Structural Characterization of Nonstoichiometry in CuxBa2Ca3Cu4Oy Superconductor

The crystal structures of three CuxBa2Ca3Cu4Oy compounds with x = 0. 62, 0. 68 and 0. 73 and oxycarbonate (Cu,C)Ba2Ca3Cu4Oy have been precisely investigated using intensity data collected on the single-crystal X-ray four-circle diffractometer. The Cu-site occupancy x in the deficient Cu(l)02 sheet between two BaO layers increases from 0. 62 to 0. 73 together with decreasing the c-axis length in CuxBa2Ca3Cu4Oy. The size of block-layer unit decreases with decreasing the c-axis length from 8. 421(4) A for x = 0. 62 to 8. 373(3) A for x = 0. 73, respectively, while the size of the infinite-layer unit is maintained unchanged. The lattice parameters and the Cu/C ratio of (Cu,C)Ba2Ca3Cu4Oy are consistent with those in the previous report.