Lead-Free BNT–BT(0.08)/CoFe(2)O(4) Core–Shell Nanostructures with Potential Multifunctional Applications

Herein we report on novel multiferroic core–shell nanostructures of cobalt ferrite (CoFe(2)O(4))–bismuth, sodium titanate doped with barium titanate (BNT–BT(0.08)), prepared by a two–step wet chemical procedure, using the sol–gel technique. The fraction of CoFe(2)O(4) was varied from 1:0.5 to 1:1.5 = BNT–BT(0.08)/CoFe(2)O(4) (molar ratio). X–ray diffraction confirmed the presence of both the spinel CoFe(2)O(4) and the perovskite Bi(0.5)Na(0.5)TiO(3) 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–BT(0.08) core surrounded by a CoFe(2)O(4) shell with an average thickness of 4–7 nm. Cole-Cole plots reveal the presence of grains and grain boundary effects in the BNT–BT(0.08)/CoFe(2)O(4) composite. Moreover, the values of the dc conductivity were found to increase with the amount of CoFe(2)O(4) semiconductive phase. Both X-ray photoelectron spectroscopy (XPS) and Mössbauer measurements have shown no change in the valence of the Fe(3+), Co(2+), Bi(3+) and Ti(4+) cations. This study provides a detailed insight into the magnetoelectric coupling of the multiferroic BNT–BT(0.08)/CoFe(2)O(4) core–shell composite potentially suitable for magnetoelectric applications.