Structure-property relationships in the lanthanide-substituted PbBi2Nb2O9 Aurivillius phase synthesized by the molten salt method

•Single-phase samples of the Ln-substituted PbBi2Nb2O9 Aurivillius phase were prepared by a molten salt method.•All samples crystallize in the A21am orthorhombic structure and exhibit the ferroelectric properties.•The Ln ions only occupy in the perovskite layers and Pb/Bi ions disorder in both Bi2O2 and perovskite layers.•A decrease in Tc with Ln substitution is consistent with the decreased degree of BO6 tilting angle.•Relaxor-ferroelectric behavior is induced with Ln substitution.