Ferroelectric Matrix Research Articles

Electron transport properties of composite ferroelectrics

We study electron transport in composite ferroelectrics —materials consisting of metallic grains embedded in a ferroelectric matrix. Due to its complex tunable morphology the thermodynamic properties of these materials can be essentially different from bulk or thin-film ferroelectrics. We calculate the conductivity of composite ferroelectrics by taking into account the interplay between charge localization, multiple grain boundaries, strong Coulomb repulsion, and ferroelectric order parameter. We show that the ferroelectricity plays a crucial role on the temperature behavior of the conductivity in the vicinity of the ferroelectric-paraelectric transition.

Nucleation-Induced Self-Assembly of Multiferroic BiFeO3–CoFe2O4 Nanocomposites

Large areas of perfectly ordered magnetic CoFe2O4 nanopillars embedded in a ferroelectric BiFeO3 matrix were successfully fabricated via a novel nucleation-induced self-assembly process. The nucleation centers of the magnetic pillars are induced before the growth of the composite structure using anodic aluminum oxide (AAO) and lithography-defined gold membranes as hard mask. High structural quality and good functional properties were obtained. Magneto-capacitance data revealed extremely low losses and magneto-electric coupling of about 0.9 μC/cmOe. The present fabrication process might be relevant for inducing ordering in systems based on phase separation, as the nucleation and growth is a rather general feature of these systems.

Electric in-plane polarization in multiferroic CoFe2O4/BaTiO3 nanocomposite tuned by magnetic fields

Ferrimagnetic CoFe2O4 nanopillars embedded in a ferroelectric BaTiO3 matrix are an example for a two-phase magnetoelectrically coupled system. They operate at room temperature and are free of any resource-critical rare-earth element, which makes them interesting for potential applications. Prior studies succeeded in showing strain-mediated coupling between the two subsystems. In particular, the electric properties can be tuned by magnetic fields and the magnetic properties by electric fields. Here we take the analysis of the coupling to a new level utilizing soft X-ray absorption spectroscopy and its associated linear dichroism. We demonstrate that an in-plane magnetic field breaks the tetragonal symmetry of the (1,3)-type CoFe2O4/BaTiO3 structures and discuss it in terms of off-diagonal magnetostrictive-piezoelectric coupling. This coupling creates staggered in-plane components of the electric polarization, which are stable even at magnetic remanence due to hysteretic behaviour of structural changes in the BaTiO3 matrix. The competing mechanisms of clamping and relaxation effects are discussed in detail.

Ferroelectric liquid crystal matrix dispersed with Cu doped ZnO nanoparticles

10% Cu doped ZnO nanoparticles (NPs) prepared by hydrothermal and solvothermal method have been dispersed to the pure FLC 17/100 in 1% concentration of guest entity. Electro-optical, elastic and dielectric analysis has been made for the FLC-NPs composite system with the variation of temperature. The nature of the composite system clearly shows the alteration in FLC parameters with the dispersion of NPs. The interaction between crystalline NPs and non-crystalline ferroelectric liquid crystal matrix modifies the properties of the pure FLC system. The synthesis method of NPs is also responsible for the changes taking place in physical properties of the pure FLC. The size and surface defects of the NPs amend the FLC parameters like dielectric permittivity, relaxation frequency, relaxation strength, tilt angle, spontaneous polarization and rotational viscosity etc. The coupling of spontaneous polarization and tilting of the FLC molecules are factors responsible for the resultant electro-optical (E-O) parameters of the composite system.

On magnetization stability of ferrimagnetic nanocylinder in ferroelectric matrix

The model of a composite material with ferrimagnetic nanocylinders embedded into the dielectric matrix has been considered theoretically. The problem of the influence of mechanical stresses that arise in the composite upon the application of an electric field on the magnetic parameters of the inclusions has been investigated. The conditions under which the spin-reorientation transitions are made possible have been determined.

Simulation of inhomogeneous magnetoelastic anisotropy in ferroelectric/ferromagnetic nanocomposites

The magnetic response of CoFe2O4/BiFeO3 (CFO/BFO) nanocomposite thin films, in which ferromagnetic CFO nanopillars are embedded in a ferroelectric BFO matrix, has been modeled by including the position-dependent magnetoelastic anisotropy of the CFO. A finite element simulation of the strain state of an arrangement of CFO pillars was performed in which the BFO matrix surrounding one or all of the pillars was subject to a piezoelectric strain. The strain transferred to the CFO pillars was calculated and transformed into a spatially varying magnetoelastic anisotropy in the CFO, and a micromagnetic model was then used to calculate the hysteresis of the pillar, which differed significantly from a macrospin model. The position-dependent anisotropy led to a complex reversal process and to a reorientation of the easy axis to the in-plane direction at sufficient applied electric fields.

