Systematic Mössbauer study of YBa₂Cu_3−x Fe _x O_δ and PrBa₂Cu_3−x Fe _x O_δ as a function of temperature

Abstract

We study the similitudes and differences between YBa₂Cu_3−x Fe _x O_δ and PrBa₂Cu_3−x Fe _x O_δ systems, using Mössbauer spectroscopy. Both systems, withz=0.04, were studied at several temperatures. The spectra of PrBa₂Cu_3−x Fe _x O_δ showed four asymmetric quadrupole doublets with apparently different line widths, which were fitted with four symmetric superimposed quadrupole doublets with the same line width, but assuming a small (∼4–6 kOe) residual magnetic field in the Fe sites, which are mainly the Cu(1) sites of the 1–2–3 structure. On the other hand, the PrBa₂Cu_3−x Fe _x O_δ spectra showed only three asymmetric quadrupole doublets which can be fitted with three superimposed symmetric doublets and a residual magnetic field. In this case, the Fe atoms also occupy the Cu(1) sites of the 1–2–3 structure. The temperature variations of the Mössbauer spectra and their parameters seem to indicate that, in the Pr-system, a structural change takes place between 12 K and 40 K.