Hall constants (R_H) at 300 K of three families of CuO-based superconductors are presented—the 123 YBaCuO with Fe substitution, the 2212 and 2223 Bi systems with Pb, Gd, Nd. Sm substitutions. In all these systems.R_H is positive indicating hole conductivity.T_c increases initially as the hole density (p=1/R_He) increases and shows a maximum. Each family shows a maximum value ofT_c but at different values ofp. These data along with the observation ofn-type conductivity in NdCeCuO are discussed in the light of certain models.

Preparation, resistivity (ρ), field-cooled (FC) and zero field-cooled (ZFC) susceptibility (χ) of YSrCuO are reported. Zeroρ is observed at 72K. FCχ shows a superconducting transition at 68 K and also an antiferromagnetic transition at 15 K which is due to Y₂Cu₂O₅ as deduced from electron diffraction and composition analyses. It is tentatively proposed that the Y-rich phase could be responsible for the observed superconductivity.

Bi(Pb)SrCaCuO films have been deposited on single (MgO) and polycrystalline (poly MgO, CuO) substrates by DC sputtering. All the films became superconducting after post-annealing them in air. The films on single crystal MgO showedT_c onset at 120 K andT_c at 92 K. However, the extrapolated zero resistivity is obtained at 106 K. The ac susceptibility showed an onset at 106 K and a sharp transition at 85 K. The films on poly MgO and poly CuO had aT_c=72 K. The preparation, X-ray diffraction and morphology of these samples are presented.

We have studied the Mössbauer spectra of YBa₂Cu_3−xFe_xO_7−d (11 compositions) and present here the results obtained from quantitative analyses of the paramagnetic and magnetic spectra.