Nano-crystalline (Ba0.5Sr0.5)Co0.8Fe0.2O3-delta powder has been successfully synthesized by a novel sol-gel thermolysis method using a unique combination of PVA and urea. The decomposition and crystallization behaviour of the gel precursor was studied by TG/DTA analysis. The gel precursor was calcined at different temperatures and the phase evoluation was studied by X-ray diffraction (XRD) analysis. From the result of X-ray diffraction patterns, it is found that a cubic perovskite (Ba0.5Sr0.5)Co0.8Fe0.2O3-delta was formed by calcining the precursor at 450 degrees C for 5 h, but the well-crystalline cubic perovskite (Ba0.5Sr0.5)Co-0.8Fe0.2O3-delta was obtained by calcining the precursor at 650 degrees C for 5 h. Morphological analysis of the powder calcined at various temperatures was done by scanning electron microscope (SEM). Thermogravimetric (TG) results showed the lattice oxygen loss of the product was about similar to 2% in its original weight in the temperature range 40-900 degrees C. Finally, thermal expansion and electrical conductivity of the synthesized material were measured by dilatorneter and four-probe dc method, respectively. (c) 2007 Elsevier B.V. All rights reserved.