Abstract
Structured, magnetic, calorimetric and transport results are reported for the new orthorhombic Cu-1212 R(Ba <sub>2-x</sub> R′ <sub>x</sub> )Cu <sub>3</sub> O <sub>7+y</sub> cuprates (R, R′ = La, Pr, Nd; 0.65 < x < 1). Powder X-ray Rietveld refinement analysis for oxygenated R <sub>1.7</sub> Ba <sub>1.3</sub> Cu <sub>3</sub> O <sub>7+y</sub> (R = La, Pr, Nd; y ∼ 0.3) indicates that the new orthorhombic O(II)-phase with space group Cmmm and lattice parameters a <sub>0</sub> < b< ∼ 0.55 nm, c ∼ 1.16 nm is very similar to the Bi-2212 structure except that (BiO) <sub>2</sub> bi-layer is replaced by a single CuO <sub>1+y</sub> plane. For the oxygenated Pr(Ba <sub>2-x</sub> R <sub>x</sub> )Cu <sub>3</sub> O <sub>7+y</sub> O(II)-phase cuprates (R = La, Pr; y > 0.2), anomalous Pr ordering temperature T <sub>N</sub> (Pr) decreases sharply from 18 K for O(I)-phase PrBa <sub>2</sub> Cu <sub>3</sub> ,O <sub>7</sub> (space group Pmmm, a <sub>o</sub> < b <sub>o</sub> ∼ 0.39 nm and c ∼1.17 nm), to 5.5 K for Pr(Ba <sub>1.3</sub> Pr <sub>0.7</sub> )Cu <sub>3</sub> O <sub>7.25</sub> and 6 K for Pr(Ba <sub>1.3</sub> La <sub>0.7</sub> )Cu <sub>3</sub> O <sub>7.29</sub> . The dramatically decreasing T <sub>N</sub> (Pr) is closely related with longer Pr-O bond length in the O(II)-phase which effectively decreases Pr 4f-O 2p <sub>π</sub> orbital hybridization. No superconductivity was observed for these new insulating cuprates. © 2000 Elsevier Science R V. All rights reserved.