Crystal structure and superconductivity ofLaBaCu2O5+x

Three compounds have been found in the La-Ba-Cu-O system, $\mathrm{LaBa}{\mathrm{Cu}}_2{\mathrm{O}}_{5+x}$, ${\mathrm{La}}_2$BaC${\mathrm{U}}_2$ ${\mathrm{O}}_6$, and ${\mathrm{La}}_{2-x}{\mathrm{Ba}}_x\mathrm{Cu}{\mathrm{O}}_4$ ($x\le 0.1$). Single-phase samples of $\mathrm{LaBa}{\mathrm{Cu}}_2{\mathrm{O}}_{5+x}$ are studied by powder x-ray diffraction and electron microscopy. Its crystallographic structure is a tetragonal superlattice based on a cubic-perovskite subcell with $a=3.917\mathrm{}$ Å and triple periods. The superconductivity transition in this compound occurs around 15 K.