On the solid solutions in the systems Bi₂Sr₂Ca_1-xY_xCu₂O_8+δ, Bi₂Sr_2-xLa_xYCu₂O_8+δ and Bi₂Sr₂Y_1-xCe_xCu₂O_8+δ

Solid solutions of Bi₂Sr₂Ca_1-xY_xCu₂O_8+δ, Bi₂Sr_2-xLa_xYCu₂O_8+δ and Bi₂Sr₂Y_1-xCe_xCu₂O_8+δ have been investigated. In the system Bi₂Sr₂Ca_1-xY_xCu₂O_8+δ the most significant feature is a drop in the length of the c axis from 3.08 nm for the x < 0.25 to 3.02 nm for x > 0.35. With increasing amount of Ce the length of the c axis increases up to 3.08 nm. This is due to the substitution of Sr on the Ca site. In the system Bi₂Sr_2-xLa_xYCu₂O_8+δ increase of La leads to Sr partially occupying the Ca site. The Y rich material shows a significant difference between the a and the b axis. Incorporation of 20% of Y does not lead to a significant drop in T_c. When the surplus of charge due to the substitution by cations with a higher valency is more than +0.30 the material is not superconducting anymore. Often a composition range in x is obtained, with a width of at least 0.2. The observed change in the c axis and the superconducting properties is explained with a model with extra oxygen in the BiO layers. With mainly Sr on the Sr site the extra amount of oxygen seems to be restricted to 0.25 per BiO unit.