M. Rateau

structural, electrical and magnetic properties of aluminium-, gallium- and iron-substituted YBa2Cu3O7 − δ

Abstract We present X-ray, resistivity ρ, Hall effect and susceptibility /gc data for YBa 2 Cu 3 − x M x O 7 − δ ( M ≡ Al , Ga , Fe ; 0 x x ≈ 0.1, the structure changes from orthorhombic to tetragonal, although T c > 77 K . The current density derived from the magnetization data decreases faster for aluminium than for iron and gallium.

Hall effect studies of YBa2Cu3−xFexO7+y

Abstract Hall data of YBa 2 Cu 3−x Fe x O 7+y indicate hole conductivity for 0≤x≤0.15. The linear dependence of 1/R H e vs T disappears for x ⋍ 0.04. 1/R H e 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.

Resistivity and hall effect studies in YBa2Cu3O7−x

Abstract The variation of the resistivity and the Hall coefficient in ceramic samples of YBa 2 Cu 3 O 7−x as a function of oxygen content is reported and discussed in terms of a simple two-band model.

Hole density variation in the Bi(M)SrCa(M)Cu system

Abstract Hall constants (RH) of a variety of samples of Bi2−xMxSr2Can−yMyCumOz (M = Pb, Hg, Gd, Sm, Nd; x,y ⩽ 0.4; n = 1, 2; m = 2, 3, 4) are reported. The data confirm the simultataneous role in the high Tc superconductivity of the (CuO2 planes and effective free carriers (holes), by showing an universal curve Tc = f (1/RHe). The results can be understood qualitatively in terms of a bi-polaron model.

Superconductivity, electron microscopy and Josephson effect in Bi-Sr-Ca-Cu-O system

Abstract Systematic resistivity, DC susceptibility, X-ray diffraction, electron microscopy and diffraction studies in Bi-Sr-Ca-Cu-O system are reported as a function of different cationic ratios and as a function of heat treatment from 850°C. Imaging and diffraction electron microscopy studies of the crystals show very few faults and there is no crystallographic phase transition during cooling down to 15K. Current voltage characteristics at 77K reveal Josephson junctions with voltage jumps as large as 8 mV.

DC susceptibility and magnetization of YBa2Cu3−xFexO7−δ (0<x<0.1)

Abstract X-ray, dc susceptibility and magnetization data of YBa 2 Cu 3−x Fe x O 7−δ (0 86 K. The superconductivity may thus be preserved through the orthorhombic-tetragonal (t) transition which takes place near x = 0.10. The critical current J c derived from the magnetization data decreases very little for x = 0.02 with respect to x = 0. For x>0.02, J c decreases faster than T c does. The effect of heat treatment is pointed out. The data are briefly discussed taking into account the small coherence length and the presence of orthorhombic domains in t phase.

Preparation, electron microscopy and superconductivity of a new class of high Tc superconductors: Pb2Sr2Y1-xCaxCu3O8+δ (x = 0.5; 0.25)

Abstract Preparation, electron microscopy, resistivity (ζ) and field cooled susceptibility (χ) of Pb 2 Sr 2 Y 1- x Ca x Cu 3 O 8+ δ ( x =0.5; 0.25) are reported. They crystallise in an orthorhombic structure. ζ shows a two step transition with distinct onsets at 86 and 45 K with zero resistivity at 15 K. χ data show a diamagnetic onset at 74 K. These data while confirming the results of Cava et al (Nature 336, 211 1988) point out the influence of the preparation conditions on the superconducting properties calling for a systematic study.

Transport properties of BiSrCaCuO and YBaCuO

Abstract We present and discuss experimental results of resistivity (ρ) and Hall coefficient (RH) measurements on ceramic samples of the BiSrCaCuO system, and compare them with our previously reported data on YBa2Cu3O7 − x. We also report data on single crystals of the latter, both parallel and perpendicular to the ab plane. Relatively sharp superconducting transitions, as well as a reasonably high resistivity ratio ( ρ 296K ρ 117K = 2.6 in the BiSrCaCuO system, and ρ 296K ρ 96K = 2.9 in YBaCuO), indicate that the samples are of good quality. In the BiSrCaCuO system (Tonset = 112 K), the Hall coefficient is positive (with a room-temperature value of 4.18 × 10−3 cm3 C−1) and shows a temperature dependence similar to that observed in the ceramic samples of YBaCuO ( R H(117K) R H(296K) = 3.0 in BiSrCaCuO and R H(96K) R H(296K) = 2.9 in YBaCuO). We discuss these results in terms of the anisotropic nature of these compounds. The roles played by the CuO planes and the CuO chains in YBaCuO are also discussed.

Structural, electrical and magnetic properties of Al and In substituted YBa2Cu3Ov

Al seems to preferentially substitute at the Cu site in YBaCuO. For Al concentration 0.075 x c > 77 K. For In concentration the O structure and the ST is preserved. In both the cases the solubility limit seems to be less than 0.1

Magnetisation of YBaCuO and Pb-substituted BiSrCaCuO

The magnetisation as a function of magnetic field (0<H<15 kOe) and as a function of temperature (9<T<50 K) of YBaCuO and Pb-substituted BiSrCaCuO has been studied. The beneficial effect of Pb addition on the critical current Jc is pointed out. The data also show that the Jc of the Pb-substituted Bi system is comparable to that of sintered YBaCuO. In both these systems, Jc is of the order of 4*106 A cm-2 at 9 K in a field of 2 kOe.