Crystal structure of In-based cuprates: (In,Cu)S2YCu2O6+delta (1212), (In,Cu)(Sr,Ho)(2)(Ho,Ce4+)(2)Cu2O8+delta (1222)

The indium-based cuprates with perovskite-like structure (In:Cu)Sr2YCu2O6+d elta and (In,Cu)(Sr, Ho)(2)(Ho,Ce)(2) Cu2O8+delta, belonging to the homolog ous series (In,Cu)(Sr,Ln)(2)(Ln, Sr)(k-1)CukO2k+2+delta with k = 1 (In,Cu-1 212) and (In, Cu)(Sr, Ln)(2)(Ln, Ce)(k+1)Cu2O2k+6+delta with k = 1 (In,Cu-1 222) have been obtained. Their structure has been refined at room temperatu re using X-ray powder diffraction data. The samples with the nominal compos itions (In0.5Cu0.5)Sr-2 YCu2Ox and (In2/3Cu1/3) (Ho1/3Ce2/3)(3) Sr2Cu2Ox ap peared to contain phases with lattice parameters a = 3.8163(1), c = 11.9785 (6) Angstrom (In,Cu-1212, sp. gr. P4/mmm) and a = 3.8272(0), c = 29.0774(3) Angstrom (In,Cu-1222, sp. gr. 14/mmm), respectively. Rietveld refinements were carried out. The real composition of these phases may be written as (I n0.89Cu0.11(3))Sr2YCu2O6.98(4) (In,Cu-1212) and (In0.98Cu0.02(1))(Sr1.25Ho0 .75(2))(Ho1.89Ce(0.11(s))(4+)) Cu2.00O9.00 (In,Cu-1222). The refined compos ition of these phases after oxygen treatment was formal to be (In0.82Ce0.11 (5)4+)Sr2YCu2O7.00, (In,Cu-.- 1212) and (In0.87Cu0.13(1)) (Sr1.52Ho0.48(2)) (HO1.95Ce0.05(3)4+)Cu2O9.00 (In,Cu*-1222). The Cu formal charge (FC Cu) in the (In,Cu)-1212, calculated from electroneutrality condition of the refine d phase composition, was almost the same as before (FC Cu similar to 2.04) and after (FC Cu similar to 2.09) the oxygen treatment (underdoped phase). On the contrary, the FC Cu for the (In,Cu)-1222 increased after oxygen anne aling (from -2.08 to -2.30) (overdoped phase). The non-optimal values of th e Cu formal charge could be a possible reason for the absence of supercondu ctivity in these samples. (C) 2001 Elsevier Science B.V. All rights reserve d.