Shweta Thakur; Seema Sharma;Ashutosh Tiwari; Radheshyam Rai
Abstract
Polycrystalline samples of (K0.45Na0.45Li0.1NbO3)1-x-(Ba0.96La0.04Ti0.815Mn0.0025 Nb0.0025Zr0.18 O3)x ceramics (where x = 0.1, 0.3, 0.5, 0.7 and 0.9) were prepared by using a high temperature solid state reaction technique. The XRD patterns of the BLTMNZ doped KNLN at room temperature with x = 0.7 have ...
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Polycrystalline samples of (K0.45Na0.45Li0.1NbO3)1-x-(Ba0.96La0.04Ti0.815Mn0.0025 Nb0.0025Zr0.18 O3)x ceramics (where x = 0.1, 0.3, 0.5, 0.7 and 0.9) were prepared by using a high temperature solid state reaction technique. The XRD patterns of the BLTMNZ doped KNLN at room temperature with x = 0.7 have pure pervoskite phase with tetragonal structure at room temperature and have maximum value of dielectric constant at x = 0.9. Detailed studies of dielectric and impedance properties of the materials in a wide range of frequency (100Hz–1MHz) and temperatures (30 – 500 o C) showed that properties are strongly temperature and frequency dependent. The plots of Zʹʹ and Mʹʹ versus frequency at various temperatures show peaks in the higher temperature range (>300 o C). The compounds show dielectric relaxation, which is found to be of non-Debye type and the relaxation frequency shifted to higher side with increase in temperature. The Nyquist plot and conductivity studies showed the NTCR character of samples.
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.
Radheshyam Rai; M. A.Valente;Andrei L. Kholkin; Indrani Coondoo
Abstract
AnchorStructural and Magnetic properties are investigated for the Sr doped YMnO3 samples with different composition synthesized by a solid state reaction method. Sr doped YMnO3 is the most distorted perovskite of the RMnO3 series (R=rare earths); the observed sinusoidal magnetic structure is in contrast ...
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AnchorStructural and Magnetic properties are investigated for the Sr doped YMnO3 samples with different composition synthesized by a solid state reaction method. Sr doped YMnO3 is the most distorted perovskite of the RMnO3 series (R=rare earths); the observed sinusoidal magnetic structure is in contrast with those exhibited by the less-distorted members, which are commensurate-type antiferromagnetic structures. A typical anti ferromagnetic (AFM) to paramagnetic (PM) phase transition is observed for the sample with concentration x = 0.12 and the Néel temperature (TN) is about 160 K. With decreasing temperature, the sample with x = 0.12 exhibit a magnetic transition from a paramagnetic (PM) to a ferromagnetic (FM) state.
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.
N.K. Singh; Pritam Kumar; Radheshyam Rai
Abstract
Dielectric properties of (1-x)Ba(Fe0.5Nb0.5)O3-xBaTiO3 (where x = 0.00, 0.05 and 0.10) solid solution ceramics at high temperature range of RT ~ 270 o C have been characterized in this paper. The above said polycrystalline ceramics with (x = 0.0, 0.05 and 0.10) have been produced via a mixed oxide route. ...
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Dielectric properties of (1-x)Ba(Fe0.5Nb0.5)O3-xBaTiO3 (where x = 0.00, 0.05 and 0.10) solid solution ceramics at high temperature range of RT ~ 270 o C have been characterized in this paper. The above said polycrystalline ceramics with (x = 0.0, 0.05 and 0.10) have been produced via a mixed oxide route. The effects of BaTiO3 substitution on the structure and on the electrical and ferroelectric properties of Ba(Fe0.5Nb0.5)O3 samples have been studied by performing x-ray diffraction and dielectric measurements. The dielectric properties (e¢ and tan d) were investigated in the temperature range of 30-270 °C and in the frequency range of 100 Hz-5 MHz. The variation of relative dielectric permittivity (tan d) and tangent loss (tan d) has suggested a significant role of hopping of trapped charge carriers, which is resulted in an extra dielectric response in addition to the dipole response. It is observed that: (i) the relative dielectric permittivity and tangent loss (tan d) are dependent on frequency, (ii) the temperature of dielectric permittivity maximum shifts toward lower temperature side and (iii) dielectric permittivity and tangent loss rapidly increase by making solid solution of BFN with BaTiO3. X-ray diffraction analysis of the compound suggests the formation of single-phase compound with monoclinic structure. SEM photographs exhibit the uniform distribution of grains. The maximum ferroelectric transition temperature (Tc) of this system was 250-270 °C with the dielectric constant peak of 72500 at 1.09 kHz for x = 0.05.
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.
Radheshyam Rai
Abstract
Numerous metal oxide semiconductor materials were reported to be usable as semiconductor gas sensor, such as ZnO, SnO2, and TiO2 and so on. The samples of Zn and Cu doped SnO2 (SnZnO3 and SnCuO3) have been synthesized by solid-state reaction method. Some aspect of crystal structure of the compound at ...
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Numerous metal oxide semiconductor materials were reported to be usable as semiconductor gas sensor, such as ZnO, SnO2, and TiO2 and so on. The samples of Zn and Cu doped SnO2 (SnZnO3 and SnCuO3) have been synthesized by solid-state reaction method. Some aspect of crystal structure of the compound at room temperature was studied using X-ray diffraction technique. The XRD study of the compound shows that there is a change in the basic crystal structure of SnO2 on substitutions of ZnO and CuO. The patterns of the SnO2 sample are indexed as tetragonal perovskite type with a = 7.3928 Å, c = 5.2879 Å but on substitution of ZnO and CuO the structure becomes orthorhombic with lattice constant a = 23.5237Å, b = 8.2183 Å and c =5.8017 Å or a = 21.8594 Å, b = 5.3200 Å, and c = 5.1803 Å, respectively. The temperature variation of resistance shows that compounds have negative temperature coefficient of resistance. The gas sensitivity for LPG (liquefied petroleum gas) showed a drastic change in conductivity.
N. K. Singh; Pritam Kumar; Hemchand Kumar; Radheshyam Rai
Abstract
The polycrystalline samples of the pyrochlore-type Dy2(Ba0.5R0.5)2O7 (R = W, Mo) compounds have been prepared by a high-temperature solid-state reaction technique. Preliminary X-ray diffraction (XRD) studies and scanning electron micrographs (SEM) of the compounds at room temperature suggested that compounds ...
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The polycrystalline samples of the pyrochlore-type Dy2(Ba0.5R0.5)2O7 (R = W, Mo) compounds have been prepared by a high-temperature solid-state reaction technique. Preliminary X-ray diffraction (XRD) studies and scanning electron micrographs (SEM) of the compounds at room temperature suggested that compounds have single phase orthorhombic crystal structures and grain distribution throughout the surface of the samples was uniform. Dielectric studies (dielectric constant (e´) and tangent loss (tan δ) obtained both as a function of frequency (4 kHz -1 MHz) at room temperature (RT) and temperature (RT 320 0 C) at 20 kHz and 100 kHz suggest that compounds do not have dielectric anomaly in the said frequency and temperature range.