Transient Homologous Structures in NonstoichiometricYBa2Cu3O7−x

We propose that a homologous series of transient ordered structures may form during the spinodal decomposition of the nonstoichiometric superconducting oxide $\mathrm{Y}{\mathrm{Ba}}_2{\mathrm{Cu}}_3{\mathrm{O}}_{7-x}$. These transient phases provide the best kinetic accommodation of the local vacancy concentration. Their structures should be similar to those of the ${\mathrm{Ti}}_m{\mathrm{O}}_{2m-1}$ and ${\mathrm{Mo}}_m{\mathrm{O}}_{2m-1}$ series of Magneli phases. The transient phases in the oxide have the stoichiometry $\mathrm{Y}{\mathrm{Ba}}_2{\mathrm{Cu}}_3{\mathrm{O}}_{\frac{7-n}{\mathrm{}(2n+1)\mathrm{}}}$, where $n$ is an integer. The structure of the $n$ phase has a diffraction maximum at the point ($\frac{n}{\mathrm{}(2n+1)\mathrm{} 00}$). Examples have been experimentally observed.