P K Gupta
Articles written in Bulletin of Materials Science
Volume 34 Issue 4 July 2011 pp 727-733
The 𝛾-phase poly (vinylidene fluoride) (PVDF) films are usually prepared using dimethyl sulfoxide (DMSO) solvent, regardless of preparation temperature. Here we report the crystallization of both 𝛼 and 𝛾-phase PVDF films by varying preparation temperature using DMSO solvent. The 𝛾-phase PVDF films were annealed at 70, 90, 110, 130 and 160°C for five hours. The changes in the phase contents in the PVDF at different annealing conditions have been described. When thin films were annealed at 90°C for 5 h, maximum percentage of 𝛽-phase appears in PVDF thin films. The 𝛾-phase PVDF films completely converted to 𝛼-phase when they were annealed at 160°C for 5 h. From X-ray diffraction (XRD), Fourier transform infrared spectrum (FTIR), differential scanning calorimetry (DSC) and Raman studies, it is confirmed that the PVDF thin films, cast from solution and annealed at 90°C for 5 h, have maximum percentage of 𝛽-phase. The 𝛽-phase PVDF shows a remnant polarization of 4.9 𝜇C/cm2 at 1400 kV/cm at 1 Hz.
Volume 34 Issue 4 July 2011 pp 899-905
Erbium (Er) and lanthanum (La) substituted BiFeO3 (BFO) ceramics have been prepared through conventional solid solution route. X-ray diffraction data indicated a gradual phase transition from rhombohedral to monoclinic structure in Bi0.9–𝑥 La0.1Er𝑥 FeO3 (𝑥 = 0.05, 0.07 and 0.1) (BLEFO𝑥 = 0.05, 0.07,0.1) ceramics. Differential thermal analysis (DTA) measurements of BFO samples showed a ferroelectric transition at 835°C, whereas it is shifted to 792°C for BLEFO𝑥 = 0.1. The Raman spectra of BLEFO𝑥 = 0.05,0.07,0.1 samples showed the shift of Raman modes to higher wavenumbers and suppression of A1 modes indicating decrease in ferroelectricity. The Raman spectra also indicated the structural transformation due to Er and La substitution in BFO. On subsequent erbium doping, the intrinsic dielectric constant is found to decrease from 68 (for pure BFO) to 52 for BLEFO𝑥 = 0.05 to 43 for BLEFO𝑥 = 0.07 but increased to 89 for BLEFO𝑥 = 0.1 when compared to pure BFO. The increase in Er content resulted in the increase in spontaneous magnetization (0.1178 emu/g at 8T for BLEFO𝑥 = 0.1) due to collapse of spin cycloid structure. Ferroelectric remnant polarization of BLEFO𝑥 = 0.05 and BLEFO𝑥 = 0.07 decreases when compared to pure BFO while small remnant polarization (close to paraelectric behaviour) is evident for BLEFO𝑥 = 0.1.
Volume 37 Issue 6 October 2014 pp 1485-1488
We report preparation of hydrophobic platinum-doped carbon aerogel (PtCA) catalyst and its characterization for catalytic exchange reactions between hydrogen isotopes. The PtCA powder was synthesized by sol–gel polymerization method, mixed with colloidal PTFE solution, and coated on Dixon rings to obtain hydrophobic catalyst. The Pt cluster size in PtCA powder was observed to vary from 3 to 5 nm for a change in resorcinol to alkali molar ratio in synthesis solution from 20 to 200. Transmission electron microscopy of powder showed that the Pt clusters were uniformally dispersed and Pt0 metallic content estimated by X-ray photoelectron spectroscopy (XPS) was found to be of ∼ 70%. The catalytic activity was found to depend on Pt cluster size and was higher for smaller cluster size. For the smallest achieved Pt cluster size of 3 nm, catalytic activity of ∼ 0.8 m3 (STP) s-1 m-3 was obtained for hydrogen isotope exchange in atmospheric pressure conditions.
Volume 42 | Issue 6
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