ELECTROCHEMICAL INSERTION OF LITHIUM INTO THE BI2SR2CACU2O8+Y HIGH-TC SUPERCONDUCTOR

The insertion compound LixBi2Sr2CaCu2O8+y (for lithium contents up to the studied level of x = 2) was prepared by electrochemical insertion of lithium into Bi2Sr2CaCu2O8+y pellets at room temperature in galvanic cells using 1.4 M LiAsF6 in 2Me-THF as electrolyte. The reaction proceeds with retention of the host crystal structure and without the appearance of any new phases. Bulk superconductivity persists but the superconducting fraction appears to be lower in the reacted samples. XRD data show that insertion of Li ions is accompanied by interlayer expansion between Bi-O planes and a small increase in the a and b cell lattice parameters. Li-7 NMR measurements indicate a substantial donation of electrons to the 2212 host lattice. The changes in the a and b lattice parameters and the effect on superconductivity is consistent with some of the donated electrons entering the Cu-O planes and reducing holes in these layers.