NOPR Collection: Special issue: Material Science and Application

Dielectric properties of Na1−xKxNbO3, near x = 0.475 morphotropic phase region

Sun, 01 Mar 2020 00:00:00 GMT

Title: Dielectric properties of Na1−xKxNbO3, near x = 0.475 morphotropic phase region Authors: Singh, Surendra; Negi, Jyotsana; Panwar, N S Abstract: Sodium-potassium niobate (Na_1−xK_xNbO₃) ceramic pellets, with x = 0.465, 0.470, 0.475, 0.480 and 0.485, were prepared by solid state reaction method with double sintering. With varying composition (x), the dielectric properties, X-ray diffraction peaks shifting pattern, in this system. Among the prepared compositions, a break in the X-ray diffraction peaks shifting tendency; minimum dielectric constant, loss tangent and dielectric conductivity indicate a morphotropic phase transition type behavior, at the composition with x = 0.475. Page(s): 11-17

Structural and dielectric properties of 0.75PMN-0.25PT relaxor ferroelectrics with different frequencies at room temperature

Sun, 01 Mar 2020 00:00:00 GMT

Title: Structural and dielectric properties of 0.75PMN-0.25PT relaxor ferroelectrics with different frequencies at room temperature Authors: Kashyap, Sidharth; Bhatt, S C; Uniyal, Manish; Kathait, Gambheer Singh Abstract: In the present work, the composition of 0.75PMN-0.25PT solid solution was synthesized by columbite precursor method with multiple heat treatments at 920°C and 1200 °C. XRD data shows the perovskite structure with minimized pyrochlore phase and intense peaks. It has been observed that the pyrochlore phase can be reduced by increase in sintering temperature. SEM report shows the polygonal, dense and compact grain boundaries. Dielectric study shows the effect of variation in frequency to the dielectric constant and electrical conductivity at room temperature. Page(s): 18-21

Enhancement of the heat transfer through perforated fin by natural convection

Sun, 01 Mar 2020 00:00:00 GMT

Title: Enhancement of the heat transfer through perforated fin by natural convection Authors: Bhatt, Shaurya; Rawat, Kuldeep Abstract: In the present paper we have investigated the enhancement of the heat transfer using fins with circular perforation. The experiment was conducted for different voltages to obtain variation of temperature in the entire setup fabricated for this study. The area ratio factor, weight ratio factor and volume ratio factor are calculated for present setup. It has been observed that the temperature drop along the perforated fin length is consistently higher than that for the equivalent non perforated fin. Page(s): 22-27

Study of phase transition properties in rochelle salt crystal

Sun, 01 Mar 2020 00:00:00 GMT

Title: Study of phase transition properties in rochelle salt crystal Authors: Khan, Muzaffar Iqbal; Upadhyay, Trilok Chandra Abstract: The extra spin-lattice interactions terms, external electric field term, direct spin-spin interaction term and fourth-order phonon anharmonic terms have been added to two-sublattice pseudo-spin lattice couples mode(PLCM) model for Rochelle salt crystal. By applying the double-time thermal Green function method and using the modified model, theoretically, expressions for the shift, width, soft mode frequency, dielectric constant and loss tangent have been derived. By fitting model parameters values, temperature variations of the above quantities have been calculated for Rochelle salt crystal. We compare theoretical variations of soft mode frequency for Rochelle salt crystal, by getting correlated values of soft mode frequency from experimental data of dielectric constant. We compare our theoretical values for dielectric constant and loss tangent for Rochelle salt with the experimental result of Sandy and Jones [Phys Rev, 168(2), 481-493 (1968)]. Our theoretical results well agree with experimental data of others for Rochelle salt. Present expressions will also be useful for other similar crystals like sodium ammonium tartrate tetrahydrate (NaNH₄C₄H₄O₆.4H₂O) crystal, lithium ammonium tartrate monohydrate (LiNH₄C₄H₄O₆.H₂O) crystal and lithium thallium tartrate monohydrate (LiTlC₄H₄O₆.H₂O) crystal etc. Page(s): 28-31