Gel structure, gel decomposition and phase formation mechanisms in the aqueous solution-gel route to lanthanum substituted bismuth titanate

Phase pure lanthanum substituted bismuth titanate was prepared by an aqueous solution-gel route. In this route aqueous precursors are synthesized by stabilization of the metal ion in the aqueous medium through complexation with strong electron donor ligands. The chemical structure of metal-less, monometal ion as well as multimetal ion precursorgels was studied by means of FTIR and FT-Raman spectrometry. The precursors were transformed to phase pure oxides by heat treatment in an appropriate dynamic atmosphere. The decomposition reactions of the gels were studied by means of several hyphenated thermal analysis techniques (thermogravimetry coupled on-line to FUR or MS (TGA-MS, TGA-FTIR) and high temperature-diffuse reflectance infrared spectrometry by fourier transform (HT-DRIFT)) and reactions are proposed. The phase formation was studied by means of X-ray diffraction. Phase segregation during gel calcination was correlated to the oxygen partial pressure. An explanation for this phenomenon was suggested based on thermal analysis and on SEM and TEM studies.