Crystallographic and physical properties of new orthorhombic Cu-1212 R(Ba2−xR′x)Cu3O7+y system (R, R′La, Pr, Nd; 0.65<x<1)

Structural, magnetic, calorimetric and transport results are reported for the new orthorhombic Cu-1212 R(Ba 2−x R′ x )Cu 3 O 7+y cuprates (R, R′La, Pr, Nd; 0.65 < x < 1). Powder X-ray Rietveld refinement analysis for oxygenated R 1.7 Ba 1.3 Cu 3 O 7+y (RLa, Pr, Nd; y ∼ 0.3) indicates that the new orthorhombic O(II)-phase with space group Cmmm and lattice parameters a 0 < b o ∼ 0.55 nm, c ∼ 1.16 nm is very similar to the Bi-2212 structure except that (BiO) 2 bi-layer is replaced by a single CuO 1+y plane. For the oxygenated Pr(Ba 2−x R x )Cu 3 O 7+y O(II)-phase cuprates (RLa, Pr; y > 0.2), anomalous Pr ordering temperature T N (Pr) decreases sharply from 18 K for O(I)-phase PrBa 2 Cu 3 O 7 (space group Pmmm, a o < b o ∼ 0.39 nm and c ∼ 1.17 nm), to 5.5 K for Pr(Ba 1.3 Pr 0.7 )Cu 3 O 7.25 and 6 K for Pr(Ba 1.3 La 0.7 )Cu 3 O 7.29 . The dramatically decreasing T N (Pr) is closely related with longer PrO bond length in the O(II)-phase which effectively decreases Pr 4f-O 2p π orbital hybridization. No superconductivity was observed for these new insulating cuprates.