Browsing by Author "Kishor Kumar, M.J."

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Interface Dominated Dielectric Response of PS-Fe3O4 Patchy Microspheres
(American Chemical Society service@acs.org, 2019) Kishor Kumar, M.J.; Kalathi, J.T.
Polymeric-inorganic interface plays a vital role in enhancing dielectric properties of patchy microspheres, Janus particles, and nanocomposites. We performed the computational modeling and simulations along with experiments to understand the phenomena behind the improved dielectric permittivity of polystyrene-iron oxide (PS-Fe3O4) patchy microspheres. We addressed the fundamental insights into the role of the interfacial region on the dielectric properties. Based on the experimental outcomes and computational simulations on dielectric behavior including polarization and electric field formation, we propose a new mechanism of charge buildup at the interface. Computational results reveal that the creation of interface bound-charges at the inorganic-polymeric interface is responsible for the improved dielectric properties. We also fabricated PS-Fe3O4 patchy microspheres by Pickering emulsion polymerization using Fe3O4 particles as a solid stabilizer. The microstructure, composition, morphology, dielectric, and thermal properties of the synthesized patchy PS-Fe3O4 particles were investigated. The dielectric permittivity (k) of the neat PS increased from ?2.9 to ?14.8 after decorating with Fe3O4 particles. Impedance response of the patchy microspheres shows that the interface of PS-Fe3O4 stores more charges than bulk PS-Fe3O4. The dielectric behavior of patchy microspheres can be engineered by tuning the shape and position of the patches. The present studies on polymer-inorganic interface provide some insights into the mechanisms that control dielectric permittivity and nonlinear conduction in an applied electric field. © © 2019 American Chemical Society.
Low-temperature sonochemical synthesis of high dielectric Lanthanum doped Cerium oxide nanopowder
(Elsevier Ltd, 2018) Kishor Kumar, M.J.; Kalathi, J.T.
Lanthanum (La) doped Cerium Oxide (CeO2) nanopowder was synthesized at a relatively lower temperature (70°C), without calcination in a simple, faster, and efficient way through sonochemical method. X-ray diffraction (XRD) results confirmed the formation of a cubic fluorite structure of nanocrystalline CeO2 and lattice deformation due to La-doping in CeO2. TEM analysis revealed that the size of La-doped CeO2 particles is in the range of 20?50 nm. In addition, selective area electron diffraction (SAED) and high-resolution TEM (HRTEM) analyses portrayed the nano-crystallinity, lattice fringe pattern, and d-spacing details of La-doped CeO2 powder. Lanthanum doping in CeO2 was further confirmed by a shift in Raman band towards the lower frequency (from 464 cm?1 to 457cm?1) along with peak intensity increase. Photoluminescence (PL) emission spectra showed that emission intensity of the La-doped CeO2 at 510 nm is increased due to oxygen vacancy mediated charge transfer. All these results confirm the successful doping of La in CeO2. The La-doped CeO2 powder possesses a high dielectric constant (?r) of 106 and a low dielectric loss (tan ?) of < 0.4 % at 1 kHz. The La-doped CeO2 finds potential applications on developing devices in the field of a thin film capacitor, transistors, and solid oxide fuel cells. © 2018 Elsevier B.V.
PMMA-LZO Composite Dielectric Film with an Improved Energy Storage Density
(Springer New York LLC barbara.b.bertram@gsk.com, 2019) Kishor Kumar, M.J.; Kalathi, J.T.
Energy storage materials in modern electronic devices and renewable energy systems are inevitable. The incorporation of inorganic fillers into the polymer matrix is a promising option for the advancement of storage materials with high energy density. The agglomeration of inorganic fillers in the polymer matrix and phase separation remain the main obstacles to efficient applications of the composites for energy storage. Here, the primary attention was given to achieve a uniform distribution of high-k LZO (Lanthanum Zirconium Oxide) filler into a PMMA (Polymethylmethacrylate) matrix to enhance the dielectric constant and energy storage density of PMMA while keeping dielectric loss at minimum. We prepared PMMA-LZO composite films with variable LZO content by ultrasound-assisted mixing followed by spin coating the solution on ITO (Indium tin oxide) coated glass. The effect of LZO content on dielectric properties of the LZO-PMMA films was studied. Dielectric constant (k) of PMMA was found to be increased from 3.1 to 15.3 at 15 vol.% LZO loading with a dielectric loss of 0.0582. However, 10 vol.% LZO loaded PMMA showed an improved dielectric constant of 13.4 while the dielectric loss remained the same as that of the neat PMMA. The LZO-PMMA films with 10 vol.% and 15 vol.% of LZO loading exhibited maximum energy density of 5.94 J cm?3 and 6.53 J cm?3, respectively. Overall, the 10 vol.% LZO loading was found to be optimum to achieve a stable film with improved dielectric properties. This work provides a viable approach for the development of flexible, high-energy density materials with a minimum dielectric loss. © 2019, The Minerals, Metals & Materials Society.
Sonochemical Synthesis of Palladium-Metal Oxide Hybrid Nanoparticles
(Elsevier, 2018) Sivasankaran, S.; Kishor Kumar, M.J.
This chapter presents a novel green, facile, faster, and inherently safer single-step ultrasound-assisted process of making noble metal-nonnoble metal hybrid nanoparticles. The process involved the irradiation with ultrasound energy of an aqueous solution of metal salt precursors of a noble metal, nonnoble metal, and alcohol leading to the simultaneous formation of noble metal and nonnoble metal oxide nanoparticles in the slurry form. From the slurry, wet solid could be separated by centrifugation or filtration and then by drying. Further calcination may be used if required. This method could be easily extended to the synthesis of bulk Pd-multimetallic oxide hybrid nanoparticles and also supported Pd-metal oxide nanohybrids on carbon and metallic materials. © 2019 Elsevier Inc. All rights reserved..
Sonochemical Synthesis of Palladium–Metal Oxide Hybrid Nanoparticles
(Elsevier, 2019) Sivasankaran, S.; Kishor Kumar, M.J.
This chapter presents a novel green, facile, faster, and inherently safer single-step ultrasound-assisted process of making noble metal–nonnoble metal hybrid nanoparticles. The process involved the irradiation with ultrasound energy of an aqueous solution of metal salt precursors of a noble metal, nonnoble metal, and alcohol leading to the simultaneous formation of noble metal and nonnoble metal oxide nanoparticles in the slurry form. From the slurry, wet solid could be separated by centrifugation or filtration and then by drying. Further calcination may be used if required. This method could be easily extended to the synthesis of bulk Pd-multimetallic oxide hybrid nanoparticles and also supported Pd-metal oxide nanohybrids on carbon and metallic materials. © 2019 Elsevier Inc. All rights reserved.