Synthesis of platelets Bi5Fe0.5Co0.5Ti3O15 via the molten salt method

Oxide materials which exhibit both ferroelectricity and ferromagnetism are of great interest. Layered bismuth titanates with a Aurivillius structure, (BiFeO₃)_n Bi₄Ti₃O₁₂, can potentially posses ferroelectric and ferromagnetic order paramaters simultaneously. It has recently been demonstrated that one such example, Bi₅Fe_0.5Co_0.5Ti₃O₁₅ where n = 1 with half the Fe³⁺ sites substituted by Co³⁺ ions exhibits both ferroelectric and ferromagnetic properties at room temperature. Here we report on the fabrication of well oriented polycrystalline ceramics of this material, via molten salt synthesis and uniaxial pressing of high aspect ratio platelets. Electron backscatter images showed that there is an extra secondary phase within the obtained ceramic which is rich in cobalt and iron. The concentration of the secondary phase obtained from secondary electron microscopy is estimated at less than 2.5 %, below the detection limit of XRD. Further, the sintering temperature was varied and excess addition of bismuth oxide was employed in an attempt to reduce the secondary phase with limited success. The samples have been characterized by X-ray diffraction, polarization-field measurements and SQUID magnetometery as a function of sample orientation. It is inferred from the data that the resultant ferromagnetic response identified using SQUID measurements is due to the presence of the secondary phase.