Experimental discovery of structure–property relationships in ferroelectric materials via active learning

The aim of this paper was to investigate the influence of dietary fibers from oat (OF) and apple (AF) (concentration 0.2%) on the pasting properties, rheological (including thixotropic and anti-thixotropic) and textural properties of 3% and 4% (w/w) waxy potato starch pastes. The samples were characterized by their pasting characteristics, the hysteresis loop test, and textural properties measured during storage. It was found that the breakdown viscosity values of the blends, including oat fibers, were lower than those of the others (waxy potato starch (WPS), WPS-AF), which suggests that these samples would have higher resistance to retrogradation and therefore would form a more stable paste. The pattern of flow curves showed that the investigated waxy potato starch and starch-fiber pastes were non-Newtonian fluids, thinned by shear. Areas of the hysteresis loops indicated that pastes with fibers had anti-thixotropic or mixed thixotropic/anti-thixotropic character. The greatest areas of the anti-thixotropy hysteresis loops were characteristic for WPS, while its mixtures with AF and OF caused a decrease in the value of these areas. It can indicate that starch-fiber blends were more stable during shearing. Fiber-type and starch concentration strongly affected the textural parameters of the starch-fiber gels.

The complex domain structure in ferroelectrics gives rise to electromechanical coupling, and its evolution (via domain switching) results in a time-dependent (i.e. viscoelastic) response. Although ferroelectrics are used in many technological applications, most do not attempt to exploit the viscoelastic response of ferroelectrics, mainly due to a lack of understanding and accurate models for their description and prediction. Thus, the aim of this thesis research is to gain better understanding of the influence of domain evolution in ferroelectrics on their dynamic mechanical response. There have been few studies on the viscoelastic properties of ferroelectrics, mainly due to a lack of experimental methods. Therefore, an apparatus and method called Broadband Electromechanical Spectroscopy (BES) was designed and built. BES allows for the simultaneous application of dynamic mechanical and electrical loading in a vacuum environment. Using BES, the dynamic stiffness and loss tangent in bending and torsion of a particular ferroelectric, viz. lead zirconate titanate (PZT), was characterized for different combinations of electrical and mechanical loading frequencies throughout the entire electric displacement hysteresis. Experimental results showed significant increases in loss tangent (by nearly an order of magnitude) and compliance during domain switching, which shows promise as a new approach to structural damping. A continuum model of the viscoelasticity of ferroelectrics was developed, which incorporates microstructural evolution via internal variables and associated kinetic relations. For the first time, through a new linearization process, the incremental dynamic stiffness and loss tangent of materials were computed throughout the entire electric displacement hysteresis for different combinations of mechanical and electrical loading frequencies. The model accurately captured experimental results. Using the understanding gained from the characterization and modeling of PZT, two applications of domain switching kinetics were explored by using Micro Fiber Composites (MFCs). Proofs of concept of set-and-hold actuation and structural damping using MFCs were demonstrated.

In this paper, the 3D needle-punched C/SiC composite was fabricated using the chemical vapor deposition and reactive infiltration method. Four different fiber preforms were formed using the needled-punch technology. The PyC interphase was deposited on the surface of the fibers to increase the toughness of the composite under tensile loading. Cyclic loading/unloading tensile tests were conducted at different peak stresses. A micromechanical hysteresis constitutive relationship was developed considering damage mechanisms of matrix cracking, interface debonding and slip, and fiber’s fracture and pullout. Using the developed hysteresis loops models and damage models, the hysteresis loops of four different types of 3D needle-punched C/SiC composites were predicted for different peak stresses. The hysteresis parameters of unloading residual strain, peak strain, hysteresis loops width, hysteresis loops area, interface slip ratio, and inverse tangent modulus were adopted to characterize the tensile damage evolution inside of composites. Relationship between composite’s hysteresis behavior and microstructure damage evolution is established. It was found that the composite’s hysteresis loops depend on the fiber’s preform and interface properties.

Silicon technology has advanced through the past four decades at exponential rate both in performance and productivity. Along with the miniaturization, the power demand grew also exponentially. New technologies are studied in order to develop switches that commute faster and, in the near future, we might see an increasing number of hybrid approaches to overcome the limitations CMOS performance. The ferroelectric thin layers have been studied for memory applications, one transistor memory cell, and recently ferroelectrics have been proposed by Salahuddin and Datta as dielectric materials in transistors in order to overcome the 60mV/dec limit of the subthreshold swing (SS) in silicon Metal Ferroelectric Semiconductor Field Effect Transistors, Fe-FET. The objective of this thesis is to study the negative capacitance effect of the ferroelectrics that are integrated into the gate stack of a MOS transistor. For this purpose different Ferroelectric Field Effect Transistors (Fe-FETs) have been designed, fabricated and characterized. Due to its remarkable characteristics, like low temperature deposition, medium-k and low leakage current, vinylidene fluoride trifluorethylene, P(VDF-TrFE), an organic ferroelectric copolymer, of 100 nm and 160 nm thickness was integrated into several MOS devices. Three devices were fabricated, a metal-ferroelectric-oxide-semiconductor transistor, a metal-ferroelectric-metal-oxide-metal capacitor and a metal-ferroelectric-metal-oxide-semiconductor transistor. The internal metal was introduced in-between the two dielectrics so that the potential at that point could be probed. For the first time, subthreshold slopes as low as 48mV/dec were obtained over more than three decades of drain current. The polarization was accurately extracted and the S-shape polarization and the negative slope could be observed. The polarization presented both hysteresis and negative slope polarization. A first-order model, that can accurately characterize a Fe-FET without the negative capacitance effect, was developed and validated with the measurements. Furthermore, a model for predicting the subthreshold slope improvement in case of the negative capacitance transistor, based on the Landau's ferroelectric parameters, was presented. Among others, two possible applications of the ferroelectric transistor are highlighted, one a temperature sensor using the metal-ferroelectric-metal-oxide-semiconductor device and the other one is a Schmitt trigger based on the metal-ferroelectric-oxide-semiconductor transistor.

