Novel Aurivillius Bi4Ti3_2xNbxFexO12 phases with increasing magnetic-cation fraction until percolation: a novel approach for room temperature multiferroism

[EN] Aurivillius oxides with general formula (BiO)(ABO) are being extensively investigated for room-temperature multiferroism and magnetoelectric coupling. The chemical design strategy behind current investigations is the incorporation of magnetically active BiMOunits (M: Fe, Mn, Co…) to the pseudoperovskite layer of known ferroelectrics like BiTiO, increasingm. The percolation of magnetic cations at the B-site sublattice is required for magnetic ordering and thus, phases withm≥ 5 are searched. Alternatively, one can try to directly substitute magnetic species for Tiin the perovskite slab, without introducing additional oxygen octahedra. We report here the mechanosynthesis of Aurivillius BiTiNbFeOphases with increasingxvalues up to 1. A maximum magnetic fraction of 1/3, surpassing the threshold for percolation, was reached. Preliminary structural analysis indicated a continuous solid solution, though hints of structural changes betweenx= 0.25 and 0.5 were found. Ceramic processing was accomplished by spark plasma sintering of the mechanosynthesized phases, including those with high-xones with reduced thermal stability. This has enabled us to carry out full electrical characterization and to demonstrate ferroelectricity for all phases up tox= 1. Magnetic measurements were also carried out, and weak ferromagnetism was found forx= 1. Therefore, BiTiNbFeOis proposed to be a novel room-temperature multiferroic.Research is funded by Spanish MICINN through project MAT2017-88788-R. Technical support by Ms I. Martínez, at ICMM-CSIC is also acknowledged.Peer reviewe