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Author

Sujoy Saha

Other affiliations: Bose Institute
Bio: Sujoy Saha is an academic researcher from Indian Institute of Science. The author has contributed to research in topics: Dielectric & Rietveld refinement. The author has an hindex of 12, co-authored 33 publications receiving 392 citations. Previous affiliations of Sujoy Saha include Bose Institute.

Papers
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Journal ArticleDOI
TL;DR: In this paper, the frequency dependence of real and imaginary parts of dielectric permittivity is analyzed using Cole-Cole equation and the frequency dependent conductivity spectra follow the power law.

48 citations

Journal ArticleDOI
TL;DR: In this paper, the phase formation with Pnma symmetry of the sample is confirmed by the Rietveld refinement of X-ray diffraction data, which is obtained by transmission electron microscopy.
Abstract: The neodymium chromate nanoparticles are synthesized by the sol–gel process. The phase formation with Pnma symmetry of the sample is confirmed by the Rietveld refinement of X-ray diffraction data. The particle size of the sample is determined by transmission electron microscopy. The band gap of the material is found to be 1.78 eV which is obtained by Tauc relation to UV-absorption spectrum. The room temperature Raman spectrum is fitted with the sum of 22 Lorentzian peaks. Dielectric relaxation of the sample has been investigated in the frequency range from 42 Hz to 1.1 MHz and in the temperature range from 303 to 573 K. The Cole–Cole model is used to explain the dielectric relaxation mechanism of the material. The complex impedance plane plot confirms the existence of the grain-boundary contribution to the relaxation of the sample. The frequency-dependent conductivity spectra follow the power law.

48 citations

Journal ArticleDOI
TL;DR: Strontium modified barium zirconium titanate with general formula Ba1-xSrxZr005Ti095O3 ceramics have been prepared by solid state and high energy ball milling technique as mentioned in this paper.

46 citations

Journal ArticleDOI
TL;DR: In this paper, the electronic energy band structure, site and angular momentum decomposed density of states (DOS) and charge-density contours of perovskite CaTiO3 are calculated by the first principles tight-binding linear muffin-tin orbitals method with atomic sphere approximation.
Abstract: The electronic-energy band structure, site and angular momentum decomposed density of states (DOS) and charge-density contours of perovskite CaTiO3 are calculated by the first principles tight-binding linear muffin-tin orbitals method with atomic sphere approximation using density functional theory in its local density approximation. The calculated band structure shows an indirect (R-Γ) band gap of 1.5 eV. The total DOS as well as the partial density of states (PDOS) are compared with the experimental photoemission spectra. The calculated DOS are in reasonable agreement with the experimental energy spectra and the features in the spectra are interpreted by a comparison of the spectra with the PDOS. The origin of the various experimentally observed bands have been explained. From the DOS analysis, as well as charge-density studies, we conclude that the bonding between Ca and TiO3 is mainly ionic and that the TiO3 entities bond covalently. Using the projected DOS and band structure we have analyzed the interband contribution to the optical properties of CaTiO3. The real and imaginary parts of the dielectric function and hence the optical constants such as refractive index and extinction coefficient are calculated. The calculated spectra are compared with the experimental results for CaTiO3 and are found to be in good agreement with the experimental results. The effective number of electrons per unit cell participating in the interband transitions are calculated. The role of band structure calculation as regards the optical properties of CaTiO3 is discussed.

42 citations

Journal ArticleDOI
TL;DR: In this paper, the double perovskite oxide Dy2NiMnO6 (DNMO) was synthesized in nano and bulk phase by the sol-gel citrate method and the Rietveld refinement of X-ray diffraction pattern of the sample at room temperature shows the monoclinic P21/n phase.

37 citations


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TL;DR: In this paper, a generalization of the Local Density Approximation (LDA) method for the systems with strong Coulomb correlations is presented which gives a correct description of the Mott insulators.
Abstract: The generalization of the Local Density Approximation (LDA) method for the systems with strong Coulomb correlations is presented which gives a correct description of the Mott insulators. The LDA+U method is based on the model hamiltonian approach and allows to take into account the non-sphericity of the Coulomb and exchange interactions. parameters. Orbital-dependent LDA+U potential gives correct orbital polarization and corresponding Jahn-Teller distortion. To calculate the spectra of the strongly correlated systems the impurity Anderson model should be solved with a many-electron trial wave function. All parameters of the many-electron hamiltonian are taken from LDA+U calculations. The method was applied to NiO and has shown good agreement with experimental photoemission spectra and with the oxygen Kα X-ray emission spectrum.

