Multiferroic properties of Ba/Ni co-doped KNbO₃with narrow band-gap

In this paper, the influence of Ba/Ni co-doping on the multiferroic properties of (K_1−xBa_x)(Nb_1−x/2Ni_x/2)O_3−δwas investigated. A gradual transition from orthorhombic to tetragonal, and to cubic phase with increasing the doping ratio x was observed in the single phase perovskite structure at room temperature. The weakened antiferromagnetism and high ferroelectric polarization with narrow optical band-gaps (1.18–1.84 eV) for x = 0.1–0.3 were observed. Based on the first-principles calculations with GGA+U, we confirm that the Ni: 3d electronic states have a major contribution to the variation of band-gap size and the antiferromagnetic properties. Our results may shed some light on the understanding of the band-gap tuning and multiferroic mechanism in perovskite-type materials.