Electrochemical lithium intercalation into the Bi-2212 phase

Effects of lithium intercalation into the Bi-2212 phase on its structural and superconducting properties were studied using monophasic samples of Bi₂Sr_1.5Ca_1.5Cu₂O_z lithiated through an electrochemical method at a constant applied voltage at room temperature. The amount of doped lithium was found by ICP analysis to be in the range of 0 ≤ y ≤ 0.37 for Li_yBi₂Sr_1.5Ca_1.5Cu₂O _z depending upon experimental conditions. However, the oxygen content determined by coulometric titration remained almost unchanged after the lithiation. The electrochemical lithium intercalation led to a very interesting change in T_c, though the original tetragonal structure and oxygen content remained essentially the same: T_c first increased rapidly as y increased, reached a maximum of 94 K, and then decreased to zero. The drastic T_c change is ascribed to a decrease in the hole concentration. Thus, the electrochemical lithium-doping provides us with a great advantage of easily controlling T_c at room temperature by changing electrochemical conditions while keeping the original crystal symmetry.