Substitution of "CO3" groups for copper in YBCO: the oxycarbonates YnBa2nCu3n-1CO3O7n-3

Abstract

The substitution of carbonate groups for copper in the oxide YBa[sub 2]Cu[sub 3]O[sub 7] has been studied by HREM. Two new phases, members of the series Y[sub n]Ba[sub 2n]Cu[sub 3n[minus]1]CO[sub 3]O[sub 7n[minus]3] have been evidenced for n = 2 and 3, respectively. The corresponding superstructures [open quotes]2a[sub 123] [times] b[sub 123] [times] 2c[sub 123][close quotes] and [open quotes]3a[sub 123] [times] b[sub 123] [times] 2c[sub 123][close quotes] correspond to the ordered substitution of one row of CO[sub 3] groups for one row of CuO[sub 4] groups out of two and three, respectively. The existence of 90[degrees]-oriented domains and of chemical twinning is also shown and the role of CO[sub 3] groups at the domain boundaries discussed. 7 refs., 5 figs.