HOMOGENEITY RANGE, HOLE CONCENTRATION, AND ELECTRICAL-PROPERTIES OF THE 8-LESS-THAN-OR-EQUAL-TO-X-LESS-THAN-OR-EQUAL-TO-2) SUPERCONDUCTORS(Y (1)

The homogeneity range of Bi-Sr-Ca-Cu oxides with two-layers (''2212'') structure has been investigated with X-ray powder diffraction and ele ctron microprobe determination on materials with nominal Bi2Sr3-xCaxCu 2O8+y (x=1 divided by 2 in 0.1 steps) composition and being prepared a t two different oxygen partial pressures. The results show Bi over-sto ichiometry and a wide range of Sr/Ca substitution. DC resistivity meas urements indicate that the hole concentration is controlled by both ox ygen non-stoichiometry and cation molecularity. It is shown that a sin gle phenomenological relation between hole concentration and electrica l properties can explain in a consistent way the complex behaviour of the whole set of materials with different oxygen non-stoichiometry and cation molecularity.