共查询到17条相似文献,搜索用时 62 毫秒
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制备了铅基弛豫铁电体0.9 Pb(Mg1/3Nb2/3)O3-0.1 PbTiO3和Pb(Zn1/3Nb2/3)O3基陶瓷.利用修正的局域冻结玻璃模型研究了弛豫铁电体微畴-宏畴转变动力学和微畴生长动力学,结果表明,微畴-宏畴转变过程是量子化的过程,微畴-宏畴转变的驱动力主要是热驱动力和能量驱动力,微畴-宏畴转变稳定性由活化能和状态数来判断,而微畴生长动力学的稳定性可以用稳定性判据值大小确定. 相似文献
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在广义梯度近似(GGA)下利用全电势线性化的缀加平面波法(FPLAPW)计算了钛酸钙(CaTiO3)的电子结构.将实验测得的晶胞体积记为V0,计算中所用的晶胞体积记为V.当V/V0=1.0时, Ti离子位移为零相应于总能量低能态,钛酸钙不会发生铁电相变.但如果其体积膨胀10%,则Ti离子的位移将导致能量极小值.这意味着在立方钛酸钙中有发生铁电相变的趋势,表明在钛酸钙中存在着体积诱发的铁电相变,即钛酸钙为先兆型铁电体.态密度在V/V0=1.1时, Ti d电子和O(2) p电子之间存在强烈的轨道杂化,这种杂化是出现铁电性的必要条件.电场梯度的结果也表明了这一点. 相似文献
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采用基于第一性原理的密度泛函方法对SnO2(110)表面的构型和电子结构进行了系统研究. 结果表明, 与理想表面相比, 表面弛豫导致表层五配位Sn原子向体相方向位移, 六配位Sn原子以及表面氧原子往真空方向移动, 而桥氧原子位置基本保持不变. 当表面厚度小于3 nm时, 表面能和表层原子的弛豫大小随着层数的增加出现振荡现象. 由能带计算结果得知, 以桥氧的2py/2i>pz轨道为主要成分的能带出现在体相的带隙中. 进一步考察了弛豫对表面电子结构的影响. 相似文献
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铅基复合钙钛矿型弛豫铁电单晶体PMNT的生长基元为多种[BO_6]配位八面体,晶体生长过程可视为多种八面体基元与Pb~(2 )的组装过程.这些生长基元向{111}面叠合时易采取法向生长机制,向{001}面叠合时易采取层状生长机制,由此决定了晶体生长速度的各向异性与晶体的形貌.Bridgman法生长的PMNT晶体在生长过程中由内向生长机制形成规则的负晶结构;在晶体生长过程中,在其自然表面上可形成正形与负形两种形貌;在高温退火过程中,由于PbO的分解,晶体表面上可形成类似“蚀象”的构型,这些可从[BO_6]八面体生长基元的组装或拆分方面获得解释. 相似文献
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钨青铜结构Ba6Zn0.67M9.33O30(M=Nb,Ta)的合成与介电特性 总被引:1,自引:0,他引:1
Two compounds Ba6Zn0.67M9.33O3 and Ba6Zn0.67M9.33O30 with tungsten bronze structure were synthesized in the BaO-ZnO-Nb2O5/Ta2O5 systems by the conventional high temperature solid-state reaction.The structure and dielectric properties of Ba6Zn0.67M9.33O3 and Ba6Zn0.67M9.33O30 were determined by X-ray powder diffraction,scanning electron microscope and dielectric measurements.The results show that Ba6Zn0.67M9.33O30 belongs to paraelectric phase of fully filled tetragonal tungsten bronze structure at room temperature with unit cell parameters a:1.26256(4) nm, c:0.39698(2) nm. The room temperature dielectric constant (ε) of Ba6Zn0.67M9.33O30 ceramic reached 108 combined with a low dielectric loss of 0.005 at 1 MHz. While Ba6Zn0.67M9.33O3 belongs to fully filled tetragonal tungsten bronze structure at room temperature with the unit cell parameters a:1.25940 (3) nm, c=0.40008(2) nm. Ba6Zn0.67M9.33O30 ceramic shows significant relaxor behaviors, and the phase transition from ferroelectric to paraelectric occurred at 55℃ (at 1 MHz). The room temperature dielectric constant (ε) of ceramic reached 570 at 1 MHz. 相似文献
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铅基复合钙钛矿型弛豫铁电单晶体PMNT,PZNT的生长基元为多种[BO~6]配位八面体。这些同型生长基元受本身稳定性的制约而在熔体中存在的几率不同。相对于[MgO~6]^1^0^-,[ZnO~6]^1^0^-八面体基元来说,[NbO~6]^7^-,[TiO~6]^8^-是更为有利的八面体基元。在基元组装过程中,各种[BO~6]八面体基元在稳定性、尺寸大小与电价上的分异致使生长界面对基元有一定的选择性,从而造成了晶体生长时成分与结构的短程起伏,并为有序畴及其它化学缺陷团簇的形成提供了条件。当加入掺质PbTiO~3时,由于[TiO~6]^8^-与[NbO~6]^7^-两种基元在组装时的类聚性及[TiO~6]^8^-对晶体稳定性的贡献,晶体的微区成分与结构得以调制,焦发石相得以抑制,这构成了用Bridgman法能直接从熔体中生长出纯钙钛矿相PMNT单晶的基础。而[MgO~6]^1^0^-与[ZnO~6]^1^0^-八面体基元的差致使PMNT,PZNT两单晶的生长难度有别,这在选择合适的生长方法时需加以考虑。 相似文献
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铅基复合钙钛矿型弛豫铁电单晶体PMNT,PZNT的生长基元为多种[BO~6]配位八面体。这些同型生长基元受本身稳定性的制约而在熔体中存在的几率不同。相对于[MgO~6]^1^0^-,[ZnO~6]^1^0^-八面体基元来说,[NbO~6]^7^-,[TiO~6]^8^-是更为有利的八面体基元。在基元组装过程中,各种[BO~6]八面体基元在稳定性、尺寸大小与电价上的分异致使生长界面对基元有一定的选择性,从而造成了晶体生长时成分与结构的短程起伏,并为有序畴及其它化学缺陷团簇的形成提供了条件。当加入掺质PbTiO~3时,由于[TiO~6]^8^-与[NbO~6]^7^-两种基元在组装时的类聚性及[TiO~6]^8^-对晶体稳定性的贡献,晶体的微区成分与结构得以调制,焦发石相得以抑制,这构成了用Bridgman法能直接从熔体中生长出纯钙钛矿相PMNT单晶的基础。而[MgO~6]^1^0^-与[ZnO~6]^1^0^-八面体基元的差致使PMNT,PZNT两单晶的生长难度有别,这在选择合适的生长方法时需加以考虑。 相似文献
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Weichuan Zhang Maochun Hong Junhua Luo 《Angewandte Chemie (International ed. in English)》2020,59(24):9305-9308
