S. Das

Bio: S. Das is an academic researcher. The author has contributed to research in topics: Variable-range hopping & Seebeck coefficient. The author has an hindex of 1, co-authored 1 publications receiving 20 citations.

Effect of alkaline-earth and transition metals on the electrical transport of double perovskites

Abstract: The transport properties of A2BMoO6 (A=Ca, Sr, and Ba; B=Cr, Mn, and Fe) crystals are investigated from studies of x-ray diffraction, thermoelectric power (TEP) S, and resistivity ρ measurements over a wide temperature range (20–900 K). The resistivity of A2FeMoO6 (A=Ca, Sr, and Ba) crystals shows a metallic character and its analysis suggests that the electron-electron scattering is one of the contributions governing the conduction mechanism of these compounds. On the other hand, Ca2MnMoO6 shows an insulator-metal transition similar to that reported in rare earth nickelate [Phys. Rev. B 45, 8209 (1992)]. The conductivity σ(T) data of Sr2CrMoO6 can be best fitted in terms of simultaneous contributions to σ with an activated-type process and variable range hopping (VRH) mechanism. In the case of Sr2MnMoO6, ρ(T) behavior follows an activated-type hopping for T>400 K whereas for T<85 K it can be described satisfactorily by VRH mechanism. For all the compounds, TEP exhibits negative values (n type) except for...

Influence of Ni/Mo ratio on structural and electrical properties of double perovskite system Sr 2 Ni 1+x Mo 1−x O 6−δ

Abstract: Technologically important double perovskite system Sr2Ni1+x Mo1−x O6−δ with x = 0.00, 0.05, 0.10, and 0.15 was prepared by solution combustion method. The structural and the Rietveld analysis of compositions revealed the formation of double perovskite tetragonal phase Sr2NiMoO6 with space group I4/m as a major phase. SrMoO4 and NiO were also observed as minor phases. Microstructural studies depicted the formation of uniform grains for all the samples. The average grain size was found to lie between the ranges of 1–4 μm. XPS analysis of the synthesized compositions showed the decreasing ratio of Mo5+ to Mo6+ ions in the system with increasing Ni content, which played an important role in the conduction mechanism. The thermal expansion coefficient (TEC) of all compositions indicated that it is more compatible to the TEC of standard electrolytes. The electrical conductivity for all the compositions was studied using impedance spectroscopy in the temperature range 200–600 °C. Composition with x = 0.05 showed better electrical conductivity with good catalytic activity.

Half-Metallic Ferromagnetism in Double Perovskite Ca2CoMoO6 Compound : DFT + U Calculations

Abstract: A systematic investigation on magnetism and spin-resolved electronic properties in double perovskite Ca2CoMoO6 compound was performed by using the full-potential augmented plane wave plus local orbitals (APW+lo) method within the generalized gradient approximation (GGA-PBE) and GGA-PBE+U scheme. The stability of monoclinic phase (P21∕n #14) relative to the tetragonal (I4∕m#87) and cubic (Fm3m #225) phase is evaluated. We investigate the effect of Hubbard parameter Uon the ground-state structural and electronic properties of Ca2CoMoO6 compound. We found that the ferromagnetic ground state is the most stable magnetic configuration. The calculated spin-polarized band structures and densities of states indicate that the Ca2CoMoO6 compound is half-metallic (HM) and half-semiconductor (HSC) ferromagnetic (FM) semiconductor with a total magnetic moment of 6.0 using GGA-PBE and GGA-PBE+U, respectively. The Hubbard U parameter provides better description of the electronic structure. Using the Vampire code, an est...

First principles analysis of oxygen vacancy formation and migration in Sr2BMoO6 (B = Mg, Co, Ni)

Abstract: Molybdenum-based double perovskites have been extensively studied as electrode materials in solid oxide fuel cells (SOFCs) due to their mixed ionic/electronic conductivity (MIEC) characteristics. Since the ionic conductivity in perovskite crystals arises primarily from oxygen ion diffusion via a vacancy-hopping mechanism, both the formation energy of the oxygen vacancy and the migration energy barrier play an essential role in the MIEC performance. In this work, we present a detailed first-principles investigation on the stoichiometric and oxygen-deficient structures of double perovskites, Sr2BMoO6 (B = Mg, Co and Ni), using the density functional theory (DFT) method plus Hubbard U for Co and Ni. The electronic ground states of the oxygen-stoichiometric cells exhibited apparent eigenvalue gaps which are consistent with the measured insulating features. The oxygen-deficient structures were studied by removing a neutral oxygen atom according to SOFC working conditions, and the minimum energy path (MEP) of oxygen ion migration was optimized using the nudged elastic band (NEB) method which produced the theoretical migration energy barriers at the DFT+U level. The vacant oxygen sites released electrons to the adjacent cation d states, coupled with the delocalization characteristics of the Mo 4d state, which led eventually to the transition from an insulator to the electronic conductivity of the oxygen-deficient crystals. The electronic structure analysis suggested that the outer shell electrons of Mg, Co and Ni significantly affected the energies of oxygen vacancy formation and migration. Our results elucidate the effect of B-site substitution elements on the electronic properties and MIEC characteristics which provides theoretical support for the enhancement of the MIEC properties for these Mo-based double perovskites.