Characterization of Ca-doped Bi2 +xSr2 –xCuOz

Abstract

The ‘R’ phase in the Bi–Sr–Cu–O system, which is actually a solid solution of formula Bi_{2 +x}Sr_{2 –x}CuO_z, forms an extensive solid solution by partial substitution of Ca for Sr. This has formula, Bi_{2 +x}Sr_{2 –x–y}Ca_yCuO_z, with 0 < y≲ 0.45 and 0.15 ≲x≲ 0.40 at 800 °C. Lattice parameters of the solid solutions are given; pseudotetragonal symmetry is retained throughout but the incommensurate superstructure becomes less marked with increasing contents of both Ca and Bi. The excess oxygen content of the solid solutions, determined by iodometry, is unchanged by replacement of Sr by Ca, but for a given composition, can be varied by heating at 750 °C in different atmospheres.