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Results for “molecule ferroelectrics”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Self–Healing and Stretchable Molecular Ferroelectrics with High Expandability

The interplay between crystal ordering and stretchability is frequently encountered in contemporary materials science, particularly in the case of ferroelectrics. The inherent dilemma arises when these materials need to withstand repetitive mechanical deformations or stretching without sacrificing their crystal integrity, all while retaining their remarkable ferroelectric properties and even exhibiting self-healing capabilities. This complexity further presents a significant challenge in the design and engineering of mechanically rigid molecular ferroelectric crystals, particularly for applications where both precise crystalline structure and mechanical adaptability are crucial. In this study, the humidity-controlled expansion and contraction, dissolution, and recrystallization of a self-assembled molecular ferroelectric-in-hydrogel framework are reported. Self-healing ferroelectric-in-hydrogel networks exhibit a recyclable humidity-tailored ionic conductivity from 2.86 × 10 –6 to 1.36 × 10 –5 S cm –1 , facilitating the stretchable piezoelectric sensing. Additionally, the dynamic bond reforming interactions are observed, leading to the tailoring of Young's modulus from 452 to 170 MPa, maintaining ferroelectricity under a strain of 20% with a piezoelectric coefficient of 15.7 pC N –1 . Upon lattice contraction, the molecular contacts undergo reforming, leading to the restoration of stretchable ferroelectrics/piezoelectrics and paving the way for stretchable bioelectronics for full-body motion monitoring. The capabilities highlighted here open avenues for stretchable and self-healing ferroelectric-in-hydrogel bioelectronic technologies.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Probing ferroelectricity by x-ray absorption spectroscopy in molecular crystals

We carry out x-ray absorption spectroscopy experiment at the oxygen $K$ edge in croconic acid (C 5 H 2 O 5 ) crystal as a prototype of ferroelectric organic molecular solid, whose electric polarization is generated by proton transfer. The experimental spectrum is well reproduced by the electron-hole excitation theory simulations from configuration generated by ab initio molecular dynamics simulation. When inversion symmetry is broken in the ferroelectric state, the hydrogen bonding environment on the two bonded molecules become inequivalent. Such a difference is sensitively probed by the bound excitation in the pre-edge, which is strongly localized on the excited molecules. Our analysis shows that a satellite peak in the pre-edge will emerge at higher excitation energy, which serves as a clear signature of ferroelectricity in the material.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Surface chemistry on a polarizable surface: Coupling of CO with KTaO 3 (001)

Polarizable materials attract attention in catalysis because they have a free parameter for tuning chemical reactivity. Their surfaces entangle the dielectric polarization with surface polarity, excess charge, and orbital hybridization. How this affects individual adsorbed molecules is shown for the incipient ferroelectric perovskite KTaO 3 . This intrinsically polar material cleaves along (001) into KO- and TaO 2 -terminated surface domains. At TaO 2 terraces, the polarity-compensating excess electrons form a two-dimensional electron gas and can also localize by coupling to ferroelectric distortions. TaO 2 terraces host two distinct types of CO molecules, adsorbed at equivalent lattice sites but charged differently as seen in atomic force microscopy/scanning tunneling microscopy. Temperature-programmed desorption shows substantially stronger binding of the charged CO; in density functional theory calculations, the excess charge favors a bipolaronic configuration coupled to the CO. These results pinpoint how adsorption states couple to ferroelectric polarization.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Proton-controlled molecular ionic ferroelectrics

Abstract Molecular ferroelectric materials consist of organic and inorganic ions held together by hydrogen bonds, electrostatic forces, and van der Waals interactions. However, ionically tailored multifunctionality in molecular ferroelectrics has been a missing component despite of their peculiar stimuli-responsive structure and building blocks. Here we report molecular ionic ferroelectrics exhibiting the coexistence of room-temperature ionic conductivity (6.1 × 10 −5 S/cm) and ferroelectricity, which triggers the ionic-coupled ferroelectric properties. Such ionic ferroelectrics with the absorbed water molecules further present the controlled tunability in polarization from 0.68 to 1.39 μC/cm 2 , thermal conductivity by 13% and electrical resistivity by 86% due to the proton transfer in an ionic lattice under external stimuli. These findings enlighten the development of molecular ionic ferroelectrics towards multifunctionality.

