Synthesis and superconductivity of (Hg0.7Bi0.3)Sr2(Ca1-xLax)Cu2O6+σ system

The problems of making phase-pure (Hg0.7Bi0.3)Sr2(Ca1-xLax)Cu2O6+σ system for 1.0≧x≧0.0 are discussed in detail. This system with the tetragonal HgBa2CaCu2O6-type (1212) structure was found only for x=0.25, 0.5 and 0.75. The a and c lattice parameters increase with the increasing La concentration due to the decreasing in oxidation state of Cu and the replacement of smaller Ca+2 ions (1.12 A) by larger La3+ ions (1.16 A). The transition temperature Tc decreases as the La substitution parameter x increase. We observed the maximal Tc at x=0.25 with 87K and 72K for x=0.5.