Electrical conductivity, internal friction techniques and dilatometer have been used to investigate the oxygen relaxation, phase transition and thermal expansion behavior of GdBaCo2O5+delta. The main electronic charge carriers in GdBaCo2O5+delta are electronic holes, which could be assigned to the formation of Co4+. The oxygen exchange kinetics intensely depends on oxygen partial pressure and is also closely related to temperature. Both electrical conductivity and internal friction give rise to an abnormal at about 75 degrees C. which are related to the insulator-metal transition occurring in GdBaCo2O5+delta. One large relaxation internal friction peak, due to the motion of oxygen within Gd-O plane, is also found in the oxide. The average thermal expansion coefficient (TEC) of GdBaCo2O5+delta is about 21.4 x 10(-6) K-1 between 500 degrees C and 900 degrees C. (C) 2010 Elsevier B.V. All rights reserved.