Showing papers by "Ashok Kumar published in 2019"

Structural transformations and physical properties of (1 - x) Na0.5Bi0.5TiO3 - x BaTiO3 solid solutions near a morphotropic phase boundary.

Abstract: Piezoelectric and other physical properties are significantly enhanced at (or near) a morphotropic phase boundary (MPB) in ferroelectrics. MPB materials have attracted significant attention owing to both fundamental physics as well as the possibility of well-regulated energy and information storage devices which are dominated by lead (Pb)-based materials. Here, we report the crystal structure, Raman spectra, dielectric constant and polarization near the MPB of lead free (1 - x) Na0.5Bi0.5TiO3 - x BaTiO3 (0.00 ⩽ x ⩽ 0.10) solid-solution, prepared by sol-gel auto combustion technique and sintered by microwave sintering technique. With the addition of BaTiO3 into Na0.5Bi0.5TiO3, it induces a structural phase transition from R3c (a single phase) to R3c + P4mm (a dual phase) close to x = 0.06 and 0.07 and transform to a high symmetry tetragonal phase P4mm at higher compositions (x = 0.08 to 0.10) as evident from our x-ray Rietveld refinement and Raman spectroscopic results. We perform first-principles calculations based on density functional theory that confirm a structural transition from a rhombohedral to a tetragonal phase under increasing x. In the prepared solid solution, an anomalous enhancement of remnant polarization ([Formula: see text]) was observed for x = 0.06 and 0.07, which has been explained based on the existence of the MPB. On the other hand, the value of coercive field [Formula: see text] was found to be decreased linearly from x = 0.00 to 0.06; it is constant for higher compositions. Further details of the ferroelectric properties on the electric field poled samples have been studied and compared with the as-grown (unpoled) samples.

Enhanced dielectric properties and theoretical modeling of PVDF–ceramic composites

Abstract: The ceramic-polymer composites, consisting of (Bi0.5K0.5)(Fe0.5Nb0.5)O3 [BKFN] as fillers and poly (vinylidene fluoride) (PVDF) as matrix, with different ratios (weight ratio of BKFN to PVDF, are 10%, 30% and 50%) have been prepared by using a solution casting method. The X-ray diffraction (XRD) pattern evidenced a semi-crystalline structure containing mixed α-, β- and γ- phases of PVDF which was further confirmed by Fourier transform-infrared spectroscopy. Using scanning electron micrograph, the dispersion of the particulate filler in PVDF matrix is examined. With an increase of BKFN content, in the BKFN–PVDF composite films, both the dielectric constant and remnant polarizations showed a remarkable increase as compared to those of PVDF. Different theoretical models were proposed with experimental data to determine the effective dielectric constants of the prepared composites. Also, increased optical band gap is observed due to addition of BKFN in PVDF.

Economic Impact Studies of Pressure and Vacuum Metrology at CSIR-NPL, India

Abstract: Measurement standards and metrological activities provide scientific and metrological infrastructure in the country. The Pressure and Vacuum Metrology (PVM) activity has a major role in national and international metrological research and development. The PVM group is successfully providing national calibration and measurement services and fulfilling its national duty as per the mandate of CSIR-National Physical Laboratory (CSIR-NPL). Since last 35 years, no significant efforts were made to assess socio-economic impact of the services provided. Such impact studies are carried out by several National Metrology Institutes, but in India it is still an unexplored area so far. This motivated us to carry out the impact assessment, and present paper is an attempt made in this direction. Systematic studies of the contribution of PVM, established at CSIR-NPL, on national industrial growth and economy, are carried out by assessment of impact. The aim of the present paper is to present the summary of the results thus obtained which is based on the investment made over the years and the estimated benefits to the users. The studies are based on some industrial survey, personal interviews and interactions with stakeholders and sampling of services provided over the years. An overall social rate of return, an indicator of system efficiency, is found to be 180% which is quite high as compared to the present rate of return (8%). This indicates that the PVM activity is quite efficient, and future investment in the activity is safe and would provide excellent returns. The studies are very useful for broader understanding of the economic benefits of PVM and to improve understanding of the decision and policy makers about the relevance, continuation and further investment in PVM activity. This present case study may be explored and applied for other metrological fields also.

Properties of the low-frequency phonon spectra of ferroelectric barium titanate-based heterostructures

Abstract: Polarized Raman spectra of the epitaxial Ba0.5Sr0.5TiO3 film, bi-color BaTiO3/Ba0.5Sr0.5TiO3 superlattice and tri-color BaTiO3/Ba0.5Sr0.5TiO3/SrTiO3 superlattice were studied in a broad temperature...

Properties of the low-frequency phonon spectra of ferroelectric barium titanate-based heterostructures

Abstract: Polarized Raman spectra of the epitaxial Ba0.5Sr0.5TiO3 film, bi-color BaTiO3/Ba0.5Sr0.5TiO3 superlattice, and tri-color BaTiO3/Ba0.5Sr0.5TiO3/SrTiO3 superlattice were studied in a broad temperature range of 80-700 K. Based on the temperature dependence of the polar modes we determined the phase transitions temperatures in the studied heterostructures. In the sub-THz frequency range of the Y(XZ)Y spectra, we revealed the coexistence of the Debye-type central peak and soft mode in bi-color BaTiO3/Ba0.5Sr0.5TiO3 superlattice.

A Study of Efficacy of Levamisole in Children with Frequently Relapsing and Steroid-dependent Nephrotic Syndrome

Abstract: Objectives: To assess the efficacy of levamisole in frequentlyrelapsing nephrotic syndrome and steroid-dependent nephroticsyndrome. Study Design: Retrospective analysis of hospital case records . Participants: 62 children with frequently relapsing nephroticsyndrome and 35 children with steroid-dependent nephroticsyndrome. Methods : Case records of children who were diagnosed assteroid-dependant or frequently-relapsing nephrotic syndrome, were reviewed. Levamisole was given daily (2 mg/kg/d) along with tapering doses of alternate daysteroids after remission on daily steroids. Results: Levamisole was effective in 77.3% children with a better(80.6%) efficacy in frequently relapsing nephrotic syndrome. Atotal of 34 children completed 1 year follow-up post levamisoletherapy. The cumulative mean (SD) steroid dose 1-year beforetherapy was 4109(1154) mg/m2 and 1-year post therapy was 661(11) mg/m2 (P<0.001). The relapses were also less during theperiod of post-levamisole therapy. Conclusion: Levamisole is an effective alternative therapy infrequently relapsing and steroid-dependent nephrotic syndrome .