CRYSTAL-STRUCTURE AND SUPERCONDUCTIVITY OF IODINE-INTERCALATED BI2SR2CACU2O8IX (0-LESS-THAN-OR-EQUAL-TO-X-LESS-THAN-OR-EQUAL-TO-1) - DEPENDENCE ON THE IODINE CONCENTRATION

Variations of the crystal structure and superconductivity with iodine concentration have been investigated for iodine-intercalated sintered-samples of Bi2Sr2CaCu2O8Ix With 0 less-than-or-equal-to x less-than-or-equal-to 1. It has been found from powder X-ray diffraction that samples with 0.4 less than or similar x less than or similar 0.7 are composed of mixed phases of the host compound Bi2Sr2CaCu2O8 and the stage-1 iodine-intercalation compound Bi2Sr2CaCu2O8I. Diffraction peaks due to the stage-3 structure are vaguely observed for a sample with x=0.24. In spite of the mixed-phase structure for 0.4 less than or similar x less tha or similar 0.7, the superconducting phase is single and of the bulk for all x values. The superconducting transition temperature decreases with increasing x for 0 less-than-or-equal-to x less than or similar 0.4 and is almost constant for 0.4 less than or similar x less-than-or-equal-to 1. A model of the x dependence of the spatial distribution of intercalated iodine atoms is proposed, and the x dependence of T(c) is discussed in relation to that of the charge transfer between iodine atoms and the CuO2 sheets.