Hideaki Inaba

Electronic conductivity, Seebeck coefficient, defect and electronic structure of nonstoichiometric La1-xSrxMnO3

Abstract In order to elucidate the relationship between the electrical properties and composition ( d and x ) of La 1− x Sr x MnO 3+ d , precise measurements were made on the conductivity, σ , and Seebeck coefficient, Q , for the oxide with 0≤ x ≤0.7 as a function of T and P (O 2 ) up to 1273 K. Analysis was made for the high-temperature paramagnetic state using the nonstoichiometry data and defect and electronic structure models reported by the present authors. It was shown that σ and Q in the oxygen excess La 1− x Sr x MnO 3+ d ( d >0) are fixed to the value at those of the stoichiometric oxygen content, d =0. In the oxygen deficient La 1− x Sr x MnO 3+ d , they are essentially determined by the mean Mn valence and temperature. The predominant electrical conduction was found to take place by the electron hopping on the e g ↑ level of Mn. In La 1− x Sr x MnO 3+ d ( d ≤0) under the condition of z = x +2 d ≤1/3, σ is given by: σ=(2.8×10 6 /T){2 (−z 2 −z+6)(6−18z)/(17−z) 2 +(−z 2 −z+6) (z 2 +18z+5)/(17−z) 2 } exp {(−Ea/(kT)} where the activation energy Ea=−0.59(3+z)+2.00 eV . For z ≥1/3, it is given by: σ=(2.8×10 6 /T) z(1−z) exp {(−Ea/(kT)} where Ea=−0.036(3+z)+0.16 eV . Q is also described essentially by this model. However, the effect of minority carrier conduction is clearly found in Q in addition to the major conduction on e g ↑ level. The major carrier conduction is p-type and the minor carrier is n-type for z ≤0.5 and vice versa for z ≥0.5.

Structural consideration on the ionic conductivity of perovskite-type oxides

Abstract Ionic conductivity of perovskite-type oxides is discussed in terms of structurally related parameters. Electrical conductivity data of perovskite-type oxides, reported as oxygen ion conductors, were collected from literatures and the correlation between the electrical conductivity of these compounds and the structurally related parameters, such as tolerance factor, specific free volume and oxygen deficiency was examined. The tolerance factor and the specific free volume were both a function of ionic radius and the tolerance factor decreased with increasing the specific free volume. The optimum tolerance factor was found to be around 0.96 due to the balance between the specific free volume and the tolerance factor in order to obtain the maximum electrical conductivity for A III B III O 3 -type perovskites. The optimum oxygen deficiency to obtain the maximum electrical conductivity was around 0.2. The effect of ionic size of dopant ions in A and B site on electrical conductivity was also discussed.

Effect of the magnetic field on the melting transition of H2O and D2O measured by a high resolution and supersensitive differential scanning calorimeter

The magnetic effect on the melting transition of H2O and D2O was measured by using a high resolution and supersensitive differential scanning calorimeter working in a magnetic bore. The melting temperature of H2O and D2O at 6T was 5.6 and 21.8mK higher than that without the magnetic field, respectively. The temperature shifts of the melting transition of H2O and D2O were proportional to the square of the magnetic field. The temperature shifts of the melting transition due to the magnetic field did not obey the magneto-Clapeyron equation quantitatively. A dynamic effect due to the magnetic field was discussed for an alternative interpretation.

Electrochemical Oxidation in a CH 4 ‐ H 2 O System at the Interface of a Pt Electrode and Y 2 O 3‐Stabilized ZrO2 Electrolyte II. The Rates of Electrochemical Reactions Taking Place in Parallel

The rate processes of electrochemical reactions were clarified in a CH 4 -H 2 O system at the interface of a porous Pt electrode/Y 2 O 3 -stabilized ZrO 2 electrolyte. Direct-current polarization measurements and ac impedance spectroscopy were made with gas analysis before and after the reaction at 1073 K. We proposed an analytical method to determine the rates of electrochemical reactions taking place in parallel. When the ratio p(H 2 O)/p(CH 4 ) of the inlet gas was close to zero, the observed relationship between the polarization current and electrode potential was interpreted by the electrochemical oxidation processes of H 2 , CO, C, and CH 4 in parallel using the proposed method. For example, the ratio of the oxidation rates for C/CO/CH 4 /H 2 is 1/1.3 x 10/1.9 x 10 2 /2.8 x 10 3 at E = -600 mV vs. air. This result was obtained under very low CH 4 concentration. The estimated oxidation rates of H 2 and CO as functions of the electrode potential were described by the model proposed by Mizusaki et al. for the reaction of H 2 -H 2 O and CO-CO 2 .