Study of the oxygen desorption from GdBa1−xSrxCo2O5+δ (x = 0, 0.25, 0.5 and 1): Effect of the Sr-content on the oxidation state of cobalt ions

In this work, the crystal structure at room temperature of GdBa1−xSrxCo2O5+δ (x = 0.0, 0.25, 0.5 and 1.0), prepared by a modified sol-gel route, has been investigated. In addition, total conductivity was determined by the Van der Pauw method and the existence of structural phase transitions has been investigated by differential scanning calorimetry. The latter show us that reported structural phase transitions at ∼75 °C and ∼470 °C for GdBaCo2O5+δ are not revealed when Ba2+ is partially substituted by Sr2+. This can be explained regarding a complete stabilization of the high temperature tetragonal symmetry at room temperature. Moreover, the effect of the increase of Sr-content on the oxidation state of cobalt ions has been studied by means of the oxygen temperature programmed desorption (O2-TPD) method.