Large Polarization Change Research Articles

Exploring Electro‐Thermal Interconversion in Oxide Superlattices Across Polarization Behavior Transition

AbstractDue to the great demand for global energy consumption, electro‐thermal energy interconversion has drawn great attention. Ferroelectrics as promising candidates realize energy conversion through pyroelectric and electrocaloric effects, but their efficiency is not sufficiently high. Herein, using phase‐field simulations, it is demonstrated that superlattices with polar topologies tend to have various polarization behaviors, and the antiferroelectric‐ to paraelectric‐like phase transition induces a large polarization change and thus a high pyroelectric response. In KNbO3/KTaO3 superlattices, the pyroelectric energy conversion has a scaled efficiency of 50% and the equivalent ZT of 7.2, and the electrocaloric cooling temperature reaches 40 K. The operation temperature can be tuned by changing the thickness of the superlattice. The results reveal that oxide superlattices are competitive in energy harvesting and conversion, thus creating new application prospects for polar topologies.

Correlation between multi-factor phase diagrams and complex electrocaloric behaviors in PNZST antiferroelectric ceramic system

Ferroelectric (FE) phase transition with a large polarization change benefits to generate large electrocaloric (EC) effect for solid-sate and zero-carbon cooling application. However, most EC studies only focus on the single-physical factor associated phase transition. Herein, we initiated a comprehensive discussion on phase transition in Pb_0.99Nb_0.02[(Zr_0.6Sn_0.4)_1−<i>x</i>Ti_<i>x</i>]_0.98O₃ (PNZST100<i>x</i>) antiferroelectric (AFE) ceramic system under the joint action of multi-physical factors, including composition, temperature, and electric field. Due to low energy barrier and enhanced zero-field entropy, the multi-phase coexistence point (<i>x</i> = 0.12) in the composition–temperature phase diagram yields a large positive EC peak of maximum temperature change (Δ<i>T</i>_max) = 2.44 K (at 40 kV/cm). Moreover, the electric field–temperature phase diagrams for four representative ceramics provide a more explicit guidance for EC evolution behavior. Besides the positive EC peaks near various phase transition temperatures, giant positive EC effects are also brought out by the electric field-induced phase transition from tetragonal AFE (AFE_T) to low-temperature rhombohedral FE (FE_R), which is reflected by a positive-slope boundary in the electric field–temperature phase diagram, while significant negative EC responses are generated by the phase transition from AFE_T to high-temperature multi-cell cubic paraelectric (PE_MCC) with a negative-slope phase boundary. This work emphasizes the importance of phase diagram covering multi-physical factors for high-performance EC material design.

Composition-tailor induced electrocaloric effect near room temperature in (Pb,Ba)HfO3 films

More and more researchers start to pay attention to the electrocaloric temperature change (ΔT) in polar materials, which is caused by an applied electric field. In this paper, Ba-doped PbHfO3 (PBH) films were prepared by sol-gel method. Their components, microstructures, dielectric polarization and electrocaloric effects (ECEs) were investigated. With the addition of Ba2+, PBH films went from antiferroelectric (AFE) to ferroelectric (FE). At the same time, their dielectric peaks shifted toward lower temperature. The maximum ΔT obtained in Pb0.8Ba0.2HfO3 FE film is 41.1 K, which is an order of magnitude larger than PbHfO3 film (ΔT ∼ −4 K at 50 °C) and Pb0.9Ba0.1HfO3 film (ΔT < 4 K at 120 °C). In order to explain this phenomenon, the Landau-Devonshire theory was adopted. Our analysis shows that the rapid variation of energy barrier height near the phase transition temperature is beneficial to obtain large polarization change and high △T, which is needed in solid-state cooling devices.