Pressure-induced phase transitions and structure of chemically ordered nanoregions in the lead-free relaxor ferroelectric Na1/2Bi1/2TiO3

We investigate the phase stability of Na${}_{1/2}$Bi${}_{1/2}$TiO${}_{3}$, a prototype lead-free relaxor material, under pressure. By means of total energy calculations within density functional theory, we study the pressure stability of several structures with polar and antipolar distortions, in-phase and out-of-phase tilts, and different chemically ordered configurations. Under positive (compressive) pressure an orthorhombic $Pbnm$-like phase is stabilized above 3 GPa. At negative (tensile) pressure a non-tilted polar $P4mm$-like phase is stable. At zero pressure two phases are coexisting. The local chemical configuration determines whether the high-pressure $Pbnm$-like or another tilted and polar $R3c$-like structure is favored. Thus, two different variants of pressure phase diagrams depending on the cation arrangement are obtained, which raises the question of the existence of a mixed phase ground state in the disordered system. We discuss the stability of the mixed phase state in terms of lattice and tilt misfits and possible shapes and ferroic properties of the coexisting regions with different average structures. Our results clearly support the view that there are chemically ordered nanoregions with their own local ferroic properties embedded in a chemically disordered ferroelectric matrix representing the ground state.

Position-controlled functional oxide lateral heterostructures consisting of artificially aligned (Fe,Zn)3O4 nanodots and BiFeO3 matrix

We demonstrate an advanced fabrication method for perfectly position-controlled ferromagnetic semiconductor (Fe,Zn)3O4 nanodot arrays down to several hundred nanometers in size surrounded by a ferroelectric BiFeO3 matrix. By performing position-selective crystal growth of perovskite BiFeO3 on the position-controlled epitaxial spinel (Fe,Zn)3O4 nanodot-seeding template, which is prepared using a hollow molybdenum mask lift-off nanoimprint lithography process on a perovskite La-doped SrTiO3(001) substrate, we produce functional oxide three-dimensional lateral heterojunctions. The position-selectivity can be explained based on standard surface diffusion theory with a critical nucleation point. Establishing this fabrication process could lead to innovative nanointegration techniques for spintronic oxide materials.

Electron Microscopy Study of Porous and Co Functionalized BaTiO3 Thin Films

Multiferroics are currently of great interest for applications in microelectronics namely in future data storage and spintronic devices. These materials couple simultaneously ferroelectric and ferromagnetic properties and have potentially different applications resulting from the coupling between their dual order parameters. A true multiferroic material is single phase. However, the known true multiferroic materials possess insufficient coupling between the two phenomena or their magnetoelectric response occurs at temperatures too low to be useful in practical applications. But a tremendous progress in the field of microelectronics can be expected if one is able to design an effective multiferroic material with ideal coupling of the ferromagnetic and ferroelectric properties to suit a particular application. Within this context composite structures are gaining considerable interest and different strategies in terms of materials microstructure have been proposed including horizontal multilayers and vertical heterostructures. In the horizontal multilayer heterostructures, the alternating layers of conventional ferro/ferrimagnetic and ferroelectric phases are grown, while in the vertical heterostructures nanopillars of the ferro/ferrimagnetic phase are embedded in a ferroelectric matrix. The later structures show advantages over the first ones because promote larger interfacial surface area and are intrinsically heteroepitaxial in three dimensions; which is expected to allow a stronger coupling between ferroelectric and ferromagnetic components.

Synthesis and Magnetic Properties of Cobalt Ferrite Nanoparticles

ABSTRACTNanopowders of cobalt iron oxide (CoFe2O4) were successfully fabricated by the co-precipitation method followed by a technique to prevent particle agglomeration. Particle sizes were in the range of 24 to 44 nm. The size of cobalt iron oxide particles decreases with increasing the concentration of the precipitation agent. The crystal structure was confirmed by X-ray diffraction (XRD), the chemical composition by energy dispersive spectroscopy (EDS), and phase changes by thermogravimetric differential thermal analysis (TGA-TDA). The particle morphology was analyzed by scanning electron microscopy (SEM). Magnetic properties were investigated by SQUID magnetometry and Mössbauer spectroscopy. Being nearly monodisperse and non-agglomerated the prepared cobalt iron oxide powders are the base for synthesizing magnetoelectric composites embedded in a ferroelectric BaTiO3 matrix.

