基于二维铁电体PVDF的电控磁性研究

基于第一性原理计算,引入色散修正方法(DFT-D2),通过PVDF铁电极矩调控了铁磁层的磁矩和磁晶各向异性能.特别地,通过电荷注入方法,证实电控磁性源自铁电极矩的静电屏蔽而非化学成键.该研究将促进电场控制的磁存储技术的发展.     

Effects of the Anthraquinone Dye on the Electro-Optical Properties of Dye Guest-Host Polymer Dispersed Ferroelectric Liquid Crystal

Abstract

The effects of the anthraquinone dye on the electro-optical characteristics of DGHPDFLC have been investigated. The results show that PDFLC doped with dichroic dye was found to have no influence on phase separation. When dye concentration is over M483-1.0%, it causes the response time of DGHPDFLC to become slower, the frequency becomes dependent, the rotational viscosity increases, and the tilt angle becomes lower, but, on the whole, electro-optical properties are still very practical.     

Aggregation of Anthraquinone Dye Molecules in a Nematic Liquid Crystal

We report an experimental evidence that molecules of anthraquinone dye aggregate in an anisotropic solvent, a nematic liquid crystal (NLC). We observe strong nonlinear dependencies of the dielectric permittivity and anisotropy of light absorption on the dye concentration c. Moreover, the data suggest that the aggregates are linear, but, in contrast to the isotropic case, their formation in a NLC undergoes two different concentration regimes with a well pronounced crossover. These effects are explained by the interplay between the aggregates’ lengths and their orientational ordering due to the interaction with the nematic director.     

循环电场下钙钛矿铁电薄膜的极化疲劳机制

将循环电场引起电荷注入并产生局部相分解的理论引入到氧空位模型中,建立了一个解析形式的钙钛矿结构铁电薄膜极化疲劳模型.结合该模型讨论了铁电薄膜与金属电极间的低介电常数界面层对疲劳特性的影响,认为界面层对疲劳的产生起关键作用.运用该模型分析了不同松弛时间、电压、温度下的疲劳特性,并与已报道的实验结果进行了对比,模型计算结果与实验数据具有很好的一致性.     

Polarization and Viscosity Measurements in a Ferroelectric Liquid Crystal by the Field Reversal Method

With the aim to develop a standard method for measurements of the polarization of ferroelectric chiral smectic C liquid crystalline materials, we have studied thin, well-aligned samples of MBRA-8 using the field-reversal method. The method also provides an estimate for the rotational viscosity and for the response times.     

吸收对光子晶体偏振态的影响

引入复折射率并利用特征矩阵法,研究了光子晶体的吸收对TE波和TM波的禁带的影响.得出:对TE波其禁带的反射率随消光系数的增加而迅速降低,当消光系数增加为0.03时其反射率降低到0.5.对TM波其禁带的反射率在小角度范围(0～0.9 rad)内随消光系数的变化特征与TE波相同,但在大角度范围出现"广义布儒斯特角"现象."广义布儒斯特角"的位置不随消光系数变化,但"广义布儒斯特角"现象对应的入射角宽度随消光系数的增加而增大.     

Pb过量对以Ti-Al为阻挡层的硅基铁电电容器极化翻转性能的影响

以射频磁控溅射法生长的La0.5Sr0.5CoO3( LSCO)为电极,采用溶胶-凝胶法在以Ti-Al为导电阻挡层的Si基片上生长了用不同Pb过量前驱体溶液(溶胶)制备的LSCO/Pb( Zro4Ti0.6)O3(PZT)/LSCO电容器,以此构造了Pt/LSCO/PZT/LSCO/Ti-Al/Si异质结.Pb过量对LSCO/PZT/LSCO电容器极化翻转性能的影响表明:不同Pb过量溶胶对电容器的极化翻转性能影响很大,其中Pb过量15;的溶胶制备的样品在550℃常规退火1h后相对具有较好的翻转性能.在5V的外加电场下,LSCO/PZT/LSCO电容器的矫顽电压和剩余极化强度分别为1.25V和24.6μC/cm2.疲劳和电阻率测试分析表明:在经过109翻转后,不同样品的抗疲劳性能均很好,而电阻率随前驱体溶液Pb过量的增加呈现下降的趋势.     

快速退火对PZT铁电薄膜结构的影响

采用射频磁控溅射方法在Pt/Ti/SiO2/Si衬底上制备出(PZT)铁电薄膜,在550℃、600℃、650℃、700℃几个温度下对薄膜进行了快速退火热处理,并在退火处理后用X射线衍射、原子力显微镜和热释电系数测试系统研究了PZT铁电薄膜的薄膜结构、表面形貌及热释电性能.在650℃快速退火后,PZT铁电薄膜已经形成较好的钙钛矿相结构,并获得了较好的热释电性能,热释电系数达到1.5×10-8C·cm-2·k-1.     

