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Atsuo Fukuda - One of the best experts on this subject based on the ideXlab platform.
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gradual phase transition between the smectic c and smectic c a phases and the thresholdless Antiferroelectricity
Physical Review E, 2008Co-Authors: Jang-kun Song, Atsuo Fukuda, J K VijAbstract:We have constructed the phase diagrams for a binary-mixture system of antiferroelectric and ferroelectric liquid-crystalline materials in both thick and thin cells. In the phase diagrams the boundary between the smectic-${C}^{*}$ and smectic-${C}_{A}^{*}$ phases runs almost parallel to the temperature axis below from ca. $70\phantom{\rule{0.2em}{0ex}}\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}$ down to at least $\ensuremath{-}25\phantom{\rule{0.2em}{0ex}}\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}$. The $\mathrm{Sm}{C}^{*}\text{\ensuremath{-}}\mathrm{Sm}{C}_{A}^{*}$ phase transition for a thin cell shows a large supercooling, and a gradual transition occurs near the boundary. Moreover, the thin cell shows a continuous evolution from the antiferroelectric to the ferroelectric state by increasing the electric field applied across the cell. The continuous evolution seemingly reflects the phenomenon of thresholdless Antiferroelectricity. In order to explain these phenomena and in clarifying the mechanism of the so-called frustration between ferroelectricity and Antiferroelectricity, we have measured the interlayer interaction energy by varying the constituent concentrations in the binary-mixture system. The measured interlayer interaction close to the boundary indicates that the gradual phase transition and continuous evolution result from the suppression of the solitary-wave propagation by the effect of surfaces.
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Gradual phase transition between the smectic- C and smectic- C{A} phases and the thresholdless Antiferroelectricity.
Physical review. E Statistical nonlinear and soft matter physics, 2008Co-Authors: Jang-kun Song, Atsuo Fukuda, J K VijAbstract:We have constructed the phase diagrams for a binary-mixture system of antiferroelectric and ferroelectric liquid-crystalline materials in both thick and thin cells. In the phase diagrams the boundary between the smectic- C and smectic- C{A} phases runs almost parallel to the temperature axis below from ca. 70 degrees C down to at least -25 degrees C . The SmC-SmC_{A} phase transition for a thin cell shows a large supercooling, and a gradual transition occurs near the boundary. Moreover, the thin cell shows a continuous evolution from the antiferroelectric to the ferroelectric state by increasing the electric field applied across the cell. The continuous evolution seemingly reflects the phenomenon of thresholdless Antiferroelectricity. In order to explain these phenomena and in clarifying the mechanism of the so-called frustration between ferroelectricity and Antiferroelectricity, we have measured the interlayer interaction energy by varying the constituent concentrations in the binary-mixture system. The measured interlayer interaction close to the boundary indicates that the gradual phase transition and continuous evolution result from the suppression of the solitary-wave propagation by the effect of surfaces.
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two kinds of smectic c alpha subphases in a liquid crystal and their relative stability dependent on the enantiomeric excess as elucidated by electric field induced birefringence experiment
Physical Review E, 2005Co-Authors: N M Shtykov, A D L Chandani, A V Emelyanenko, Atsuo FukudaAbstract:: The electric-field-induced birefringence has been investigated by using a photoelastic modulator, with a view to obtaining a molecular model for the subphases produced by the frustration between ferroelectricity and Antiferroelectricity in the chiral smectic liquid crystals. It has been found that even in the bulk, there exist two subphases in the smectic-C(alpha)* (Sm-C(alpha)*) temperature range. By extending the Emelyanenko-Osipov model [Phys. Rev. E 68, 051703 (2003)] to include the temperature dependence of the tilt angle, we have alluded to a possible lifting of the degeneracy at the frustration point P(alpha) , where Sm-C(A)*, Sm-C*, and Sm-A have the same free energy. This leads to the appearance of uniaxial Sm-C(alpha)* characterized by short-pitch helical structures and consequently with a pitch much lower than the optical wavelength. The numerical calculations indicate that the short pitch may generally increase or decrease monotonically with temperature. Depending on the parameter value that represents the relative strength of ferroelectricity and Antiferroelectricity, the short-pitch temperature variation may abruptly change from increase to decrease at a temperature; this can be assigned to the observed phase transition between the two Sm-C(alpha)* subphases.
