共查询到20条相似文献,搜索用时 187 毫秒
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利用双轴向列相液晶表面能对指向矢和序参量矩阵的旋转不变性,构造了与指向矢^a,^b,^c对易取向轴^a0,^b0,^c0的偏离有关的表面能Fs(a,b,c),以及与序参量矩阵有关的表面能Fs(Q),并得到两种表达式的等价形式.在Fs(a,b,c)和Fs(Q)中分别有四个和两个独立参量.为讨论上述独立参量的物理意义,假设一液晶分子对表面相互作用的简单模型,将液晶分子沿易取向轴^b0,^c0的双轴性取向看成是受到沿^b0,^c0两相互垂直的平均场作用的结果.为测量表面锚泊系数,考虑了三种简单形变位型,即在外磁
关键词:
液晶
弹性能
表面能 相似文献
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基于Gruhn-Hess两体势修正模型,用Monte Carlo方法模拟向列相液晶微滴.Gruhn-Hess两体势是空间各向异性的,修正模型的势参数依赖于液晶的弹性常数K11、K22、K33及表面弹性常数K13.假设向列相液晶微滴具有自由表面,在低温下计算分子二阶序参数和切向内禀强度在微滴内不同区域的变化,并与Gruhn-Hess两体势模型一作对比分析.结果表明:附加K13项的修正模型在微滴表面产生内禀锚定,其大小决定了内禀易取向方向及内禀锚定强度的大小,且内禀强度的大小与K33/K11值有关;空间不完整的向列相液晶微滴由内层到外层有序度逐渐降低. 相似文献
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在三方铁电(FE)-四方反铁(AFE)的准同型相界附近制备了一系列组份为(Pb0.97La0.02)(Zr1-x-ySnyTix)O3(x=0.09或0.1;0.16≤y≤0.38)的反铁电陶瓷.研究了Sn含量y对电场诱导AFE→FE相变电场Ec、反铁电双电滞回线损耗ΔE、以及温度诱导FE→AFE相变温度TFE,AFE→顺电(PE)相变温度Tc的影响.沿AFE-FE相界Ti含量一定的条件下,Ec随着Sn含量y的增加而增大,ΔE减小,TFE与Tc均降低.场诱相变的回线参量Ec,ΔE与相变温度TFE和Tc相关联.在直流偏压下用原位X-射线衍射表征了相变时晶格结构的变化,结果表明,当电场达到AFE→FE相变临界场时,伴随相变的发生,晶格结构由四方相转变为三方相,晶胞体积增大.
关键词: 相似文献
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选用双轴性并含有多个手征中心的分子作用势,引入手征中心分布结构因子ζχ,采用格胞模型,求得液晶SmC*相的螺距表达式和螺旋性反转条件.计算了TDOBAMBCC,FLC,PACMB和H6/10等4种典型SmC相液晶的螺距随温度的变化及其受ζχ的影响.结果与实验相符.
关键词: 相似文献
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本文根据Freiser关于向列相液晶分子相互作用模型,利用平均场理论,建立了梳型高分子聚合物向列相液晶分子的哈密顿量,导出序参数自洽方程,得到各向同性相至单轴向列相以及单轴至双轴向列相的相变,结果表明,当分子主、侧链耦合项中排斥作用及主、侧链中较强向列相场的场强增大时,单轴至双轴向列相相变温度升高,并从一级相变逐渐变为二级相变。
关键词: 相似文献
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应用Saupe形式的弹性自由能,研究了简单的扭曲,展曲和弯曲形变对相变的影响.结果表明,弹性形变可以产生从各向同性相至双轴丝状相的一级相变,对螺状相液晶,当系统手征性增加并超过某一临界值时,一级相变可过渡到二级相变.
关键词: 相似文献
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基于分子两体势,用Monte Carlo方法计算向列相液晶微滴.两体势基于格点模型,是空间各向异性的且依赖于液晶的弹性常数.假定向列相液晶微滴具有自由表面,引入切向内禀强度定量描写表面引发的分子内禀易取向的强弱.通过各向异性势的两种方案,在低温下计算切向内禀强度和二阶序参数在微滴内不同区域的变化,与Lebwohl-Lasher模型作对比分析.结果表明:只有一种方案在微滴表面产生内禀易取向,且内禀强度值的大小与K33/K11值有关;空间不完整的向列相液晶使得微滴由内层到外层有序度越来越低. 相似文献
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采用格胞模型,定义在格胞中心上的极化序参量.选用双轴性并具有横向电矩的分子作用势,求得系统的自由能,得到自发极化强度的大小和螺旋变化螺距的表达式.计算了DOBAMBC和3M2CPOOB等4种典型SmC*相液晶的自发极化强度大小和螺距随温度的变化及其受分子横向电矩的影响,结果与实验相符.表明SmC*相的自发极化强度主要产生于分子的双轴性和横向电矩.
