PRESSURE-DEPENDENCE OF THE SUPERCONDUCTING TRANSITION-TEMPERATURE ANDTHE HALL-COEFFICIENT IN IBI2.2SR1.8CACU2O8-CRYSTALS(Y SINGLE)

The superconducting transition temperature T(c) and the Hall coefficie nt have been measured on IBi2.2Sr1.8CaCu2O8+y single crystals under hy drostatic pressure. The T(c) linearly decreases at the rate dT(c)/dP a pproximately -3.5 K/GPa, indicating the facts that the charge transfer occurs between intercalated iodine atoms and CuO2 layers, and the hol e concentration situates in the overdoped region. The facts have been further identified by our Hall-coefficient measurements at ambient pre ssure, showing an increase of the hole concentration after intercalati on. The number of holes transferred from intercalated iodine atoms was calculated to be 0.3 per iodine atom. The pressure derivative of the Hall coefficient is -0.39 X 10(-3) cm3 C-1 GPa-1, which is approximate ly twice as large as the value on the pristine crystal, indicating the valence change of the intercalated iodine under pressure.