Polarization switching mechanisms in ferroelectric materials are fundamentally linked to local domain structure and the presence of the structural defects, which both can act as nucleation and pinning centers and create local electrostatic and mechanical depolarization fields affecting wall dynamics. However, the general correlative mechanisms between domain structure and polarization dynamics are only weakly explored, precluding insight into the associated physical mechanisms. Here, the correlation between local domain structures and switching behavior in ferroelectric materials is explored using convolutional encoder-decoder networks, enabling image to spectral (im2spec) and spectral to image (spec2im) translations via encoding of latent variables. The latter reflect the assumption that the relationship between domain structure and polarization switching is parsimonious, i.e., is based upon a small number of local mechanisms. The analysis of latent variables distributions and their real-space representations provides insight into the predictability of the local switching behavior and hence associated physical mechanisms. We further pose that the regions where these correlative relationships are violated, i.e., predictability of the polarization dynamics from domain structure is reduced, represent the obvious target for detailed studies, e.g., in the context of automated experiments. This approach provides a workflow to establish the presence of correlation between local spectral responses and local structure and can be universally applied to spectral imaging techniques such as piezoresponse force microscopy (PFM), scanning tunneling microscopy (STM) and spectroscopy, and electron energy loss spectroscopy (EELS) in scanning transmission electron microscopy (STEM).

Scanning Probe Microscopy (SPM) based techniques probe material properties over microscale regions with nanoscale resolution, ultimately resulting in investigation of mesoscale functionalities. Among SPM techniques, piezoresponse force microscopy (PFM) is a highly effective tool in exploring polarization switching in ferroelectric materials. However, its signal is also sensitive to sample-dependent electrostatic and chemo-electromechanical changes. Literature reports have often concentrated on the evaluation of the Off-field piezoresponse, compared to On-field piezoresponse, based on the latter's increased sensitivity to non-ferroelectric contributions. Using machine learning approaches incorporating both Off- and On-field piezoresponse response as well as Off-field resonance frequency to maximize information, switching piezoresponse in a defect-rich Pb(Zr,Ti)O3 thin film is investigated. As expected, one major contributor to the piezoresponse is mostly ferroelectric, coupled with electrostatic phenomena during On-field measurements. A second component is electrostatic in nature, while a third component is likely due to a superposition of multiple non-ferroelectric processes. The proposed approach will enable deeper understanding of switching phenomena in weakly ferroelectric samples and materials with large chemo-electromechanical response.

Objective.Magnetic fluid hyperthermia is a promising adjuvant cancer therapy presently approaching clinical application. The therapeutic effect stems from the heat produced by magnetic nanoparticles (MNPs) administered to the tumor site and exposed to an AC magnetic field applied from outside the body. The objective of our study is to improve the integration of magnetic particle imaging (MPI) and hyperthermia as a theranostic application by allowing a real-time monitoring of local heat generation.Approach.The area of the dynamic hysteresis loop of the MNP is a measure of the heat produced by the MNP. However, depending on the specifics of the measurements, an accurate determination of the dynamic hysteresis loop of MNPs by conventional magnetic particle spectroscopy (MPS) can be hindered due to missing information of the first harmonic. The method presented in this work provides a solution to this problem by extracting the area of the hysteresis loop from measured MPS spectra through the reconstruction of the first harmonic.Main results.The method was tested on three distinct commercial MNP systems and found to be in good agreement with hysteresis loops directly obtained through AC magnetometry, confirming the method's reliability.Significance.This advancement enables accurate real-time monitoring of the energy dissipated as heat by the particles during MPS measurements and thus directly contributes to the development of MPI-guided hyperthermia.

