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 Bi2Sr1.5Ca1.5Cu2Oz 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 less than or equal to y less than or equal to 0.37 for LiyBi2Sr1.5Ca1.5Cu2Oz 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. (C) 1997 Elsevier Science B.V.