In the abstract by Shiratori et al., 2007, we can read "BaTiO3 powders with various crystallite sizes, which were prepared through microemulsion-mediated synthesis, were thoroughly studied by Raman spectroscopy. Clear evidence for the presence of the tetragonal phase was found for ultrafine powders with an average crystallite size above 30 nm. … In particles as fine as 100 nm, the short mean free path of phonons, mainly due to internal pressure, causes decoupling of the coupled A1(TO) phonons and a diffuse phase transition behaviour (TC = 115°C). Coupled A1(TO) phonons, which give a spectral dip at around 180 cm -1 and a lesser extent of diffuseness, were revealed for powders consisting of particles as large as 0.17 µm (TC = 123°C). Further coarsening upon annealing induced the formation of aggregates, resulting in the shift of phase transition points to higher temperatures for the rhombohedral to orthorhombic and the orthorhombic to tetragonal transitions and to lower temperatures for the tetragonal to cubic transition, respectively" . The researchers investigated the Raman spectra by means of a Jobin-Yvon T64000 Raman spectrometer and a Spectrum One CCD detection system. The powder samples were excited with laser radiation at 514.5 nm.