THE IMPORTANCE OF THE PRECURSOR IN HIGH-PRESSURE SYNTHESIS OF HG-BASED SUPERCONDUCTORS

The formation process of high-pressure synthesized Hg-based supercondu ctors is characterized in terms of the average copper valence ([V-Cu]) of the precursor, This parameter is varied by oxygen intake of non-st oichiometric phases during the precursor synthesis at specific tempera ture, time and cooling process treatment. The average copper valence i s shown to be a controllable parameter that determines both the overal l composition of the precursor and the proportion of the different pha ses present in it. More important, the average copper valence of the p recursor seems to control the formation of a given member n of the HgB a2Can-1CunO2n+2+delta homologous series. We find that higher precursor copper valences favor lower members of the series while higher member s are only obtained with lower [V-Cu].