Crystal structure of Ru(Sr,Gd)2(Gd,Sr)Cu2O8 and Ru(Sr,Eu)2(Eu,Ce)2Cu2O10 phases

Authors investigated the synthesis, crystal structure, resistivity and magnetic measurements of phases in the Ru(Sr,Gd)2(Gd,Sr)Cu2O8-d (Ru-1212) and Ru(Sr,Eu)2(Eu,Ce)2Cu2O10-d (Ru-1222) systems. Rietveld refinement of the structure was carried out. The refined compositions before and after O treatment are Ru1.00(1)(Sr1-yGdy)2(Gd1-zSrz)Cu2O8 (y=0.03(1), z=0.19(1)) (Ru-1212; Tc < 4.2 K) and (Ru1-xCux)(Sr1-yGdy)2(Gd1-zSrz)Cu2O8 (x=0.05(1), y=0.02(1), z=0.16(1)) (Ru,Cu-1212; Tc < 4.2 K) and (Ru1-xCux)(Sr1-yEuy)2(Eu1-zCez)Cu2O10 (x=0.04(2), y=0.09(2), z=0.44(3)) (Ru,Cu-1222; Tc < 4.2 K) and (Ru1-xCex)(Sr1-yEuy)2(Eu1-zCez)2Cu2O10 (x=0.08(2), y=0.15(2), z=0.25(3)) (Ru,Ce-1222; Tc(onset)=40 K, Tc(zero)=12 K). Ru atoms in these structures are octahedrally coordinated as the (Ru5+O6)7- species. The formal charge of Cu (FC Cu) calculated from the electroneutrality condition of refined phase composition increases after O treatment and achieves an optimal value (FC Cu2.14) for the superconducting (Ru,Ce)-1222 phase (t=1000 C, p=1 GPa, t=72 h). 15 refs.