Gabriel Caruntu

Ferroelectric Barium Titanate Nanocubes as Capacitive Building Blocks for Energy Storage Applications

Highly uniform polymer-ceramic nanocomposite films with high energy density values were fabricated by exploiting the unique ability of monodomain, nonaggregated BaTiO3 colloidal nanocrystals to function as capacitive building blocks when dispersed into a weakly interacting dielectric matrix. Monodisperse, surface-functionalized ferroelectric 15 nm BaTiO3 nanoparticles have been selectively incorporated with a high packing density into poly(vinylidene fluoride-co-hexafluoropropene) (P(VDF-HFP)) leading to the formation of biphasic BaTiO3-P(VDF-HFP) nanocomposite films. A systematic investigation of the electrical properties of the nanocomposites by electrostatic force microscopy and conventional dielectric measurements reveals that polymer-ceramic film capacitor structures exhibit a ferroelectric relaxor-type behavior with an increased intrinsic energy density. The composite containing 7% BaTiO3 nanocrystals displays a high permittivity (ε = 21) and a relatively high energy density (E = 4.66 J/cm(3)) at 150 MV/m, which is 166% higher than that of the neat polymer and exceeds the values reported in the literature for polymer-ceramic nanocomposites containing a similar amount of nanoparticle fillers. The easy processing and electrical properties of the polymer-ceramic nanocomposites make them suitable for implementation in pulse power capacitors, high power systems and other energy storage applications.

Multicaloric effect in bi-layer multiferroic composites

The multicaloric effect was theoretically proposed in 2012 and, despite numerous follow up studies, the effect still awaits experimental confirmation. The main limitation is the fact that the multicaloric effect is only observed at a temperature equal to the transition temperature of the magnetic and electric phases coexisting within a multiferroic (MF) (i.e., T ≈ Tc m ≈ Tc e ). Such condition is hard to fulfill in single phase MFs and a solution is to develop suitable composite MF materials. Here, we examine the multicaloric effect in a bi-layer laminated composite MF in order to determine the optimal design parameters for best caloric response. We show that magnetically induced multicaloric effect requires magnetic component of heat capacity smaller than that of the electric phase, while the layer thickness of the magnetic phase must be at least 5 times the thickness of the electric phase. The electrically induced multicaloric effect requires the magnetic layer to be 10% of the electric phase thickness, while its heat capacity must be larger than that of the electric phase. These selection rules are generally applicable to bulk as well as thin film MF composites for optimal multicaloric effect.

Measurement techniques of the magneto-electric coupling in multiferroics

The current surge of interest in multiferroic materials demands specialized measurement techniques to support multiferroics research. In this review article we detail well-established measurement techniques of the magneto-electric coupling coefficient in multiferroic materials, together with newly proposed ones. This work is intended to serve as a reference document for anyone willing to develop experimental measurement techniques of multiferroic materials.

1D core–shell magnetoelectric nanocomposites by template-assisted liquid phase deposition

We demonstrate here that the liquid phase deposition (LPD) method, a simple, low cost and highly reproducible synthetic approach generally used for the deposition of high quality metal oxide thin films, can be reliably extended to the rational design of 1D magnetoelectric core–shell nano-architectures. In the first step of the process, highly crystalline ferroelectric (BaTiO3) nanotubes with an average diameter of 200 nm and controllable wall thickness were synthesized by the controlled hydrolysis of metal oxyfluoride precursors upon immersing alumina templates into a treatment solution at temperatures as low as 40 °C. The resulting perovskite nanotubes immobilized within the channels of the anodic aluminum oxide (AAO) membranes have been subsequently filled with a spinel ferrite phase, with the chemical composition Zn1.5Fe1.5O4 yielding spinel-perovskite 1D core–shell magnetoelectric architectures. The resulting core–shell tubular nanocomposites have been characterized structurally, morphologically and compositionally and their ferroelectric, magnetic and magnetoelectric properties have been measured. A change from a superparamagnetic to a ferrimagnetic behavior was observed when the pristine spinel ferrite nanotubes were incorporated into the spinel-perovskite core–shell nanocomposites, indicating the existence of a magnetoelectric coupling between the two ferroic phases. Moreover, the measured magnetoelectric coupling coefficient was α = 1.08 V cm−1 Oe−1, a value which is superior to the values reported for similar thin film and tubular spinel ferrite magnetoelectric nanocomposites, thereby indicating a strong strain-mediated coupling between the ferroelectric and magnetostrictive phase in the 1D core–shell nanocomposites and making these materials suitable for implementation into various functional devices.

