Homogeneity Range , Hole Concentration , and Electrical Properties of the Bi 2 Sr 3 _ x Ca x Cu 2 0 8 + 3 , ( l ^ x g 2 ) Superconductors

The homogeneity range of B i S r C a C u oxides with two-layers ("2212") structure has been investigated with X-ray powder diffraction and electron microprobe determination on materials with nominal Bi2Sr3_J tCaxCu208 + ) , (x = 1-h2 in 0.1 steps) composition and being prepared at two different oxygen partial pressures. The results show Bi over-stoichiometry and a wide range of Sr/Ca substitution. DC resistivity measurements indicate that the hole concentration is controlled by both oxygen non-stoichiometry and cation molecularity. It is shown that a single phenomenological relation between hole concentration and electrical properties can explain in a consistent way the complex behaviour of the whole set of materials with different oxygen non-stoichiometry and cation molecularity.