共查询到20条相似文献,搜索用时 15 毫秒
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Qiang Pan Zhi‐Bo Liu Han‐Yue Zhang Wan‐Ying Zhang Yuan‐Yuan Tang Yu‐Meng You Peng‐Fei Li Wei‐Qiang Liao Ping‐Ping Shi Rong‐Wei Ma Ru‐Yuan Wei Ren‐Gen Xiong 《Advanced materials (Deerfield Beach, Fla.)》2017,29(29)
An outstanding advantage of inorganic ceramic ferroelectrics is their usability in the polycrystalline ceramic or thin film forms, which has dominated applications in the ferroelectric, dielectric, and piezoelectric fields. Although the history of ferroelectrics began with the molecular ferroelectric Rochelle salt in 1921, so far there have been very few molecular ferroelectrics, with lightweight, flexible, low‐cost, and biocompatible superior properties compared to inorganic ceramic ferroelectrics, that can be applied in the polycrystalline form. Here, a multiaxial molecular ferroelectric, guanidinium perchlorate ([C(NH2)3]ClO4), with a record‐high phase transition temperature of 454 K is presented. It is the rectangular polarization–electric field (P –E ) hysteresis loops recorded on the powder and thin film samples (with respective large P r of 5.1 and 8.1 µC cm?2) that confirm the ferroelectricity of [C(NH2)3]ClO4 in the polycrystalline states. Intriguingly, after poling, the piezoelectric coefficient (d 33) of the powder sample shows a significant increase from 0 to 10 pC N?1, comparable to that of LiNbO3 single crystal (8 pC N?1). This is the first time that such a phenomenon has been observed in molecular ferroelectrics, indicating the great potential of molecular ferroelectrics being used in the polycrystalline form like inorganic ferroelectrics, as well as being viable alternatives or supplements to conventional ceramic ferroelectrics. 相似文献
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Jianming Deng Yanyu Liu Mingqiang Li Sheng Xu Yingzhuo Lun Peng Lv Tianlong Xia Peng Gao Xueyun Wang Jiawang Hong 《Small (Weinheim an der Bergstrasse, Germany)》2020,16(1)
van der Waals (vdW) layered materials have rather weaker interlayer bonding than the intralayer bonding, therefore the exfoliation along the stacking direction enables the achievement of monolayer or few layers vdW materials with emerging novel physical properties and functionalities. The ferroelectricity in vdW materials recently attracts renewed interest for the potential use in high‐density storage devices. With the thickness becoming thinner, the competition between the surface energy, depolarization field, and interfacial chemical bonds may give rise to the modification of ferroelectricity and crystalline structure, which has limited investigations. In this work, combining the piezoresponse force microscope scanning, contact resonance imaging, the existence of the intrinsic in‐plane polarization in vdW ferroelectrics CuInP2S6 single crystals is reported, whereas below a critical thickness between 90 and 100 nm, the in‐plane polarization disappears. The Young's modulus also shows an abrupt stiffness at the critical thickness. Based on the density functional theory calculations, these behaviors are ascribed to a structural phase transition from monoclinic to trigonal structure, which is further verified by transmission electron microscope technique. These findings demonstrate the foundational importance of structural phase transition for enhancing the rich functionality and broad utility of vdW ferroelectrics. 相似文献
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Xiang Wang Anyang Cui Fangfang Chen Liping Xu Zhigao Hu Kai Jiang Liyan Shang Junhao Chu 《Small (Weinheim an der Bergstrasse, Germany)》2019,15(46)
Many van der Waals layered 2D materials, such as h‐BN, transition metal dichalcogenides (TMDs), and group‐III monochalcogenides, have been predicted to possess piezoelectric and mechanically flexible natures, which greatly motivates potential applications in piezotronic devices and nanogenerators. However, only intrinsic in‐plane piezoelectricity exists in these 2D materials and the piezoelectric effect is confined in odd‐layers of TMDs. The present work is intent on combining the free‐standing design and piezoresponse force microscopy techniques to obtain and directly quantify the effective out‐of‐plane electromechanical coupling induced by strain gradient on atomically thin MoS2 and InSe flakes. Conspicuous piezoresponse and the measured piezoelectric coefficient with respect to the number of layers or thickness are systematically illustrated for both MoS2 and InSe flakes. Note that the promising effective piezoelectric coefficient (deff33) of about 21.9 pm V?1 is observed on few‐layered InSe. The out‐of‐plane piezoresponse arises from the net dipole moment along the normal direction of the curvature membrane induced by strain gradient. This work not only provides a feasible and flexible method to acquire and quantify the out‐of‐plane electromechanical coupling on van der Waals layered materials, but also paves the way to understand and tune the flexoelectric effect of 2D systems. 相似文献
