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An achiral swallow-tailed material, 2-propylpentyl 4-(4′-decyloxybiphenyl-4-carbonyloxy)benzoate, p, showing SmA and SmCalt phases was prepared for mixing (by weight percentage) with an antiferroelectric liquid crystal, (S)-MHPOBC, m, for the study. The binary mixture p/15/m85 using (S)-MHPOBC (85%) as a host doped with achiral material (15%) resulted in a phase sequence SmA-SmC*-SmC*A. The electro-optic response of this mixture in the ferroelectric SmC* phase displayed V-shaped switching, while that in the antiferroelectric SmC*A phase displayed a double hysteresis switching. The mixture p85/m15 possessed SmA* and SmC*A phases; V-shaped switching was found in the antiferroelectric SmC*A phase of this mixture. These optical phenomena implied that a binary mixture containing a larger amount of achiral swallow-tailed material and/or possessing relatively lower polarization favours the occurrence of V-shaped switching in the antiferroelectric phase. The results of this work also suggested that thresholdless V-shaped switching in chiral smectic liquid crystals can be achieved by mixing an achiral swallow-tailed material with an antiferroelectric liquid crystal. 相似文献
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通过采用容易无序的胺,我们合成了2种有机无机杂化晶体,分别为基于bempy (bempy=1-甲基-1-溴乙基吡咯烷阳离子)的溴盐化合物(bempy) Br (1)和镉基溴化物(bempy)2CdBr4(2),并对其结构相变、介电相变和蓝白荧光进行了详细的表征分析。化合物1在测试温度范围内未观察到可逆相变,化合物2为高温介电相变,介电和差示扫描量热法测试表征其相变温度为357 K。同时,化合物1和2均具备蓝白光致发光特性,荧光测试表明,化合物1和2分别在538 nm和547、750 nm处存在发射峰。化合物2具备介电相变和蓝白光致发光的双重特性。 相似文献
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A. K. Lyashchenko D. V. Loginova A. S. Lileev N. A. Ivanova I. A. Efimenko 《Russian Journal of Coordination Chemistry》2009,35(9):633-639
The MW-dielectric properties of aqueous solutions of K2[PtCl4] (I) and K2[PdCl4] (II) were studied at 298 and 313 K in the frequency range (12–25 GHz) corresponding to the maximum dielectric constant dispersion
for water and aqueous solutions of these salts. The low-frequency conductivities were measured. The static dielectric constant,
the dielectric relaxation time, and the enthalpy of activation of the dielectric relaxation of the solutions were determined.
Compared to pure water, in solutions of salts I and II, the orientational mobility of water molecules is increased and the network of H-bonds is violated more strongly than that
of most other ions with hydrophilic hydration. It was demonstrated for the first time that dielectric spectroscopy can be
used for analyzing complexation processes in systems containing aqua and hydroxo chloride complexes of metals. 相似文献
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Novel chiral swallow-tailed amide materials, N,N-dipropyl-(S)-2-{6-[4-(4-alkoxyphenyl)benzoyloxy]-2-naphthyl}propionamides, DPmPBNPA (m=9-13), have been designed and synthesized for the investigation of mesomorphic properties. The materials DPmPBNPA (m=9-11) display a monotropic phase sequence of I-SmA*-SmCA*-Cr. The antiferroelectric SmCA* phase for the materials was characterized by microscopic texture, switching behaviour, dielectric permitivity and electro-optical response. The measured maximum P s values in the SmCA* phase of the materials are in the range 80–87 nC cm-2. 相似文献
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Artificial smart materials with switchable multifunctionality are of immense interest owing to their wide application in sensors, displays and memory devices. Lanthanide complexes are promising multifunctional materials integrating optical and magnetic characteristics. However, synergistic manipulation of different physical properties in lanthanide systems is still challenging. Herein we designed and synthesized a mononuclear complex [DyIII(SCN)3(depma)2(4-hpy)2] (1), which incorporates 9-diethylphosphonomethylanthracene (depma) as a photo-active component and 4-hydroxypyridine (4-hpy) as a polar component. This compound shows several unusual features: (a) reversible thermo-responsive phase transition associated with the order–disorder transition of 4-hpy and SCN−, which leads to thermochromic behavior and dielectric anomaly; (b) reversible photo-induced dimerization of anthracene groups, which leads to synergistic switching of luminescence, magnetic and dielectric properties. To our knowledge, compound 1 is the first example of lanthanide complexes that show stimuli-triggered synergistic and reversible switching of luminescence, magnetic and dielectric properties.[DyIII(SCN)3(depma)2(4-hpy)2] (1) shows reversible thermo-induced phase transition associated with thermochromism and dielectric anomaly and photo-induced dimerization with synergistic switching of luminescence, magnetic and dielectric properties. 相似文献
