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B. S. Semwal

Bio: B. S. Semwal is an academic researcher from Hemwati Nandan Bahuguna Garhwal University. The author has contributed to research in topics: Dielectric & Dissipation factor. The author has an hindex of 4, co-authored 10 publications receiving 150 citations.

Papers
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Journal ArticleDOI
TL;DR: In this paper, the authors measured the dielectric constant, loss tangent, and conductivity of ceramic Na1−xKxNbO3 (x = 0, 0.2 and 0.5) samples using XRD and SEM.
Abstract: Pellets of ceramic Na1−xKxNbO3 (x = 0, 0.2 and 0.5), were prepared by conventional solid-state reaction method. Prepared samples were characterized using XRD and SEM. The frequency and temperature variation of dielectric constant, loss tangent and dielectric conductivity of prepared samples were measured in the frequency range from 10 KHz-1 MHz, and in the temperature range from 50–250°C for x = 0.2 and 0.5, and between 50 and 480°C for x = 0 compositions. It was observed that the dielectric constant and loss tangent decrease, and conductivity increases with increasing frequency. Near the transition temperature the material shows anomalous behaviour for the observed properties, and the peaks of dielectric constant and loss tangent were observed shifting towards lower temperature with increasing frequency.

68 citations

Journal ArticleDOI
TL;DR: In this article, a solid solution reaction reaction method was used to prepare ceramic pellets of Potassium Sodium Niobate (K x Na 1−x NbO 3 ) system using X-ray diffraction method and grain size was calculated using SEM photographs.

58 citations

Journal ArticleDOI
TL;DR: In this article, the temperature and frequency dependence of dielectric constant and loss tangent peak heights of ceramic pellets of NaNbO 3, Na 06 K 04 NbO3 and Na 05 K 05 Nb O 3 have been studied using solid state reaction method.
Abstract: Using solid state reaction method, ceramic pellets of NaNbO 3 , Na 06 K 04 NbO 3 and Na 05 K 05 NbO 3 have been prepared Temperature and frequency dependence of dielectric constant and loss tangent of the prepared samples have been studied It has been observed that, at the transition temperature, dielectric constant peak shifts to lower temperature, and the dielectric constant and loss tangent peak heights decrease, with increasing frequency; which shows the relaxational behavior of this system

9 citations

Journal ArticleDOI
TL;DR: In this article, the subcell parameters and grain size have been calculated using X-ray diffraction data for mixed K 1-x Na x NbO 3 system where x is varied from 0, 20, 40, 50, 80, 100%.
Abstract: Birthday UNIVERSITY OF COLOMBO Birthday 11.6568 Normal 0 false false false MicrosoftInternetExplorer4 /* Style Definitions */ table.MsoNormalTable {mso-style-name:"Table Normal"; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-parent:""; mso-padding-alt:0cm 5.4pt 0cm 5.4pt; mso-para-margin:0cm; mso-para-margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:10.0pt; font-family:"Times New Roman"; mso-ansi-language:#0400; mso-fareast-language:#0400; mso-bidi-language:#0400;} Pellets of K 1-x Na x NbO 3 mixed system of different concentration have been prepared by solid solution reaction method. The subcell parameters & grain size have been calculated using X-ray diffraction data for mixed K 1-x Na x NbO 3 system where x is varied from 0, 20, 40, 50, 80, 100%. The variation of unitcell parameters and grain size with composition, at room temperature have been reported. Dielectric constant and loss tangent at room temperature and at different frequencies have also been reported. doi:10.4038/sljp.v2i0.176 Sri Lankan Journal of Physics, Vol.2 (2001) 13-19

6 citations


Cited by
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Journal ArticleDOI
TL;DR: In this paper, general guidelines for the development of lead-free piezoelectric ceramics are presented, ranging from atom to phase diagram, and the current development stage in lead free piezoceramics is then critically assessed.
Abstract: A large body of work has been reported in the last 5 years on the development of lead-free piezoceramics in the quest to replace lead–zirconate–titanate (PZT) as the main material for electromechanical devices such as actuators, sensors, and transducers. In specific but narrow application ranges the new materials appear adequate, but are not yet suited to replace PZT on a broader basis. In this paper, general guidelines for the development of lead-free piezoelectric ceramics are presented. Suitable chemical elements are selected first on the basis of cost and toxicity as well as ionic polarizability. Different crystal structures with these elements are then considered based on simple concepts, and a variety of phase diagrams are described with attractive morphotropic phase boundaries, yielding good piezoelectric properties. Finally, lessons from density functional theory are reviewed and used to adjust our understanding based on the simpler concepts. Equipped with these guidelines ranging from atom to phase diagram, the current development stage in lead-free piezoceramics is then critically assessed.

2,510 citations

Journal ArticleDOI
TL;DR: In this article, the crystal structure and phase transitions of K x Na 1− x NbO 3 (0.4 − 0.6) were presented. But the phase transitions were not characterized.

175 citations

Journal ArticleDOI
TL;DR: In this paper, a Landau free energy expansion was developed to describe the elastic constant variations of stishovite (SiO2) associated with the P42/mnm (rutile-type) ⇌ Pnnm (CaCl2)-type phase transition as a function of pressure.
Abstract: A Landau free energy expansion has been developed to describe the elastic constant variations of stishovite (SiO2) associated with the P42/mnm (rutile-type) ⇌ Pnnm (CaCl2-type) phase transition as a function of pressure. The transition appears to display classical second-order character, with an equilibrium transition pressure which is renormalized by coupling of the soft optic mode with spontaneous strain. Lattice parameter data from the literature show that the symmetry breaking strain is large, while the nonsymmetry breaking strains are small. These have been used to constrain the numerical values of the strain/order parameter coupling coefficients, which in turn have been used to constrain values for the Landau coefficients. When substituted into expressions for all the individual elastic constants, taking values for experimental and calculated values of the bare elastic constants from the literature, a clear view of the pattern of elastic constant variations is produced. Variations of P and S wave velocities derived from the calculated elastic constants for a second-order transition show a dip as the transition point is approached from high pressure and from low pressure but do not show a discontinuity. The velocity anomaly provides a signature for the presence of free silica in the lower mantle.

120 citations

Journal ArticleDOI
TL;DR: In this article, the effect of sintering temperature on structural and electrical properties of BZT-BCT 50/50 ceramics were studied in detail, and the coexistence of tetragonal-monoclinic structures confirmed the MPB nature of bZT−BCT-50/50 Ceramics.

104 citations