Investigation on structure, dielectric and magnetic properties of the four-layer Aurivillius phase Pb1-xBi3.5+xNd0.5Ti4-xMnxO15 prepared via molten salt method

Abstract

In this study, the four-layer Aurivillius phases, Pb1-xBi3.5+xNd0.5Ti4-xMnxO15 (x ​= ​0, 0.1, 0.3, and 0.5), were prepared by the molten salt method, in order to investigate the effects on crystal structure, morphology, dielectric and magnetic properties of varying x composition. XRD patterns revealed that of the all samples were single-phase products with an orthorhombic structure. The refinement result demonstrates a compressive unit cell volume with increasing x composition. Moreover, FTIR spectroscopy showed a single mode of BO6 octahedra, and the shifting of this mode indicates that the Mn3+ ions occupy the perovskite B-site. The anisotropic plate-like grain was probed by SEM, the size of which showed an increase with a higher x composition, as the proportion of Bi3+ increases. The dielectric properties also increase with an increasing x composition, which results from the increasing structural distortion and grain size. The investigation of the magnetic properties indicates that the ferromagnetic behavior for the x ​= ​0.5 sample, presumably originated from the double-exchange interactions between Mn3+ and Mn4+ and the spin canting of distorted Mn(1)O6 octahedra via the Dzyaloshinskii–Moriya interaction. The formation of the mixed-valent Mn3+/Mn4+ could likely be caused by the oxidizing environment, produced by the oxobasicity properties of the sulfate salt in this molten-salt method. Therefore, the multiferroic properties exhibited at room temperature were due to the optimum dielectric and magnetic properties that were obtained at x ​= ​0.5.