SUPERCONDUCTIVITY IN THE MG-DOPED CUBA2CA3CU4O12-GAMMA SYSTEM

Synthesis of CuBa2Ca3Cu4O12-y (Cu-1234) with Mg doping at the Ca sites , hitherto unexplored, is attempted and reported here. Different sampl es with 5%, 10%, 20%, and 33% Mg (in nominal stoichiometry) have been prepared in gold capsules under 3.5 GPa pressure and at about 1000 deg rees C temperature using a cubic anvil-type high-pressure machine. The samples were characterized through x-ray diffractometry, resistivity, de susceptibility, and Hall effect measurements. The samples were the n aligned along their c axis under 10 T held at room temperature. Magn etization (both in H parallel to ab and H parallel to c) was measured between 120 and 5 K in different field values up to 5 T. The supercond ucting anisotropy (defined as xi(ab) / xi(c) = H-c2(ab)/H-c2(c)), esti mated in the reversible magnetization regime, comes out to be about 1. 4, and is lower than that of the pristine sample. Improvement in the a nisotropy factor obtained has been discussed in light of the observed changes in the lattice parameters and the hole concentration, emanatin g from Mg doping in the Cu-site vacancies in charge reservoir blocks o f the 1234 structure. [S0163-1829(98)07538-9].