Dynamical information for Fe-doped ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_7$ superconducting oxides obtained from high-temperature Mössbauer studies

In situ high-temperature ${}_{}{}^{57}{}_{}{}^{}\mathrm{Fe}$ Mössbauer measurements were performed on samples of ${\mathrm{YBa}}_2$(${\mathrm{Cu}}_{1\mathrm{-}\mathit{x}}$ ${\mathrm{Fe}}_{\mathit{x}}$ ${)}_3$ ${\mathrm{O}}_{7\mathrm{-}\mathrm{\delta }}$, in pure oxygen or in air, both at a pressure of about 1 atm. Three samples were studied with x=0.005 and 0.010, respectively, in the temperature range from 295 to 640 K. As in previously published papers, the fitted quadrupole doublets were associated to different oxygen configurations around the Fe ions on the Cu(1) chain site, whose temperature-dependent behavior can be summarized by (i) the f factor for the different configurations are very similar; (ii) the effective Debye temperature (≃350 K) is rather insensitive to the Fe content and oxygen coordination; (iii) the electronic configuration of Fe is very stable up to 320 °C; and (iv) the quadrupole splitting q(T) can be well described within the picture used for noncubic metals. Finally a partial change from doublet A to B induced by temperatures is observed. This change is completely or partially reversible, depending on the sample.