New family of layered copper oxide compounds with ordered cations: Prospective high-temperature superconductors

A new family of layered copper oxide compounds with ordered rare-earth cations has been designed and synthesized. The compounds are partially Sr-substituted $L_1$ ${\mathrm{La}}_1$ ${\mathrm{CuO}}_4$, where L(=Sm, Eu, and Gd) and La ions are sequentially ordered thus: [-L-L-La-La-]. As a result, the Cu-O network of the new compound forms single-layer sheets of ${\mathrm{CuO}}_5$ pyramids, which is essentially the same as in the 30-K superconductor (Nd,Ce,Sr${)}_2$ ${\mathrm{CuO}}_4$ discovered recently by Akimitsu et al. Extensive oxygen annealing makes the new compounds metallic, indicating their possibility as a new class of high-temperature superconductors with hole-type charge carriers.