Papers by Keyword: Valence State

Abstract: Cu-doped ZnO (CZO) with Cu %mole of 0, 13, 14, and 15% have been synthesized by the co-precipitation method with controlled pH at 9. The diffraction pattern of CZO shows that a single phase of ZnO with wurtzite structure (w-ZnO) was achieved in the parent compound. In contrast, small fractions of the secondary phase of CuO monoclinic (m-CuO) were identified in the doped compounds. Rietveld-refinement on the X-Ray Diffraction (XRD) patterns reveals that the crystallite size of CZO is estimated in the range of 84 - 148 nm with instrumental correction factor and that CZO14 exhibits the most considerable fraction of m-CuO among the samples. Interestingly, lattice constants decrease by Cu doping. The effects of Cu doping on the valence state and the local structure were investigated by X-Ray Absorption Spectroscopy (XAS). Based on our analysis on both Cu K-edge and Zn K-edge XANES spectra, oxidation states of Cu and Zn ions are about +2 with no evidence of other valence states. Cu atom is likely to incorporate into wurtzite crystal lattice by occupying Zn sites in a small portion, and the doped compounds create a few oxygen vacancies.

Abstract: We report the results of studies on the electronic state of the hole-doped Y-based pyrochlore iridate, (Y_1-x-yCu_xCa_y)₂Ir₂O₇. We carried out the resistivity, Muon Spin Relaxation (μSR), X-ray Photoemission Spectroscopy (XPS) measurements and Density Functional Theory (DFT) calculations on the non-doped (x=y=0) and doped (x=0.05, y=0.15) systems. We found in the non-doped system that the magnetic ordering of Ir spins which was accompanied by the metal-insulator transition (MIT) occurred at around 157 K and disappeared in the doped system in which MIT seems to disappear or smeared out. We suggest from the current study that a quantum critical point which shows a change in the electronic ground state from insulating to metallic to exist between those two systems.

Abstract: This study investigated the resistance of Deinococcus radiodurans to Cr6+ and Cr3+, the redox activity of this bacterium for Cr6+ and Cr3+ and the contributions of various bacterial components to the observed chromium resistance. The results showed that at 0.2 and 0.5 mmol/L of Cr6+, D. radiodurans displayed high growth with an early logarithmic phase. This organism also exhibited moderate growth at 2 mmol/L Cr3+. This strain exhibited strong reduction activity against Cr6+. At 0.2 mmol/L Cr6+, the 8-hour Cr6+ clearance rate was 92.13%. However, the clearance rate decreased sharply with increasing concentrations of Cr6+. At 0.5 mmol/L Cr6+, the 24-hour clearance rate was only 32.81%. By studying the effects of the cellular environment and individual bacterial components on the level of Cr6+, we discovered that D. radiodurans counteracted the effects of Cr6+ primarily through reduction and secondarily through adsorption. The primary activity was found to occur in the extracellular space and the cell culture supernatant. D. radiodurans had no significant oxidation effects on Cr3+. In conclusion, this study showed that D. radiodurans strongly reduces and is highly tolerant of Cr6+ and that the primary reducing agent is secreted from the cell.

Abstract: For the use of Fuel Cells in transportation, one of the key points is to reduce Pt loading in Pt/C catalytic electrode. In our study, a new type of Pt/C membrane electrodes, PtCuLaO_x heterogeneous structure, in which with developing different La content homogeneously dispersed on the surface of carbonaceous substrates was manufactured by Ion Beam Sputtering (IBS) technology, and also was treated by different annealing temperature in muffle furnace. It was found that PtCuLaO_x heterogeneous membrane with Pt loading less than 0.05mg/cm² (the electrode area) in which its having complicated valence state, indicated that Pt had mutual effect with Cu, La and O, respectively. In addition, along with increases the annealing temperature, the instant result was to promote alloying of Pt, Cu and La in PtCuLaO_x/C catalytic electrodes.