Piezoelectric/ferromagnetic BNT-BT0.08/CoFe2O4 coaxial core-shell composite nanotubes for nanoelectronic devices

In this paper we report on a novel 1-D piezoelectric/ferroelectric nanostructure. Composites of piezoelectric (0.92Na0.5Bi0.5TiO3e0.08BaTiO3 abbreviated as BNT-BT0.08) and ferromagnetic (CoFe2O4) nanotubes were assembled and studied in order to envisage new multifunctional applications. Using a polycarbonate membrane template and sols precursors of BNT-BT0.08 and CoFe2O4, heterostructured BNT-BT0.08/CoFe2O4 core-shell composite nanotubes were created. Selective methods such as SEM, TEM, AFM, PFM and MFM were used for the characterization of the as-prepared hybrid piezoelectric/ferromagnetic coaxial nanotubes structure. This composite shows two crystalline phases: rhombohedral BNTBT0.08 and cubic CoFe2O4. The piezoelectric and ferromagnetic properties have been characterized. Piezo force microscopy (PFM) images evidenced ferroelectric domains with opposite polarity due to lead free piezoelectric BNT-BT0.08 outer tube. Magnetic force microscopy (MFM) images evidenced magnetic domains attributed to the CoFe2O4 inner tube. Magnetic hysteresis curves demonstrate a weak ferromagnetic behavior, accompanied by a linear variation of the magnetization at higher magnetic fields, especially at room temperature. From dielectric measurements, high tunability values reaching about 70% at 0.5 kHz and E = 80 kV/cm have been obtained. An effective dielectric constant ?r = 32 has been measured. The results obtained from this work provide a base for the design of tubular multi-layered materials with novel functionalities and applications in various multifunctional electronic devices such as actuators, transducers, and energy storage microsystems.