Study of Dielectric Properties and Phase Transformation of Thermally Modified Nano-Composite PbIn1/2Nb1/2O3

Differential thermal analysis as well as Raman and dielectric studies of PbIn1/2Nb1/2O3 single crystals exhibiting a different degree of order were performed. For this purpose two ordering procedures were applied. In Procedure A the as grown crystals were annealed at 650°C for different periods of time. Whereas in Procedure B the crystals were annealed at various temperatures, ranging from 650 to 850°C, long enough to reach the thermodynamic equilibrium state. With the increase of the degree of order, the heat anomaly related to the antiferroelectric-paraelectric phase transitions in the ordered regions, increase and shifts towards higher temperatures. Simultaneously the diffuse and frequency dependent maximum of the dielectric permittivitty ϵ(T), characteristic for disordered crystals, gradually forms a sharp maximum typical for ordered crystals and shifts towards higher temperatures. The evolution of Raman spectra at room temperature also indicates their sensitivity to the ordering state. Systematic dielectric investigations allowed us to distinguish two contributions to the dielectric response, one originating from the antiferroelectric and other from the ferroelectric nano-regions. The diagrams showing temperatures of the observed phase transitions versus annealing conditions as well as the coexistence of different phases are given in the paper. The experiments performed showed that lead indium niobate presents a thermally modified nano-composite structure composed of ordered antiferroelectric regions embedded in a disordered ferroelectric matrix.

Electrical control of photoluminescence wavelength from semiconductor quantum dots in a ferroelectric polymer matrix

We report controllable tuning of the room temperature photoluminescence band of CdSe semiconductor quantum dots embedded in thin films of ferroelectric copolymer of vinylidene fluoride and trifluoroethylene made by Langmuir-Blodgett deposition. The high breakdown strength of the polymer permits the application of electric fields of up to 400 MV/m and results in a shift in the photoluminescence peak by up to 9 nm, nearly half the fluorescence band width. Moreover, we found that at these high electric fields, the Stark effect exhibits unusual fourth power dependence.

Large strain response in acceptor- and donor-doped Bi0.5Na0.5TiO3-based lead-free ceramics

Effects of Fe and La addition on the dielectric, ferroelectric, and piezoelectric properties of Bi0.5Na0.5TiO3–Bi0.5Li0.5TiO3–BaTiO3–Mn ceramics were investigated. Similar to the doping effect in lead-based piezoelectric materials, here the Fe-doped ceramic created a hard effect with an improved mechanical quality factor (Qm) ~ 160, coercive field (Ec) ~ 2.9 kV/mm, decreased dielectric constant \( \left( {\varepsilon_{33}^{T} /\varepsilon_{0} } \right)\sim 80 3, \) and loss (tanδ) ~ 0.024 while the La-doped one indicated a soft feature with improved piezoelectric constant (d33) ~ 184 pC/N, \( \varepsilon_{33}^{T} /\varepsilon_{0} \,\sim { 983}, \) tanδ ~ 0.033, and decreased Ec ~ 2.46 kV/mm. In addition, the temperature dependence of the ferroelectric hysteresis loops and strain response under unipolar electric field was also studied. Around the depolarization temperature Td, large strain value was obtained with the normalized \( d_{33}^{*} \) up to ~1,000 pC/N, which was suggested originated from the development of the short-range order or non-polar phases in the ferroelectric matrix. All these would provide a new way to realize high piezoelectric response for practical application in different temperature scale.

Polymer nanocomposites for electrical energy storage

AbstractThis review highlights the frontier scientific research in the development of polymer nanocomposites for electrical energy storage applications. Considerable progress has been made over the past several years in the enhancement of the energy densities of the polymer nanocomposites via tuning the chemical structures of ceramic fillers and polymer matrix and engineering the polymer–ceramic interfaces. This article summarizes a range of current approaches to dielectric polymer nanocomposites, including the ferroelectric polymer matrix, increase of the dielectric permittivity using high‐permittivity ceramic fillers and conductive dopants, preparation of uniform composite films based on surface‐functionalized fillers, and utilization of the interfacial coupling effect. Primary attentions have been paid to the dielectric properties at different electric fields and their correlation with film morphology, chemical structure, and filler concentration. This article concludes with a discussion of scientific issues that remain to be addressed as well as recommendations for future research. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 49: 1421–1429, 2011

Resistive Switches: Spinodal Decomposition of Blends of Semiconducting and Ferroelectric Polymers (Adv. Funct. Mater. 10/2011)

The operation of resistive switches based on phase-separated blends of organic ferroelectrics and semiconductors depends significantly on the microstructure of such systems. On page 1887, Kamal Asadi and co-workers show that the preferred bicontinuouse microstructure is formed by spinodal-decomposition phase separation of the blend. The cover image shows the corresponding microstructure probed by atomic force microscopy: the smooth valley is the featureless amorphous semiconductor phase surrounded by a crystalline ferroelectric matrix.