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probable langevin like director reorientation in an interface induced disordered smc like state of liquid crystals characterized by frustration between ferro and Antiferroelectricity
Physical Review Letters, 2001Co-Authors: Naoki Hayashi, Atsuo Fukuda, Takayuki Aoki, Tatsuhisa Kato, Tomohiro Ando, S S SeomunAbstract:To clarify the thresholdless, hysteresis free V-shaped switching due to frustration between ferro- and Antiferroelectricity, we have studied a prototype binary mixture system. The apparent orientational order parameters, and , obtained from polarized Raman scattering in thin homogeneous cells indicate that substrate interfaces induce some randomization of local in-plane directors at the tip of the V. Their correlation lengths, xi( parallel) approximately 3.5 nm and xi( perpendicular) approximately 75 nm, have been estimated by assuming the Langevin-like reorientation. Because of the much shorter xi(parallel) and xi(perpendicular) than the visible light wavelength, the switching process looks uniform.
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TARGET RESPONSE TIMES OF LIQUID CRYSTAL DISPLAYS ESTIMATED BY ANALYZING THE FRONT AND REAR PART GRAY LEVELS OF MOVING SQUARE PATTERNS
Japanese Journal of Applied Physics, 1999Co-Authors: Guo-ping Chen, Masahiko Yamaguti, Naoki Ito, Takayuki Aoki, Atsuo FukudaAbstract:The slow response of nematic materials causes the blurring of moving pictures on commercial liquid crystal displays (LCDs). We have estimated the critical response time τ90 necessary for apparently eliminating the blurring as a function of the gray level difference ΔG. The estimation is based on the observation that a running square pattern is hardly perceived when it differs from the background only by one in the 256 gray scale. For example, τ90 is 300 µs for ΔG=255 and 10 ms for ΔG=3, which can be attained by using advanced smectic materials with ferro- and/or Antiferroelectricity. Comments are given on another cause of blurring due to the characteristic feature of hold-type displaying in LCDs.
Lei Zhao - One of the best experts on this subject based on the ideXlab platform.
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Antiferroelectricity and ferroelectricity in a site doped silver niobate lead free ceramics
Journal of The European Ceramic Society, 2021Co-Authors: Aizhen Song, Jing Wang, J M Song, Jin Zhang, Lei ZhaoAbstract:Abstract AgNbO3-based ceramics have been considered as promising lead-free materials for energy storage applications. The Antiferroelectricity stability is a key factor for energy storage performance, which can be affected by Goldschmidt tolerance factor (t), phase structure and so on. The competition between t and phase structure was designed in A-site doped AgNbO3 ceramics. Li-doping leads to reduced t and a phase transition from monoclinic antiferroelectric phase to rhombohedral ferroelectric phase. Na-doping results in decreased t without phase transition. K-doping causes a phase transition from monoclinic antiferroelectric phase to orthorhombic ferroelectric phase. The enhanced ferroelectricity in (Ag1-xLix)NbO3 and (Ag1-xKx)NbO3 ceramics is due to the appearances of rhombohedral and orthorhombic phase, respectively. The enhanced Antiferroelectricity in (Ag1-xNax)NbO3 ceramics is attributed to the decreased t. By analyzing t, phase structure and Antiferroelectricity/ferroelectricity, it seems that the phase structure is dominating in determining the ferroelectricity/Antiferroelectricity rather than t in A-site doped AgNbO3 ceramics.
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Flexoelectricity in antiferroelectrics
Applied Physics Letters, 2018Co-Authors: Pablo Vales-castro, Lei Zhao, Krystian Roleder, D. Kajewski, Gustau CatalanAbstract:Flexoelectricity (coupling between polarization and strain gradients) is a property of all dielectric materials that has been theoretically known for decades, but only relatively recently it has begun to attract experimental attention. As a consequence, there are still entire families of materials whose flexoelectric performance is unknown. Such is the case of antiferroelectrics: materials with an antiparallel but switchable arrangement of dipoles. These materials are expected to be flexoelectrically relevant because it has been hypothesised that flexoelectricity could be linked to the origin of their Antiferroelectricity. In this work, we have measured the flexoelectricity of two different antiferroelectrics (PbZrO3 and AgNbO3) as a function of temperature, up to and beyond their Curie temperature. Although their flexocoupling shows a sharp peak at the antiferroelectric phase transition, neither flexoelectricity nor the flexocoupling coefficients are anomalously high, suggesting that it is unlikely that flexoelectricity causes Antiferroelectricity.
