Experimental results for the thermal conductivities of imidazolium-based ionic liquid + CO2 mixtures are reported. The thermal conductivities were measured with a transient short-hot-wire method. The experimental temperatures were from 294 K to 334 K, and pressures were 10.0 MPa and 20.0 MPa. The CO2 mole fractions of the mixtures covered a range up to 0.42. It was found that the thermal conductivities of ionic liquids have a very small CO2 mole fraction dependence.

Thermal conductivities are reported for a series of 1-alkyl-3-methylimidazolium hexafluorophosphates having butyl, hexyl, and octyl groups, which are expressed by [bmim][PF6], [hmim][PF6], and [omim][PF6], respectively. The experimental method used was a transient short-hot-wire method. Since only a small amount of sample liquid is required, this method was found to be effective for the thermal-conductivity measurements of ionic liquids (ILs). The experimental temperatures ranged from 294 to 335 K at pressures up to 20 MPa. The values of the thermal conductivities of ILs at normal pressure are similar to those of benzene. It was found that an effect of the length of the alkyl chain on the thermal conductivities in ILs is negligible. From the data for the thermal conductivity and viscosity at 293.15 K and 0.1 MPa of ILs and normal alkanes, a simple correlation was developed based on the Mohanty theory. From comparisons between the thermal conductivities of ILs and those of organic liquids (n-hexane, benzene, and methanol), the temperature and pressure dependences of the thermal conductivity of ILs are relatively weak.

Temperature and magnetic field dependence of surface acoustic wave (SAW) velocity has been measured for Y1-xPrxBa2Cu3Oy films with x = 0.3 and x = 1. SAW velocity shows step-like anomaly at the superconducting transition Tc and a remarkable softening at low temperatures. The amount of the anomaly at Tc is 4.5 × 10−5, which is the same order as bulk samples. SAW velocity below Tc is enhanced by applying the magnetic field, which is caused by interaction between the vortices and SAW.

The angular dependence of the resistivity ϱ(θ) has been measured in the superconducting transition region at various magnetic fields on films of the Y1−xPrxBa 2Cu3Oy system. The angular dependence of ϱ(θ) was analyzed on the basis of the effective mass model. The obtained anisotropy ratio ɛ=ξab/ξc between the c-axis and the c-plane is almost constant in the samples with x below 0.08 and then increases with the Pr concentration x from 5.5 for x=0.08 to 10.1 for x=0.45. Superconducting properties are not affected by the small substitution of Pr ions below x=0.08 and the two-dimensional character is enhanced with increasing x above x=0.1. It is pointed out that the increase of the anisotropy is due to a weakening interlayer coupling between the superconducting CuO2 planes and is caused by the suppression of superconductivity in the CuO chains which is similar to that in the oxygen-reduced YBa 2Cu3Oy system.

Electrical resistivity of Y1−xPrxBa2Cu3Oy with x=0.45 has been measured around the superconducting transition temperature in applied magnetic fields. The superconducting transition becomes once broad above 1T and then narrowing of the transition appears in higher magnetic field above 9T for H∥c-axis. Furthermore, the pinning energy U0 of the vortex which is estimated from the temperature dependence of the resistivity in the low resistivity region of the transition behaves differently with respect to the magnetic field above and below 1T. These phenomena are discussed based on the temperature dependence of the depinning field, Hc2 and on pinning by the twin boundary.

We have measured magnetoresistance in the normal state of Y1−xPrxBa2Cu3Oy films. Negative magnetoresistance was observed in the samples with concentrations 0.5 ≤ x ≤ 0.7 around the disappearance of superconductivity, which is more conspicuous for H ∥ c-axis than for H ⊥ c-axis. The obtained results could be explained by 2-dimensional weak localization theory. These indicate that localization effect plays an important role on the disappearance of superconductivity in the present system.

The magnetoresistance was measured for both H parallel-to c-axis and H perpendicular-to c-axis, using c-axis oriented films with x greater-than-or-equal-to 0.6 of the Y1-xPrxBa2Cu3Oy system. The sheet resistance for the CuO2 layer of the sample with x=0.6 is in agreement with h/4e2=6400 OMEGA/square which is the threshold value of a superconducting-insulator (S-1) transition in the two-dimensional system. Furthermore, in the samples with x=0.6 and 0.7 a negative magnetoresistance was observed in a wide temperature range below 50 K. Its magnitude is much larger for H parallel-to I c-axis than for H perpendicular-to c-axis. The origin of the negative magnetoresistance is interpreted as a localization effect because those samples have the Pr concentration around the S-1 transition in the present system. It is pointed out that the disappearance of the superconductivity at x(cr) approximately 0.55 originates from the localization effect by Pr doping.

The magnetoresistance was measured for both H∥c-axis and H⊥;c-axis, using c-axis oriented films with x≥0.6 of the Y1−xPrxBa2Cu3Oy system. The sheet resistance for the CuO2 layer of the sample with x=0.6 is in agreement with h4e2=6400 Ω□ which is the threshold value of a superconducting-insulator (SI) transition in the two-dimensional system. Furthermore, in the samples with x=0.6 and 0.7 a negative magnetoresistance was observed in a wide temperature range below 50 K. Its magnitude is much larger for H∥c-axis than for H ⊥;c-axis. The origin of the negative magnetoresistance is interpreted as a localization effect because those samples have the Pr concentration around the SI transition in the present system. It is pointed out that the disappearance of the superconductivity at xcr∼0.55 originates from the localization effect by Pr doping.