铁电畴反转机理的研究

从铁电畴极化反转的动力学出发,针对铁电畴反转过程中的新畴成核和畴壁运动两个过程,对用外加极化电场实现铁电畴反转的机理进行了理论分析研究,并就低电场和高电场两种条件下的开关时间进行了实验验证.结果表明,实验值与模型计算值吻合较好.     

Electrical and Optical Properties of Ferroelectric Liquid Crystals and Influence of Applied Pressure

Much larger dielectric constants and spontaneous polarizations are evaluated in the smectic-C phase of p-alkoxybenzylidene-p'-amino-2-chloropropyl-cinnamate (HOBACPC, OOBACPC and DOBACPC) which have dipole moments at the chiral part compared with those of p-alkoxybenzylidene-p'-amino-2-methylbutyl-cinnamate. In the mixture of D-DOBAMBC and L-DOBACPC with inverse chirality, the pitch of the helical structure is longer compared with those of original compounds. On the other hand, the dielectric constant and the spontaneous polarization of the compounds are nearly linearly dependent on the concentration of L-DOBACPC.

The phase transition temperature from smectic-A to chiral smectic-C phases in DOBAMBC decreases remarkably with the mixing of organic molecules (PAA, eicosane, etc.) but increases with applied pressure.

The threshold field of electro-optical effects (transmission increase, colour switching, memory effects) in DOBACPC and HOBACPC etc. is lower than that in DOBAMBC etc. in accordance with the increase of the spontaneous polarization in the former.     

CdS纳米晶的稳定化处理及介质极性对荧光光谱的影响

用硫脲、聚乙烯吡咯烷酮、L-半胱氨酸水溶液对水热法合成的硫化镉纳米晶进行稳定化处理,发现L-半胱氨酸和聚乙烯吡咯烷酮(PVP)能有效地稳定硫化镉纳米晶,荧光发射强度比处理前增强了五十倍以上.以氯仿、氧化三(正)辛基膦(TOPO)氯仿溶液以及3-巯基丙酸为萃取(或处理)剂,对水热法合成的水溶性CdS半导体纳米晶进行处理,经过荧光光谱分析,发现介质水、氯仿、氧化三(正)辛基膦(TOPO)氯仿溶液以及3-巯基丙酸会对CdS纳米晶的最大荧光激发峰与发射峰的位置产生不同影响,极性大的水分子使得荧光峰蓝移,极性小的氯仿、氧化三(正)辛基膦(TOPO)氯仿溶液以及3-巯基丙酸使得荧光峰红移,最大位移为31nm左右.     

羟基磷灰石对氟离子的吸收作用

用基准NaF配置标准溶液,用氟离子选择性电极测定氟离子的标准曲线,将自制的羟基磷灰石(HAP)粉体放入三组不同配方的NaF溶液浸泡,测定HAP在吸收氟离子的过程中溶液的pH值和氟离子浓度的变化,并利用XRD、TEM、EDS等对吸附氟离子的HAP粉体进行检测.结果表明,HAP对氟离子的吸附动力学相对于Lagergren拟一级速率方程,更符合Lagergren拟二级速率方程,线性相关系数R2为1.降低pH值可以提高氟离子吸收率,HAP在吸收氟离子的同时释放出大量的氢氧根,提高了溶液的pH值.吸收氟离子后粉末晶体的XRD图谱的测试结果与FAP的图谱相一致,微观结构相近均为棒状结构,EDS结果表明粉体晶体结构中掺杂了大量的氟离子,得到的粉末晶体为FAP.     

NBT-KBT-xLN系陶瓷的介电与铁电性能研究

采用传统电子陶瓷工艺制备了(1-x)(0.88Na0.5Bi0.5TiO3-0.12K0.5Bi0.5TiO3)-xLiNbO3(简写为NBT-KBT-xLN)无铅压电陶瓷体系,研究了该陶瓷体系的相结构、显微结构、铁电及介电性能.结果表明:在材料组成范围内(0.02≤x≤0.08),系列试样均形成了稳定的三方相钙钛矿结构;随着LiNbO3含量的增加,系列试样的矫顽场从4.41 kV/mm显著下降至1.51 kV/mm;LiNbO3的引入对材料的介电性能作用明显,随着LiNbO3含量的增加,系列试样的铁电-反铁电相变峰明显向低温方向移动,而反铁电-顺电相变峰则表现为明显的压峰效应.     