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Fei Xue Xin He Jos Ramn Durn Retamal Ali Han Junwei Zhang Zhixiong Liu Jing‐Kai Huang Weijin Hu Vincent Tung Jr‐Hau He Lain‐Jong Li Xixiang Zhang 《Advanced materials (Deerfield Beach, Fla.)》2019,31(29)
Memristive devices have been extensively demonstrated for applications in nonvolatile memory, computer logic, and biological synapses. Precise control of the conducting paths associated with the resistance switching in memristive devices is critical for optimizing their performances including ON/OFF ratios. Here, gate tunability and multidirectional switching can be implemented in memristors for modulating the conducting paths using hexagonal α‐In2Se3, a semiconducting van der Waals ferroelectric material. The planar memristor based on in‐plane (IP) polarization of α‐In2Se3 exhibits a pronounced switchable photocurrent, as well as gate tunability of the channel conductance, ferroelectric polarization, and resistance‐switching ratio. The integration of vertical α‐In2Se3 memristors based on out‐of‐plane (OOP) polarization is demonstrated with a device density of 7.1 × 109 in.?2 and a resistance‐switching ratio of well over 103. A multidirectionally operated α‐In2Se3 memristor is also proposed, enabling the control of the OOP (or IP) resistance state directly by an IP (or OOP) programming pulse, which has not been achieved in other reported memristors. The remarkable behavior and diverse functionalities of these ferroelectric α‐In2Se3 memristors suggest opportunities for future logic circuits and complex neuromorphic computing. 相似文献
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Real‐Time Observation of Order‐Disorder Transformation of Organic Cations Induced Phase Transition and Anomalous Photoluminescence in Hybrid Perovskites 下载免费PDF全文
Bin Yang Wenmei Ming Mao‐Hua Du Jong K. Keum Alexander A. Puretzky Christopher M. Rouleau Jinsong Huang David B. Geohegan Xiaoping Wang Kai Xiao 《Advanced materials (Deerfield Beach, Fla.)》2018,30(22)
A fundamental understanding of the interplay between the microscopic structure and macroscopic optoelectronic properties of organic‐inorganic hybrid perovskite materials is essential to design new materials and improve device performance. However, how exactly the organic cations affect the structural phase transition and optoelectronic properties of the materials is not well understood. Here, real‐time, in situ temperature‐dependent neutron/X‐ray diffraction and photoluminescence (PL) measurements reveal a transformation of the organic cation CH3NH3 + from order to disorder with increasing temperature in CH3NH3PbBr3 perovskites. The molecular‐level order‐to‐disorder transformation of CH3NH3 + not only leads to an anomalous increase in PL intensity, but also results in a multidomain to single‐domain structural transition. This discovery establishes the important role that organic cation ordering has in dictating structural order and anomalous optoelectronic phenomenon in hybrid perovskites. 相似文献
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Emergent Low‐Symmetry Phases and Large Property Enhancements in Ferroelectric KNbO3 Bulk Crystals 下载免费PDF全文
Tom T. A. Lummen J. Leung Amit Kumar X. Wu Y. Ren Brian K. VanLeeuwen Ryan C. Haislmaier Martin Holt Keji Lai Sergei V. Kalinin Venkatraman Gopalan 《Advanced materials (Deerfield Beach, Fla.)》2017,29(31)
