Lead-Free Aurivillius Phase Bi₂LaNb_1.5Mn_0.5O₉: Structure, Ferroelectric, Magnetic, and Magnetodielectric Effects

Abstract

Aurivillius phase Bi₂LaNb_1.5Mn_0.5O₉, derived from ferroelectric PbBi₂Nb₂O₉ by simultaneous substitution of the <i>A</i>-site and <i>B</i>-site cations, was synthesized using a molten-salt method. Here, we discuss the structure-property relationships in detail. X-ray and neutron diffraction show that Bi₂LaNb_1.5Mn_0.5O₉ adopts an <i>A</i>2₁<i>am</i> orthorhombic crystal structure. Rietveld refinement analysis, supported by Raman spectroscopy, indicates that the Bi³⁺ ions occupy the bismuth oxide blocks, La³⁺ ions occupy the perovskite <i>A</i>-site, and Nb⁵⁺/Mn³⁺ ions occupy the perovskite <i>B</i>-site. Ferroelectric ordering takes place at 535 K, which coexists with local ferromagnetic order below 65 K. The cation disorder on the <i>B</i>-site results in relaxor-ferroelectric behavior, and the short-range ferromagnetic order can be attributed to Mn³⁺/Mn⁴⁺ double-exchange. Magnetodielectric coupling measured at 5 K and 100 kHz in a field of 5 T suggests the existence of intrinsic spin-lattice coupling with a magnetodielectric coefficient of 0.20%. These findings will provide significant impetus for further research into potential devices based on the magnetodielectric effect in Aurivillius materials.