42 ENGINEERING↗
DOE OSTI2021

Two-dimensional multifunctional materials from endohedral fullerenes

A multifunctional two-dimensional (2D) material is theoretically predicted based on systematic ab initio calculations and model simulations for the honeycomb lattice of endohedral fullerene W@C 28 molecules. It has structural bistability, ferroelectricity, multiple magnetic phases, and excellent valley characters and can be easily functionalized by the proximity effect with magnetic isolators such as MnTiO 3 . Furthermore, we may also manipulate the valley Hall and spin transport properties by selectively switching a few W@C 28 molecules to the metastable phase. These conclusions contribute to integrating different functions in a single 2D material for technological innovations.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2024

Peptide programming of supramolecular vinylidene fluoride ferroelectric phases

Ferroelectric structures have spontaneous macroscopic polarization that can be inverted using external electric fields and have potential applications including information storage, energy transduction, ultralow-power nanoelectronics and biomedical devices. These functions would benefit from nanoscale control of ferroelectric structure, the ability to switch polarization with lower applied fields (low coercive field) and biocompatibility. Soft ferroelectrics based on poly(vinylidene fluoride) (PVDF) have a thermodynamically unstable ferroelectric phase in the homopolymer, complex semi-crystalline structures, and high coercive fields. Here, in this work, we report on ferroelectric materials formed by water-soluble molecules containing only six VDF repeating units covalently conjugated to a tetrapeptide, with the propensity to assemble into the β-sheet structures that are ubiquitous in proteins. This led to the discovery of ribbon-shaped ferroelectric supramolecular assemblies that are thermodynamically stable with their long axes parallel to both the preferred hydrogen-bonding direction of β-sheets and the bistable polar axes of VDF hexamers. Relative to a commonly used ferroelectric copolymer, the biomolecular assemblies exhibit a coercive field that is two orders of magnitude lower, as the result of supramolecular dynamics, and a similar level of remnant polarization, despite having a peptide content of 49 wt%. Furthermore, the Curie temperature of the assemblies is about 40 °C higher than that of a copolymer containing a similar amount of VDF. This supramolecular system was created using a biologically inspired strategy that is attractive in terms of sustainability and that could lead to new functions for soft ferroelectrics.

36 MATERIALS SCIENCE↗
DOE OSTI2023

The nature of dynamic local order in CH 3 NH 3 PbI 3 and CH 3 NH 3 PbBr 3

Hybrid organic-inorganic lead-halide perovskites (LHPs) are a class of semiconductors with remarkable properties relevant to optoelectronic applications. The structure-property-function relationship in LHPs, however, is poorly understood, leading to incomplete descriptions of optoelectronic properties and a persistent problem of device degradation due to ion migration. Here, we reveal the true structure to contain an assembly of dynamic, two-dimensional short-range structural correlations in the lead-halide octahedral sublattice, with additional correlations between organic molecules. Here, we propose that these correlations are the origin of large-amplitude halide displacements, which govern charge carrier mobility and the sharpness of the absorption edge. Correlations between organic molecules may introduce regions of transient ferroelectricity or antiferroelectricity, which increase charge carrier lifetime. Finally, the correlations introduce an ion diffusion barrier that is static on the timescale of diffusive jumps.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Ferroelectrics and photovoltaics in endohedral fullerenes-based van der Waals heterostructures

Using the density functional theory calculations, we studied the ferroelectric, electronic, and optical properties of a series of bias-controllable endohedral fullerene molecules (TM@C28, TM = Ti-Ni). One important finding is that Cr@C28 has a large electric dipole moment and an appropriate bandgap (∼1.2 eV). By sandwiching Cr@C28 molecules between two graphene or transition metal dichalcogenide layers, the heterostructures may combine strong ferroelectricity and excellent optical properties. This paves the way for the development of two-dimensional van der Waals ferroelectric-photovoltaic materials.