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silver niobate lead free antiferroelectric ceramics enhancing energy storage density by b site doping
ACS Applied Materials & Interfaces, 2018Co-Authors: Lei Zhao, Jing Gao, Qing Liu, Shujun ZhangAbstract:Lead-free dielectric ceramics with high recoverable energy density are highly desired to sustainably meet the future energy demand. AgNbO3-based lead-free antiferroelectric ceramics with double ferroelectric hysteresis loops have been proved to be potential candidates for energy storage applications. Enhanced energy storage performance with recoverable energy density of 3.3 J/cm3 and high thermal stability with minimal energy density variation (<10%) over a temperature range of 20–120 °C have been achieved in W-modified AgNbO3 ceramics. It is revealed that the W6+ cations substitute the B-site Nb5+ and reduce the polarizability of B-site cations, leading to the enhanced Antiferroelectricity, which is confirmed by the polarization hysteresis and dielectric tunability. It is believed that the polarizability of B-site cations plays a dominant role in stabilizing the Antiferroelectricity in AgNbO3 system, in addition to the tolerance factor, which opens up a new design approach to achieve stable antiferroelec...
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lead free antiferroelectric silver niobate tantalate with high energy storage performance
Advanced Materials, 2017Co-Authors: Lei Zhao, Shujun Zhang, Jingfeng LiAbstract:Antiferroelectric materials that display double ferroelectric hysteresis loops are receiving increasing attention for their superior energy storage density compared to their ferroelectric counterparts. Despite the good properties obtained in antiferroelectric La-doped Pb(Zr,Ti)O3-based ceramics, lead-free alternatives are highly desired due to the environmental concerns, and AgNbO3 has been highlighted as a ferrielectric/antiferroelectric perovskite for energy storage applications. Enhanced energy storage performance, with recoverable energy density of 4.2 J cm−3 and high thermal stability of the energy storage density (with minimal variation of ≤±5%) over 20–120 °C, can be achieved in Ta-modified AgNbO3 ceramics. It is revealed that the incorporation of Ta to the Nb site can enhance the Antiferroelectricity because of the reduced polarizability of B-site cations, which is confirmed by the polarization hysteresis, dielectric tunability, and selected-area electron diffraction measurements. Additionally, Ta addition in AgNbO3 leads to decreased grain size and increased bulk density, increasing the dielectric breakdown strength, up to 240 kV cm−1 versus 175 kV cm−1 for the pure counterpart, together with the enhanced Antiferroelectricity, accounting for the high energy storage density.
Xianlin Dong - One of the best experts on this subject based on the ideXlab platform.
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enhanced Antiferroelectricity and double hysteresis loop observed in lead free 1 x nanbo3 xcasno3 ceramics
Applied Physics Letters, 2019Co-Authors: Genshui Wang, Fei Cao, Xuefeng Chen, Xianlin DongAbstract:Well-defined polarization-electric field double hysteresis loops are rarely observed in pure NaNbO3 (NN) ceramics due to the metastability of the field-induced ferroelectric phase. In order to stabilize the antiferroelectric phase, various ABO3-type binary oxides were incorporated into a NaNbO3 ceramic, where the B-site is occupied with transition elements. In this work, CaSnO3 was chosen to construct the NaNbO3-based solid solution by reducing the Goldschmidt tolerance factor and ionic polarizability. X-ray diffraction patterns, transmission electron microscopy images, and Raman spectra indicate enhanced Antiferroelectricity. Typical double hysteresis loops were also observed from polarization-electric field measurements in ambient conditions with slightly weakened maximum polarization as the content of CaSnO3 increased. Our results reveal the generality of this strategy and pave the way for various applications involving high-power energy for NaNbO3-based ceramics.Well-defined polarization-electric field double hysteresis loops are rarely observed in pure NaNbO3 (NN) ceramics due to the metastability of the field-induced ferroelectric phase. In order to stabilize the antiferroelectric phase, various ABO3-type binary oxides were incorporated into a NaNbO3 ceramic, where the B-site is occupied with transition elements. In this work, CaSnO3 was chosen to construct the NaNbO3-based solid solution by reducing the Goldschmidt tolerance factor and ionic polarizability. X-ray diffraction patterns, transmission electron microscopy images, and Raman spectra indicate enhanced Antiferroelectricity. Typical double hysteresis loops were also observed from polarization-electric field measurements in ambient conditions with slightly weakened maximum polarization as the content of CaSnO3 increased. Our results reveal the generality of this strategy and pave the way for various applications involving high-power energy for NaNbO3-based ceramics.