An All‐Printed Ferroelectric Active Matrix Sensor Network Based on Only Five Functional Materials Forming a Touchless Control Interface

Macroelectronic components combining different classes of devices often suffer from the high complexity and costs of the manufacturing processes. The printing of an active-matrix sensor network using only five functional inks is demonstrated. The result is an all-printed monolithically integrated touchless input interface, including ferroelectric sensor pixels, organic transistors for impedance matching, and an electrochromic display.

PbTiO3 – P(VDF-TrFE) – Nanocomposites for Pressure and Temperature Sensitive Skin

Nanocomposites of a ferroelectric matrix polymer with dispersed ferroelectric ceramic nanoparticles can be polarized to be piezo- or pyroelectric alone at a given temperature, due to the different origin of piezoelectricity in polymers (dipole density) and ceramics (intrinsic). With a two-step poling procedure, which allows selective poling of the ceramic inclusion and the ferroelectric polymer, bifunctionality is achieved in the same material. The selective poling of filler and matrix phase is proved by ferroelectric hysteresis measurements at room temperature. Such bifunctional materials may be interesting for artificial skin, sensitive to changes in pressure and temperature.

Dynamic response of a fast near infra-red Mueller matrix ellipsometer

The dynamic response of a near infra-red ferroelectric liquid crystal-based Mueller matrix ellipsometer (NIR FLC-MME) is presented. A time-dependent simulation model, using the measured time response of the individual FLCs, is used to describe the measured temporal response. Furthermore, the impulse response of the detector and the pre-amplifier is characterized and included in the simulation model. The measured time-dependent intensity response of the MME is reproduced in simulations, and it is concluded that the switching time of the FLCs is the limiting factor for the Mueller matrix measurement time of the FLC-based MME. Based on measurements and simulations, our FLC-based NIR-MME system is estimated to operate at the maximum speed of approximately 16 ms per Mueller matrix measurement. The FLC-MME may be operated several times faster, since the switching time of the crystals depends on the individual crystal being switched, and to what state it is switched. As a demonstration, the measured temporal response of the Mueller matrix and the retardance of a thick liquid crystal variable retarder upon changing state is demonstrated.

Imaging liquid crystals dispersed in a ferroelectric polymer matrix by means of thermal-pulse tomography

A new arrangement of the optical elements in a Thermal-Pulse-Tomography (TPT) setup allows to scan micrometer structures in composite and heterogeneous samples such as polymer-dispersed liquid crystals (PDLCs). The non-destructive TPT technique allows the determination of three-dimensional profiles of polarization and space charge in dielectrics. The samples under study were 12 μm thick films of a copolymer of vinylidene fluoride with trifluoroethylene P(VDF-TrFE) (65/35) with embedded liquid-crystal droplets. The poling process was performed in direct contact well above the coercive field of the copolymer. The 3D map obtained from scanning with a 10 μm wide spot shows elliptically shaped areas with liquid-crystal droplets. Considering the droplets as oblate spheroids, their major axis lies in the x-y plane, while their minor axis in the z direction measures 0.5 μm or more. This result is in good agreement with scanning electron micrographs. It is believed that the major axis is overestimated due to imaging of liquid-crystal clusters.

Piezoelectric PZT / PVDF-copolymer 0-3 composites: aspects on film preparation and electrical poling

Composite films of lead zirconate titanate (PZT) and different (non-polar and polar) polyvinylidene fluoride (PVDF) copolymers are prepared as 30 to 150 μm thick freestanding, relatively flexible films. For low ceramic-volume fractions the ceramic fillers are homogeneous distributed within the polymer matrix as indicated by scanning electron microscopy studies. Ceramic-volume fractions higher than approximately 0.5 lead to porous composite films which became brittle. The brittle films are difficult to polarize and not suitable as piezoelectric transducers. The permittivities of non-porous composite films follow the Bruggeman model for dielectric mixtures. Different procedures are presented and verified in order to polarize the ferroelectric PZT particles and the ferroelectric polymer matrix. In detail, the overall polarization is discussed by taking into account the polarities of the applied poling voltage and of the measured piezoelectric signals. In summary, for composites with high ceramic-volume fractions piezoelectric coefficients of up to 8.6 pC/N and 22.1 pC/N (for PZT / P(VDFTrFE) composites) and up to 11.3 pC/N and 24.8 pC/N (for PZT / P(VDF-HFP) composites) are reached after short-term, room-temperature and long-term, high-temperature poling, respectively.