Lead-Free BNT-BT0.08/CoFe2O4 Core-Shell Nanostructures with Potential Multifunctional Applications

Herein we report on novel multiferroic core-shell nanostructures of cobalt ferrite (CoFe2O4)-bismuth, sodium titanate doped with barium titanate (BNT-BT0.08), prepared by a two-step wet chemical procedure, using the sol-gel technique. The fraction of CoFe2O4 was varied from 1:0.5 to 1:1.5 = BNT-BT0.08/CoFe2O4 (molar ratio). X-ray diffraction confirmed the presence of both the spinel CoFe2O4 and the perovskite Bi0.5Na0.5TiO3 phases. Scanning electron microscopy analysis indicated that the diameter of the core-shell nanoparticles was between 15 and 40 nm. Transmission electron microscopy data showed two-phase composite nanostructures consisting of a BNT-BT0.08 core surrounded by a CoFe2O4 shell with an average thickness of 4-7 nm. Cole-Cole plots reveal the presence of grains and grain boundary effects in the BNT-BT0.08/CoFe2O4 composite. Moreover, the values of the dc conductivity were found to increase with the amount of CoFe2O4 semiconductive phase. Both X-ray photoelectron spectroscopy (XPS) and Mössbauer measurements have shown no change in the valence of the Fe3+, Co2+, Bi3+ and Ti4+ cations. This study provides a detailed insight into the magnetoelectric coupling of the multiferroic BNT-BT0.08/CoFe2O4 core-shell composite potentially suitable for magnetoelectric applications.