Sensors and actuators based on ferroelectric materials have become indispensable in the fields of aerospace, high technology, and medical instruments. Most devices rely on the linear piezoelectric behavior of formulations of PZT which offer high bandwidth, linear actuation but very low strains of around 0.1%. The nonlinear electromechanical behavior of these materials is largely governed by the motion of domains and is highly affected by stress as well as electric field. The recent theories of Shu and Bhattacharya have sought to address some of the issues related to the structure and behavior of these materials at the mesoscale. One result of the theories is the prediction of another mode of actuation in ferroelectric crystals based on a combined electrical and mechanical loading that could result in strains of up to 6%. Descriptions of the phenomenological theories of ferroelectrics are presented including the classical Landau-Ginsburg-Devonshire theory and the more recent theory of Shu and Bhattacharya. Predictions are made, based on the theory, of the electromechanical behavior of ferroelectric crystals that are addressed by the experiments. An experimental setup has been designed to investigate large strain actuation in single crystal ferroelectrics based on combined electrical and mechanical loading. An investigation of the stress dependence of the electrostrictive response has been carried out with in situ observations of the domain patterns under constant compressive stress and variable electric field. Experiments have been performed on initially single domain crystals of barium titanate with (100) and (001) orientation at compressive stresses between 0 and 5 MPa. Global strain and polarization histories have been recorded. The electrostrictive response is shown to be highly dependent on the level of applied stress with a maximum strain of 0.9% measured at a compressive stress of about 2 MPa. An unusual secondary hysteresis has been observed in the polarization signal at high levels of stress that indicates an intermediate structural configuration, possibly the orthorhombic state. Polarized light microscopy has been used to observe the evolution of the domain pattern simultaneously with the strain and polarization measurement. These results are discussed and suggestions for future work are proposed.

This paper studies the relaxation processes and electromechanical hysteresis in relaxor piezoceramics based on the PZT system. Measurements and analysis of the electric displacement and mechanical strain hysteresis loops recorded in bipolar AC electric fields in the frequency range 0.001–5[Formula: see text]Hz were performed by means of the electromechanical response characterization system (STEPHV) and program (STEP). It was found that the coercive field, remnant and saturation electric displacement, area of hysteresis loops and relative mechanical strain values are strongly dependent on frequency. As a result of this study, complete sets of parameters characterizing the switching and ferroelectric hysteresis processes in relaxor piezoceramics were obtained.

Fatigue and reliability analysis of nano-modified scarf adhesive joints in carbon fiber composites

Characterization of domain structure and imprint of Pb(Zn1/3Nb2/3)O3-4.5%PbTiO3 (PZN-4.5%PT) single crystals by using PFM and SS-PFM techniques

In this article, Monte Carlo simulation methods were used to investigate the influence of interface layers between the ferroelectric core material and the electrodes on the hysteresis loop in ferroelectric thin films. The hysteresis loops were calculated using an existing Monte Carlo model. For certain interface configurations, the simulations resulted in asymmetric hysteresis loops, similar to imprinted loops, due to asymmetric nucleation kinetics. Although the results might not offer a new explanation for imprint in ferroelectric thin films, they provide insight into the often observed phenomenon of initially imprinted hysteresis loops of as-prepared thin-film samples.

The director orientation of the ferroelectric liquid crystal molecules within a surface-stabilised is measured by means of Diamant capacitance bridge. It turns out that the polarisation versus voltage curve has a strongly frequency-dependent hysteresis loop. For example, the width of the hysteresis loop (i.e. the coercive voltage) increases with increasing frequency f like f12/, over a large range of frequencies. A simple mathematical model, which considers the director orientation to be uniform throughout the display, explains these experimental facts.

Ferroelectric (FE) ultrathin films tend to favor a homogeneous polar state at strong interfacial bound charge screening conditions. Reducing screening parameter (β) may induce topological textures such as vortices, labyrinth stripes, and skyrmion bubbles (sk-bs). Here, we exploreβ- and temperature-induced phase transitions of polarization reversal in FE PbZr0.2Ti0.8O3(PZT) thin films using phase-field simulations under a 1% compressive strain. The results unveil a phase diagram comprising polarization reversal, hysteresis loop and topological structures. At room temperature, a phase transition from FE to antiferroelectric-like (AFE*) state occurs atβ∼0.53. At increasing temperatures, the FE and AFE* phases convert to a paraelectric state and form a tricritical point atβ∼0.78 andT∼ 770 K. Notably, at the phase boundary, a coexistence region of uniform polarization and isolated sk-bs emerges in a narrow screening range, which can be modulated by an applied electric field. Moreover, simulations of thermal effects on the FE to AFE* phase transition via the indirect method reveal a large electrocaloric effect around room temperature at low electric fields. Our findings uncover rich phenomena and elucidate underlying mechanisms in FE thin films, which hold promise for advanced device applications.

Extensive research demonstrated that a memristor can be used as a memory storage system. Subsequent studies have been carried out to facilitate the use of memristor as an electronic synapse. However, the price of the memristor is very high due to the high cost of fabricating a memristor. In order to continue research in this field, it is necessary to design memristor models and emulators. One of three significant fingerprints of the memristor is Hysteresis Loop. This loop area is useful to measure the memory effect of a memristor. In this paper, the area of hysteresis loop for a current-controlled generic memristor emulator is derived. An current controlled memristor emulator circuit design is developed using Multisim software with available low-cost electronic components. All three fingerprints of the memristor are realized through simulations and mathematical analysis. The obtained results are verified by modified memristor emulator system.