(Ba0.7Sr0.3)TiO3 (BST) thin films doped with La, Nb, and Mg ions were prepared by metal-organic deposition method (MOD) on Pt/Ti/SiO2/Si substrates. An intermediate phase formed under an annealing temperature of 550-650 degreesC, and disappeared at higher temperatures during the formation of BST. The intermediate phase was analyzed by X-ray diffraction (XRD) analysis, transmission electron microscopy (TEM), Fourier transform-infrared spectroscopy (FT-IR) and Raman spectra and found to be an oxycarbonate with a chemical formula of (Ba,Sr)(2)TiO5CO3. The stability of this intermediate phase increased with the addition of dopants, irrespective of doping types. It is proposed that distortion of crystal structure, physical constraint in the two-dimensions and small grain size favor the existence of poor crystallized (Ba,Sr)(2)Ti2O5CO3. (C) 2002 Elsevier Science B.V. All rights reserved.