Raju Kumar; Rashmi Rani; Seema Sharma
Abstract
Polycrystalline samples of 1- x(Na0.5 K0.5)(Nb0.95 Ta0.05) ) -x(Bi Fe)O3 with x=0, 0.003, 0.005, 0.007) hereby denoted as NKNT-BF were prepared by the mixed oxide method. Preliminary structural studies carried out by X-ray diffraction technique showed the formation of perovskite structure with orthorhombic ...
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Polycrystalline samples of 1- x(Na0.5 K0.5)(Nb0.95 Ta0.05) ) -x(Bi Fe)O3 with x=0, 0.003, 0.005, 0.007) hereby denoted as NKNT-BF were prepared by the mixed oxide method. Preliminary structural studies carried out by X-ray diffraction technique showed the formation of perovskite structure with orthorhombic symmetry. Addition of BF in the NKNT system lowered the sintering temperature by 500C. The nature of the frequency dependence of ac conductivity of NKNT compounds follows Jonscher power law. Complex impedance and modulus spectra confirm the significant contribution of both grain and grain boundary to the electrical response of the materials. Above the ferroelectric–paraelectric phase transition temperature, the electrical conduction is governed by the thermal excitation of charge carriers from oxygen vacancies exhibiting Negative temperature coefficient (NTCR) behaviour. Detailed study on the multiferroic properties (where magnetism and ferroelectricity are strongly coupled together) of the system is under process which is likely to form key components in the development of future technology, for example, in memories and logic devices.
Seema Sharma; Rashmi Rani; Radheshyam Rai; T. S. Natarajan
Abstract
One dimensional nanofibers of organic and inorganic materials have been used in filters, optoelectronic devices, sensors etc. It is difficult to obtain ultra fine fibers of inorganic materials having lengths in the order of millimeter as they tend to break during formation due to thermal and other mechanical ...
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One dimensional nanofibers of organic and inorganic materials have been used in filters, optoelectronic devices, sensors etc. It is difficult to obtain ultra fine fibers of inorganic materials having lengths in the order of millimeter as they tend to break during formation due to thermal and other mechanical stresses. In this study, we have investigated the mechanism to prevent the defect formation and the breaking of CuO nanofibers by using optimized heat flow rates. CuO nanofibers were obtained by heat treating the poly(vinyl acetate) PVA composite fibers formed by electrospinning. The morphology and structural characteristics of prepared samples were investigated by Scanning electron microscopy, Transmission electron microscopy and X-ray diffraction. It was found that the morphology of the composite and annealed nanofibers could be influenced by the concentration of the polymer content. A lower concentration favors the formation of defects along the fiber and the number of defects reduces when the concentration is increased.
Seema Sharma
Abstract
Nanotechnology is one of the rapidly growing scientific disciplines due to its enormous potential in creating novel materials that have advanced applications. Electrospinning has been found to be a viable technique to produce materials in nanofiber form. Ferroelectric and/or piezoelectric materials in ...
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Nanotechnology is one of the rapidly growing scientific disciplines due to its enormous potential in creating novel materials that have advanced applications. Electrospinning has been found to be a viable technique to produce materials in nanofiber form. Ferroelectric and/or piezoelectric materials in nanofiber and/or nanowire form have been utilized for producing energy harvesting devices, high frequency transducers, implanted biosensors, vibration absorbers and composite force sensors, etc. An in-depth review of research activities on the development of ferroelectric nanofibers, fundamental understanding of the electrospinning process, and properties of nanostructured fibrous materials and their applications is provided in this article. A detailed account on the type of fibers that have been electrospun and their characteristics is also elaborated. It is hoped that the overview article will serve as a good reference tool for nanoscience researchers in ferroelectric materials.
Seema Sharma; Radheshyam Rai; D. A. Hall; Judith Shackleton
Abstract
Polycrystalline samples of Bi(Mg0.5Ti0.5)O3-PbTiO3 (BMT-PT) solid solutions exhibit high ferroelectric Curie temperatures and are promising materials for high temperature piezoelectric devices. A morphotropic phase boundary (MPB) between ferroelectric rhombohedral and tetragonal phases occurs between ...
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Polycrystalline samples of Bi(Mg0.5Ti0.5)O3-PbTiO3 (BMT-PT) solid solutions exhibit high ferroelectric Curie temperatures and are promising materials for high temperature piezoelectric devices. A morphotropic phase boundary (MPB) between ferroelectric rhombohedral and tetragonal phases occurs between BMT-PT ratio of 70-30 and 65-35 compositions. In the present investigation, ceramics having BMT-PT ratios in the range from 70-30 to 50-50 were prepared by a conventional solid state reaction method. The change of crystal structure as a function of composition and temperature has been studied using high temperature X-ray diffraction. Polarisation-Electric field hysteresis curves at different temperatures show antiferroelectric behaviour for x = 0.30, 0.35 and 0.40 compositions while 0.45 and 0.50 show a ferroelectric behavior.
Kavita Verma; Seema Sharma; Dhananjay K Sharma; Raju Kumar; Radheshyam Rai
Abstract
Ba0.5Sr0.3TiO3 (BST 70/30) nanopowders have been prepared by the modified sol-gel method using barium acetate, strontium acetate and titanium isopropoxide as the precursor. The formation mechanism, phase evolution, and particle size have been investigated using TG/DTA, XRD, and SEM. The fine particles ...
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Ba0.5Sr0.3TiO3 (BST 70/30) nanopowders have been prepared by the modified sol-gel method using barium acetate, strontium acetate and titanium isopropoxide as the precursor. The formation mechanism, phase evolution, and particle size have been investigated using TG/DTA, XRD, and SEM. The fine particles of the nano-powders calcined are homogeneous and well-dispersed and their narrow size distribution is about 15–25 nm. The as-formed gel was dried at 2000 C and then calcined in the temperature range 6500 C to 8500 C for crystallization. Phase evolution during calcination was studied using X-ray diffraction (XRD) technique which exhibited cubic crystal structure with perovskite phase. Sintering of the pellet was performed at 9500 C and the study on the dielectric relaxation and the ac electrical conductivity behavior of modified Barium titanate, Ba0.5Sr0.3TiO3 ferroelectric ceramic exhibit that these are thermally activated process.
Radheshyam Rai; Seema Sharma
Abstract
In the present paper, we synthesized the CdS hollow spheres by using PMMA sphere templates of 298-301 nm diameters and 20-51 nm of shell thickness. A CdS hollow sphere was characterized by X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), optical absorption and photoluminescence technique. ...
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In the present paper, we synthesized the CdS hollow spheres by using PMMA sphere templates of 298-301 nm diameters and 20-51 nm of shell thickness. A CdS hollow sphere was characterized by X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), optical absorption and photoluminescence technique. CdS products are all cubic face-centered structure with the cell constant a = 5.815 Å. We also explore the morphology, structure and possible synthesis mechanism. A possible template mechanism has been proposed for the production of the hollow CdS nano-particles. The band gap of bulk CdS is about 2.45 eV, showing an absorption onset of bulk at about 513 nm. This shows a blue shift in the absorption spectra due to the quantum size effect, which is quite possible due to the small size of the CdS nano crystals as is evident in XRD pattern. The diameter of the beads is about 265-310 nm. The change in beads size due to the CdS over-layer is not so apparent in structures, due to its small thickness. The average diameter of the sphere is similar to that of the beads. Therefore, the spherical shells were obtained after the removal of PMMA core.
