Structural changes upon electrochemical insertion of lithium into the Bi2Sr2CaCuO8+y high Tc superconductor

The insertion compound LixBi2Sr2CaCu2O8+y (x≤2) was prepared by electrochemical insertion of lithium into Bi2Sr2CaCu2O8+y pellets at room temperature in galvanic cells. 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. The lithiated product was analyzed by crystallographic and chemical measurements. The results show that insertion of Li ions is accompanied by an expansion of the interlayer spacing between Bi-O planes and a small increase in the a- and b-cell parameters. This change is consistent with some, but not all, of the donated electrons entering the Cu-O planes, with a corresponding reduction in hole concentration. At higher levels of Li content, a substantial breakdown of the lattice is observed