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

We have investigated the synthesis, crystal structure, resistivity and magn etic measurements of phases in the Ru(Sr,Gd)(2)(Gd,Sr)Cu2O8-delta (Ru-1212) and Ru(Sr,Eu)(2)(Eu,Ce)(2)Cu2O10-delta (Ru-1222) systems. Rietveld refinem ent of the structure was carried out. The refined compositions before and a fter oxygen treatment are Ru-1.000(l)(Sr1-y- Gd-y)(2)(Gdl-zSrz)Cu2O8 (y= 0. 03(1), z = 0.19(1)) (Ru-1212; T-c< 4.2 K) and (Rul-xCux)(Srl-yGdy)(2)(Gdl-z Srz)Cu2O8 (x = 0.05 (1), y = 0.02(1), z = 0.16(1)) (Ru,Cu-1212; Tc< 4.2 K) and (Rul-xCux)(Srl-yEuy)(2)(Eul-zCez)Cu2O10 (x = 0.04(2), y = 0.09(2), z = 0.44(3)) (Ru,Cu-1222; T-c< 4.2 K) and (Rul-xCex)(Srl-yEuy)(2)(Eul-zCez)(2)C u2O10 (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 octahedrall y coordinated as the (Ru5+O6)(7-) species. The formal charge of Cu (FC Cu) calculated from the electroneutrality condition of refined phase compositio n increases after oxygen treatment and achieves an optimal value (FC Cu <si milar to> 2.14) for the superconducting (Ru,Ce)-1222 phase (t = 1000 degree sC, p = 1 GPa, tau= 72 h). (C) 2001 Elsevier Science B.V. All rights reserv ed.