Circuit-Level Analysis on Opto-Electronic Characteristics of Ferroelectric Liquid Crystal

We propose an electronic model in Spice, instead of traditional mathematical analysis, for analyzing the performance of ferroelectric liquid crystal （FLC） under various working conditions. Using this equivalent circuit model,it is easy to simulate and analyze the behavior of an FLC layer in three different typical parameters,including temperature, input light wavelength, and the frequency of driving voltage. We conclude that the response velocity drops as the wavelength increases in the range of visible light, and for the parameter of temperature, the velocity reaches its lowest value when the temperature reaches a certain degree,meanwhile,the frequency of driving voltage exerts important effects on the response velocity only when the frequency is beyond a critical value. Excellent agreement is achieved between simulation and experimental results.

Macro-circuit simulation and optimal design for ferroelectric liquid crystal based on dielectric properties

A macro-circuit equivalent model for ferroelectric liquid crystal （FLC） is proposed. The model includes both effects of ferroelectric toque and dielectric torque and is utilized to simulate the switching response and memory behavior of a single FLC cell . Simulation results show that the delay time has a minimum while increasing the amplitude of drive voltage and the amplitude of bipolar pulses should be controlled within a certain range to realize the memory behavior. Also the switching angle is successfully enhanced to the reference value of 22.5° by adopting ＂AC stabihzation＂ addressing method.

ORGANOMETALLIC FERROELECTRIC LIQUID CRYSTALS Ⅰ. LIQUID CRYSTAL PROPERTIES OF ORTHO—PALLADATED BINUCLEAR COMPLEXES OF AZINE, IMINE AND AZO DERIVATIVES

The mesomorphie properties of title complexes are investigated by means of DSC and polarizing microscopy. The mesophase temperature ranges of complexes are wider than that of corresponding organic ligands. The bridging groups of the complexes have profoand effects on the mesomorphic behavior, When the bridging groups are opticallhy active. the compleve show chiral smectic

Helix unwinding in ferroelectric liquid crystals induced by tilted electric field

Helix unwinding in ferroelectric liquid crystals induced by an electric field is theoretically studied on the basis of the continuum theory. By applying a weak electric field tilted to the smectic layers, the contribution of the dielectric interaction energy density to the total free energy density is increased. Approximation methods are used to calculate the free energy for different tilt angles between the electric field and the smectic layers. The obtained results suggest selecting the optimal number of pitches in the film that matches to the minimum of the free energy.

The growth status of relaxor-based ferroelectric crystals and their development trends

Our progress in the growth of ternary system Pb(In_(1/2)Nb_(1/2))O_(3)–Pb(Mg_(1/3)Nb_(2/3))O_(3)–PbTiO_(3)(PIMNT)crystals and reviews on the possible developing trends in the piezoelectric crystals are presented.Large PIMNT crystals with 3 inches in diameter have been grown by using a modified Bridgman method.Meanwhile,Mn-doped PIMNT crystals have also been obtained.PIMNT crystals exhibit Curie temperature Tc
190C,rhombohedral–tetragonal phase transition temperature Trt>100℃ and coercive field Ec
5:0–7.0 kV/cm on(001)cuts.Meanwhile,higher piezoelectric constant d_(32)-1500–2200 pC/N,d_(15)
4000–6000 pC/N and coercive field E_(c)-7:0–9.0 kV/cm have been achieved on(110)cuts.The development trends of relaxor-based ferroelectric crystals are suggested to grow novel crystals with high rhombohedral–tetragonal phase transition temperature T_(rt)>150-160℃ and/or high coercive field Ec and mechanical quality factor Q_(m),to promote growth efficiency of PIMNT crystals and to create new growth methods fitting for the growth of metastable or instable crystals.

Fabrication and structure of Langmuir-Blodgett films of ferroelectric liquid crystal

The molecular aggregation, orientation, and structure in Langmuir-Blodgett films of ferroelectric liquid crystal were studied by ultraviolet and Fourier transform infrared spectra. The results show that medium strong (H-aggregates) in the Langmuir-Blodgett films of ferroelectric liquid crystal are formed by chromophores where the alkyl chains are nearly perpendicular to the film surface. Compared with the cast films, the CO stretching bands, due to the rotational isomerism around the O—C axis of the chiral part, can be identified clearly in Langmuir-Blodgett films.

