Abstract
We present a first-principles and experimental study of the structural, ferroelectric, and magnetic properties of the potentially multiferroic three-layer Aurivillius compound Bi4TiFeNbO12. This system can be realized by inserting a BiFeO3 formula unit into the two-layer Aurivilius Bi3TiNbO9 matrix. The calculations are performed using the PBEsol exchange–correlation functional within the DFT+U framework. First we search for potential cation site preference by comparing the relative stability of different Fe, Nb and Ti arrangements. We find a preference for the Fe3＋ ions to occupy the inner site within the pseudoperovskite block. This configuration exhibits a band gap of 1.2 eV (UFe=4eV) and ferroelectric and magnetic orders. A value of 66 μC/cm2 is obtained for the spontaneous polarization, which is similar to the one obtained for Bi4Ti3O12 (BIT). The magnetic ground state of this system is characterized by a strong antiferromagnetic coupling between the Fe3＋ ions located in the central layer. By mapping to a Heisenberg model, the superexchange antiferromagnetic coupling between nearest-neighbor Fe3＋ cations is estimated to be J=53 meV. Finally, we synthesize Bi3.25La0.75TiFeNbO12 ceramics by the solid-state reaction method. Their structural, electric and magnetic properties are confronted with the theoretical predictions.
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