Double-layered Aurivillius-type ferroelectrics with magnetic moments

We have synthesized the double-layer Aurivillius phase Bi2LnNbTiO9 where Ln = Nd–Gd, Bi. All compounds adopt the orthorhombic polar space group A21am. The magnetic Ln-ion occupies the cuboctahedral position in the middle of the perovskite double-layer, and thus controls the octahedral tilt of the perovskite block. This tilt modifies the ferroelectric displacement of the (Nb,Ti) towards the octahedral faces. This provides a mechanism to systematically modify the polarization. Mn-substitution on the (Nb,Ti) site for Ln = Bi is homogeneous up to x = 0.2. The magnetic moments of Ln do not order down to 5 K.