K. Kawamura

Determination of Oxygen Vacancy Concentration in a Thin Film of La0.6Sr0.4CoO3 − δ by an Electrochemical Method

Equivalent circuit analysis was undertaken on a mixed conductor electrode/solid oxide electrolyte system. In a limited case where surface reaction is the predominant rate-controlling process, the equivalent circuit was simplified to parallel connection of a resistor (surface reaction resistance) and a capacitor (chemical capacitance due to oxygen nonstoichiometry). Equilibrium oxygen vacancy concentration was correlated with the chemical capacitance. The model was applied to a dense film of La 0.6 Sr 0.4 CoO 3-δ deposited on a sintered plate of Ce 0.9 Gd 0.1 O 1.95 by a laser ablation method. Frequency response of the electrochemical impedance was measured under dc bias at 873-1073 K in O 2 -Ar gas mixtures. The observed capacitance was extremely large, e.g., around 0.1 to I F cm -2 for the 1.5 μm thick film. The oxygen vacancy concentration in the film was calculated from the capacitance and compared with the literature data measured by thermogravimetry. The film was found to show smaller oxygen nonstoichiometry. The enthalpy for oxygen vacancy formation in the film was about 40 kJ mol -1 larger than the bulk.

Mass transport properties of Ce0.9Gd0.1O2−δ at the surface and in the bulk

Abstract The isothermal thermogravimetry was performed on the system of Ce 0.9 Gd 0.1 O 2− δ (CGO10) to determine the oxygen nonstoichiometry, δ , in the temperature range between 1073 and 1173 K and the oxygen partial pressure range of 10 −22 –1 bar. In addition, chemical diffusion coefficients, D chem , and surface reaction rate constants, k , were obtained in CO–CO 2 and H 2 –H 2 O atmospheres through the analysis of a weight relaxation process. The values of obtained chemical diffusion coefficients were consistent with those estimated from partial conductivity and oxygen nonstoichiometry through the P O 2 regions from predominant ionic conduction to predominant electronic conduction. Surface reaction rate constants are not directly related with oxygen partial pressure but depend on the gas species and the composition. The isotope exchange depth profiling with secondary ion mass spectrometry (SIMS) was done to examine the relationship between k and surface exchange coefficients, k s . It was shown that the hydrogen partial pressure dependence of k s converted from k was the same, although the absolute value was about 1 over 30 of those from SIMS analysis.

Nanometer-sized Ge particles in GeO2-SiO2 glasses produced by proton implantation: Combined effects of electronic excitation and chemical reaction

It was reported [H. Hosono et al., Appl. Phys. Lett. 65, 1632 (1994)] that nanometer-sized crystalline (nc) Ge colloid particles were formed by implantation of protons into 0.1 GeO2–0.9 SiO2 glasses at room temperature. The depth profiles of Ge colloids and the density of Si–OH or Ge–OH created by the implantation were measured and compared with those of energy deposition in order to examine the formation mechanism of Ge colloids by proton implantation. The depth region of nc-Ge particles was found to correspond to the overlapped region between the OH distribution and the peak of electronic energy deposition. Transmission electron microscopic observation revealed that the size of Ge colloid particles created by proton implantation was close to that of GeO2-rich particles occurring in the substrate glasses. These results indicate that GeO2-rich particles are converted into Ge particles by a combined effect of the electronic excitation and the chemical reaction of implanted protons. A mechanism was proposed...

Formation and photobleaching of 5 eV bands in ion-implanted SiO2:Ge and SiO2 glasses for photosensitive materials

Formation and photobleaching of optical absorption bands in the 5 eV region were examined in proton-implanted 5GeO-95SiO2 glasses and SiO2 glasses implanted with Si, Ge, B or P ions. A conspicuous increase in the intensity of the 5 eV band, which is attributed to oxygen vacancies, was seen in both substrates after implantation. However, a distinct difference was observed in bleaching with 5 eV light between the H-implanted SiO2:Ge glasses and the implanted SiO2 glasses. In the former the 5 eV band was bleached and intense absorptions above 5 eV emerged, whereas in the latter bleaching occurred in the whole UV region. This distinct bleaching nature provides implanted glasses with the possibility of modification of the refractive index by UV illumination.

Electrochemical Luminescence of Rare Earth Metal Ion Doped MgIn2O4 Electrodes

Anodic dc electrochemical luminescence (ECL) property of nondoped and rare earth (RE) ion-doped MgIn 2 O 4 electrodes, famous as a transparent electronic conducting material, was investigated. Nondoped and Dy 3+ , Sm 3+ , Ho 3+ , Er 3+ , Eu 3+ , and Tm 3+ doped MgIn 2 O 4 , usually exhibiting no or very weak photoluminescence (PL), showed ECL under anodic polarization over 20 V. ECL luminescence can be attributed to that from the oxygen defect for nondoped MgIn 2 O 4 and to that from the doped emission centers (RE ions) for MgIn 2 O 4 :RE, respectively. Doped RE ions form solid solution within MgIn 2 O 4 host. From the Rietveld refinement analysis of X-ray patterns, we concluded that RE ions are located at the 16d site in MgIn 2 O 4 . The ECL intensity dependence on the Er 3+ ion concentration of MgIn 2 O 4 :Er 3+ showed a maximum at [Er 3+ ] = 2% and then decreased, whereas PL intensity monotonously increased with increasing Er 3+ concentration. These results suggest that electron conductivity of MgIn 2 O 4 host are also related with the ECL property.