Tb oxidation state and hybridization in ${\mathrm{Y}}_{0.9}$${\mathrm{Tb}}_{0.1}$${\mathrm{Ba}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{7\mathrm{-}\mathrm{\delta }}$ (δ=0.02, 0.84): A magnetic-susceptibility and x-ray-absorption study

A variety of experimental techniques are employed to probe the electronic state of Tb in the supeconductor ${\mathrm{Y}}_{0.9}$ ${\mathrm{Tb}}_{0.1}$ ${\mathrm{Ba}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_{7\mathrm{-}\mathrm{\delta }}$. An analysis of neutron-diffraction data reveals that Tb is incorporated into the sample, replacing Y. There are no anomalies observed in the lattice constants or the planar oxygen thermal parameters determined from the neutron data, but the low concentration of Tb prohibits the determination of Tb oxidation state from these data alone. A comparison of experimentally determined magnetic susceptibilities with those calculated from single-ion, crystal-field models assuming either ${\mathrm{Tb}}^{3+}$ or ${\mathrm{Tb}}^{4+}$ shows a close agreement between the ${\mathrm{Tb}}^{3+}$ model and experiment. The presence of ${\mathrm{Tb}}^{3+}$ is confirmed by x-ray absorption near-edge spectroscopy. ${\mathit{L}}_3$-edge data are used to argue that the Tb ions are not significantly hybridized in ${\mathrm{Y}}_{0.9}$ ${\mathrm{Tb}}_{0.1}$ ${\mathrm{Ba}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_{7\mathrm{-}\mathrm{\delta }}$.