Reversible Adhesion Switching Using Spiropyran Photoisomerization in a High Glass Transition Temperature Polymer

Previous work has shown that photoisomerization of dopant molecules in a polystyrene film can either enhance or suppress its adhesion to a polar glass surface (Mostafavi, S. H. Macromolecules 2018, 51, 2388−2394; Mostafavi, S. H. Macromolecules 2019, 52, 6311–6317). In this paper, a different polymer host, Zeonex (ZX), is used in conjunction with the photochrome spiropyran. Nonpolar ZX has a higher glass transition temperature that makes it resistant to nanoscale mechanical deformations, while the spiropyran (SP) → merocyanine (MC) photoisomerization is a reversible reaction with a large polarity change. Ultraviolet light isomerizes SP to the polar MC form, increasing both the shear and pull-off adhesion forces to a clean glass surface by a factor of 5. Visible irradiation switches it back to the nonpolar SP form and returns the film back to its original weak adhesion, in contrast to the previously studied polystyrene films. The ability of visible light to switch off the polymer–glass adhesion is harnessed to make a light-controlled payload release device as well as to accelerate the polymer film delamination rate in water by a factor of 100. The kinetics of the water delamination, as well as the origin of residual adhesion after switching back to the SP form, are investigated. This work demonstrates how light-controlled noncovalent adhesion can be used as a solvent-free method to remove protective coatings or to disassemble structures.

NaNbO3-based antiferroelectric multilayer ceramic capacitors for energy storage applications

Antiferroelectric materials feature electric-field-induced phase transitions followed by a large polarization change characterized by double polarization hysteresis loops. Therefore, antiferroelectrics are engaging for high-energy density and high-power density applications, especially in the form of multilayer ceramic capacitors (MLCCs). However, the development of lead-free antiferroelectrics with stable double hysteresis loops is still challenging, especially for compositions based on NaNbO3. To this end, we have prepared MLCCs with the newly developed antiferroelectric composition 0.90NaNbO3-0.06SrSnO3-0.04(Na0.5Bi0.5)TiO3. The double hysteresis loops were determined at 24 kV/mm in the temperature range of 25–150 °C, with resulting recoverable energy storage ranging from 1.16 to 1.42 J/cm3, respectively. Moreover, the energy efficiency is rather constant at 0.4 in the same temperature range. Finally, the MLCCs exhibit resistance to electric field cycling and could withstand up to 1000 cycles. These results verify that NaNbO3-based antiferroelectrics in the form of MLCCs are promising for use in applications.

Demonstration of Enhanced Piezo-Catalysis for Hydrogen Generation and Water Treatment at the Ferroelectric Curie Temperature.

SummaryHydrogen can contribute significantly to the energy mix of the near future, as it is an attractive replacement for fossil fuels due to its high energy density and low greenhouse gas emission. A fascinating approach is to use the polarization change of a ferroelectric due to an applied stress or temperature change to achieve piezo- or pyro-catalysis for both H2 generation and wastewater treatment. We exploit low Curie temperature (Tc) ferroelectrics for polarization-driven electrochemical reactions, where the large changes in polarization and high activity of a ferroelectric near its Tc provides a novel avenue for such materials. We present experimental evidence for enhanced water splitting and rhodamine B degradation via piezo-catalysis by ultrasonic excitation at its Tc. Such work provides an effective strategy for water splitting/treatment systems that employ low Tc ferroelectrics under the action of mechanical stress or/and thermal fluctuations.

All-Mechanical Polarization Control and Anomalous (Electro)Mechanical Responses in Ferroelectric Nanowires.

Piezoelectric and ferroelectric nanowires exhibit properties and phases that are not available in the bulk. They are extremely promising for functional nanoscale application. On the basis of atomistic first-principles-based simulations, we predict an all-mechanical polarization control in ferroelectric nanowires. We report that the application of uniaxial compressive stress to ferroelectric nanowires with poor surface charge compensation leads to a reversible phase switching between the polar phase with axial polarization and macroscopically nonpolar flux-closure phase. The phase switching is associated with anomalously large changes in polarization and piezoelectric and mechanical response. In particular, in PbTiO3 nanowires the values as large as 5400 pC/N and 140 TPa-1 are predicted for the piezoelectric coefficient and elastic constant, respectively. Remarkably, the effect persists up to the gigahertz frequency which is potentially promising for nanoscale applications, such as nanogenerators, biomedical electronics, monitoring devices, nanosensors, nanotransducers, and nanoactuators.