376 citations

Journal ArticleDOI
TL;DR: In this paper, the electronic energy band structure, density of states (DOS) and charge density contour of KNbO3 in the paraelectric cubic phase have been studied using the full-potential linearized augmented plane wave method within the generalized gradient approximation for exchange and correlation.
Abstract: The electronic energy band structure, density of states (DOS) and charge density contour of KNbO3 in the paraelectric cubic phase have been studied using the full-potential linearized augmented plane wave method within the generalized gradient approximation for exchange and correlation. The band structure shows an indirect (R–Γ) band gap. From the DOS analysis as well as charge density studies, we find that the bonding between K and NbO3 is mainly ionic while that between Nb and O is covalent. We have also reported results on the pressure variation of the energy gap of this compound and found that the band gap increases with increasing pressure. In order to understand the optical properties of the perovskite, the real and imaginary parts of the dielectric function, reflectivity, absorption coefficient, optical conductivity, electron energy-loss function, refractive index and extinction coefficient were calculated. The general profiles of the optical spectra were analysed and origins of the structures discussed.

370 citations

01 Jan 1996
TL;DR: Ahn et al. as discussed by the authors studied the effect of Fe doping on the Mn site in the ferromagnetic and antiferromagnetic phases of (Formula presented) and found that conduction and ferromagnetism were consistently suppressed by Fe doping.
Abstract: Author(s): Ahn, KH; Wu, XW; Liu, K; Chien, CL | Abstract: The effect of Fe doping (l20%) on the Mn site in the ferromagnetic ((Formula presented)) and the antiferromagnetic ((Formula presented)) phases of (Formula presented) has been studied. The same ionic radii of (Formula presented) and (Formula presented) cause no structure change in either series, yet conduction and ferromagnetism have been consistently suppressed by Fe doping. Colossal magnetoresistance has been shifted to lower temperatures, and in some cases enhanced by Fe doping. Doping with Fe bypasses the usually dominant lattice effects, but depopulates the hopping electrons and thus weakens the double exchange. © 1996 The American Physical Society.

273 citations

Journal ArticleDOI
TL;DR: In this article, the authors present an overview on the current state-of-the-art lead-free bulk ceramics for electrical energy storage applications, including (SrirTiO3, CaTiO), BaTiO, (Bi0.5Na 0.5), (K0.1 Na 0.1), (NbO3), BiFeO, AgNiO, and NaNbo3-based Ceramics.
Abstract: Compared with fuel cells and electrochemical capacitors, dielectric capacitors are regarded as promising devices to store electrical energy for pulsed power systems due to their fast charge/discharge rates and ultrahigh power density. Dielectric materials are core components of dielectric capacitors and directly determine their performance. Over the past decade, extensive efforts have been devoted to develop high-performance dielectric materials for electrical energy storage applications and great progress has been achieved. Here, we present an overview on the current state-of-the-art lead-free bulk ceramics for electrical energy storage applications, including SrTiO3, CaTiO3, BaTiO3, (Bi0.5Na0.5)TiO3, (K0.5Na0.5)NbO3, BiFeO3, AgNbO3 and NaNbO3-based ceramics. This review starts with a brief introduction of the research background, the development history and the basic fundamentals of dielectric materials for energy storage applications as well as the universal strategies to optimize their energy storage performance. Emphases are placed on the design strategies for each type of dielectric ceramic based on their special physical properties with a summary of their respective advantages and disadvantages. Challenges along with future prospects are presented at the end of this review. This review will not only accelerate the exploration of higher performance lead-free dielectric materials, but also provides a deeper understanding of the relationship among chemical composition, physical properties and energy storage performance.

191 citations

Journal ArticleDOI
TL;DR: In this article, the relationship among the structure, dielectric, and impedance properties of Sr2+ substituted barium titanate (BST) ceramics is investigated. But, the analysis is limited to the case where the as-prepared samples are characterized by X-ray diffraction and Raman spectroscopy.

181 citations