Circuit-level simulation of the hysteresis inversion frequency of the ferroelectric liquid crystals

The V-shaped electro-optical properties control is investigated by an equivalent circuit model.Simu-lation results show that genuine V-shaped form is only observed at hysteresis inversion frequency,and be-low and above this frequency an anomalous and normal hysteresis are observed.And the inversion fre-quency decreases with the resistance of ferroelectric liquid crystal(FLC)layer following logf_i=-alogR_(LC)+b .The results are in good accordance with the reported experimental results.

Noncolinear Second-Harmonic Generation Pairs and Their Scatterings in Nd3+:SBN Crystals with Needle-Like Ferroelectric Domains

Second-harmonic generation in Nd3＋ ：SBN crystal with needle-like ferroelectric with aperiodic domain structures is investigated. Two pairs of second harmonic （SH） waves appearing in lines are observed in unpoled Nd3＋ ：SBN crystals with aperiodic needle-like domains. A pair of SH waves emit from the exit face, whose intensities are angle-dependent. The angular dependence is corresponding to the spatial frequency spectrum of the aperiodic domain structure. Another pair of SH waves emit from both the side surfaces, which are mainly the scattered SH waves by needle-like domain walls and obey the theory of Rayleigh scattering.

Ferroelectric Liquid Crystal Optical Switches

The dynamic response of molecular orientation, and the temperature and pulse shape dependences of the switching behavior in ferroelectric liquid crystal are described. The switching speed and the surface energy of ferroelectric liquid crystal are given.

Kerr effect and Kerr constant enhancement in vertically aligned deformed helix ferroelectric liquid crystals

In this article,we review recently achieved Kerr effect progress in novel liquid crystal（LC） material：vertically aligned deformed helix ferroelectric liquid crystal（VADHFLC）.With an increasing applied electric field,the induced inplane birefringence of LCs shows quadratic nonlinearity.The theoretical calculations and experimental details are illustrated.With an enhanced Kerr constant to 130 nm/V2,this VADHFLC cell can achieve a 2π modulation by a small efficient electric field with a fast response around 100 μs and thus can be employed in both display and photonics devices.

Recent Developments in Functional Crystals in China

Functional crystals are the basic materials for the development of modern science and technology and are playing key roles in the modern information era. In this paper, we review functional crystals in China, including research history, significant achievements, and important applications by highlighting the most recent progress in research. Challenges for the development of functional materials are discussed and possible directions for development are proposed by focusing on potential strengths of these materials.

Interplay between polarization rotation and crack propagation in PMN-PT relaxor single crystals

Investigations on the interconnection between the polarization rotation and crack propagation are performed for [110J-oriented 74Pb（Mg1/3Nb2/3）O3- 26PbTiO3 relaxor ferroelectric single crystal under electric loadings along [001] direction. The crystal is of predominantly monoclinic MA phase with scatter dis- tributed rhombohedral （R） phase under a moderate poling field of 900 V/mm in [00l] direction. With magnitude of 800 V/ram, a through thickness crack is initi- ated near the electrode by electric cycling. Static electric loadings is then imposed to the single crystal. As the applied static electric field increases, domain switch- ing in the monoclinic MA phase and phase transition from MA to R phase occur near the crack. The results indicate that the crack features a conducting one. Whether domain switching or phase transition occurs depends on the intensity of the electric field component that is perpendicular to the applied electric field.

High sensitivity gravimetric sensor made of unidirectional carbon fiber epoxy composite on (1-x)Pb(Zn_(1/3)Nb_(2/3))O_3-xPbTiO_3 single crystal substrate

We have derived a general formula for sensitivity optimization of gravimetric sensors and have used it to design a high sensitivity gravimetric sensor using unidirectional carbon fiber epoxy composite （CFEC） waveguide layer on （1 -x）Pb（Znl/3Nbz/3）O3-xPbTiO3 （PZN-xPT） single crystal substrate with the carbon fibers parallel to the xj and x2 axes, respectively. The normalized maximum sensitivity （｜sfm｜λ）max exhibits an increasing tendency with the decrease of （h/λ）opt and the maximum sensitivity （｜sfm｜λ）max increases with the elastic constant c6E6 of the piezoelectric substrate material. For the CFEC/[011]c poled PZN-7%PT single crystal sensor configuration, with the carbon fibers parallel to the xa axis at λ = 24 ktm, the maximum sensitivity ｜sfm｜max can reach as high as 1156 cmZ/g, which is about three times that of a traditional SiO2/ST quartz structure gravimetric sensor. The better design selection is to have the carbon fibers parallel to the direction of propagation of Love wave in order to obtain the best sensitivity.

