Oxygen adsorption properties of YBaCo4O7-type compounds

The oxygen adsorption and desorption of newly found compounds RBaCo4O7 (R = Y, Dy-Lu, In) were investigated by thermogravimetry (TG) in the temperature range from room temperature to 1100 degrees C. The influence of Co replaced by Zn and Fe on the oxygen diffusion properties of YBaCo4O7 was also studied. TG results showed clearly that all RBaCo(4)O7 compounds basically experience two oxygen adsorption and desorption processes in the temperature range 20 similar to 1100 degrees C in oxygen flow. One happens at about 200 similar to 450 degrees C and the another happens at about 660 similar to 1050 degrees C. The differences between the resulting states by adsorbing oxygen at lower and high temperature were discussed based on the X-ray diffiraction (XRD) patterns and TG data. We showed evidence that the oxygen adsorption at the lower temperature has a small activation energy, while the oxygen adsorption at the higher temperature has a large activation energy. The oxygen adsorbed at high temperature will destroy the RBaCo4O7 structure. Zn substituting in the YBaCo4-xZnxO7 influences the oxygen diffusion behavior prominently, the amount of oxygen adsorbed becomes increasingly weak with the increase of Zn content and disappears completely for the samples with x >= 2.0. However, replacement of Co by Fe has little effect on the oxygen absorption process. (c) 2006 Elsevier B.V. All rights reserved.