Abstract
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.
Highlights
Multifunctional materials combine materials with different physical properties inti one single structure in order to improve their final functionality [1,2,3]. Multifunctional materials combining both electric and magnetic properties produce a single device component that performs more than one task
We report on the multiferroic core-shell nanostructures of (Bi0.5Na0.5)0.92Ba0.08TiO3 abbreviated as BNT–BT0.08 and CoFe2O4 for multi-functional devices
We focused on CoFe2O4/BNT–BT0.08 composites with core–shell architectures and various molar ratios since there is only one previously published report on 0.65BaTiO3–0.35Bi0.5Na0.5TiO3/CoFe2O4 composites with 0–3 connectivity [10]
Summary
Multifunctional materials combine materials with different physical properties inti one single structure in order to improve their final functionality [1,2,3]. Multifunctional materials combining both electric and magnetic properties produce a single device component that performs more than one task. We report on the multiferroic core-shell nanostructures of (Bi0.5Na0.5)0.92Ba0.08TiO3 abbreviated as BNT–BT0.08 and CoFe2O4 for multi-functional devices. BNT–BT0.08 and CoFe2O4 species can form composites that should combine their piezoelectric and magnetic properties and lead to performance surpassing their individual components. There are few reports on hybrid piezoelectric/ferromagnetic structures, such as: CoFe2O4/BaTiO3 [8,11,12,13,14,15,16], Pb(Zr0.52Ti0.48)O3/NiFe2O4 [12] and NiFe2O4/BaTiO3 [17] core–shell composites in which the authors studied the influence of the variation of the ferrite fraction on the magnetic properties of the multiferroic core–shell–type nanostructures
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