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

Marin Cernea; Roxana Radu; Harvey Amorín; Simona Gabriela Greculeasa; Bogdan Stefan Vasile; Vasile Adrian Surdu; Paul Ganea; Roxana Trusca; Marwa Hattab; Carmen Galassi

doi:10.3390/nano10040672

Lead-Free BNT-BT_0.08/CoFe₂O₄ Core-Shell Nanostructures with Potential Multifunctional Applications

Nanomaterials (Basel). 2020 Apr 3;10(4):672. doi: 10.3390/nano10040672.

Authors

Affiliations

¹ National Institute of Materials Physics, Atomistilor 405A, 077125 Magurele, Romania.
² Instituto de Ciencia de Materiales de Madrid, CSIC, Cantoblanco, 28049 Madrid, Spain.
³ Department of Science and Engineering of Oxide Materials and Nanomaterials, Faculty of Applied Chemistry and Materials Science, University Politehnica of Bucharest, 060042 Bucharest, Romania.
⁴ Research Laboratory of Environmental Science and Technologies, Carthage University, BP.1003, Hammam-Lif, Ben Arous 2050, Tunisia.
⁵ Faculty of Mathematical, Physical and Natural Sciences of Tunis, University of Tunis Elmanar, Belvedere, Tunis 1002, Tunisia.
⁶ National Research Council of Italy-Institute of Science and Technology for Ceramics (CNR-ISTEC), Via Granarolo 64, I-48018 Faenza, Italy.

Abstract

Herein we report on novel multiferroic core-shell nanostructures of cobalt ferrite (CoFe₂O₄)-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 CoFe₂O₄ was varied from 1:0.5 to 1:1.5 = BNT-BT_0.08/CoFe₂O₄ (molar ratio). X-ray diffraction confirmed the presence of both the spinel CoFe₂O₄ and the perovskite Bi_0.5Na_0.5TiO₃ 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-BT_0.08 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-BT_0.08/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-BT_0.08/CoFe₂O₄ core-shell composite potentially suitable for magnetoelectric applications.

Keywords: composite core–shell; dielectric properties; magnetic properties; magnetoelectric properties; oxide materials; piezoelectric/ferromagnetic composites; sol-gel processes.