ASSESSMENT OF STRUCTURE AND CRITICAL-TEMPERATURE CORRELATION IN HGBA2CUO4-LA-BA-CU-O SUPERCONDUCTORS(DELTA AND CA)

HgBa2CuO4+delta and (CaxLal-x) (Ba-1.75-x La-0.25+x)CU3O7+/-delta supe rconducting systems were structurally investigated employing Rietveld analysis. The doping of holes in Hg compounds was done by oxygenation and reduction methods. In Ca-La-Ba-Cu-O system the doping of holes was introduced via cation cosubstitution of Ca+2 for La+3 and La+3 for Ba +2, so that the nominal charge of non-copper cations remained constant (= 7.25). The electronic structure was assessed by calculating Madelu ng site potentials. It was found that the difference a Delta V-A of Ma delung potentials on the apical and planar oxygen sites correlates wit h T-c similar to the trends reported in the literature. Based on a VA analysis it was possible to separate the intrinsic 'chemical pressure' effect on T-c from the one caused by electron density redistribution in Ca-La-Ba-Cu-O system upon cosubstitution. (C) 1997 Academic Press L imited.