ESR experiments and spectra simulations in ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{7\mathrm{-}\mathrm{x}}$, ${\mathrm{Y}}_2$${\mathrm{BaCuO}}_5$, and ${\mathrm{BaCuO}}_{2+\mathrm{x}}$

Room-temperature X- and Q-band ESR spectra of the high-$T_c$ superconductor ${\mathrm{YBa}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_{7\mathrm{-}\mathrm{x}}$ and the semiconductors ${\mathrm{Y}}_2$ ${\mathrm{BaCuO}}_5$ and ${\mathrm{BaCuO}}_{2+\mathrm{x}}$ are studied experimentally and theoretically by measuring, calculating, and fitting the powder spectra corresponding to an anisotropic Zeeman Hamiltonian for ${\mathrm{Cu}}^{2+}$ in orthorhombic and tetragonal local symmetries. ESR and x-ray studies in their correspoinding oxygen-deficient stoichiometries, obtained by heat treatment under vacuum, were also done. Our results support those of Bowden et al. and Vier et al. in R${\mathrm{Ba}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_{7\mathrm{-}\mathrm{x}}$ (R=Y, Eu), indicating that the Cu(1) and Cu(2) atoms in the pure ${\mathrm{YBa}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_{7\mathrm{-}\mathrm{x}}$ phase are not ESR active and the small resonance observed in these compounds comes from other residual phases. The purest ${\mathrm{YBa}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_{7\mathrm{-}\mathrm{x}}$samples that we were able to prepare still have 0.1–0.5 % mass fraction of other residual copper compounds which are responsible for the observed resonance.