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

Abstract We have investigated the synthesis, crystal structure, resistivity and magnetic measurements of phases in the Ru(Sr,Gd) 2 (Gd,Sr)Cu 2 O 8− δ (Ru-1212) and Ru(Sr,Eu) 2 (Eu,Ce) 2 Cu 2 O 10− δ (Ru-1222) systems. Rietveld refinement of the structure was carried out. The refined compositions before and after oxygen treatment are Ru 1.00(1) (Sr 1− y Gd y ) 2 (Gd 1− z Sr z )Cu 2 O 8 ( y =0.03(1), z =0.19(1)) (Ru-1212; T c 1− x Cu x )(Sr 1− y Gd y ) 2 (Gd 1− z Sr z )Cu 2 O 8 ( x =0.05(1), y =0.02(1), z =0.16(1)) (Ru,Cu-1212; T c 1− x Cu x )(Sr 1− y Eu y ) 2 (Eu 1− z Ce z )Cu 2 O 10 ( x =0.04(2), y =0.09(2), z =0.44(3)) (Ru,Cu-1222; T c 1− x Ce x )(Sr 1− y Eu y ) 2 (Eu 1− z Ce z ) 2 Cu 2 O 10 ( x =0.08(2), y =0.15(2), z =0.25(3)) (Ru,Ce-1222; T c(onset) =40 K, T c(zero) =12 K). Ruthenium atoms in these structures are octahedrally coordinated as the (Ru 5+ O 6 ) 7− species. The formal charge of Cu (FC Cu) calculated from the electroneutrality condition of refined phase composition increases after oxygen treatment and achieves an optimal value (FC Cu∼2.14) for the superconducting (Ru,Ce)-1222 phase ( t =1000°C, p =1 GPa, τ =72 h).