Showing papers by "V. R. K. Murthy published in 2015"
TL;DR: Temperature- and composition-induced phase transition in SmNbO4 was studied by differential scanning calorimetry, Raman spectroscopy and high-temperature powder X-ray diffraction measurements and revealed a monoclinic fergusonite crystal structure at ambient temperature and transforms to a tetragonal scheelite structure above the transition temperature.
Abstract: Temperature- and composition-induced phase transition in SmNbO4 was studied by differential scanning calorimetry, Raman spectroscopy and high-temperature powder X-ray diffraction measurements. In situ X-ray diffraction studies revealed that SmNbO4 possesses a monoclinic fergusonite crystal structure at ambient temperature and transforms to a tetragonal scheelite structure above the transition temperature (To ≥ 800 °C). The second-order nature of this transition was confirmed by observing a linear relationship between the spontaneous strain (es) of SmNbO4 and the Landau order parameter (η) around the phase transition temperature. We stabilized this high-temperature tetragonal scheelite phase at ambient temperature by substituting Si4+ and Mo6+ into the Nb site of SmNbO4. The SmNb1−x(Si1/2Mo1/2)xO4 (x = 0.0–0.69) ceramic compositions were prepared by the conventional solid-state reaction method. Rietveld refinement was carried out on all the compositions to examine the phase purity, and the compositions where x < 0.06 all formed a monoclinic fergusonite structure (I2/a space group, Z = 2). Both the X-ray diffraction and Raman spectroscopy measurements revealed that increasing the concentration of x transformed the structure from monoclinic fergusonite to tetragonal scheelite (I41/a space group, Z = 4) at a critical concentration (xc). Both the monoclinic and tetragonal phases coexisted in the composition range of 0.06 ≤ x < xc. The Hakki–Coleman and reflection cavity techniques were used to measure the dielectric constant and quality factor of these stabilized phases, respectively. The temperature coefficient of the resonant frequency was measured by using an invar cavity attached to a programmable hot plate. The high-density samples possessed good microwave dielectric properties.
26 citations
TL;DR: In this article, the dependence of microwave dielectric properties on the structural characteristics of BaA2Ti3O10 (A ǫ, Nd and Sm) was investigated.
22 citations
TL;DR: In this article, the magnetoelectric (ME) response in 0-3 particulate composites of Ba 0.9 Sr 0.1 TiO 3-Ni 0.98 O 4−δ assisted by high energy ball milling was reported.
19 citations
TL;DR: The present work mainly focuses on the magnetodielectric effect in polycrystalline Ni0.9-yCuyZn0.1Fe1.98O3.5 ferrite synthesized by a solid-state reaction method, which showed the formation of CuO-rich grain boundary segregation in the present material chemically inhomogeneous and electrically heterogeneous.
Abstract: The present work mainly focuses on the magnetodielectric (MD) effect in polycrystalline Ni0.9−yCuyZn0.1Fe1.98O3.97 (y = 0, 0.1, 0.2, 0.3, 0.4, 0.5) ferrite synthesized by a solid-state reaction method. Sintered samples showed the formation of CuO-rich grain boundary segregation for y ≥ 0.2. The appearance of segregation made the present material chemically inhomogeneous and electrically heterogeneous. A negative MD response was observed in homogeneous ferrite for y = 0 and 0.1 due to lattice distortion (an intrinsic effect), whereas a positive MD response occurs in chemically inhomogeneous segregated ferrite (y ≥ 0.2) due the collective effects of Maxwell–Wagner (MW) polarization with intrinsic magnetoresistance (an extrinsic effect).
11 citations
TL;DR: In this article, the grain size dependent phase transition and polarization behavior of ferroelectric Ba 0.9 Sr 0.1 TiO 3 (BST) powders were investigated and all samples were found to possess diffuse phase transition characteristics with frequency independent broad dielectric maxima near transition temperature.
Abstract: In this article, we investigate the grain size dependent phase transition and polarization behavior of ferroelectric Ba 0.9 Sr 0.1 TiO 3 (BST). Starting with nanocrystalline powders (crystalline size≈22 nm), various grain sizes were obtained in nano–submicron domain (202–745 nm) by regulating the sintering temperatures ( T sin ) in the range of 1050–1300 °C. All samples were found to possess diffuse phase transition characteristics with frequency independent broad dielectric maxima near transition temperature due to the lattice strain contribution. Dielectric stiffness showed tarnished step-like anomalous behavior in the paraelectric state for T sin ≥1200 °C due to the existence of polar (superparaelectric) nano-regions generated by local polarization by off-centered Ti 4+ ions exhibiting an exceptionally rare delicate polarization hysteresis loop.
9 citations
TL;DR: The Li 2 SrTa 2(1− x ) Nb 2x O 7 (x ǫ = 0-1.0) with layered-perovskite type structure were synthesized by conventional solid state reaction method as discussed by the authors.
6 citations
Journal Article•
TL;DR: In this paper, the dielectric spectra of propylene glycol, aniline and their binary mixtures with different concentrations were studied at 303K-323K by using Coaxial cable method in the microwave frequency range 20 MHz-20 GHz.
Abstract: Dielectric spectra of propylene glycol, aniline and their binary mixtures with different concentrations were studied at 303K-323K by using Coaxial cable method in the microwave frequency range 20 MHz-20 GHz. The relaxational response of the propylene glycol, aniline and their binary liquid mixtures over the entire composition range is analysed by using Cole-Cole relaxation model. Dipole moments obtained from the Higasi’s method are compared with the quantum mechanical HF and DFT calculations. From the experimental datadipole moment, Bruggeman parameter, Kirkwood g factor, excess dielectric and thermodynamic parameters have been calculated. The obtained data have been analysed in terms of the parallel and anti parallel orientation of the dipoles, chain length and hydrogen bond interaction in the mixture composition. Keywords--Relaxation Time, Dipole Moment, Excess Dielectric And Thermodynamic Parameters
2 citations