The superstructure and superconductivity of Ru1222 based RuSr2Gd2-x-yYyCexCu2O10-delta compounds

For the first time, the local structure and physical properties of Ru1222 based compounds (RuSr2Gd1.4Ce0.6Cu2O10-delta and RuSr(2)Gd(1.8-x)Y(0.2)CexCu(2)O(10) (x = 0.90-0.55)) have been investigated and analyzed together on the very same compounds. The Ru1222 superstructure was confirmed by TEM at a local scale and was suggested to have an orthorhombic symmetry with space group Aba2 and lattice parameters a(s) similar or equal to root 2a, b(s) similar or equal to root 2a and c(s) = c. This new Ru1222 superstructure distortion from tetragonal symmetry is proposed to have a positive correlation with the superconductivity variation of these compounds. The more the distortion towards orthorhombic symmetry, the higher the critical superconducting temperature these compounds can achieve. The T-c(0) of RuSr2Gd1.8-xY0.2CexCu2O10-delta (x = 0.85-0.55) increases monotonically from 4 to 16 K when x decreases from 0.85 to 0.70, then RuSr2Gd2Cu2O8 defects emerge and the T-c decreases with decreasing x. Ru1212 defects are observed to intergrow epitaxially with the Ru1222 structure as lamellas along the c-axis in RuSr2Gd1.4Ce0.6Cu2O10-delta. Although Ru1212 is a superconductor, the intergrowth severely restrains its superconductivity.