Li, Jie (ORCID:0000000237334587)↗
DOE OSTI2020

Controllable skyrmion chirality in ferroelectrics

Chirality, an intrinsic handedness, is one of the most intriguing fundamental phenomena in nature. Materials composed of chiral molecules find broad applications in areas ranging from nonlinear optics and spintronics to biology and pharmaceuticals. However, chirality is usually an invariable inherent property of a given material that cannot be easily changed at will. Here, we demonstrate that ferroelectric nanodots support skyrmions the chirality of which can be controlled and switched. We devise protocols for realizing control and efficient manipulations of the different types of skyrmions. Our findings open the route for controlled chirality with potential applications in ferroelectric-based information technologies.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2022

Observation of a uniaxial ferroelectric smectic A phase

We report the observation of the smectic A F , a liquid crystal phase of the ferroelectric nematic realm. The smectic A F is a phase of small polar, rod-shaped molecules that form two-dimensional fluid layers spaced by approximately the mean molecular length. The phase is uniaxial, with the molecular director, the local average long-axis orientation, normal to the layer planes, and ferroelectric, with a spontaneous electric polarization parallel to the director. Polarization measurements indicate almost complete polar ordering of the ∼10 Debye longitudinal molecular dipoles, and hysteretic polarization reversal with a coercive field ∼2 × 10 5 V/m is observed. The SmAF phase appears upon cooling in two binary mixtures of partially fluorinated mesogens: 2N/DIO, exhibiting a nematic (N)–smectic Z A (SmZ A )–ferroelectric nematic (N F )–SmA F phase sequence, and 7N/DIO, exhibiting an N–SmZ A –SmA F phase sequence. The latter presents an opportunity to study a transition between two smectic phases having orthogonal systems of layers.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

An Integrated Theoretical and Experimental Approach to Achieve Highly Polarizable Relaxor Ferroelectric Liquid Crystalline Polymers

In this project, we have designed and synthesized a series of aliphatic sulfonlyated chiral and achiral polyether. The major objective is to achieve ferroelectric liquid crystalline polymers with a high spontaneous polarization (0.04-0.08 C/m2). Due to the strong dipole-dipole interaction among the sulfonyl side groups, which resembles that among water molecules, these polyethers can exhibit various liquid crystalline self-assemblies without any rigid mesogens. By tuning the position of the sulfonyl groups, single versus double sulfonyl groups, and spacer/tail length and methyl branches, the liquid crystalline phases include smectic A, smectic C, and hexagonal columnar phases. When the single sulfonyl group is next to the main chain or disulfonyl groups are separated by a short C3 spacer, the dipolar interaction is too strong to allow any dipole switching. As a result, the linear dielectric behavior is observed with a low dielectric constant of 5-7. When the single sulfonyl groups are away from the main chain, the paraelectric behavior is obtained with a high dielectric constant around 20. From this study, we predict that by further tailoring the intermolecular interactions among the disulfonyl side groups, it is possible to achieve ferroelectric property for these liquid crystalline polymers. If successful, these ferroelectric liquid crystalline polymers can be used for efficient electrocaloric cooling applications.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Giant Electrostriction via Nanodomain Engineering in Relaxor Ferroelectric Polymers

Relaxor ferroelectric (RFE) polymers hold great promise for artificial muscles due to their high actuation strain, high loading stress, and fast response. However, the structural origin underlying their large electrostrictive deformation remains elusive. In this study, we investigate poly(vinylidene fluoride-co-trifluoroethylene) [P(VDF-TrFE)]-based RFE terpolymers, incorporating 1,1-chlorofluoroethylene (CFE) or chlorotrifluoroethylene (CTFE) (the terpolymers are denoted as terP-CFE and terP-CTFE, respectively) as termonomers. Although both terpolymers show similar semicrystalline morphology, drastically different electrostrictive properties are observed. Specifically, the terP-CFE annealed at 100 °C achieves a record-high transverse strain of ∼10.6%, whereas 100 °C-annealed terP-CTFE only shows a much lower actuation strain of ∼4.2% at the same poling field of 190 MV/m. To elucidate the origin of this difference, time-resolved wide-angle X-ray diffraction, small-angle X-ray scattering, and Fourier transform infrared experiments are performed during in situ electric poling. An RFE-to-ferroelectric (FE) crystal phase transition is observed for terP-CFE but is absent for terP-CTFE. Beyond the contribution of the crystalline phase, the oriented amorphous fraction and crystalline defects (e.g., taut-tie molecules) also play significant roles in enhancing electrostriction. In conclusion, this mechanistic insight provides a valuable foundation for the rational design of next-generation RFE polymers with tunable properties through defect engineering of their semicrystalline structures.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Energy conversion and storage via photoinduced polarization change in non-ferroelectric molecular [CoGa] crystals

