Normal-state Hall-effect measurements on Y1-xPrxBa2Cu3O7- delta single crystals

Apparatus for the room temperature measurement of low field Nernst and magneto-Seebeck coefficients

Nernst coefficient measurements are a classic approach to investigate charge carrier scattering in both metals and semiconductors. However, such measurements are not commonly performed, despite the potential to inform material design strategies in applications such as thermoelectricity. As dedicated instruments are extremely scarce, we present here a room temperature apparatus to measure the low field Nernst coefficient (and magneto-Seebeck coefficient) in bulk polycrystalline samples. This apparatus is specifically designed to promote accurate and facile use, with the expectation that such an instrument will make Nernst measurements de rigueur. In this apparatus, sample loading and electrical contacts are all pressure-based and alignment is automatic. Extremely stable thermal control (10 mK of fluctuation when ΔT = 1 K) is achieved from actively cooled thermoelectric modules that operate as heaters or Peltier coolers. Magneto-Seebeck measurements are integrated into the system to correct for residual probe offsets. Data from the apparatus are provided on bulk polycrystalline samples of bismuth, InSb, and SnTe, including raw data to illustrate the process of calculating the Nernst coefficient. Finally, we review how Nernst measurements, in concert with Seebeck, Hall, and electrical resistivity, can be analyzed via the Boltzmann equation in the relaxation time approximation to self-consistently predict the Fermi level, effective mass, and energy-dependent relaxation time.

Percolative nanostructure and superconductivity in the mixed crystalline cuprate Nd(1 - x)Pr(x)Ba2Cu3O(7 - δ)

The Pr-substituted cuprate Nd(1 - x)Pr(x)Ba(2)Cu(3)O(7 - δ) (NdPr-123) has been investigated with particular attention on the relationship between the solid solution structure and the superconducting properties concerning the resistivity ρ and diamagnetic susceptibility χ. The compound NdPr-123 is regarded as a mixed crystalline solid solution that consists of unit-cells of Nd-123 and Pr-123, where a percolative nanostructure is constructed. The properties ρ and χ are largely characterized by such structural inhomogeneity. Several characteristic points (x(1), x(2), x(3)) are observed in χ as a function of x. Occurrence of these characteristic points is well explained in terms of a nonclassical percolation process, where the Nd-123 cell adjacent to the Pr-123 cells is converted into a different cell, thereby creating virtual percolation thresholds that appear as the characteristic points. The effective Pr-concentration x* is newly considered in reference to the cell-conversion. The concept of x* will provide clues for understanding various issues on the Pr-substituted cuprates. In addition, as an alternative case, a thoroughly different type of effective Pr-concentration has also been discussed in reference to the irregular substitution of Pr at Ba sites, which may happen to take place in RPr-123 (R = rare earth including Nd).