The design of new or enhanced functionality in materials is traditionally viewed as requiring the discovery of new chemical compositions through synthesis. Large property enhancements may however also be hidden within already well‐known materials, when their structural symmetry is deviated from equilibrium through a small local strain or field. Here, the discovery of enhanced material properties associated with a new metastable phase of monoclinic symmetry within bulk KNbO3 is reported. This phase is found to coexist with the nominal orthorhombic phase at room temperature, and is both induced by and stabilized with local strains generated by a network of ferroelectric domain walls. While the local microstructural shear strain involved is only ≈0.017%, the concurrent symmetry reduction results in an optical second harmonic generation response that is over 550% higher at room temperature. Moreover, the meandering walls of the low‐symmetry domains also exhibit enhanced electrical conductivity on the order of 1 S m?1. This discovery reveals a potential new route to local engineering of significant property enhancements and conductivity through symmetry lowering in ferroelectric crystals. 相似文献
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Molecular Dynamics of Flexible Polar Cations in a Variable Confined Space: Toward Exceptional Two‐Step Nonlinear Optical Switches 下载免费PDF全文
Wei‐Jian Xu Chun‐Ting He Cheng‐Min Ji Shao‐Li Chen Rui‐Kang Huang Rui‐Biao Lin Wei Xue Jun‐Hua Luo Wei‐Xiong Zhang Xiao‐Ming Chen 《Advanced materials (Deerfield Beach, Fla.)》2016,28(28):5886-5890
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Bart Smit Florian Hüwe Nancy Payne Olufemi Olaoye Irene Bauer Jens Pflaum Markus Schwoerer Heinrich Schwoerer 《Advanced materials (Deerfield Beach, Fla.)》2019,31(19)
Among functional organic materials, low‐dimensional molecular crystals represent an intriguing class of solids due to their tunable electronic, magnetic, and structural ground states. This work investigates Cu(Me,Br‐dicyanoquinonediimine)2 single crystals, a charge transfer radical ion salt which exhibits a Peierls insulator‐to‐metal transition at low temperatures. The ultrafast electron diffraction experiments observe collective atomic motions at the photoinduced phase transition with a temporal resolution of 1 ps. These measurements reveal the photoinduced lifting of the insulating phase to happen within 2 ps in the entire crystal volume with an external quantum efficiency of conduction band electrons per absorbed photon of larger than 20. This huge cooperativity of the system, directly monitored during the phase transition, is accompanied by specific intramolecular motions. However, only an additional internal volume expansion, corresponding to a pressure relief, allows the metallic state for long times to be optically locked. The identification of the microscopic molecular pathways that optically drive the structural Peierls transition in Cu(DCNQI)2 highlights the tailored response to external stimuli available in these complex functional materials, a feature enabling high‐speed optical sensing and switching with outstanding signal responsivity. 相似文献
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Kaichen Dong Hwan Sung Choe Xi Wang Huili Liu Bivas Saha Changhyun Ko Yang Deng Kyle B. Tom Shuai Lou Letian Wang Costas P. Grigoropoulos Zheng You Jie Yao Junqiao Wu 《Small (Weinheim an der Bergstrasse, Germany)》2018,14(14)
Micro‐electromechanical (MEM) switches, with advantages such as quasi‐zero leakage current, emerge as attractive candidates for overcoming the physical limits of complementary metal‐oxide semiconductor (CMOS) devices. To practically integrate MEM switches into CMOS circuits, two major challenges must be addressed: sub 1 V operating voltage to match the voltage levels in current circuit systems and being able to deliver at least millions of operating cycles. However, existing sub 1 V mechanical switches are mostly subject to significant body bias and/or limited lifetimes, thus failing to meet both limitations simultaneously. Here 0.2 V MEM switching devices with ?106 safe operating cycles in ambient air are reported, which achieve the lowest operating voltage in mechanical switches without body bias reported to date. The ultralow operating voltage is mainly enabled by the abrupt phase transition of nanolayered vanadium dioxide (VO2) slightly above room temperature. The phase‐transition MEM switches open possibilities for sub 1 V hybrid integrated devices/circuits/systems, as well as ultralow power consumption sensors for Internet of Things applications. 相似文献
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Ultrahigh Pyroelectric Figures of Merit Associated with Distinct Bistable Dielectric Phase Transition in a New Molecular Compound: Di‐n‐Butylaminium Trifluoroacetate 下载免费PDF全文
Zhihua Sun Yuanyuan Tang Shuquan Zhang Chengmin Ji Tianliang Chen Junhua Luo 《Advanced materials (Deerfield Beach, Fla.)》2015,27(32):4795-4801