Synthesis and characterization of novel ferrite–piezoelectric multiferroic core–shell-type structure
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Hybrid ferromagnetic/piezoelectric core–shell nanoparticles and ceramics have potential for a wide range of applications due to their tunability, electronic and magnetic properties. In this study, we designed a core–shell-type nanostructure of composition CoFe2O4/BNT-BT0.08, where BNT-BT0.08 is the abbreviation of bismuth, sodium titanate (Bi0.5Na0.5TiO3, BNT) doped with 8 mol% barium titanate (BaTiO3, BT). This multiferroic composite was prepared by covering CoFe2O4 nanoparticles with a shell of BNT-BT0.08 using the sol–gel technique. Scanning and transmission electron microscopy confirmed formation of a core–shell structure. The results of microstructure, dielectric, piezoelectric and magnetic investigations demonstrated that this heterostructure shows simultaneously electrical and magnetic behavior, at room temperature. XRD pattern of core–shell composite CoFe2O4/BNT-BT0.08 powder reveals only cubic CoFe2O4 and rhombohedral Bi0.5Na0.5TiO3 phases. CoFe2O4/BNT-BT0.08 core–shell nanostructure sample shows high values of permittivity (ε ≥ 600) together with high dielectric losses (tan δ ≥ 1) in the low-frequency range (ν ≤ 104 Hz). PFM and polarization hysteresis indicated a ferroelectric domains structure and remnant polarization of ~ 2.6 µC/cm2 for the ceramics pellets samples of CoFe2O4/BNT-BT0.08. The present study reveals the possibility of coating nanoparticles onto nanometer-sized core particles, using controlled sol–gel process, in order to prepare multifunctional core–shell composites for piezoelectric and magnetoelectronic sensors.
The authors would like to thank Dr. L. Diamandescu for helpful comments on the XRD analyses. The SEM analyses on the samples were possible due to EU-funding grant POSCCE-A2-O2.2.1-2013-1/Priority direction 2, Project No. 638/12.03.2014, cod SMIS-CSNR 48652.
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Conflict of interest
The authors and the institutes where the work has been carried out declare that there are no conflicts of interest regarding the publication of this article.