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W. Weissflog L. Kovalenko I. Wirth S. Diele G. Pelzl H. Schmalfuss 《Liquid crystals》2013,40(5):677-681
A new achiral five-ring banana-shaped mesogen is presented which has a cyano substituent in the 4-position of the central core. Microscopical, X-ray, dielectric and electro-optical investigations give evidence for the unusual phase sequence B2, SmC, SmA. The B2 phase shows an antiferroelectric switching behaviour; the spontaneous polarization was found to be 330 nCcm-2. 相似文献
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D. Richter 《Macromolecular Symposia》1997,121(1):147-161
This short review presents quasielastic neutron scattering and dielectric experiments on the α and βslow relaxation in polybutadiene. Exploiting the momentum transfer dependent dynamic structure factor, spatial information about the underlying molecular motions is obtained. While the βslow process reveals itself as a local jump with average jump distances of about 1.5 Å, the α relaxation is diffusive and occurs statistically independently from the βslow process. With this result a consistent interpretation of dielectric spectra on the same polymer is achieved. 相似文献
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Z. Raszewski J. Kedzierski J. Rutkowska J. Zieliński J. Żmija R. D. Dabrowski 《Liquid crystals》2013,40(6):1959-1966
Abstract We have measured the dielectric constants of 6CHBT. The results from studies of various alignments and thicknesses measured under different electric and magnetic fields are presented. We discuss how the dielectric properties depend on boundary conditions, sample thickness and the magnitudes of electric and magnetic fields. Experimental results and discussion in the terms of continuum theory make it possible to compute the diamagnetic anisotropy (Δχ), as well as the splay and bend elastic constants (K 11, K 33) of 6CHBT. 相似文献
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A Chemically Triggered and Thermally Switched Dielectric Constant Transition in a Metal Cyanide Based Crystal
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Chao Shi Xi Zhang Ying Cai Prof. Ye‐Feng Yao Prof. Wen Zhang 《Angewandte Chemie (International ed. in English)》2015,54(21):6206-6210
A dielectric constant transition is chemically triggered and thermally switched in (HPy)2[Na(H2O)Co(CN)6] ( 2 , HPy=pyridinium cation) by single‐crystal‐to‐single‐crystal transformation and structural phase transition, respectively. Upon dehydration, (HPy)2[Na(H2O)2Co(CN)6] ( 1 ) transforms to its semi‐hydrated form 2 , accompanying a transition from a low‐dielectric state to a high‐dielectric state, and vice versa. This dielectric switch is also realized by a structural phase transition in 2 that occurs between room‐ and low‐temperature phases, and which corresponds to high‐ and low‐dielectric states, respectively. The switching property is due to the variation in the environment surrounding the HPy cation, that is, the hydrogen‐bonding interactions and the crystal packing, which exert predominant influences on the dynamics of the cations that transit between the static and motional states. 相似文献
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Sidra Khan Shikha Chauhan Achu Chandran Michał Czerwiński Jakub Herman Ashok M. Biradar 《Liquid crystals》2020,47(2):263-272
ABSTRACT Here, we present the effect of copper (II) oxide nanoparticles (nCuO) on dielectric and electro-optical parameters of a newly prepared ferroelectric liquid crystal (FLC) mixture, namely W302. The FLC mixture, comprising of pyrimidine compounds, was characterised through dielectric spectroscopy, differential scanning calorimetry (DSC), polarising optical microscopy (POM) and other electro-optical methods. The material parameters such as spontaneous polarisation, rotational viscosity, response time and tilt angle of W302 were found to be 14 nC/cm2, 240 mPa.s, 150 µs and 28?, respectively. The phase transition temperatures of W302 were observed through DSC and further confirmed by the dependence of dielectric loss factor in homogeneously aligned FLC sample with temperature. We also demonstrate the observance of a low-frequency dielectric relaxation mode due to the unwinding of the helix, called as partially unwound helical mode (p-UHM) along with Goldstone mode. The behaviour of p-UHM has been systematically studied with temperature and applied bias field. Further, dispersion of nCuO into host W302 has shown a significant increase in dielectric permittivity. Also, the p-UHM relaxation peak in the dielectric regime has disappeared with the incorporation of nCuO. These studies would be useful to fabricate better electro-optical devices for display, switching and beam steering applications. The formulation and characterization of a ferroelectric liquid crystal (FLC) mixture W302 composed of pyrimidine compounds is presented. Then, we observed the effect of copper (II) oxide nanoparticles (nCuO) on dielectric and electro-optical parameters of a newly prepared and characterized FLC mixture. 相似文献
