Size effect on the ferroelectric phase transition in SrBi2Ta2O9 nanoparticles

We report the size effect on the ferroelectric phase transition in ${\mathrm{SrBi}}_2{\mathrm{Ta}}_2{\mathrm{O}}_9$ nanoparticles. Samples with particle sizes between 11 and 71 nm were prepared by a room-temperature mechanical activation process followed by postannealing at different temperatures. The size of the particles was determined by x-ray diffraction with the aid of Scherrer’s equation. The ferroelectric phase transition in both ${\mathrm{SrBi}}_2{\mathrm{Ta}}_2{\mathrm{O}}_9$ nanoparticles and bulk sample were investigated by in situ Raman scattering. The results show that the transition temperature ${\mathrm{(T}}_c)$ decreases from its bulk value (605 K) as the size decreases. The size dependence of $T_c$ can be described as $T_c\text{=605−1150/(D−2.1)}$ (K), where $D$ (nm) is the particle size. A critical size of 2.6 nm, below which ferroelectricity disappears, was obtained from this empirical expression.