Quantification of polarization distribution from polarizing light microscopy images of ferroelectric single crystals

Qualification of polarization can be realized either on a macroscopic scale as an average property by P-E hysteresis measurements or on a nano/micro scale by piezoelectric force microscopy,transmission electron microscopy,scanning electron microscopy,and so on.However,visualization and qualification of polarization distribution in the micron to millimeter scale is still a challenge.Polarizing light microscopy(PLM)is often used in the study of ferroelectric domain structures mainly for domain patterns.A phe-nomenon called“chromatic polarization”has been observed in transparent ferroelectric crystals by using a crossed-PLM system viewed with white light,which contains rich information about local polariza-tion distribution.In this study,an automatic full-angle light intensity detection(AFALID)algorithm com-bined with colorimetry is developed to analyze the distribution of nonuniform local spontaneous polar-ization distribution in transparent ferroelectric single crystals.Temperature-dependent spontaneous po-larizations from the color analysis for PMN-0.36PT single crystals with single tetragonal domain state are in good coincidence with those extracted from temperature-dependent hysteresis loops and pyroelectric current measurements.We further apply this method to quantify the nonuniform domain distributions with nano-indentations.This non-contact and non-destructive characterization can provide fast and au-tomatic detection of polarization distributions in ferroelectric materials.

Boosting the piezoelectric property of relaxor ferroelectric single crystal via active manipulation of defect dipole polarization

To further enhance the property of piezoelectric materials is of great significance to improve the overall performance of electro-mechanical devices.Here in this work,we propose a thermal annealing and high temperature poling approach to achieve significantly enhanced piezoelectricity in Pb(In_(1/2)Nb_(1/2))O_(3)single bondPb(Mg_(1/3)Nb_(2/3))O_(3)single bondPbTiO_(3)(PIN-PMN-PT)crystals with a morphotropic phase boundary(MPB)composition.The main idea of our approach is to realize a more sufficiently polarized crystal via active manipulation of defects and orientation of defect polarization.Manipulation of defect dipoles by the high temperature poling is proved by the piezo-response force microscopy.Finally,a d_(33)of 3300 pC/N and a SE of 0.25%are obtained,nearly 60%higher than that of conventionally poled crystals.Moreover,such a boosting of piezoelectric property is obtained under a maintained Curie temperature.Our research not only reveals the active control of defect dipole via modified poling method in the PIN-PMN-PT crystal,but also provides a feasible strategy to further improve the property of piezoelectric materials.

