized and characterized by 1H-NMR, 13C-NMR, mass, and elemental analysis. The synthesized compounds 7a, 7d, and 7g have been...     

A short review on latest developments in catalytic depolymerization of Poly (ethylene terephathalate) wastes

Chemical recycling of plastic wastes is top among the effective management of the solid wastes. Particularly the post-consumer polyethylene terephthalate (PET) plastic wastes mainly generated from the disposal of beverage bottles and placed third most produced polymeric waste. However, PET wastes could be chemically recycled using several types of homo-/heterogeneous acid or base catalysts, and an effective recycling process has yet to be achieved. Therefore, the present short review is intended to display recent reports on the depolymerization of PET polymer wastes. The review aimed to cover glycolysis and aminolytic depolymerization using various catalytic systems. There is a wide spectrum of catalytic systems such as metal oxides, ionic liquids, organic bases, nanoparticles, porous materials and microwave-assisted rapid depolymerization methods have been developed toward the yield enhancement of the depolymerized products. Ideologically, the present review would benefit the researchers in familiarizing themselves with the latest developments in this field.     

Investigating the effect of π-configurations and methoxy substitution on donor and π- spacers based dyes for dye-sensitized solar cell applications–computational approach

Research on Chemical Intermediates - Triphenylamine and methoxy substituted triphenylamine-based dyes are examined by density-functional theory and time-dependent density-functional theory. The...     

Synthesis,Characterization and Properties of Single-Walled Carbon Nanohorns

Single-walled nanohorns (SWNHs) have been prepared by sub-merged arc discharge of graphite electrodes in liquid nitrogen. The samples were examined by scanning electron microscopy, transmission electron microscopy and Raman spectroscopy. Nitrogen and boron doped SWNHs have been prepared by the sub-merged arc discharge method using melamine and elemental boron as precursors. Intensification of Raman D-band and stiffening of G-band has been observed in the doped samples. The electrical resistance of the SWNHs varies in opposite directions with nitrogen and boron doping. Functionalization of SWNHs through amidation has been carried out for solubilizing them in non-polar solvents. Water-soluble SWNHs have been produced by acid treatment and non-covalent functionalization with a coronene salt. SWNHs have been decorated with nanoparticles of Au, Ag and Pt. Interaction of electron donor (tetrathiafulvalene, TTF) and acceptor molecules (tetracyanoethylene, TCNE) with SWNHs has been investigated by Raman spectroscopy. Progressive softening and stiffening of Raman G-band has been observed respectively with increase in the concentration of TTF and TCNE.     

A low-cost Raman spectrometer design used to study Raman scattering from a single-walled carbon nanotube

The paper discusses the design of a low cost Raman spectrometer. Single-walled nanotubes (SWNT) have been studied to demonstrate the reach of such a system. We observe both the radial-breathing mode (RBM) and the tangential mode from the SWNT. The tube diameters of the SWNT used in these experiments have been determined using RBM to be predominantly 1.4 and 1.6 nm. These are consistent with the TEM images taken of the same sample. The new method of producing SWNT using Ni-Y catalyst in electric-arc discharge method produces nanotubes with very small dispersion in diameter and high yields. The chirality of the SWNT can be deduced from their radial breathing modes, and it suggests that they are metallic in nature. Dedicated to Professor C N R Rao on his 70th birthday     

TDPAC measurements in textured hcp samples

Time differential perturbed angular correlation measurements done on the 482 keV level of¹⁸¹Ta probe nuclei in well annealed reference foil samples ofα-ZrHf,α-TiHf andα-Hf indicate that all probe nuclei are defect free, substitutional and experience quadrupole frequencies characteristic of these matrices. But mostly the ratio of the intensities of the harmonic components of the quadrupole frequency is never in 3:2:1, which is understood to be due to the selective orientation of microcrystallites brought out by the pre thermo-mechanical treatments on the sample. This paper illustrates as to how texturing in general could cause ambiguities in the measurements of the hyperfine interaction parameters of probe nuclei particularly in hcp foil samples with or without the association of any defects and the ways to delineate the effect of texturing.     

The presence of a thermally reversing window in Al-Te-Si glasses revealed by alternating differential scanning calorimetry and electrical switching studies

Alternating differential scanning calorimetric (ADSC) studies and electrical switching experiments have been undertaken on Al₁₅Te_85−xSi_x (2 ? x ? 12) system of glasses. These glasses are found to exhibit two crystallization reactions (T_c1 and T_c2), for compositions with x < 8. Above x = 8, a single-stage crystallization is seen. Further, a trough is seen in the composition dependence of non-reversing enthalpy (ΔH^NR), based on which it is proposed that there is a thermally reversing window in Al₁₅Te_85−xSi_x glasses, in the composition range 4 ? x ? 8. Electrical switching studies indicate that Al₁₅Te_85−xSi_x glasses exhibit a threshold type electrical switching at ON state currents less than 2 mA. Further, the switching voltages are found to increase with the increase in silicon content. It is interesting to note that the start (x = 4) and the end (x = 8) of the thermally reversing window are exemplified by a kink and a saturation in the composition dependence of switching voltages, respectively.