CRYSTAL STRUCTURE DATA ON A NEW CUBIC PHASE ACTING AS ANTAGONIST IN THE SYNTHESIS OF Hg(Re)-1223 SUPERCONDUCTOR

Abstract

During the attempts to improve sealed-quartz tube synthesis of Hg(Re)-1223 superconductor, a new compound was systematically identified in certain unsuccessful experimental conditions. It was characterized by a well distinct powder diffraction pattern with cubic diamond-like extinctions and lattice parameter 8.48-8.53 Å. The composition was determined as Hg 2 Re 0.5 Ba 4 Ca 1.5 O 8.5 and an univocal interpretation was found in terms of the high-symmetry space group Fm3m(225), with Z=2, (= 6.70 g/cm 3; the reliability factor was 5.0%. This phase, Cu-free and not superconductive, rather than a precursor can be considered as an unwanted accident in Hg(Re)-1223 preparation route. Its existence was confirmed by a successful synthesis starting from the above reported stoichiometry.