This paper deals with the chemical expansion measurements and modelling of La0.8Sr0.2Fe0.7CaO3O3-delta. The expansion behavior has been evaluated using a dilatometer and X-ray diffraction over a wide range of temperatures (RT to 1373 K) and oxygen partial pressures (10(-21) to 1 atm). The material stoichiometry evolution with temperature and oxygen partial pressure has been measured using thermogravimetry analysis at different oxygen partial pressure, from 10(-21) to 0.5 atm and from RT to 1473 K. Considering a typical defect model for lanthanum ferrite oxides, chemical expansion depends linearly on the Fe4+ concentration rather than on the oxygen vacancy concentration. A model of chemical expansion as a function of pO(2) and temperature is then proposed. It helps to understand and anticipate the chemical expansion behavior exhibited by this material when used as Ionic Transport Membrane (ITM). (C) 2011 Elsevier B.V. All rights reserved.