Okram G. Singh

Bio: Okram G. Singh is an academic researcher from Indian Institute of Technology Bombay. The author has contributed to research in topics: Cerium & XANES. The author has an hindex of 4, co-authored 8 publications receiving 55 citations.

Phase diagram for the electron-doped Nd2−xCexCuOy superconducting system

Abstract: We report a refined phase diagram for the electron-doped Nd 2- x Ce x CuO y superconducting system in the range 0.120⩽ x ⩽0.190 with Δx =0.005. It is found that the highest T c ( ϱ =0) ∼17 K is confined to the very narrow range 0.145⩽ x ⩽0.150; a T conset ∼ 24 K with sharp superconducting transition is also observed. An attempt is made to understand the T c dependence on the variation of the oxygen content ( y ) in the Nd 2- x Ce x CuO y system.

Evidence for the revival of superconductivity in Nd1.82Ce0.18CuO4- delta by doping with divalent alkaline-earth elements.

Abstract: The revival of superconductivity in the electron-excess T'-type compound Nd 1.82 Ce 0.18 CuO 4-δ by hole doping has been observed. The normal-state resistivity (ρ) changes from semiconducting (dρ/dT 0) as the hole doping increases up to a certain level.

XANES studies of the NdSrCeCuO superconducting system

Abstract: We describe XANES studies of electron-doped superconductors based on neodymium cuprate doped with cerium. The mechanism for observed changes in the transition temperature on co-doping with divalent Sr is investigated using measurements of the Nd, Cu, Ce and Sr absorption edges.

XANES studies of the Nd-Sr-Ce-Cu-O superconducting system

Abstract: We describe XANES studies of electron-doped superconductors based on neodymium cuprate doped with cerium. The mechanism for observed changes in the transition temperature on co-doping with divalent Sr is investigated using measurements of the Nd, Cu, Ce and Sr absorption edges

A Transmission Electron Microscopy Study of the Reactivity Mechanism of Tailor-Made CuO Particles toward Lithium

Abstract: The electrochemical reactivity of tailor-made CuO powders prepared according to a new low-temperature synthesis method was studied by a combination of transmission electron microscopy (TEM) and electrochemical techniques. All the processes involved during cycling were successfully identified. We show that the reduction mechanism of CuO by lithium involves the formation of a solid solution of Cu II 1x Cu I x O 1 1/2 :, 0 ≤ x ≤ 0.4, a phase transition into Cu 2 O, then the formation of Cu nanograins dispersed into a lithia matrix ( Li 2 O) followed by the growth of an organic-type coating. This one is responsible for the extra capacity observed on the voltage vs. composition curve. During the subsequent charge, the organic layer vanishes first, and then the Cu grains are partially or fully oxidized with a concomitant decomposition of Li 2 O. The formation of Li 2 O and Cu nanograins and then the one of Cu. CuO, and Cu 2 O nanograins on the first discharge and subsequent charge, respectively, were identified by high-resolution TEM studies. These results enabled a better understanding of the processes governing the reactivity of 3d metal oxides vs. lithium down to 0.02 V.

Nature and amount of carriers in Ce doped Nd2CuO4 I. High-temperature characterization

Abstract: DC conductivity, ionic transport number, and thermopower have been measured of Nd2−xCexCuO4±δ materials (x = 0, 0.05, 0.10, 0.15, 0.20) at different temperatures [300 ⩽ T ⩽ 900°C] and under different oxygen partial pressures [1 atm ⩽ P(O2) ⩽ 3 × 10−6 atm]. For the most heavily doped samples, the current carriers are electrons essentially produced by the substitutional defect CeNd., while the crystal-gas equilibria involving Oi″ account for a smaller amount of carriers. The behavior of Nd1.95Ce0.05CuO4±δ is intermediate between more doped and undoped materials. When coupled with oxygen non-stoichiometry data, the results indicate that the mobility of the electronic carriers exhibits a transition from small-polaron to large-polaron behavior with increasing doping level.

The atomic and electronic structure of cerium substitutional defects in Nd2−xCexCuO4+δ : an XAS study

Abstract: The local atomic and electronic structure of cerium substitutional defects in Nd 1.80 Ce 0.20 CuO 4+δ was investigated by means of X-ray absorption spectroscopy (EXAFS and XANES of Ce L III edge), as a function of the oxygen partial pressure. It has been found that in all of the experimental conditions investigated (1, 10 −3 and 10 −6 atm), the Ce formal oxidation state should be regarded as IV. This is explained in terms of the bond configuration in this material. The consequences for the electron counting in the CuO 2 planes are discussed. As is shown by EXAFS, the increased charge on the 4e site in the T′ structure mandates a local lattice distortion around cerium: the co-ordination cuboid collapses along the (001) direction. Consequently, the CeO bond length is shorter than the NdO bond length.