Internal friction study of the phase transition inGdBaCo2O5+δbulk materials

Abstract

The internal friction and shear modulus at low frequency together with the electrical and magnetic properties have been measured for an ordered oxygen-deficient perovskite ${\mathrm{GdBaCo}}_{2}{\mathrm{O}}_{5+\ensuremath{\delta}}$ ceramics ($\ensuremath{\delta}=0.005$, 0.499, and 0.515). For $\ensuremath{\delta}=0.005$, an internal friction peak at $225\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ and the corresponding softening of shear modulus were observed, showing the existence of lattice distortion. This lattice distortion indicates the presence of charge ordering, which conforms to the slight upturn on the electrical resistivity curve. The anomalies in shear modulus and the internal friction peak at about ${T}_{\mathrm{CO}}$ were suggested to be correlated with the structure change caused by the Jahn-Teller effect of ${\mathrm{Co}}^{3+}$ (HS state) located in square pyramidal sites. For $\ensuremath{\delta}=0.499$ and 0.515, a large softening of shear modulus accompanied by an increasing of internal friction was observed at low temperature, which is related to the antiferromagnetic-ferromagnetic transition. And the internal friction peak with the features of phase transition at about $350\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ can be ascribed the metal-insulator transition. At high temperature, the relaxation internal friction peak accompanied by the corresponding decrease of shear modulus originates from the oxygen hopping in $[{\mathrm{GdO}}_{\ensuremath{\delta}}]$ planes.