Jun Tateno

Thermodynamics of MgyU1−yO2+x by EMF measurements. I. Properties at high magnesium concentrations

Phase stability and thermodynamic properties of a solid solution, MgyU1−yO2+x, have been investigated at high magnesium concentrations. The lattice constant of this cubic solid solution varies differently withx in the two regions of positive and negativex values. The relation between the lattice constant and the composition was determined in the respective regions. Solid-state emf measurements on MgyU1−yO2+x revealed that both partial molar entropy and enthalpy of oxygen are temperature independent in the experimental range 700 ∼ 1050°C and that−ΔS¯O2 and −ΔH¯O2 increase withx andy of MgyU1−yO2+x. Least-squares calculations showed that−ΔS¯O2 and−ΔH¯O2 could be expressed as logarithmic functions ofx andy. The negative partial molar free energy,−ΔG¯O2, btained by the−ΔS¯O2 and−ΔH¯O2 formulas was found to decrease with temperature more rapidly for the solid solutions of largery values, which indicates the greater effect of divalent magnesium on the thermodynamic properties of MgyU1−yO2+x.

An empirical relation on the melting temperature of some ionic crystals

Abstract An empirical formula on the melting temperature for some ionic crystal is obtained using the cohesive energy, the exponent in the repulsive term and the dielectric constant at high frequency.

Thermodynamics of MgyU1−yO2+x by EMF measurements

Abstract Thermodynamic properties of a solid solution, MgyU1−yO2+x, at low magnesium concentrations have been investigated using the solid galvanic cell technique. The emf values were found to vary linearly with temperature in the range 850 ∼1050 °C, from which the linear temperature dependence of partial molar free energy of oxygen, Δ G O 2 , and the temperature independence of Δ H O 2 and Δ S O 2 were derived. These thermodynamic quantities were obtained as a function of x and y. Agreement of these values with those from theoretical considerations was examined. The effect of magnesium incorporation on Δ G O 2 was expressed using Δ G O 2 of UO2+x as −Δ G O 2 ( Mg y U 1−y O 2+x = −Δ G O 2 ( UO 2+x ) −0.0035 T ln [1 + 0.07( y 1 2 x )] − 60y .

Electron Spin Resonance of Gamma‐Ray Irradiated Single Crystals of Sodium Nitrite

Single crystals of sodium nitrite were irradiated with Co60 gamma rays of about 109 R at room temperature and studied by ESR method. The spectrum consists of a triplet and a quintet associated with different paramagnetic species; the former is believed to be NO2 and the latter N2O4—. From the analysis of the anisotropy of the hyperfine tensor the molecular plane of NO2 lies in the crystal ac plane, being different from the result obtained with irradiation at 77°K by Zeldes and Livingston. Molecular orbital of the unpaired electron of N2O4— was also calculated.

On the phase transition in mixed valence type oxides

Abstract The origin of phase transitions occuring in some mixed valence-type oxides is attributed to electronic ordering. In these transitions the ordering energy is found to be proportional to the activation energy of hopping conduction in low temperature phase. The ordering energy is estimated based on the electronic ordering mechanism and by considering the energy of crystalline distortion. The ordering energy numerically calculated for U 4 O 9 agrees fairly well with the observed.

Electronic properties in La2CuO4 at low temperatures

Abstract Dielectric constants at 9 GHz and dc resistivity were measured on La 2 CuO 4 in the temperature range 5–150 K. The conductivity behavior of the variable-range hopping was observed in the low temperature region (5–25 K) and the Debye type dielectric relaxation with the activation energy 0.024 eV was observed in the high temperature region (40–100 K). The experimental results indicate that holes are localized by the disorder potential (Anderson localization) at low temperatures and are localized by a unique potential at high temperature.

On the dielectric properties of U4O9 and UO2

Abstract Dielectric properties of U4O9 and UO2 were measured at various temperatures and at various frequencies. From the experimental result the phase transition in U4O9 at about 80°C is not considered to be ascribed to dielectric origin. The dielectric constants of both U4O9 and UO2 increase as the temperature increases.

Electrical properties and phase stabilities of some ceramics irradiated by neutrons and ions

Abstract The electrical properties of silicon nitride (Si 3 N 4 ) and tetragonal zirconia polycrystals (TZP) were measured as a function of temperature in the frequency range 5 Hz to 13 MHz. Dielectric properties at 9.1 GHz were also measured by the standing-wave method. The dielectric loss tangent tan δ at 9.1 GHz of unirradiated hot-pressed Si 3 N 4 with small amounts of MgO was lower than 2 × 10 −3 up to 500°C. On the other hand, TZP with 3 mol% Y 2 O 3 (3Y-TZP) had about 10 times higher values of tan δ than Si 3 N 4 .

Coexistence of Anderson localization and small polarons in the normal phase of La2−xSrxCuO4

Abstract The feature of the electrical resistivity in the normal phase of La 2- x Sr x CuO 4 is explained by the coexistence model of Anderson localization and small polarons. The estimated concentration of the small polarons from this model attains a maximum at the optimum concentration, where the superconducting transition temperature attains its maximum. The variation of the activation energy of the hopping conduction with x is explained by taking into account the transfer mechanism accompanied with a change of states between Anderson localization and a small polaron state. From this analysis the Bose condensation of bipolarons is considered to be valid as the origin of superconductivity in this material.

Measurement of RF Superconductivity in YBa2Cu3O7-x with the Standing-Wave Method at 9 GHz

RF properties of superconducting YBa2Cu3O7-x were measured with the standing-wave method in the microwave region. The power absorption (Joule loss) of the powder specimen, calculated from the data of the voltage standing-wave ratio (VSWR), changes markedly at the transition temperature, and decreases with decreasing temperature in the superconducting state. In a lower temperature region, it tends to the formula A=17.6 exp (- 0.031 eV/ kT). Microwaves were found to penetrate considerably into the superconducting specimen.