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T. Badapanda,S. Sarangi,B. Behera,P.K. Sahoo,S. Anwar,T. P. Sinha,G.E. Luz Jr.,E. Longo,L.S. Cavalcante 한국물리학회 2014 Current Applied Physics Vol.14 No.5
For this study, a microcrystalline Ba(Zr0.05Ti0.95)O3 (BZT) powder was prepared by a high energy ball milling method followed by calcination at 1100 C for 4 h. The calcined powder was structurally characterized by X-ray diffraction and Rietveld refinement data, which showed that this material has a perovskite-type tetragonal structure with a space group of (P4mmm). The micro-Raman spectrum revealed local lattice distortions due to distorted octahedral [TiO6] clusters. The temperature and frequency-dependent dielectric study of the BZT ceramic showed normal phase transition behavior. The ferroelectric property was studied by a PeE hysteresis loop. Optical band gap was investigated by ultravioletevisible (UVevis) absorption spectroscopy at room temperature. The UVevis spectrum indicated that the BZT powder has an optical band gap of 3.15 eV.
Dielectric Behavior of Yttrium doped Barium-zirconium-titanate Ceramics
T. Badapanda,S. Panigrahi,T. P. Sinha,우성일,S. K. Rout 한국물리학회 2009 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.55 No.2
The ferroelectric behavior of the yttrium-doped barium-zirconium-titanate perovskite ceramics Ba1−xY2x/3Ti.75Zr0.25O3 (with x = 0.0, 0.01, 0. 025, 0.05) has been studied. The room temperature X-ray diffraition study suggests that all the compositions have a single-phase cubic symmetry with space group Pm-3m The temperature dependent dielectric constant of the ceramics was investigated in the frequency range from 50 Hz to 1 MHz. The density of the samples was determined using Archimedes’ principle and was found to be ~98% of the X-ray density. A broad dielectric anomaly coupled with a shift of the dielectric maximum towards a higher temperature with increasing frequency indicates relaxor-type behavior in the ceramics With increasing in yttrium content, the Curie temperature decreased, except for x = 0.01 where the Curie temperature increased. The relative permittivity decreased and broadened with increasing yttrium content.
Phase formation and dielectric study of Bi doped BaTi0.75Zr0.25O3 ceramic
T. Badapanda,S.K. Rout,S. Panigrahi,T.P. Sinha 한국물리학회 2009 Current Applied Physics Vol.9 No.4
Perovskite types Ba1-xBi2x/3Ti0.75Zr0.25O3 (with x = 0.0, 0.025, 0.05) ceramics have been prepared through solid state reaction route. The room temperature XRD study suggests that all the compositions have single phase cubic symmetry with space group Pm-3m. Temperature dependent dielectric studies of the ceramics have been investigated in the frequency range of 50 Hz–1 MHz. The densities of the samples are determined using Archimedes’ principle and found to be ~98% of X-ray density. The dielectric study revealed diffuse phase transition of second order. A broad dielectric anomaly coupled with the shift of dielectric maxima toward a higher temperature with increasing frequency indicates the relaxor-type behavior in the ceramics. The diffusivity increases with increase in Bi contents in the studied composition range. The transition temperature decreases with increase in Bi contents due to the decrease in grain size. Perovskite types Ba1-xBi2x/3Ti0.75Zr0.25O3 (with x = 0.0, 0.025, 0.05) ceramics have been prepared through solid state reaction route. The room temperature XRD study suggests that all the compositions have single phase cubic symmetry with space group Pm-3m. Temperature dependent dielectric studies of the ceramics have been investigated in the frequency range of 50 Hz–1 MHz. The densities of the samples are determined using Archimedes’ principle and found to be ~98% of X-ray density. The dielectric study revealed diffuse phase transition of second order. A broad dielectric anomaly coupled with the shift of dielectric maxima toward a higher temperature with increasing frequency indicates the relaxor-type behavior in the ceramics. The diffusivity increases with increase in Bi contents in the studied composition range. The transition temperature decreases with increase in Bi contents due to the decrease in grain size.
Tailoring magnetic energies to form dipole skyrmions and skyrmion lattices
Montoya, S. A.,Couture, S.,Chess, J. J.,Lee, J. C. T.,Kent, N.,Henze, D.,Sinha, S. K.,Im, M.-Y.,Kevan, S. D.,Fischer, P.,McMorran, B. J.,Lomakin, V.,Roy, S.,Fullerton, E. E. American Physical Society 2017 Physical Review B Vol.95 No.2
<P>The interesting physics and potential memory technologies resulting from topologically protected spin textures such as skyrmions have prompted efforts to discover new material systems that can host these kinds of magnetic structures. Here, we use the highly tunable magnetic properties of amorphous Fe/Gd multilayer films to explore the magnetic properties that lead to dipole-stabilized skyrmions and skyrmion lattices that form from the competition of dipolar field and exchange energy. Using both real space imaging and reciprocal space scattering techniques, we determined the range of material properties and magnetic fields where skyrmions form. Micromagnetic modeling closely matches our observation of small skyrmion features (similar to 50 to 70 nm) and suggests that these classes of skyrmions have a rich domain structure that is Bloch-like in the center of the film and more Neel-like towards each surface. Our results provide a pathway to engineer the formation and controllability of dipole skyrmion phases in a thin film geometry at different temperatures and magnetic fields.</P>
T. Badapanda,V. Senthil,S.K. Rout,L.S. Cavalcante,A.Z. Simões,T. P. Sinha,S. Panigrahi,M.M. de Jesus,E. Longo,J.A. Varela 한국물리학회 2011 Current Applied Physics Vol.11 No.6
In this work, we report the Rietveld refinement, microstructure, conductivity and impedance properties of Ba[Zr_0.25Ti_0.75]O_3 ceramic synthesized by solid state reaction. This ceramic was characterized by X-ray diffraction, Rietveld refinement, scanning electron microscopy and energy dispersive X-ray spectrometry. Impedance spectroscopy analyses reveals a non-Debye relaxation phenomenon being its relaxation frequency moving toward to positive side with increase of temperature. A significant shift in impedance loss peaks toward higher frequency side indicates conduction in material and favoring the long range motion of mobile charge carriers. The frequency dependent ac conductivity at different temperatures indicates that the conduction process is thermally activated. The variation of dc conductivity exhibited a negative temperature coefficient of resistance behavior. The ac conductivity data are used to evaluate the density of states at Fermi level and activation energy of this ceramic. The dc electrical and thermal conductivities of grain and grain boundary have been discussed.
