Relationship between average and local crystal structure and the ferroelectric properties of a Sr–Bi–Ta–Si–O ferroelectric material

We investigated the relationship between the average and local crystal structures and the ferroelectric properties of Bi2SiO5, Bi4Si3O12, or Bi2O3 added Sr1−xBi2+xTa2O9 (x=0, 0.2) produced by a solid-state reaction. By measuring the P–E hysteresis, we found that Sr1−xBi2+xTa2O9 (x=0, 0.2) has higher Pr and Ec than SrBi2Ta2O9 (SBT). Pr increased and Ec decreased by adding Bi2SiO5, Bi4Si3O12, or Bi2O3 to Sr1−xBi2+xTa2O9. The average crystal structures were determined by the Rietveld method. On the other hand, the local structure is important, because the ferroelectric property is related to the distortion, and ferroelectric complex oxides have domains. We also investigated the local crystal structure using atomic pair distribution function (PDF) analysis. Based on the results, the bond angle variance, σ2, of each TaO6 octahedron increased by substituting Si for the Ta site. The tilting angle, αa,αb, of each TaO6 octahedron increased relative to that of the average structure, and the symmetry of the TaO6 octahedron in the local structure deteriorated in comparison to that of the average structure. This distortion and symmetry of TaO6 contributes to the remanent polarization.