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Besides the structure and oxygen content, the resistance-temperature relationship, Hall carrier concentration (nH) and midpoint temperature of superconducting transition (Tc) were measured for more than six 123-phase systems with elemental substitution. No correlation is found between the oxygen content and Tc, nor is between the orthorhombic structure and Tc. Instead, an unmonotonic relationship is found between nH and Tc. The optimum nH for the highest Tc is about 3.8 × 1021 cm-3. All this draws a conclusion that nH is a parameter to describe the high Tc superconductivity.

The difference between the longitudinal and transverse d.c. resistivity in oriented YBa2Cu3O7-δ films has been observed by special design of electrical contacts. It is attributed to the anisotropy of the in-plane resistivity, which at least indicates that some untwinned regions exist in the films. A sign change of the off-diagonal element of the resistivity tensor is also observed in the superconducting transition region for one of the films. Its possible origin is discussed.

The temperature dependence of the Hall coefficient RH has been measured between 50 and 250 K for the superconducting compounds with nominal compositions Bi2Ca2Sr2Cu3Oy and Bi1.6Pb0.4Ca2Sr2Cu3Oy. It is found that the Hall number, nH, is linearly T-dependent and field-independent in the normal state and decreases rapidly on doping with lead. This result is quite in agreement with the recent theoretical calculation proposed by Xing and co-workers (1988). A large anomaly in RH is observed around Tc, which is discussed in terms of the intergranular structure of this material.

Crystal structure, oxygen content, AC susceptibility and DC resistance versus temperature, and Hall coefficient (RH) at 100 K have been investigated for the 123 phase YBa2Cu3−xSnxO7+δ. The RH is found positive for the single phase samples w ith x=0.05, 0.1, 0.2 and 0.3 but negative for that with x=0.4 which contains SnO and other phases. This negative RH is considered the contribution of the n-type SnO. It is also found that, as the Sn content is increased, the lattice parameters, RH and the mid-point temperature of superconducting transition (Tc,mid) change a little, whereas the oxygen content increases. We speculate that the donor effect of Sn4+ is compensated for by the acceptor effect of O2− or O1−, keeping the Fermi level unshifted, thus we conclude that the position of the Fermi level in the 123 structure is an important factor to the high-Tc superconductivity.

X-ray Photoelectron Spectroscopy (XPS) was employed to study the single phase high-Tc superconductor YBa2Cu3O9-δ. Comparison of the observed valence band spectrum with the theoretical spectrum of Mattheiss is given. The core level spectrum of Ba 3d5/2 was examined. The results of Y2Cu2O5 and Y2BaCuO5 are also reported.

The R(H) and Jc(T) of single phase material Bi3PbCa3Sr3Cu4Oy were investigated. As the temperature belows 65K, the sample likely shows the characteristics of homogeneous superconductors. Very high critical current density and no negative magnetoresistance are observed. This distinct property distinguishes the new material from other ceramic superconductors.

Results of resistivity, a.c. magnetic susceptibility, Hall effect and superconductivity for single phase Ba 2 YCu 3 O 7− δ are reported. The positive value of Hall constant above T c indicates that the carriers of the sample are hole-like in normal state and its concentration is about 1.1×10 21 cm -3 at room temperature. A large anomaly of R H near T c is observed which may be indicative of granular superconductivity or be related to the intrinsic quality of this class of oxides.

The Raman spectra of a set of samples with nominal composition Ba x Y 1−x CuO 3 (0.005 ⩽ x ⩽ 0.8) which are synthesized under the same condition have been measured. It is observed that the main characters of Raman spectrum are quite different for the two groups of samples with Ba concentration being 0.3 ⩽ x ⩽ 0.8 and 0.005 ⩽ x ⩽ 0.075 respectively. It just coincides with the results two types of phase structures and the difference in superconductivity related to the two ranges of composition. Based on a comprehensive analysis of the results above, the authors suggest that the Raman peak near 605cm -1 likely corresponds to the vibration of CuO 6 octahedra breathing-mode, which play an important role in this system for achieving high transition temperature.

The measurements of X-ray diffraction, dependence of d.c. resistance on temperature and Hall effect have been performed for YBa2Cu3−xZnxOy system. The doped samples in 1-2-3 phase all exhibit metallic behavior and the hole carrier concentration experiences a nonmonotonous variation, but still larger than that of the perfect sample. The picture of localization is applied to explain these phenomena. The TC suppression mechanism has been discussed for this system.

Results of resistivity, ac magnetic susceptibility, and Hall-effect measurements for Ba1.2Y0.9V0.9Cu3O7-δ are reported. The positive value of Hall constant indicates that the material conducts via hole with a carrier concentration of 1.6×1021cm-3 at room temperature. A large anomaly in RH near Tc is observed.

The Orthorhombic 123 phase compounds Y 1−x Pr x Ba 2 Cu 3 O y (x=0.1, 0.3, 0.5, 0.7 and 1.0) were synthesized. By Hall coefficient measurements of the samples, it is found that, with the increase of Pr content, the concentration of hole-type carriers decreases. Simultaneously, a transition from metal to semiconductor indicated by the R(T) curves occurs. The carrier concentration exhibits an activated behavior. A band structure model involved Pr 4+ as a donor (found by XPS) is used in discussing the effect of Pr substitution, suggesting that the position of Fermi level is very important to the high-T c superconductivity of the 123 phase compounds.

Single phase samples of PrBa2Cu3O7-δ with orthorhombic structure were prepared by solid State reaction method. Resistance measurement was performed by a standard dc four-probe technique. It is found that the resistance exhibits semiconductor-like behavior. Results of XPS measurement indicate obviously the existence of Pr4+ in PrBa2Cu3O7-δ. Finally, the band structure was used to discuss the reasor why PrBa2Cu3O7-δ does not show superconductivity.