Metastability in EuBa2(Cu1-xSnx)3O7-y studied by 119Sn and 151Eu Mössbauer spectroscopy.

Abstract

The metallic oxide compound system $\mathrm{Eu}{\mathrm{Ba}}_{2}{({\mathrm{Cu}}_{1\ensuremath{-}x}{\mathrm{Sn}}_{x})}_{3}{\mathrm{O}}_{7\ensuremath{-}y}$ ($x=0.05, 0.10, 0.20$) was prepared for investigation with $^{151}\mathrm{Eu}$ and $^{119}\mathrm{Sn}$ M\ossbauer spectroscopy. The best fits of the $^{119}\mathrm{Sn}$ M\ossbauer lines reveal at least two different ${\mathrm{Sn}}^{\mathrm{IV}}$ sites. The $^{151}\mathrm{Eu}$ spectra are characteristic for ${\mathrm{Eu}}^{\mathrm{III}}$ state in these compounds. We have found a considerable difference between the shapes of $^{119}\mathrm{Sn}$ M\ossbauer spectra recorded at room temperature and those recorded at the temperature of liquid nitrogen in the case of the sample having the highest tin content. Nevertheless, there is no evidence that this difference has a direct connection with the superconducting behavior. A time-dependent splitting was found in the $^{119}\mathrm{Sn}$ spectra of $\mathrm{Eu}{\mathrm{Ba}}_{2}{({\mathrm{Cu}}_{0.8}{\mathrm{Sn}}_{0.2})}_{3}{\mathrm{O}}_{7\ensuremath{-}y}$ at 78 K. It had a maximum at about 350 h after the synthesis of the sample. Some anomalous temperature dependences were also found in the $^{151}\mathrm{Eu}$ and $^{119}\mathrm{Sn}$ M\ossbauer parameters. Our findings can be associated with different Sn sites as well as low-temperature phase transformation in these oxide compounds.