No abstract

We discuss the effects of hydrostatic pressure on the superconducting properties of MgB2 within the framework of Eliashberg theory. By considering the pressure dependences of all parameters appearing in the McMillan formula, we show that the calculated pressure derivative of Tc as well as the variation of Tc with pressure are in good agreement with recent measurements. The pressure dependences of the energy gap ∆0, the effective interaction strength N (EF )v, the critical magnetic field Hc(0), and the electronic specific heat coefficient γ are also predicted for this system. A comparison of pressure effect in non-transition elements clearly suggests that MgB2 is an electronphonon mediated superconductor.

To get some information about the interaction of two totally different kinds of superconductors in a mixture, we prepared the samples of mixture of two kinds of superconductors ( YBa 2 Cu 3 O 7+ MgB 2), using normal annealing method at low temperature (400 °C ~ 600 °C). The variations of the transition temperature (Tc) and critical current (Jc) of the mixtures are investigated. We also prepared a series of samples of MgB 2 with small ratios of YBCO or Bi -2223 as addition. Carefully comparison shows that the Jc drops when the ratio of YBCO additions increases, but in the Bi -2223 additions the trend goes just the opposite.