[en] Films of thickness ranging from 50 to 400 microns were deposited on alumina and copper sustrates in air by means of a plasma torch starting from prefabricated UBaCuO powder. The samples became superconducting after a heat treatment in oxygen at 500⁰C. The lattice parameters, resistivity and magnetic properties are presented

[en] We report on the preparation, structural, electrical and magnetic properties in the Y-Ba-Cu-O system. The appearance of superconductivity in this system is dictated by the preparation conditions. The single phase YBa₂Cu₃O₈ shows a superconducting transition at Tsub(c) = 91 K. Replacing Y with 20% Eu does not change Tsub(c) significantly. (author)

[en] The preparation, X-ray diffraction (XRD), resistivity, AC susceptibility and Hall constant of Y_1-xCa_xSrBaCu_2.7Co_0.3O_6+z (x=0, 0.1 and 0.2) are reported. All the samples crystallized with a tetragonal symmetry. The room temperature resistivity decreased from 27 mΩcm to about 2 mΩcm when x increased from 0 to 0.2. The critical temperature Tc increased remarkably from 22 K (for x=0) to 40 and 58 K for x=0.1 and 0.2, respectively. A relation between the Ca concentration, Tc and the hole density derived from Hall measurements was established. The data are compared to those earlier reported in the case of (0.3) Al substitution. These results suggest that Ca injects holes into Cu-O planes. (orig.)

[en] A1 seems to preferentially substitute at the Cu site in YBaCuO. For A1 concentration 0.075 less than x less than 0.1, the structure changes from orthorhombic (0) to tetragonal but the superconductivity is still retained at T greater than 77 K. For In concentration, on the other hand the 0 structure as well as the superconductivity (T greater than 77 K) is preserved. The data seem to point out the feeble role played by the Cu-O chains in the mechanism of high temperature superconductivity

No abstract available

[en] Hall data of YBa₂Cu_3-x Fe_xO_7+y indicate hole conductivity for 0≤x≤0.15. The linear dependence of 1/R_He vs T disappears for x≅0.04. 1/R_He follows a regular curve as a function of T_c, identical to that observed for undoped samples with varying oxygen concentration. The data indicate that the relation between t_c and the carrier density is nearly independent of the way in which the latter is varied

[en] Hall constants R_H of a variety of samples of Bi_2-xM_xSr₂Ca_n-y M_yCu_mO_z (M = Pb, Hg, Gd, Sm, Nd; x, y ≤ 0.4; n = 1, 2; m = 2, 3, 4,) are reported. The data confirm the simultaneous role in the high T_c superconductivity of the (CuO₂) planes and effective free carriers (holes), by showing a universal curve T_c = f(1/R_He). The results can be understood qualitatively in terms of a bi-polaron model

[en] 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=1R_He) increases and shows a maximum. Each family shows a maximum value of T_c but at different values of p. These data along with the observation of n-type conductivity in NdCeCuO are discussed in the light of certain models. (author). 28 refs., 2 figs., 1 tab

[en] We report X-ray diffraction, resistivity and Moessbauer studies on several substituted 2201 Bi cuprates, Bi₂Sr₂Cu_1-xFe_xO_y(O ≤ x ≤ 1) and Bi₂Sr_1.6La_0.4Cu_1-xFe_xO_y and Bi_1.6Pb_0.4Sr_1.6La_0.4Cu_1-xFe_xO_y(O ≤ x ≤ 0.04). The first series is not superconducting and a new phase appears for x = 1. For La substituted samples, Tc increases up to 35K and decreases strongly with x. All Moessbauer spectra were fitted well with four quadrupole doublets, with relative population depending on samples. (orig.)

[en] We report Hall-constant (R_H) measurements on the Bi-Sr-Ca-Cu-O system. Two systems, 2:2:1:2 and 2:2:2:3, have been studied with a variety of heat treatments and cationic substitutions (Pb, Gd, Nd, Sm). The carrier density (n=1/eR_H) at 300 K as a function of T_c for these polycrystalline samples show two distinct maxima---one corresponding to the low-T_c (2:2:1:2) phase and the other to the high-T_c (2:2:2:3) phase. The data point to compelling evidence of correlations between charge carriers and superconductivity confirming similar Hall data on Y- and La-based cuprates. A discussion of some relevant models is presented