A new synthesis method using melting zone technique via the double mirror furnace around 1600 degrees C is used to obtain homogenous brownmillerite compounds Ca1-xSrxFeO2.5+delta in the range 0.3 <= x <= 0.7. These compounds play important role in understanding the mystery of the oxygen diffusion in the perovskite-related oxides. We have successfully solved the miscibility gap problem by synthesizing a good quality of homogenous powder samples of Ca0.5Sr0.5FeO2.5+delta compound. Our result was confirmed by X-rays diffraction, Raman spectroscopy and energy dispersive spectroscopy analysis. Thermal treatment was also applied until 800 degrees C under vacuum to confirm again the homogeneity of powder samples, improve its quality and show that no decomposition or return to form Ca- and Sr-enriched microdomains takes place as a result of phase separation. (C) 2011 Elsevier Ltd. All rights