Bismuth layer-structured ferroelectrics with cation vacancies

The effects of Bi and La substitution on the crystal structure and polarization properties of SrBi2Ta2O9 (SBT) were investigated. The Rietveld refinement of neutron powder diffraction demonstrated that Bi3+ and La3+ substitution preferentially at the Sr2+ site (perovskite A site) resulted in A-site vacancies for charge compensation. The substitution of Bi enhanced ferroelectric distortion of perovskite blocks, leading to a larger remanent polarization (P-r), while the incorporation of La led to a much lower coercive field (E-c) as well as a larger P-r than SBT. The presence of cation vacancies at A site facilitated a polarization switching, thus the larger P-r and lower E-c were obtained for La-substituted SBT.