Visible Light-Controlled Inversion of Pickering Emulsions Stabilized by Functional Silica Microspheres.

A new class of donor-acceptor Stenhouse adduct (DASA)-functionalized silica microspheres (SMs) is designed and described to formulate Pickering emulsions with inversion property and large polarity change upon visible light irradiation. By tuning the hydrophilicity of the functional SM particles with visible light, these Pickering emulsions can easily perform inversion from water-in-oil to oil-in-water. The inversion performance of the emulsions is ascribed to DASA photoisomerization from an extended, hydrophobic, and intensely purple-colored triene to a compact, zwitterionic, and colorless cyclopentenone upon irradiation with visible light. This unique inversion behavior has been applied to control encapsulation and the release of fluorescein sodium salt.

Ultrafast Photoinduced Electric-Polarization Switching in a Hydrogen-Bonded Ferroelectric Crystal.

Croconic acid crystals show proton displacive-type ferroelectricity with a large spontaneous polarization reaching 20 μC/cm^{2}, which originates from the strong coupling of proton and π-electron degrees of freedom. Such a coupling makes us expect a large polarization change by photoirradiations. Optical-pump second-harmonic-generation-probe experiments reveal that a photoexcited croconic-acid crystal loses the ferroelectricity substantially with a maximum quantum efficiency of more than 30 molecules per one absorbed photon. Based on density functional calculations, we theoretically discuss possible pathways toward the formation of a one-dimensional domain with polarization inversion and its recovery process to the ground state by referring to the dynamics of experimentally obtained polarization changes.

Materials and device concepts for electrocaloric refrigeration

Electrocaloric (EC) materials provide a solid-state cooling technology without polluting liquid refrigerants and noisy mechanical parts. Currently, basic research in this field is mainly focused on materials with a first-order phase transition exhibiting a large polarization change in a narrow temperature region near the phase transition point (Curie temperature) and, thus, a large EC effect. In this contribution, device operation above Curie temperature will be discussed. In this case, the polarization change originates from the temperature coefficient of the dielectric permittivity. To optimize material properties for EC refrigerator applications, we adapt the modified Curie–Weiss law describing a large class of ferroelectrics with a diffuse phase transition. Device performance will be evaluated based on the expected cooling power in dependence on thermodynamic cycle time, total thermal resistance and EC material thickness.

Large Electrocaloric Effect in a Dielectric Liquid Possessing a Large Dielectric Anisotropy Near the Isotropic–Nematic Transition

AbstractThe recent findings of large electrocaloric effects (ECEs) in ferroelectric polymers and in ferroelectric ceramic thin films have attracted great interest for developing new cooling cycles that are environmental friendly and have the potential to reach better efficiency than the existing vapor‐compression approach. Compared with these solid state ECE materials, a dielectric fluid with a large ECE can be more interesting because it may lead to new cooling cycles with simpler structures than these based on solid state ECE materials. Here it is shown that a large ECE can be realized in the liquid crystal (LC) 5CB near its nematic–isotropic (N‐I) phase transition. 5CB has a large dielectric anisotropy, which facilitates the electric‐field‐induced large polarization change. As a result, a large ECE, i.e., an isothermal entropy change of more than 23.6 J kg−1 K−1 is observed just above the N‐I transition.

Large Electrocaloric Effect from Electrical Field Induced Orientational Order-Disorder Transition in Nematic Liquid Crystals Possessing Large Dielectric Anisotropy

ABSTRACTLarge electrocaloric (EC) effects in ferroelectric polymers and in ferroelectric ceramics have attracted great attention for new refrigeration development which is more environmental friendly and more efficient and thus could be an alternative to the existing vapor-compression refrigerators which consume large energy and release large amount of green house gas. However in the past, all EC effects investigations have been focused on solid state dielectrics. It is interesting to ask whether a large EC effect can also be realized in dielectric fluids. A dielectric fluid with large EC effect could lead to new design of cooling devices with simpler structures than these based on solid state EC materials, for example, they can be utilized as both the refrigerant and heat exchange fluid. Here we present that a large EC effect can be realized in the liquid crystal (LC) 5CB near it's nematic-isotropic (N-I) phase transition. The LC 5CB possesses a large dielectric anisotropy which can induce large polarization change from the isotropic phase to the nematic phase near the N-I transition. An isothermal entropy change of more than 23 Jkg-1K-1 was observed near 39 oC that is just above the N-I transition.

