The oxygen deficient perovskites, Bi(0.15)Sr(0.85-x)Ae(x)CoO(3-delta), x = 0 and Ae(x) = Ba-0.28, Ca-0.17, were studied with in-situ neutron powder diffraction and combined TGA/DSC in order to investigate their behaviour at elevated temperatures in oxidising conditions. The phase stability of the I4/mmm supercell structure adopted by Bi0.15Sr0.85-xCoO3-delta is shown to be dependent on temperature and the oxygen content of the phase, with three structural events, at T similar to 250,590 and 880 degrees C, detected. The first transition occurs as the perovskite supercell vanishes due to oxygen absorption; the second transition is also associated with oxidation and involves the decomposition of the perovskite phase via an exothermic process to yield a dominant hexagonal phase. Finally, at T similar to 900 degrees C the perovskite phase re-forms. For the Ba and Ca containing materials the decomposition to the hexagonal phase occurs at T similar to 600 degrees C and similar to 650 degrees C respectively. The presence of Ca at the A-site is found to stabilise the I4/mmm supercell structure in the range RT - 650 degrees C. The antiferromagnetic to paramagnetic transitions occur at T-N similar to 250 degrees C, T-N similar to 175 degrees C and T-N similar to 145 degrees C for the samples with Ae(x) = Ba-0.28, x = 0 and Ae(x) = Ca-0.17, respectively. (C) 2010 Elsevier Ltd. All rights reserved.