Halide double perovskites have recently emerged as a promising environmentally friendly optoelectronic and photovoltaic material for their inherent thermodynamic stability, high defect tolerance, and appropriate band gaps. However, to date, no ferroelectric material based on halide double perovskites has been discovered. Herein, by hetero‐substitution of lead and cation intercalation of n‐propylamine, the first halide double perovskite ferroelectric, (n‐propylammonium)2CsAgBiBr7 ( 1 ), is reported and it exhibits distinct ferroelectricity with a notable saturation polarization of about 1.5 μC cm?2. More importantly, single‐crystal photodetectors of 1 exhibit extraordinary performance with containing high on/off ratios of about 104, fast response rates of 141 μs, and detectivity as high as 5.3×1011 Jones. This finding opens a new way to design high‐performance perovskite ferroelectrics, and provides a viable approach in the search for stable and lead‐free optoelectronic materials as an alternative to the lead‐containing system. 相似文献
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Yun-Fang Zhang Fang-Fang Di Prof. Peng-Fei Li Prof. Ren-Gen Xiong 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(5):e202102990
In recent years, molecular ferroelectrics have received great attention due to their low weight, mechanical flexibility, easy preparation and excellent ferroelectric properties. Among them, crown-ether-based molecular ferroelectrics, which are typically composed of the host crown ethers, the guest cations anchored in the crown ethers, and the counterions, are of great interest because of the host-guest structure. Such a structure allows the components to occur order-disorder transition easily, which is beneficial for inducing ferroelectric phase transition. Herein, we summarized the research progress of crown ether host-guest molecular ferroelectrics, focusing on their crystal structure, phase transition, ferroelectric-related properties. In view of the small spontaneous polarization and uniaxial nature, we outlook the chemical design strategies for obtaining high-performance crown-ether-based molecular ferroelectrics. This minireview will be of guiding significance for the future exploration of crown ether host-guest molecular ferroelectrics. 相似文献
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Lizhen Liu Prof. Hongwei Huang 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(16):e202103975
The rapid development of industrialization and population has brought water, air-pollution and energy crises. Solar-driven catalysis is expected to relieve these issues. However, limited by poor light harvesting, serious charge recombination of semiconductors, and high surface reaction barriers, the low efficiency of solar conversion is far from satisfactory for industrial needs. Ferroelectrics are considered to be promising photocatalysts to overcome these shortcomings. Herein, perovskite ferroelectrics such as BaTiO3, PbTiO3, BiFeO3 and LiNbO3, layered bismuth-based ferroelectrics like Bi2WO6 and Bi2MoO6, and other ferroelectrics are introduced, and their crystal structure, polarity source and synthetic method are highlighted. Subsequently, research progress in ferroelectrics for photocatalysis is summarized, including pollution degradation, water splitting and CO2 reduction. Finally, the current challenges and future prospects of ferroelectric photocatalysts are provided. The purpose of this review is not only to provide a timely summary for the application of ferroelectrics in photocatalysis, but also to present deep insight and a guideline for future research work into ferroelectrics. 相似文献
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Hayato Anetai Kohei Sambe Dr. Takashi Takeda Dr. Norihisa Hoshino Prof. Tomoyuki Akutagawa 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(48):11233-11239
