Evolution of high Tc superconductivity of Bi4Sr3−xLaxCa3Cu4Oy upon iodine intercalation

X-ray photoelectron spectroscopic study has been performed to investigate the chemical bonding nature of the iodine intercalated in the lattice of Bi4Sr3−xLaxCa3Cu4Oy, which is strongly correlated with the evolution of superconductivity. X-ray diffraction analyses indicate the formation of first staged iodine intercalates, I2Bi4Sr3−xLaxCa3Cu4Oy, whose superconducting transition temperatures were changed depending upon La substitution rate(x). X-ray photoelectron spectroscopic results exhibit the coexistence of the negative-charged iodine(Iδ−) and the highly oxidized periodate(I+VII) with a different ratio, depending upon the amount of La substitution. The periodate species seems to increase as the increase of the La substitution rate(x), which has led to a conclusion that the excess oxygen may oxidize the intercalated iodine to a highly oxidized periodate. Remarkable depression of periodate concentration during Ar+-ion sputtering underlines that such a highly oxidized species are surely enriched on the surface and/or the grain boundary. Tc evolution upon iodine intercalation will be discussed in view of charge transfer and enhancement of two dimensionality.