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significantly enhanced energy storage performance of rare earth modified silver niobate lead free antiferroelectric ceramics via local chemical pressure tailoring
Journal of Materials Chemistry C, 2019Co-Authors: Hengchang Nie, Genshui Wang, Ningtao Liu, Mingxing Zhou, Fei Cao, Xianlin DongAbstract:Silver niobate (AgNbO3) is considered as one of the most promising lead-free replacements for lead-containing antiferroelectric (AFE) ceramics, and has been drawing progressively more attention because of its relatively high energy storage density. However, weak ferroelectricity in pure AgNbO3 exerts a negative impact on the energy storage performance, thus impeding the application of AgNbO3-based ceramics in high-power systems. In this study, an A-site doping strategy was employed to suppress the ferroelectric distortion and boost the AFE distortion of AgNbO3, based on local chemical pressure tailoring. An ultrahigh recoverable energy density (Wrec) of 4.5 J cm−3 was achieved in Ag0.88Gd0.04NbO3 ceramics, which is superior to that of other reported lead-free systems. The enhancement of energy storage performance is ascribed to two reasons: first, Antiferroelectricity could be boosted by smaller ions and suitable vacancies on A-sites, evidenced by X-ray diffraction patterns, Raman spectroscopy, and selected-area electron diffraction measurements. Moreover, the decreasing freezing temperature (Tf) and the increasing forward switching field (EF) as well as backward switching field (EA) with the increment of the gadolinium (Gd) content also confirmed the enhanced Antiferroelectricity in Gd-doped AgNbO3 ceramics. Second, the introduction of Gd2O3 could effectively decrease the grain size and increase the dielectric breakdown strength (DBS = 290 kV cm−1). The performance due to local chemical pressure tailoring makes Gd-doped AgNbO3 materials the most promising energy storage lead-free ceramics for dielectric energy storage capacitors.
Shujun Zhang - One of the best experts on this subject based on the ideXlab platform.
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silver niobate lead free antiferroelectric ceramics enhancing energy storage density by b site doping
ACS Applied Materials & Interfaces, 2018Co-Authors: Lei Zhao, Jing Gao, Qing Liu, Shujun ZhangAbstract:Lead-free dielectric ceramics with high recoverable energy density are highly desired to sustainably meet the future energy demand. AgNbO3-based lead-free antiferroelectric ceramics with double ferroelectric hysteresis loops have been proved to be potential candidates for energy storage applications. Enhanced energy storage performance with recoverable energy density of 3.3 J/cm3 and high thermal stability with minimal energy density variation (<10%) over a temperature range of 20–120 °C have been achieved in W-modified AgNbO3 ceramics. It is revealed that the W6+ cations substitute the B-site Nb5+ and reduce the polarizability of B-site cations, leading to the enhanced Antiferroelectricity, which is confirmed by the polarization hysteresis and dielectric tunability. It is believed that the polarizability of B-site cations plays a dominant role in stabilizing the Antiferroelectricity in AgNbO3 system, in addition to the tolerance factor, which opens up a new design approach to achieve stable antiferroelec...