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The structures and isomerization of silylenoid H2SiLiF are investigated by density functional theory (DFT) at B3LYP/6-311+G(d,p) level. The solvent effects are modeled using
the self-consistent reaction field (SCRF) method with Tomasi’s polarized continuum model (PCM). Five representative solvents,
i.e. benzene, ether, THF, acetone, and DMSO, are chosen for this work. Special attention is paid to THF solvent. The results
indicate that the polarity of solvents has played an important role on the structures and relative stabilities of different
isomers. Contrary to the three-membered ring structure 1, the relative stability of the “classical” tetrahedron structure 4 increases with increasing dielectric constants (ε) of solvents. The σ-complex isomer 3 is most unstable structure. Although the relative energies are reduced with increasing dielectric constants (ε) of solvents, the p-complex structure 2 still has the lowest energy. The effects of solvents on the dipole moments and charge distributions are also discussed. 相似文献
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Xiujian Chou Maoxiang Guo Yating Zhang Jun Liu Wendong Zhang 《Journal of Sol-Gel Science and Technology》2012,61(1):62-68
Pb0.97La0.02Zr0.95Ti0.05O3 (PLZT) antiferroelectric thick films of highly preferred-(100) orientation with different thickness were successfully deposited
on Pt(111)/Ti/SiO2/Si(100) substrates depending on the sol–gel process technique. The effects of the PLZT thick films in the preparation and
electric properties are investigated. The films show polycrystalline perovskite structure with a (100) preferred orientation
by X-ray diffractometer analyses. The antiferroelectric nature of the thick films is demonstrated by P (polarization)–E (electric
field). The temperature dependence of the dielectric constant and dielectric loss displays the similar behavior in both cases
at 100 kHz while the values of polarization characteristic are decreased with the increase of the film thickness. The phase
switching current are studied as a function of a gradually change dc electric field and the voltage dependent current density
of the most highly (100)-oriented PLZT film is 1.49 × 10−8 A/cm2 over electric field range from 0 to ±261 kV/cm. The film at 2,498 nm exhibits excellent dielectric properties and highly
preferred-(100) orientation. 相似文献
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Co-crystal [4,4?-bipyridine]2[1,4-dihydroxybenzene] (1) was prepared by evaporating methanol solution of 4,4?-bipyridine with 1,4-dihydroxybenzene at 4°C. 1 shows a fascinating dielectric anomaly with a maximum at ~210 K, which is independent on ac frequency. However, the absence of thermal anomaly and structural phase transition is related to the dielectric anomaly. The co-crystal [4,4?-bipyridine]2[1,4-dihydroxybenzene-d2] (2) was further obtained via H+/D+ exchange in 1 and the deuteration gives rise to the maximum shifting to 254 K in the dielectric spectrum of 2. The dielectric anomaly corresponds to disorder-to-order transformation of H+/D+ in the O–H/D···N H-bond in 1 and 2. 相似文献
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Novel liquid crystal materials based on 3,4-di-n-alkoxybenzoylthiosemicarbazides (3a–h, n = 5–10, 12, 14) were synthesised. The mesomorphic properties of these compounds were characterised and studied by differential scanning calorimetry, polarising optical microscopy and X-ray diffraction. Compound 3a did not show mesomorphic properties; 3b shows a monotropic hexagonal columnar (Colh) phase. Compounds 3c–h display an enantiotropic Colh phase. The mesomorphic properties were found to be dependent on the length of alkoxy side chains. In N,N-dimethylformamide solution, all the compounds displayed a room temperature emission with λmax at 361–332 nm. A thermogravimetric analysis also was performed. 相似文献
18.