Studies of Two-Photon Property of Intensely Luminescent Alkynyl−Phosphine Gold(I)−Copper(I) Complexes

Two-photon absorption (TPA) spectra of a series of highly symmetric, strong phosphorescence Au(I)-Cu(I) complexes 1-7 bearing alkynyl-phosphine ligands in solution were obtained over the biological windows (760-840 nm) by the two-photon-induced emission technique under femtosecond laser excitation. The resulting TPA cross sections are further confirmed by the open-aperture Z-scan method, which offers the advantage of reducing the excited-state reabsorption for these long-lived phosphorescence dyes. The results of these two methods are mutually in good agreement, showing that complexes 1-7 exhibit moderately strong TPA cross section, for example, approximately 710 GM at 760 nm for 1 in CH2Cl2. Owing to the highly centrosymmetric property, the resulting trend in TPA values for 1-7 can be rationalized by the unit of X-group-alkynyl-heterometallic-core-alkynyl-X-group fragment, categorized as A-pi-D-pi-A or D-pi-A-pi-D structural motif, which renders large changes in polarization upon excitation and provides significant near-IR TPA strength.

Cover Picture: Assembly and Photoinduced Organization of Mono‐ and Oligopeptide Molecules Containing an Azobenzene Moiety (Adv. Funct. Mater. 9/2007)

AbstractAn illustration of the phototriggered organization and dispersion of tri‐peptide‐substituted azobenzene derivatives, as reported on p. 1507 by Yoko Matsuzawa and co‐workers. The tri‐peptide units form a beta‐sheet structure through hydrogen bonding to assemble a fibrous network system. Cis–trans photoisomerization of the azobenzene moiety leads to a large polarity change of the component molecule to break and re‐form hydrogen bonds between the tri‐peptide units.Assembled systems consisting of an azobenzene moiety as the photofunctional component and valyl units as the network backbone are investigated. The molecular ordering of these assemblies is examined by spectroscopy and theoretical calculations. The number of valyl units greatly influences the molecular order in the organized systems. Only N‐(L‐valyl‐L‐valyl‐L‐valyl)azobenzene‐4‐carboxamide (3) forms a complete β‐sheet structure in this artificial assembly. Upon photoirradiation, the azobenzene moieties isomerize completely, revealing the reversibility in the structural organization through the flexibility of the β‐sheet network in this system.

Polarization rotation enhancement and scattering mechanisms in waveguide magnetophotonic crystals

Intermodal coupling in photonic band gap optical channels in magnetic garnet films is found to leverage the nonreciprocal polarization rotation. Forward fundamental-mode to high-order mode backscattering yields the largest rotations. The underlying mechanism is traced to the dependence of the grating-coupling constant on the modal refractive index and profile of the propagating beam. Large changes in polarization near the band edges are observed in first and second orders. Extreme sensitivity to linear birefringence exists in second order.

Large polarization change in two-dimensional metallic photonic crystals in subterahertz region

Interesting polarization characteristics of two-dimensional metallic photonic crystals (2D-MPC) in the subterahertz region have been found. We measured the temporal wave form of the THz wave transmitted thorough the 2D-MPC using a THz time domain spectroscopic system. The linear polarization of the incident THz wave transmitted through the 2D-MPC becomes elliptical with a slight tilting of the incident angle from the normal incidence. This result indicates that the 2D-MPC behaves not only as a band-pass filter already reported, but also as a wave plate. This large polarization change is attributed to the strong TE–TM polarization mixing in the 2D-MPC.

