Effect of synthesis conditions on microstructure and multiferroic properties of magnetoelectric Ca2Bi4Ti3.5Mn1.5O18 solid solutions

The effects of synthesis conditions on the structural evolution and multiferroic properties were investigated in Ca₂Bi₄Ti_3.5Mn_1.5O₁₈ ceramics synthesized by molten salt methods. An optimized calcining temperature of 800 °C was found to be sufficient for obtaining the desired Aurivillius structure. The ceramics possess a morphotropic phase with the orthorhombic-tetragonal biphasic structure. The weight fractions and unit cell volumes of orthorhombic and tetragonal phases change with varying mass ratio of chlorides/oxides, which can effectively regulate the multiferroic properties at room temperature. The layered structure of several tens nanometers appears in all the Ca₂Bi₄Ti_3.5Mn_1.5O₁₈ samples prepared with various chlorides/oxides mass ratios showing lossy ferroelectric behavior. The occurrence of magnetoelectric coupling effect is attributed to long-range magnetic order structure. The ceramic prepared with chlorides/oxides mass ratio equaling to 4 exhibits optimum properties with the highest remnant magnetization of ∼0.06 emu/g and the highest ME coefficient of ∼5.05 mV/(cm·Oe).