Assessment of structure and critical temperature correlation in HgBa 2 CuO 4 + delta and Ca-La-Ba-Cu-O superconductors

Author: Mogilyanski D.   Gartstein E.  

Publisher: Academic Press

ISSN: 0749-6036

Source: Superlattices and Microstructures, Vol.21, Iss.3, 1997-04, pp. : 451-457

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Abstract

HgBa 2 CuO 4 + delta and Ca x La 1 - x Ba 1.75 - x La 0.25 + x Cu 3 O 7 ± delta superconducting 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 Madelung site potentials. It was found that the difference Delta V A of Madelung potentials on the apical and planar oxygen sites correlates with T c similar to the trends reported in the literature. Based on Delta V A }$ 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.