Nowadays, an increasing number of experimental and theoretical studies deal with the question of reduction of size in ferroelectric and related systems, motivated by numerous applications already existing or potential in microelectronic. In this framework ferroelectric compounds are considered in the form of thin films, or more generally in the form of nanostructures such as superlattices etc., but also in the form of nanoparticles or nanostructured ceramics (including for instance nanocomposites). These latter fields are particularly important for multilayer ceramic capacitors and actuators.
SrTiO3 (STO) is a textbook example of quantum paraelectric materialswith very high value of the dielectric constant at low temperature. It exhibits an anti-ferrodistortive cubic (Pm-3m) to tetragonal (I4mcm) phase transition at Ta = 105 K . In bulk material, its primary (rotation angle of the TiO6 octahedra) and secondary (spontaneous strain c/a-1) order parameters are linearly coupled with 2 c/a-1. In STO ceramics, a core-shell structure was assumed to interpret the behavior of the low-temperature permittivity, with probably a static polarization in the shell and large stress fields affecting the core grain .
In this talk the grain size effect on the structural and vibrational properties of strontium titanate (SrTiO3) ceramics, using different experimental techniques such as X-ray diffraction, neutron diffraction, Raman and hyper-Raman (HRS) spectroscopy, will be discussed [3-6].