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Two unit cells to 200 A thick ultrathin YBa2Cu3O7-δ films have been synthesized and their growth mechanism and physical properties have been studied. Atomic force microscopy showed that the films grow with both spiral and layer by layer modes and the screw dislocations appeared even in the 6 unit cells thick films. In the initial growth stages of the films, the strong dependence of Tc on the film thickness is discussed.

In this paper, the preparation process of the tetragonal LaBaCaCu3O7-x (LBCCO) superconductor with Tc=84 K is repored. The superconductivity and structure of the LBCCO superconducting phase are investigated by means of x-ray diffraction (XRD), transmission electron microscope(TEM) and superconductivity measurements. The results indicate that the superconducting phase with Tc=82 K in the LBCCO system has a tetragonal structure with a=0.3966 nm, c=1.1838 nm and space group P4/mmm. About 50% of the Ca and La atoms are located in 1d sites (i.e. Y site in the YBCO structure). It is confirmed that there is in fact no orthorhombic to tetragonal transition in this material. The relationship between the oxygen content and Tc is also presented.

The nearly single phase (R0.4Pr0.6)(0.5)Ca0.5Ba2Cu3O7-delta compounds (R = La, Pr, Nd, Sm, Eu, Gd and Y) with T-c about 100K were prepared under high pressure and high temperature using the cubic-anvil apparatus. The T-c is much higher than that of the traditional R-123 superconductors without doping Ca on the rare-earth site. For various rare earths with different ionic radii, the (R0.4Pr0.6)(0.5)Ca0.5Ba2Cu3O7-delta compounds have almost the same critical temperature. This is different from the result of the ion-size effect of rare-earth ions in R1-xPrxBa2Cu3O7-delta compounds. Our results show that Pr has the same properties as other rare earths in the 123-phase compounds due to the doping of Ca.

The new superconductor MgB2 has been prepared in two ways, by high pressure and ambient pressure synthesis. The superconducting properties were measured and compared. It is found that the sample prepared by high pressure is much denser than that prepared under ambient pressure. Accordingly the high pressure sample has a very narrow transition width and a much higher bulk critical current density.

High critical temperature superconductors of mercury-based system were synthesized under high pressure and high temperature. The resistance and ac magnetic susceptibility measurements for sample prepared at 25 kbar and 850°C for 1.5 h show that the sample without any added treatment was a mixture of Hg-1201 and Hg-1223. The Tc values of Hg-1223 phase and Hg-1201 phase are 132 and 98 K, respectively.

Flux method was used to grow large 2201 single crystal in Bi-Sr-Cu oxide. The as-grown crystal was nonsuperconductor and showed semiconductivity in resistivity curve. After it was reduced in flowing N2 at 570°C and appropriate oxygen vacancies were induced, superconductivity with Tcon = 6K was obtained. The great influence of oxygen deficience on superconductivity is evident. Also, the incorporation of Pb adjusted the modulation pattern.

The nearly single phase (R0.4Pr0.6)0.5Ca0.5Ba2Cu3O7-δ superconductors (R=La, Pr, Nd, Sm, Eu, Gd, Y) were prepared under high temperature and high pressure using the cubic anvil apparatus. The measured result shows that we can get superconductivity in all these Ca doping compounds with Tc above 100K.

The new bulk superconductors of Pr1-xCaxBa2Cu3O1-δ (0.4≤x≤0.6) have been synthesized under high pressure for the first time to our knowledge. The highest Tc of 98K was observed for Oxygen-deficient tetragonal Pr0.5Ca0.5Ba2Cu3O7-δ sample. Our results demonstrate the valence state of Pr in 123 structure is a mixed sate greater than 3+, hole filling and hybridization are the primary cause of the suppression of superconductivity by Pr in 123 structure.

The effect of grinding on superconductors of Y-123 and Bi(Pb)-2223 phases and phase formation have been studied by means of X- ray diffraction, differential thermal analysis, scanning electron microscope and measurements of the superconductivity. The experimental results show that there is significant difference of grinding effect on Y-123 and Bi(Pb)-2223 phase superconductors. Grinding causes a change of crystalline state to amorphous one for Bi(Pb)-2223 phase superconductor. The effect of the mechanical strain from preparing process and accident on superconductivity of material should be taken into consideration.