SYNTHESIS AND CHARACTERIZATION OF CdS NANOCRYSTALLITES DISPERSED IN POLYMER MATRIX
O. P. SINHA,RITU SRIVASTAVA,T. SHRIPATHI 성균관대학교(자연과학캠퍼스) 성균나노과학기술원 2010 NANO Vol.5 No.2
Cadmium sulphide (CdS) nanocrystallites were prepared by sulphuration route with capping in polyethylene oxide (PEO) polymer matrix. It is found that PEO could provide a confined environment for particle nucleation and growth of CdS nanocrystallites. The scanning electron microscopy (SEM) with energy dispersive analysis by X-ray (EDAX) studies confirms the presence of CdS nanocrystallites in polymer matrix. X-ray diffraction (XRD) studies and transmission electron microscopy (TEM) selected area diffraction (SAD) patterns show that these crystallites have hexagonal structure. The TEM and UV-Visible absorption studies indicate uniform size distribution having size around 2.3 nm and band gap of 2.7 eV. X-ray photoelectron spectroscopy (XPS) studies reveal that core level energy positions of the Cd is shifted towards the lower binding energy and has similar chemical environment to that of bulk CdS.
Tailoring the electronic properties of Ca<sub>2</sub>RuO<sub>4</sub> via epitaxial strain
Dietl, C.,Sinha, S. K.,Christiani, G.,Khaydukov, Y.,Keller, T.,Putzky, D.,Ibrahimkutty, S.,Wochner, P.,Logvenov, G.,van Aken, P. A.,Kim, B. J.,Keimer, B. American Institute of Physics 2018 APPLIED PHYSICS LETTERS Vol.112 No.3
Dielectric relaxation of ZnO nanostructure synthesized by soft chemical method
Ramna Tripathi,Akhilesh Kumar,Chandrahas Bharti,T.P. Sinha 한국물리학회 2010 Current Applied Physics Vol.10 No.2
Thioglycerol capped nanoparticles of ZnO have been prepared in methanol through chemical technique. Nanostructures of the prepared ZnO particles have been confirmed through X-ray diffraction measurement. The Debye–Scherrer formula is used to obtain the particle size. The average size of the prepared ZnO nanoparticles is found to be 50 nm. The frequency-dependent dielectric dispersion of the sample is investigated in the temperature range from 293 to 383 K and in a frequency range from 100 Hz to 1 MHz by impedance spectroscopy. An analysis of the complex permittivity (ε' and ε") and loss tangent (tan δ) with frequency is performed assuming a distribution of relaxation times. The frequency-dependent maxima of the imaginary part of impedance are found to obey Arrhenius law with activation energy ~1 eV. The scaling behavior of dielectric loss spectra suggests that the relaxation describes the same mechanism at various temperatures. The frequency-dependent electrical data are analyzed in the framework of conductivity and modulus formalisms. The frequency-dependent conductivity spectra obey the power law.
Electrical Properties of Complex Perovskite Samarium Nickel Titanate
Nishant Kumar,Alo Dutta,S. Prasad,T. P. Sinha 대한금속·재료학회 2013 ELECTRONIC MATERIALS LETTERS Vol.9 No.5
The complex perovskite oxide samarium nickel titanate, Sm(Ni1/2Ti1/2)O3 (SNT) is synthesized by solid-state reaction technique. The x-ray diffraction pattern of the sample at room temperature shows monoclinic phase. The microstructure analysis of the sample is performed using scanning electron microscope. Alternating current impedance spectroscopy is used to investigate the electrical properties of SNT in a temperature range from 313 K to 673 K and in a frequency range from 100 Hz to 1 MHz. A peak is observed in the frequency dependence of imaginary part of electric modulus (M''(ω)) indicating a non-Debye type of relaxation. The relaxation peak of M''(ω) moves towards higher frequencies with the increase of temperature showing the thermally activated nature of the relaxation time. The relaxation times for M''(ω) at different temperatures are found to obey Arrhenius law with an activation energy of 0.57 eV. The scaling behaviour of M''(ω)shows that the relaxation describes the same mechanism at various temperatures. The complex impedance plane plots show that the relaxation mechanism in SNT is purely a bulk effect arising from the semiconductive grains of the sample. The frequency dependent conductivity is found to obey the power law.