NONEXISTENCE OF A SUBSTITUTIONAL Y1-XBIXBA2CU3O7-Y SUPERCONDUCTING CERAMIC, AND A CRITERION FOR ELEMENTAL SUBSTITUTION

We have resolved disagreements in the literature concerning the existence or not of a substitutional ceramic phase Y1-xBixBa2Cu3O7-y. We show through synthesizing various phases and analyzing them with various techniques that bismuth does not substitute at yttrium sites. We indicate what phases are formed, in particular YBiBa2O6. We have used x-ray-diffraction data, as well as thermally stimulated luminescence, to identify impurity phases. We show that a criterion on substitutional order can be derived from x-ray intensity-line ratios. We have analyzed the bismuth catalysis and sintering effect. We report T(c) shifts but indicate why they cannot be easily correlated to oxygen content. Microstructure and electrical properties are examined from the point of view of sintering-temperature conditions.