Switchable Dielectric Phase Transition Triggered by Pendulum‐Like Motion in an Ionic Co‐crystal
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《化学:亚洲杂志》2018,13(19):2916-2922
Molecular‐based ionic co‐crystals, which have the merits of low‐cost/easy fabrication processes and flexible structure and functionality, have already exhibited tremendous potential in molecular memory switches and other electric devices. However, dipole (ON/OFF switching) triggering is a huge challenge. Here, we introduce a pendulum‐like dynamic strategy to induce the order–disorder transition of a co‐crystal [C5H7N3Cl]3[Sb2Br9] (compound 1 ). Here, the anion and cation act as a stator and a pendulum‐like rotor (the source of the dielectric switch), respectively. The temperature‐dependent dielectric and differential scanning calorimetry (DSC) analyses reveal that 1 undergoes a reversible phase transition, which stems from the order–disorder transition of the cations. The thermal ON/OFF switchable motions make 1 a promising candidate to promote the development of bulk crystals as artificial intelligent dielectric materials. In addition, the pendulum‐like molecular dynamics and distinct arrangements of two coexisting ions with a notable offset effect promotes/hinders dipolar reorientation after dielectric transition and provides a rarely observed but fairly useful and feasible strategy for understanding and modulating the dipole motion in crystalline electrically polarizable materials. 相似文献
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We presented a theoretical study of electronic band structure of three compounds ZnAl2Te4, ZnGa2Te4 and ZnIn2Te4 using pseudo potential method within density functional theory. Calculated band structures show that all band gaps are direct with at Γ with values of 1.639eV for ZnAl2Te4, 1.026eV for ZnGa2Te4and 0.836eV ZnIn2Te4. The linear properties based on dielectric function and non-linear optical properties based on second harmonic generation (SHG) were computed. The origin of four critical points (peaks) determined from the second derivative of the imaginary part of the dielectric function is elucidated. The use of individual k-points and individual combination of valence and conduction bands dependent matrix of the dielectric function and the nonlinear optical susceptibility allowed to a precise determination of inter band optical transitions. Indeed, inter-band analysis shows the high intensity of non-linear effect compared to linear effect. Moreover, non-linear inter-band optical transitions involve lower valence bands and higher conduction bands. 相似文献
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Yao‐Zu Zhang Dong‐Sheng Sun Xiao‐Gang Chen Ji‐Xing Gao Xiu‐Ni Hua Wei‐Qiang Liao 《化学:亚洲杂志》2019,14(21):3863-3867
Molecular optical‐dielectric duple bistable switches are photoelectric (dielectric and fluorescent) multifunctional materials that can simultaneously convert optical and electrical signals in one device for seamless integration. However, exploring optical‐dielectric duple channels of dielectric and photoluminescence is still a bigger challenge than single dielectric or photoluminescence bistable ones, which are hardly reported but probably will be heavily researched owing to the new generation artificial intelligence development needs in the future. Herein, a new optical‐dielectric duple bistable switches material, [(CH3)3NCH2CH3]2MnCl4 ( I ), was obtained by a simple method for volatilization of solvents. Variable temperature single crystal X‐ray analysis indicates that material I has a reversible bistable structure (order‐disorder structure phase transition) corresponding to switching “ON′′ and ”OFF′′. Unlike the single dielectric bistable structures that were previously reported, material I also own bistable features in terms of fluorescence property. This material enriches the specific examples of photoelectric duple function switch materials and facilitates the development of required devices. 相似文献