To alleviate the energy and environmental crisis, in the last decades, energy harvesting by utilizing optical control has emerged as a promising solution. Here we report a polar crystal that exhibits photoenergy conversion and energy storage upon light irradiation. The polar crystal consists of dinuclear [CoGa] molecules, which are oriented in a uniform direction inside the crystal lattice. Irradiation with green light induces a directional intramolecular electron transfer from the ligand to a low-spin Co III centre, and the resultant light-induced high-spin Co II excited state is trapped at low temperature, realizing energy storage. Additionally, electric current release is observed during relaxation from the trapped light-induced metastable state to the ground state, because the intramolecular electron transfer in the relaxation process is accompanied with macroscopic polarization switching at the single-crystal level. It demonstrates that energy storage and conversion to electrical energy is realized in the [CoGa] crystals, which is different from typical polar pyroelectric compounds that exhibit the conversion of thermal energy into electricity.

25 ENERGY STORAGE↗
DOE OSTI2021

Chemically and electrically tunable spin polarization in ferroelectric Cd-based hybrid organic-inorganic perovskites

Density functional theory computations are used to predict the electronic structure of Cd-based hybrid organic-inorganic high-T C ferroelectric perovskites with TMCM-CdCl 3 being one representative. Here we report Rashba-Dresselhaus spin splitting in the valence band of these nonmagnetic compounds. Interestingly, we find in computations that the splitting is not necessarily sensitive to the polarization of the material but to the organic molecule itself which opens a way to its chemical tunability through the choice of the molecule. Further chemical tunability of spin splitting is shown to be possible through a substitution of Cl in the CdCl 3 chains as the valence band was found to originate from Cl-Cl weekly bonding orbitals. For example, the substitution of Cl with Br in TMCM-CdCl 3 resulted in a ten times increase of spin splitting. Furthermore, the spin polarization in these materials gives origin to persistent spin textures which are coupled to the polarization direction, and, therefore, can be controlled by the electric field. This is promising for spintronics applications.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Quasi-one-dimensional hydrogen bonding in nanoconfined ice

Abstract The Bernal-Fowler ice rules stipulate that each water molecule in an ice crystal should form four hydrogen bonds. However, in extreme or constrained conditions, the arrangement of water molecules deviates from conventional ice rules, resulting in properties significantly different from bulk water. In this study, we employ machine learning-driven first-principles simulations to identify a new stabilization mechanism in nanoconfined ice phases. Instead of forming four hydrogen bonds, nanoconfined crystalline ice can form a quasi-one-dimensional hydrogen-bonded structure that exhibits only two hydrogen bonds per water molecule. These structures consist of strongly hydrogen-bonded linear chains of water molecules that zig-zag along one dimension, stabilized by van der Waals interactions that stack these chains along the other dimension. The unusual interplay of hydrogen bonding and van der Waals interactions in nanoconfined ice results in atypical proton behavior such as potential ferroelectric behavior, low dielectric response, and long-range proton dynamics.

Science & Technology - Other Topics↗
DOE OSTI2024

Ab initio generalized Langevin equation

We introduce a machine learning–based approach called ab initio generalized Langevin equation (AIGLE) to model the dynamics of slow collective variables (CVs) in materials and molecules. In this scheme, the parameters are learned from atomistic simulations based on ab initio quantum mechanical models. Force field, memory kernel, and noise generator are constructed in the context of the Mori–Zwanzig formalism, under the constraint of the fluctuation–dissipation theorem. Combined with deep potential molecular dynamics and electronic density functional theory, this approach opens the way to multiscale modeling in a variety of situations. Here, we demonstrate this capability with a study of two mesoscale processes in crystalline lead titanate, namely the field-driven dynamics of a planar ferroelectric domain wall, and the dynamics of an extensive lattice of coarse-grained electric dipoles. In the first case, AIGLE extends the reach of ab initio simulations to a regime of noise-driven motions not accessible to molecular dynamics. In the second case, AIGLE deals with an extensive set of CVs by adopting a local approximation for the memory kernel and retaining only short-range noise correlations. The scheme is computationally more efficient than molecular dynamics by several orders of magnitude and mimics the microscopic dynamics at low frequencies where it reproduces accurately the dominant far-infrared absorption frequency.

97 MATHEMATICS AND COMPUTING↗