Structural evolution and multiferroic properties in the vicinity of MPB of Ca2Bi4Ti5-xMnxO18 solid solutions

Abstract The crystal structure transition and its effect on the multiferroic characteristics were investigated in Ca2Bi4Ti5-xMnxO18 (0 ≤ x ≤ 2) ceramics synthesized by the molten salt method. Mn substitution induces variations in a/b ratio and the distortion degree of oxygen octahedrons, which can effectively regulate the multiferroic properties at room temperature. The structure changes from orthorhombic B2cb to tetragonal I4/mmm with a morphotropic phase region forming in the ceramic at x=1.5. The Raman spectra manifest that Mn substitution not only alters the vibration mode of MnO6 octahedron but also changes the structural environment of TiO6 in the perovskite lattice. The average grain size increases gradually and the grain size distribution gets homogeneous with the increase in Mn content. All the ceramics show a lossy dielectric behavior. The addition of Mn results in a significant enhancement in macroscopic magnetization and dielectric properties. In addition to this, the magnetoelectric coupling effect has also been improved and a maximum magnetoelectric coefficient of α ≈ 12.3 mV/(cm·Oe) is attained for the ceramic sample with x = 1.5.