Fabrication of barium titanate/acrylonitrile-butadiene styrene/poly(methyl methacrylate) nanocomposite films for hybrid ferroelectric capacitors

A new organic–inorganic ferroelectric hybrid capacitor designed by uniformly incorporating surface modified monodisperse 15 nm ferroelectric BaTiO3 nanocubes into non-polar polymer blends of poly(methyl methacrylate) (PMMA) polymer and acrylonitrile-butadiene-styrene (ABS) terpolymer is described. The investigation of spatial distribution of nanofillers via a non-distractive thermal pulse method illustrates that the surface functionalization of nanocubes plays a key role in the uniform distribution of charge polarization within the polymer matrix. The discharged energy density of the nanocomposite with 30 vol% BaTiO3 nanocubes is ∼44 × 10−3 J cm−3, which is almost six times higher than that of the neat polymer. The facile processing, along with the superior mechanical and electrical properties of the BaTiO3/PMMA–ABS nanocomposites make them suitable for implementation into capacitive electrical energy storage devices.

Tutorial: Product properties in multiferroic nanocomposites

The coupling between magnetic and electric subsystems in composites of ferromagnetic and ferroelectric phases is a product property that is facilitated by mechanical strain that arises due to magnetostriction and the piezoelectric effect in the constituent phases. Such multiferroic composites are of immense interests for studies on the physics of electromagnetic coupling and for use in a variety of applications. Here, we focus on magneto-electric (ME) coupling in nanocomposites. Particular emphasis is on core-shell particles and coaxial fibers, thin film heterostructures, and planar structures with a variety of mechanical connectivity. A brief review of models that predict strong ME effects in nanostructures is followed by synthesis and characterization. Core-shell particulate composites can be prepared by hydrothermal processes and chemical or deoxyribonucleic acid-assisted assembly. Electrospinning techniques have been utilized to prepare defect free core-shell nanofibers. Core-shell particles and fibers can be assembled into superstructures with the aid of magnetic and electric fields and characterized for possible use in advanced technologies. Chemical-vapor deposition techniques have been shown to be effective for the preparation of heterostructures of ferrites and ferroelectrics. Exotic planar multiferroic structures with potential for enhancing ME coupling strengths are also considered. Scanning probe microscopy techniques are ideal for probing the nature of direct- and converse-ME coupling in individual nanostructures. Magnetoelectric characterization of assemblies of nanocomposites can be done by ME voltage coefficient, magnetic field induced polarization, and magneto-dielectric effects. We conclude with a brief discussion on possible avenues for strengthening the product properties in the nanocomposites.The coupling between magnetic and electric subsystems in composites of ferromagnetic and ferroelectric phases is a product property that is facilitated by mechanical strain that arises due to magnetostriction and the piezoelectric effect in the constituent phases. Such multiferroic composites are of immense interests for studies on the physics of electromagnetic coupling and for use in a variety of applications. Here, we focus on magneto-electric (ME) coupling in nanocomposites. Particular emphasis is on core-shell particles and coaxial fibers, thin film heterostructures, and planar structures with a variety of mechanical connectivity. A brief review of models that predict strong ME effects in nanostructures is followed by synthesis and characterization. Core-shell particulate composites can be prepared by hydrothermal processes and chemical or deoxyribonucleic acid-assisted assembly. Electrospinning techniques have been utilized to prepare defect free core-shell nanofibers. Core-shell particles and fiber...

Assemblies and Superstructures of Inorganic Colloidal Nanocrystals

Inorganic colloidal nanoparticles (NPs) possess the ability to self-assemble into complex hierarchical structures with unique properties that are different from their individual counterparts. The assembly of particles into compact 2D and 3D structures occurs only when they have a narrow size distribution and uniform shape. In this chapter, we review how various types of forces and fundamental interactions at the nanoscale govern the assembly of colloidal nanocrystals, the available methods for assembling colloidal nanocrystals with discrete geometries and the application of such assembled structures in various fields ranging from catalysis, biological diagnosis, plasmonics and electronics.