Grain size dependent phase transition and superparaelectric behavior of ferroelectric BST

In this article, we investigate the grain size dependent phase transition and polarization behavior of ferroelectric Ba_0.9Sr_0.1TiO₃ (BST). Starting with nanocrystalline powders (crystalline size ≈ 22 nm), various grain sizes were obtained in nano–submicron domain (202–745 nm) by regulating the sintering temperatures (T_sin) in the range of 1050–1300° C. All samples were found to possess diffuse phase transition characteristics with frequency independent broad dielectric maxima near transition temperature due to the lattice strain contribution. Dielectric stiffness showed tarnished step-like anomalous behavior in the paraelectric state for T_sin ≥1200°C due to the existence of polar (superparaelectric) nano-regions generated by local polarization by off-centered Ti⁴⁺ ions exhibiting an exceptionally rare delicate polarization hysteresis loop