A comparative study of the Aurivillius phase ferroelectrics CaBi4Ti4O15 and BaBi4Ti4O15

The room temperature structures of the four-layer Aurivillius phase ferroelectrics CaBi4Ti4O15 and BaBi4Ti4O15 are determined by means of single crystal X-ray diffraction. Regarding the CaBi4Ti4O15 phase, in agreement with the tolerance factor, a significant deformation of the perovskite blocks is observed. The rotation system of the octahedra is typical from even layer Aurivillius phases and leads to the use of the space group A21am. For the BaBi4Ti4O15 phase, only a weak variation with respect to the F2mm space group can be suggested from single crystal X-ray diffraction. A significant presence of Ba atoms in the [M2O2] slabs is confirmed in agreement with the previous works but specific Ba2+ and Bi3+ sites have to be considered due to the large difference in bounding requirement of these cations. Possible origins for the ferroelectric relaxor behavior of the Ba-based compound are discussed in view of the presented structural analyses.