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

Abstract

We investigated the relationship between the average and local crystal structures and the ferroelectric properties of Bi 2SiO 5, Bi 4Si 3O 12, or Bi 2O 3 added Sr 1− x Bi 2+ x Ta 2O 9 ( x=0, 0.2) produced by a solid-state reaction. By measuring the P–E hysteresis, we found that Sr 1− x Bi 2+ x Ta 2O 9 ( x=0, 0.2) has higher P r and E c than SrBi 2Ta 2O 9 (SBT). P r increased and E c decreased by adding Bi 2SiO 5, Bi 4Si 3O 12, or Bi 2O 3 to Sr 1− x Bi 2+ x Ta 2O 9. 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, σ 2, of each TaO 6 octahedron increased by substituting Si for the Ta site. The tilting angle, α a, α b, of each TaO 6 octahedron increased relative to that of the average structure, and the symmetry of the TaO 6 octahedron in the local structure deteriorated in comparison to that of the average structure. This distortion and symmetry of TaO 6 contributes to the remanent polarization.