HOLE CONCENTRATION AND TC IN BI2SR2CACU2O8+DELTA

A relation between Tc and the density of holes per CuO2 plane is presented for Bi2Sr2CaCu2O8+δ. The hole concentration was varied by replacing calcium in Bi2Sr2CaCu2O8+δ partly by yttrium, and by changing the oxygen content of samples of Bi2Sr2CaCu2O8+δ, Bi2Sr1.5Ca1.5Cu2O8+δ and Bi2Sr2Ca0.9Y0.1Cu2O8+δ. The oxygen content of samples of Bi1.7Pb0.3Sr2Ca0.7Y0.3Cu2O8+δ could not be changed, which indicates stabilization of the crystal structure as a result of bismuth being replaced by lead. The hole concentration was derived from determinations of the oxidizing power. The phase diagram of Bi2Sr2CaCu2O8+δ shows an unambiguous relation between Tc and the density of holes per CuO2 plane. Superconductivity does not occur at doping levels up to about 0.07 holes/Cu per CuO2 plane. With increasing hole content Tc shows a broad maximum of about 90 K at about 0.2 holes/Cu per CuO2 plane. At higher doping levels Tc starts to decrease. The phase diagram presented is comparable to that reported for YBa2Cu3O6+y and La2-xSrxCuO4, indicating that these phase diagrams are a universal property of p-type high-Tc cuprate superconductors. © 1990.