Organic ferroelectrics have been actively developed with the goal of fabricating environmentally friendly and low-cost memory devices. The remanent polarization of hydrogen-bonded organic ferroelectrics approaches that of the inorganic ones. Nanoscale fabrication of organic ferroelectrics is an essential aspect of high-density memory devices. A pyrene derivative with four tetradecylamide (−CONHC14H29) chains ( 1 ) formed an amide-type N−H⋅⋅⋅O hydrogen-bonded one-dimensional (1D) column, which demonstrated ferroelectricity in the discotic hexagonal columnar (Colh) liquid crystalline phase through the inversion of the orientation of the hydrogen-bonded chains. On the contrary, similar chiral pyrene derivatives bearing 3,7-dimethyl-1-octhylamide chains (S- 2 and R- 2 ) did not indicate the Colh phase and ferroelectricity. Homogeneous mixed liquid crystals ( 1 )1−x(S- 2 )x (i.e., between the ferroelectric 1 and the non-ferroelectric S- 2 ) enable the control of the nanoscale aggregation state of the organic ferroelectrics, resulting in a nanoscale effect of the 1D supramolecular ferroelectrics. Ferroelectric mixed liquid crystals ( 1 )1−x(S- 2 )x were observed at x≦0.03, where one S- 2 molecule was inserted after every thirty-three 1 molecule in the mixed liquid crystal ( 1 )33(S- 2 ). An average ( 1 )34 length of approximately 12 nm was required to maintain the 1D ferroelectricity, which was similar to the nanoscale limit of inorganic ferroelectrics, such as hafnium oxide thin film (≈15 nm). 相似文献
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Molecular Dynamics Simulation of Typical Molecular Ferroelectrics based on Polarized Crystal Charge Model 下载免费PDF全文
Molecular ferroelectrics are a promising class of ferroelectrics, with environmental friendliness, flexibility and low cost. In this work, a set of characteristic molecular ferroelectrics are simulated by molecular dynamics (MD) with polarized crystal charge (PCC). From the simulated results, their ferroelectric switching mechanisms are elucidated, with their ferroelectric hysteresis loops. The PCC charge model, recently developed by our group, containing the quantum electric polarization effect, is suitable in nature for studying molecular ferroelectrics. The simulated systems include the typical molecular ionic ferroelectrics, di-isopropyl-ammonium halide (DIPAX, X=C (Cl), B (Br), and I), as well as a pair of newly validated organic molecular ferroelectrics, salicylideneaniline and (-)-camphanic acid. In total, there are five systems under investigation. Results demonstrate that the PCC MD method is efficient and reliable. It not only elucidates the ferroelectric switching mechanism of the studied molecular ferroelectrics, but also extends the application range of the PCC MD. In conclusion, PCC MD provides an efficient protocol for extensive computer simulations of molecular ferroelectrics, with reliable ferroelectric properties and associated mechanisms, and would promote further exploration of novel molecular ferroelectrics. 相似文献
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Xiao-Li Xu Ling-Bo Xiao Dr. Jie Zhao Bing-Kun Pan Jun Li Prof. Dr. Wei-Qiang Liao Prof. Dr. Ren-Gen Xiong Prof. Dr. Gui-Fu Zou 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(45):20149-20157
The nonradiative recombination of electrons and holes has been identified as the main cause of energy loss in hybrid organic–inorganic perovskite solar cells (PSCs). Sufficient built-in field and defect passivation can facilitate effective separation of electron–hole pairs to address the crucial issues. For the first time, we introduce a homochiral molecular ferroelectric into a PSC to enlarge the built-in electric field of the perovskite film, thereby facilitating effective charge separation and transportation. As a consequence of similarities in ionic structure, the molecular ferroelectric component of the PSC passivates the defects in the active perovskite layers, thereby inducing an approximately eightfold enhancement in photoluminescence intensity and reducing electron trap-state density. The photovoltaic molecular ferroelectric PSCs achieve a power conversion efficiency as high as 21.78 %. 相似文献