Evidence of Kittel type behaviour of the permittivity of a nanostructured high sensitivity piezoelectric

The broadband dielectric properties of high sensitivity piezoelectric 0.36BiScO-0.64PbTiO ceramics with average grain sizes from 1.6 μm down to 26 nm were investigated in the 100-500 K temperature range. The grain size dependence of the dielectric permittivity was analysed within the effective medium approximation. It was found that the generalised core-shell (or brick wall) model correctly explains the size dependence down to the nanoscale. For the first time, the grain bulk and boundary properties were obtained without making any assumptions of values of the parameters or simplifications. Two contributions to dielectric permittivity of the grain bulk are described. The first is the size-independent one, which follows the Curie-Weiss law. The second one is shown to plausibly follow the Kittel's law. This seems to suggest the unexpected persistence of mobile ferroelectric domains at the nanoscale (26 nm grains). Alternative explanations are discussed.This work was supported by project TUMOCS. This project has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie [Grant Agreement No. 645660]. Financial support of the Spanish MINECO (Project Nos. MAT2014-58816-R and MAT2017-88788-R) and the collaboration in the frame of COST MP0904 Action are highly acknowledged.Peer Reviewe