Grain size-independent dielectric and ferroelectric properties of superparaelectric Mn-Nb co-doped barium titanate ceramics

The crystal structure, microstructure, dielectric and ferroelectric properties of polycrystalline BaTi(1-2x)Mn(x)Nb(x)O3 (x = 0.05 and 0.06) with different grain sizes were investigated. All the ceramics exhibited pseudo-cubic symmetry at RT. The ceramics with x = 0.05 and 0.06 exhibited different trends of grain sizes, which were measured as 29.1 and 37.5 & mu;m for the ceramic with x = 0.05 and 2.1, 2.6, 3.2, and 4.9 & mu;m for the ceramic with x = 0.06. The ceramic with x = 0.05 exhibited grain size-dependent electrical properties, possibly because the phase transition temperature depended on the grain size due to the presence of long-range order in its temperature profile. Almost grain size-independent electrical properties were exhibited by the ceramic with x = 0.06, which was attributed to its superparaelectric nature where the phonon propagation length was expressed by its critical chemical grain size, thus, governing its properties.