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

The indium-based cuprates with perovskite-like structure (In:Cu)Sr2YCu2O6+delta and (In,Cu)(Sr, Ho)(2)(Ho,Ce)(2) Cu2O8+delta, belonging to the homologous series (In,Cu)(Sr,Ln)(2)(Ln, Sr)(k-1)CukO2k+2+delta with k = 1 (In,Cu-1212) and (In, Cu)(Sr, Ln)(2)(Ln, Ce)(k+1)Cu2O2k+6+delta with k = 1 (In,Cu-1222) have been obtained. Their structure has been refined at room temperature using X-ray powder diffraction data. The samples with the nominal compositions (In0.5Cu0.5)Sr-2 YCu2Ox and (In2/3Cu1/3) (Ho1/3Ce2/3)(3) Sr2Cu2Ox appeared 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 (In0.89Cu0.11(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 composition 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 refined 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 annealing (from -2.08 to -2.30) (overdoped phase). The non-optimal values of the Cu formal charge could be a possible reason for the absence of superconductivity in these samples. (C) 2001 Elsevier Science B.V. All rights reserved.