Raman scattering study of the effect of A- and B-site substitution on the room-temperature structure of ABi4Ti4O15

Aurivillius-type materials exhibit promising ferroelectric and multiferroic properties that can be tailored via chemistry variations in the perovskite block. Hence, it is important to clarify the relations composition-structure, also on a local-scale level. The aim of this contribution is to give further insights into the effect of A- and B-site cations to the room-temperature local structure of Aurivillius four-layered ABi4Ti4O15 (A = Sr, Pb, Ba) and Pb1-xBi4+xTi4-xMn x O15 (x = 0, 0.2, 0.4) by Raman scattering. The effect of A-site cation to the local structure of perovskite block was identified by the phonon mode near 750 and 870 cm-1 arising from BO6 stretching. A-site Ba2+, having the largest ionic radius among the considered elements, significantly stiffens the TiO6 octahedra, as derived from the fact that the TiO6 stretching modes have the highest wavenumber for BaBi4Ti4O15, i.e. the Ti-O bond strength is strongest for this compound. The replacement of Ti4+ by Mn3+ cation at the B- site also influences the B-O bond. The comparison of the phonon modes near 700 and 870 cm-1 in Pb1-xBi4+xTi4-xMn x O15 with x = 0, 0.2, and 0.4 shows that the lowest wavenumber, which is due to the elongation of Ti-O bonds is observed for x = 0.4