In-situ external reflection FTIR spectroelectrochemical and XPS investigations of cobalt-cyanometallates as inorganic polymeric materials on a platinum electrode.
Cobalt-cyanometallate films electrochemically deposited on a platinum electrode were studied by cyclic voltammetry (CV), in-situ FTIR spectroelectrochemistry (FTIRs) and potential resolved XPS measurements. The experimental results reveal that the CoHCF film on Pt electrode exists in two forms. The major form of the inner layer of the film is (M(+))(2)Co(II)Fe(II)(CN)(6) where M(+)denotes a cationic counter ion, in which both the Fe(2+)and Co(2+)centers can be oxidized to Fe(3+)and Co(3+)in the potential range of 0-1.0 V vs. Ag/AgCl in NaCl solution. The major form of the outer layer is Co(II)(2)Fe(II)(CN)(6), in which electrochemical reactions in this potential range are limited by kinetic sluggishness. The FTIR and XPS spectra indicated that the Co centers change from high-spin state to low-spin state accompanying the Co(2+)/Co(3+)oxidation reaction. In addition, the cations' effect on electrochemical reactions of CoHCF is also discussed.
Thermodynamic and voltammetric study of oxygen systems in molten Na2CO3K2CO3 (56-44 mol.%) eutectic at 750°C
Abstract The acidity-potential diagrams of molten Na 2 CO 3 K 2 CO 3 have been calculated from both thermochemical tables and experimental data (literature) at different temperatures between 727 and 927°C. They allow one to define stability domains of the various redox species of oxygen (O 2 , O − 2 and O 2− 2 ) and to estimate the solubility of peroxide and superoxide species in this medium. Thermodynamic predictions are then compared with results obtained from voltammetric studies at gold electrodes. A first reduction step that should be attributed to superoxide ions was observed in moderately acidic and in moderately basic media. A second reduction step characteristic of peroxide ions was observed in moderately basic and in basic media; oxide ions are responsible of the associated oxidation current. The system O 2− 2 /O 2− is a two-electron reversible process. It is shown that the Co 2 does not participate in the rate-determining reduction steps. The solubility of Na 2 O in molten Na 2 CO 3 K 2 CO 3 has been estimated at 750°C.
Photoinduced spin-state transition of Co3+ in the layered perovskite manganite thin film
The photoinduced effect, at different temperatures, on layered perovskite manganite La1.2Sr1.8Mn1.8Co0.2O7 thin film deposited on a SrTiO3(100) substrate has been studied using a He–Ne laser (632.8 nm) with the power of output 25 mW at low temperatures. The electrical transport and magnetic properties of the film are investigated systematically in the temperature region from 20 to 300 K. The resistance shows a significant decrease at low temperatures (T<90 K) under laser irradiation, which can be interpreted in terms of the spin-state transition of Co3+ ions. The magnetic field combined with the laser is also used to detect the photoinduced effect of the spin-glass state. The time dependence of the metastable system under several applied fields was also discussed. The system has the ability to keep a persistent memory of the magnetic history imprinted in its zero-field resistance.