Synthesis and Radical Polymerization of Pyrocarbonate Functionalized Monomers: Application to Positive-Tone Photoresists

ABSTRACTThe synthesis of two new tert-butyl carbonic anhydride monomers, 4-vinylbenzoic and methacrylic tert-butyl carbonic anhydride was achieved successfully. Radical polymerization at 45°C yielded tert-butyl pyrocarbonate protected materials. Thermographic analysis showed that both polymers decompose cleanly at 135°C. The lithographic performance of both materials was evaluated in presence of 2,4,6-tris-(trichloromethyl)-s-triazine as photoacid generating species. It was demonstrated that the large polarity change resulted in a chemically amplified positive photoresist system

Polymerization ofN-(tert-butyldimethylsilyloxy)maleimide and applications of the polymers as resist materials

A new silicon-containing maleimide monomer, N-(tert-butyldimethylsilyloxy)-maleimide (SiOMI) has been synthesized. SiOMI was radically copolymerized with styrene derivatives (XSt) to obtain alternating copolymers, P(SiOMI/XSt), in high conversions. The copolymers have high glass transition temperatures above 190°C, and the tert-butyldimethylsilyloxy groups are thermally stable up to 300°C. The SiOMI units in the copolymers were converted into N-hydroxymaleimide (HOMI) units by acidolytic deprotection of the tert-butyldimethylsilyloxy protecting groups. The facile deprotection of the side-chain tert-butyldimethylsilyloxy groups from the protected copolymers provided a significant change in solubility of the polymers due to the large polarity change. Submicron positive-tone images were obtained from the copolymers containing an onium salt as a photoacid generator by irradiation with electron beam and development with alkaline solutions. The polymer films also showed very high oxygen plasma etch resistance compared with novolac resins. The silicon-containing maleimide polymers were found to have required properties, such as good alkaline solubility after deprotection, superior adhesion, low optical density, high thermal stability with high Tg, and high plasma etch resistance for applications as deep ultraviolet and electron beam resist materials. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 2507–2516, 1997

A Novel Polymer for a 193-nm Resist.

A novel methacrylate polymer for a 193-nm resist has been developed. The goal was to enhance the adhesion to Si substrates while ensuring compatibility with a TMAH developer for our methacrylate-based resist. We used two acid-cleavable compounds for the carboxylic acid protective groups: mevalonic lactone and 2-methyl-2-adamantanol. The strong hydrophilicity of mevalonic lactone ester affords good adhesion of the formulated resist patterns to Si substrates. Alicyclic 2-methyl-2-adamantanol provides dry-etch resistance. The acid-catalyzed deprotection of both protective groups generate a large polarity change in the exposed region of the resist films. This allows for high-contrast patterning with high sensitivity using a 2.38% TMAH developer. Using an ArF excimer laser exposure system, 0.17-μm L/S patterns have been resolved.

Use of synthetic peptides as tracer antigens in fluorescence polarization immunoassays of high molecular weight analytes

This paper describes a homogeneous immunoassay based on fluorescence polarization that enables subnanomolar detection of high molecular weight analytes. A monoclonal antibody (Mab) to human chorionic gonadotrophin (hCG) was screened against a panel of 221 synthetic peptides using the method of Geysen et al. (Geysen, H. M.; et al. J. Immunol. Methods 1987, 102, 259-274. Geysen, H. M.; et al. J. Mol. Immunol. 1986, 23, 709-715). One of these peptides, which was located near the C-terminus of the hCG beta chain, bound to the Mab with high affinity. It was labeled with tetramethylrhodamine (TMR) and used as the tracer antigen in a competitive fluorescence polarization immunoassay (FPIA) for hCG. The peptide-TMR conjugate binds specifically to the anti-hCG Mab with an antigen-binding affinity (Ka) of 1.5 x 10(7) M-1 at 6 degrees C. Its fluorescence intensity was enhanced by approximately 20% upon binding as a result of a prolonged excited-state lifetime. In a typical embodiment, hCG was determined at a level of 1 x 10(-9) M (95% confidence limit)--a 100-fold improvement over similar systems reported in the literature. This is mainly attributed to the large difference in hydrodynamic volume between the tracer and the antibody, which resulted in large changes in polarization of the peptide tracer upon binding. Issues related to sensitivity, specificity, and reversibility were also investigated. This method is believed to be of significant importance to rapid and economical measurements of high molecular weight antigens of clinical interest.