掺锰KLN晶体的生长及性能的研究

Potassium Lithium Niobate (KLN) crystal belongs to tetragonal system and is ferroelectric crystal,which point group is 4mm and space group is P4bm .The melt point of KLN crystal is about 1050℃.KLN crystal possesses tungsten bronze structure and its structure general expression is(A 1) 2(A 2) 4C 4(B 1) 2(B 4) 8O 3.KLN crystal is full fill up tungsten bronze structure crystal,in which the light of transmission band is 0.35-5.0μm.KLN crystal has excellent electro optical and nonlinear property and is superior double frequency crystal material for blue light.KLN crystal also is acoustic surface wave and photorefractive material.KLN crystal cracks easily during it grows.But when KLN crystal is doped in Mn 2O 3 to grow Mn∶KLN crystal,the crystal crack is reduced and the photorefractive property of the crystal is enhanced.KLN system is solid solution system and not congruent composition.The compounding ratio of Mn∶KLN crystal which we grew is 47.4mol% Nb 2O 5,17.3mol% Li 2CO 3,35mol% K 2CO 3 and 0.1mol% Mn 2O 3.The purity of Nb 2O 5,Li 2CO 3,K 2CO 3 and Mn 2O 3 is all 99.99%.Czochralski method was used to grow Mn∶KLN crystal.The technical parameters include the axial direction temperature gradient,the crystal growth rate and the rotation rate.Mn∶KLN crystal with 6mm×8mm×20mm size was grown in the condition that the axial direction temperature gradient is 30℃-40℃,the crystal growth rate is 0.5mm/h and the rotation rate is 10-15r/min.KLN crystal is one dimension ferroelectrics crystal.It has a paraelectrics ferroelectrics phase transition point curie point.So the crystal needs to be polarized in manual work.The direct current field was used to force the self polarization Ps in the same direction and the crystal turn to single domain.Before polarization,the c face needs to be confirmed exactly.The platinum pole was pasted to the two surfaces of c face and the direct current voltage about 220V was added the pole as the polarization outer electrical field.The polarization temperature is 460℃ and the polarization current density is 2mA/cm 2 .The thermal analyzer in TAS100 model was used to analyze the thermal expansion character of Mn∶KLN crystal and ascertain that the curie point of Mn∶KLN crystal is 435℃.It can be seen from the measurement result that the change of thermal expansion rate of Mn∶KLN crystal is smaller than that of pure KLN crystal. So doping Mn 2O 3 in KLN crystal to grow Mn∶KLN crystal can reduce the crack of the crystal.

Ferroelectric liquid crystals for fast switchable circular Dammann grating [Invited]

Diffractive optical elements attract a considerable amount of attention, mainly due to their potential applications in imaging coding, optical sensing, etc. Application of ferroelectric liquid crystals(FLCs) with photoalignment technology in diffractive optical elements results in a high efficiency and a fast response time. In this study we demonstrate a circular Dammann grating(CDG) with a diffraction efficiency of 84.5%. The achieved response time of 64 μs is approximately two orders of magnitude faster than the existing response time of nematic liquid crystal devices. By applying a low electric field(V = 6 V) to the FLC CDG, it is switched between the eight-order diffractive state and the transmissive diffraction-free state.

Dynamic modulation performance of ferroelectric liquid crystal polarization rotators and Mueller matrix polarimeter optimization

A ferroelectric liquid crystal polarization rotator(FLCPR)has been widely used in polarization measurement due to its fast and stable modulation characteristics.The accurate characterization of the modulation performance of FLCPR directly affects the measurement accuracy of the instrument based on liquid crystal modulation.In this study,FLCPR is accurately characterized using a self-developed high-speed Stokes polarimeter.Strong linear and weak circular birefringence are observed during modulation processes,and all the optical parameters of FLCPR are dependent on driving voltage.A dual FLCPR-based Mueller matrix polarimeter is designed on the basis of the Stokes polarimeter.The designed polarimeter combines the advantages of the high modulation frequency of FLCPR and the ultrahigh temporal resolution of the fast polarization measurement system in the Stokes polarimeter.The optimal configuration of the designed polarizer is predicted in accordance with singular value decomposition.A simulated thickness measurement of a 24 nm standard SiO2 thin film is performed using the optimal configuration.Results show that the relative error in thickness measurement caused by using the unsatisfactory modulation characteristics of FLCPR reaches up to−4.34%.This finding demonstrates the importance of the accurate characterization of FLCPR in developing a Mueller matrix polarizer.

Highly-Ordered Ferroelectric Photonic Crystals

Highly-ordered, ferroelectric, Pb-doped Ba0.7Sr0.3TiO3, inverse opal thin films were fabricated using a sol-gel spin coating technique. The excellent crystal quality is evident from the SEM images and the good agreement between the theory and experiments.

Analysis of Dielectric and Electro-optic Responses of Nanomaterials Doped Ferroelectric Liquid Crystal Mixture

Dielectric and rotational viscosity measurements of a multi-component ferroelectric liquid crystal mixture were performed by adding a small concentration （0.01 wt%） of silica and multi walled carbon nanotubes （MWCNTs）. Liquid crystals turn out to be outstanding hosts for nanomaterials. A remarkable increase in the rotational viscosity was noticed in CNT doped system as compared to silica doped same liquid crystal system. Comparison of dielectric studies shows higher value of permittivity and dielectric losses for silica-doped sample than those of CNT doped sample. The results have been interpreted both experimentally and theoretically.