PVDF薄膜铁电性能的调控研究

近年来,随着微机电系统(MEMS)地不断发展,对微型材料的柔性、可加工性以及电活性提出了更高的要求。PVDF作为优秀的柔性铁电材料而备受关注。为提高柔性PVDF薄膜的铁电性能,研究同时使用了三种方法:(1)在分子链中引入Tr FE;(2)在溶液体系中掺杂低浓度的BaTiO₃;(3)对薄膜使用热拉伸方法。考察了BaTiO₃掺杂浓度和热拉伸温度对铁电性能的影响。结果表明:三种方法均能有效提高PVDF的铁电性能;在三种方法的共同作用下,薄膜的剩余极化强度到达了19. 8μC/cm²。钛酸钡掺杂浓度过低会使整个体系无法形成致密结构,掺杂浓度过高会形成团簇,导致薄膜的缺陷增多,适当的掺杂浓度可以有效提高薄膜的铁电性能。此外,使用适当的拉伸温度使偶极子活动能力增强,增加铁电相的含量。通过三种方法对薄膜的铁电性进行优化,为有机柔性材料的电活性调控提供了一个可行思路。     

烧结温度对SBTi铁电陶瓷电性能的影响

用溶胶-凝胶法制备了钛酸锶铋层状钙钛矿结构(SBTi)铁电陶瓷,研究了不同烧结温度对其显微结构和电性能的影响,分析了相关机理,发现1100℃烧结样品的晶粒发育比较完全,居里温度为520℃;压电常数d33和剩余极化强度2Pr较大,分别为9×10-12C/N和2.1μC/cm2,矫顽场强2Ec为49.4kV/cm.     

Crystallizaton Characteristics of the Alternating Tetrafluoroethylene-Ethylene Copolymer

The alternating tetrafluoroethylene-ethylene (TFE-E) copolymer has been studied with respect to its crystallization by using differential scanning calorimetry and optical microscopy. The value of the specific surface energy σ at the melt/crystal interface is calculated to be about 2 · 10⁻³ J/m². The nucleating activity Φ of TiO₂ particles introduced into TFE-E copolymer is estimated to be approximately 0.9. The temperature dependence of the nucleation rate and of the linear growth velocity are constructed in the whole region from the melting temperature T_m to the vitrification temperature T_g. The minimum cooling rate for the formation of a crystal-free TFE-E copolymer glass is calculated and its value amounts to 10⁴ K · min⁻¹.     

弛豫铁电单晶的生长及性能优化研究进展

钙钛矿型(ABO₃)弛豫铁电单晶具有优异的机电耦合性能,被认为是研制下一代医疗超声换能器、高精度压电驱动器、水声换能器等机电耦合器件的核心关键材料。针对弛豫铁电单晶材料制备与物理性能方面尚存在的基础科学与工艺问题,本文综述了近些年弛豫铁电单晶生长与性能优化方面的研究进展,包括若干新的单晶生长方法用以改善弛豫铁电单晶的成分和性能均匀性,提升弛豫铁电单晶压电性能的系列新方法,通过铁电畴结构调控以获得高透光率的弛豫铁电单晶,以及高性能弛豫铁电单晶在电光技术领域的应用等。     

三种氟化石墨的合成与性能的研究

利用自制电解槽电解KF*2HF电解液可制得氟气,将其净化后再与鳞片石墨、人造石墨和土状石墨分别进行反应,保持温度500℃,并经15h连续不断的反应,可合成制得3种氟化石墨.测试结果表明:鳞片石墨合成的氟化石墨在红外光谱波数1219cm-1处吸收谱峰强度大于另外两种氟化石墨,且其真密度、含氟量、电阻率最高.因此,作为合成氟化石墨的原料,鳞片石墨优于人造石墨和土状石墨.     

Synthesis of the Copolymer Based on Diketopyrrolopyrrole with Didecyl Chain for OPVs

A new accepter unit, diphenylpyrrolo[3,2-b]pyrrole-2,5-dione with didecyl chain, was prepared and utilized for the synthesis of the conjugated polymer containing electron donor-acceptor pair for OPVs. The iDPP, part of the structure of a natural dye found in lichens, is the regioisomer of the known DPP with switched position of the carbonyl group and nitrogen atom. At the 4-positions of the N-substituted phenyl groups of 1,4-bis(4-butylphenyl)-pyrrolo[3,2-b]-pyrrole-2,5-dione unit in P-butyl, the butyl group was substituted with decyl group to increase solubility. The absorption spectrum of polymer with diphenylpyrrolo[3,2-b]pyrrole-2,5-dione unit exhibit two maximum peaks at about 365 and 542 nm. The spectrum of the P1 as the solid thin film shows absorption band with maximum peaks at 370 and 536 nm, and the absorption onset at 703 nm, corresponding to band gap of 1.76 eV. The oxidation and reduction potential onset of the synthesized polymer were estimated to be 0.84 and ?1.22 V, which correspond to HOMO and LUMO energy levels of ?5.64 and ?3.58 eV, respectively. The devices comprising P1 with PC₆₁BM annealed at 100°C showed a V_OC of 0.79 V, a J_SC of 1.75 mA/cm², and a FF of 0.31, leading to the power conversion efficiency of 0.43% under white light illumination (AM 1.5 G, 100 mW/cm²).     

Crystallography of the Destruction Fragments of Tubular Cyanine Dye J-Aggregates on the Mica Surface

Crystallography Reports - A crystallographic analysis of the images of destruction fragments of tubular monomethine dye J-aggregates has been performed for the first time. It is shown that the...