Preparation of barium titanate ultrafine powders from a monomeric metallo-organic precursor by combined solid-state polymerisation and pyrolysis

A recipe has been elaborated for preparing barium titanate (BaTiO3) particl es in a nucleation route which is mediated by thermal decomposition of poly meric barium titanium methacrylate. Adjustment of particle size d in the ra nge from 10 nm to 1.5 mu m is easily done by choosing appropriate reaction temperatures and tempering atmospheres. In particular, doping with paramagn etic probe ions such as Mn2+, Gd3+ or Cr3+ can be readily accomplished by j ust adding the corresponding metal acetates to the monomeric precursor. In addition to well approved standard techniques such as scanning electron mic roscopy (SEM), X-ray diffraction (XRD) and differential scanning calorimetr y (DSC), the complementary spectroscopic methods electron paramagnetic reso nance (EPR), nuclear magnetic resonance (NMR), X-ray absorption near edge s tructure (XANES) and FT-Raman are applied to characterise the micro- and na nocrystalline BaTiO3 powders prepared and to study the phase transition beh aviour in dependence on the mean particle size. In contrast to expectation from literature, the dimensionality effect does not manifest itself in a te mperature shift of the ferroelectric phase transition but, instead, the tet ragonal-to-cubic phase transition is smeared out at reduced particle size a nd an increasing tetragonal-to-cubic phase admixture is detected. (C) 1999 Kluwer Academic Publishers.