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lead free antiferroelectric silver niobate tantalate with high energy storage performance
Advanced Materials, 2017Co-Authors: Lei Zhao, Shujun Zhang, Jingfeng LiAbstract:Antiferroelectric materials that display double ferroelectric hysteresis loops are receiving increasing attention for their superior energy storage density compared to their ferroelectric counterparts. Despite the good properties obtained in antiferroelectric La-doped Pb(Zr,Ti)O3-based ceramics, lead-free alternatives are highly desired due to the environmental concerns, and AgNbO3 has been highlighted as a ferrielectric/antiferroelectric perovskite for energy storage applications. Enhanced energy storage performance, with recoverable energy density of 4.2 J cm−3 and high thermal stability of the energy storage density (with minimal variation of ≤±5%) over 20–120 °C, can be achieved in Ta-modified AgNbO3 ceramics. It is revealed that the incorporation of Ta to the Nb site can enhance the Antiferroelectricity because of the reduced polarizability of B-site cations, which is confirmed by the polarization hysteresis, dielectric tunability, and selected-area electron diffraction measurements. Additionally, Ta addition in AgNbO3 leads to decreased grain size and increased bulk density, increasing the dielectric breakdown strength, up to 240 kV cm−1 versus 175 kV cm−1 for the pure counterpart, together with the enhanced Antiferroelectricity, accounting for the high energy storage density.
Cheol Seong Hwang - One of the best experts on this subject based on the ideXlab platform.
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Fluorite-structure antiferroelectrics.
Reports on progress in physics. Physical Society (Great Britain), 2019Co-Authors: Min Hyuk Park, Cheol Seong HwangAbstract:Ferroelectricity in fluorite-structure oxides like hafnia and zirconia have attracted increasing interest since 2011. Two spontaneous polarizations of the fluorite-structure ferroelectrics are considered highly promising for nonvolatile memory applications, with their superior scalability and Si compatibility compared to the conventional perovskite-structure ferroelectrics. Besides, Antiferroelectricity originating from a field-induced phase transition between the paraelectric and ferroelectric phases in fluorite-structure oxides is another highly interesting matter. It was suggested that the field-induced phase transition could be utilized for energy conversions between thermal and electrical energy, as well as for energy storage. The important energy-related applications of antiferroelectric fluorite-structure oxides, however, have not been systematically reviewed to date. Thus, in this work, the fluorite-structure antiferroelectrics are reviewed from their fundamentals to their applications based on pyroelectricity as well as Antiferroelectricity. Another important application field of the fluorite-structure antiferroelectrics is the semiconductor memory devices. The fluorite-structure antiferroelectrics can be utilized for antiferroelectric random-access-memories, negative capacitance field-effect-transistors, and flash memories. Moreover, the recently reported morphotropic phase boundary (MPB) between the ferroelectric and antiferroelectric phases in this material system marks another significant progress in this material system, and thus, the fundamentals and applications of the MPB phase are also reviewed.
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ferroelectricity and Antiferroelectricity of doped thin hfo2 based films
Advanced Materials, 2015Co-Authors: Min Hyuk Park, Johannes Muller, Taehwan Moon, Alfred Kersch, Uwe Schroeder, Thomas Mikolajick, Cheol Seong HwangAbstract:The recent progress in ferroelectricity and Antiferroelectricity in HfO2-based thin films is reported. Most ferroelectric thin film research focuses on perovskite structure materials, such as Pb(Zr,Ti)O3, BaTiO3, and SrBi2Ta2O9, which are considered to be feasible candidate materials for non-volatile semiconductor memory devices. However, these conventional ferroelectrics suffer from various problems including poor Si-compatibility, environmental issues related to Pb, large physical thickness, low resistance to hydrogen, and small bandgap. In 2011, ferroelectricity in Si-doped HfO2 thin films was first reported. Various dopants, such as Si, Zr, Al, Y, Gd, Sr, and La can induce ferro-electricity or Antiferroelectricity in thin HfO2 films. They have large remanent polarization of up to 45 μC cm(-2), and their coercive field (≈1-2 MV cm(-1)) is larger than conventional ferroelectric films by approximately one order of magnitude. Furthermore, they can be extremely thin ( 5 eV). These differences are believed to overcome the barriers of conventional ferroelectrics in memory applications, including ferroelectric field-effect-transistors and three-dimensional capacitors. Moreover, the coupling of electric and thermal properties of the antiferroelectric thin films is expected to be useful for various applications, including energy harvesting/storage, solid-state-cooling, and infrared sensors.