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

Abstract

A recipe has been elaborated for preparing barium titanate (BaTiO₃) particles in a nucleation route which is mediated by thermal decomposition of polymeric barium titanium methacrylate. Adjustment of particle size d in the range from 10 nm to 1.5 μm is easily done by choosing appropriate reaction temperatures and tempering atmospheres. In particular, doping with paramagnetic probe ions such as Mn²⁺, Gd³⁺ or Cr³⁺ can be readily accomplished by just adding the corresponding metal acetates to the monomeric precursor. In addition to well approved standard techniques such as scanning electron microscopy (SEM), X-ray diffraction (XRD) and differential scanning calorimetry (DSC), the complementary spectroscopic methods electron paramagnetic resonance (EPR), nuclear magnetic resonance (NMR), X-ray absorption near edge structure (XANES) and FT-Raman are applied to characterise the micro- and nanocrystalline BaTiO₃ powders prepared and to study the phase transition behaviour in dependence on the mean particle size. In contrast to expectation from literature, the dimensionality effect does not manifest itself in a temperature shift of the ferroelectric phase transition but, instead, the tetragonal-to-cubic phase transition is smeared out at reduced particle size and an increasing tetragonal-to-cubic phase admixture is detected.