Layered Lead Cuprates: Promising high‐ T c superconductors

Layered lead cuprates belong to the structural family [ACuO 3−α ] m (A′O) n which are characterized by the intergrowth of oxygen deficient perovskite layers and rock salt type layers. Located in the rock salt type layers, lead sometimes exhibits the divalent state and sometimes the tetravalent state. A feature of some of these oxides is the disproportionation of Cu(II) to Cu(III) and Cu(I), which up to now has only been observed in YBa 2 Cu 3 O 7−δ . The superconducting properties of these phases are very promising with the T c ranging from 40 to 100 K, but the materials also show broad resistive transitions due to oxygen inhomogeneity. The dramatic influence of the method of synthesis on these properties is studied. The issue of the incommensurability of several of these structures is discussed.