关键词: 相似文献
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采用Green函数技术,我们讨论了温度从T=0直到T=Tc范围内铁磁体表面和界面的磁化强度随温度的变化情况,所得到表面磁化强度的结果与其他作者的结果一致;而在界面计算中,我们发现界面的Tc与体内的不同,并且找到了一个关系式:TccA,TcB)。
关键词: 相似文献
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A. M. Ziatdinov 《Physics of the Solid State》2000,42(7):1187-1191
Electrical conductivity and conduction-electron spin resonance (CESR) have been studied in stage-2 acceptor α-graphite-nitric acid intercalation compound C10HNO3. It is found that the electrical conductivity σc along the c axis in the structurally incommensurate phase of this compound is temperature independent, whereas the electrical conductivity σa along carbon layers exhibits “metallic” temperature behavior. Analysis of the temperature dependences of σc, σa, and the CESR linewidth demonstrates that, in the incommensurate phase of the graphite intercalation compound, the electrical conductivity along the c axis is realized through a nonband mechanism—the transfer of free charge carriers along thin high-conductivity channels shunting the carbon layers adjacent to the intercalate. 相似文献
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The ambient structural details and the results of room temperature high pressure angle dispersive X-ray diffraction and electrical resistance measurements on the quasi-one-dimensional sulfide, InV6S8, to a pressure of 25 GPa are reported. The material does not undergo a phase transition in this pressure range, though an anomaly in the c/a ratio has been observed around 10 Gpa. A fit of the Murnaghan equation of state to the V/V0 versus pressure data, with the value of the derivative of B0 with respect to pressure, B′0, fixed at 4 has yielded a value of the bulk modulus, B0, of 110 GPa. We also present data of the pressure dependence of the lattice constants, a and c, the ratio c/a, and the resistance at room temperature. 相似文献
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Magnetic structures and magnetocrystalline anisotropy (MCA) of tetragonal phase Fe3Pt with an L12 atomic ordering in bulk and thin film are investigated by means of the first-principles full-potential linearized augmented plane-wave method. The results obtained predict that the tetragonal phase, in which the tetragonal distortion with (c/a) = 0.95 makes an asymmetry of magnetic properties along the c-axis (out-of-plane) and a-axis (in-plane), has an out-of-plane MCA. In addition, from the thin film calculations, the presence of surface is found to strongly enhance the out-of-plane MCA. 相似文献
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H. Z. Fu M. Teng W. F. Liu Y. Ma T. Gao 《The European Physical Journal B - Condensed Matter and Complex Systems》2010,78(1):37-42
Using plane-wave pseudopotential density functional theory and Debye model,
we have studied the axial compressibility, thermal expansion and elastic
anisotropy of Hf2SC at different temperature and pressure. It is found
that the bulk moduli B
a
and B
c
(along the a and c axes, respectively)
almost linearly increase with pressure and the former is always smaller than
the latter. The ratio of B
c
/B
a
has a trend of gradual increase as
the pressure increases. We observe that the Grüneisen parameter γ and
thermal expansion coefficient α decrease when increasing pressure, on the
contrary, the anisotropy, Debye temperature, longitudinal wave velocity and
transverse wave velocity increase with pressure. 相似文献
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Magnetic structure of KFeS2 — a spin analog of the oxidized two iron ferredoxins — was determined by the neutron diffraction method. Spins are antiferromagnetically coupled along the c-axis chain, and they make ferromagnetic sheets in the planes containing a and b axes below the transition temperature of 250.0 ± 0.5 K. The iron moment of 2.43 ± 0.03 μB lies in the a?c plane and is canted by 125.3 ± 0.7 degrees from a-axis at 4.2 K. 相似文献
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The a, b, c, and β crystallographic parameters of the (CH3)2NH2Al(SO4)2 · 6H2O crystal (DMAAS) have been measured by x-ray diffraction in the 90–300-K temperature range. The thermal expansion coefficients along the principal crystallographic axes αa, αb, and αc have been determined. It was shown that, as the temperature is increased, the parameter α decreases and b increases, whereas c decreases for T<T c (where T c is the transition temperature) and increases for T>T c, so that one observes a minimum in the c=f(T) curve in the region of the phase transition (PT) temperature T c ~ 152 K. The thermal expansion coefficients αa, αb, and αc vary in a complicated manner with increasing temperature, more specifically, αa and αc assume negative values at low temperatures, and the αa=f(T), αb=f(T), and αc=f(T) curves exhibit anomalies at the PT point. The crystal has been found to be substantially anisotropic in thermal expansion. 相似文献
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The phase field of the Chevrel phase SnxMoyS8 was investigated by metallographic methods. A shift of the phase field away from the “ideal” compound SnMo6S8 towards the molybdenum-rich side of the phase diagram was observed. The degree of off-stoichiometry could not yet be determined, however, the c/a ratio of the hexagonal lattice parameters can be used to characterize the samples. Measurements of the superconducting transition temperature indicate two superconducting “phases”, which differ in the c/a ratio of the lattice parameters. While phase A showed a linear variation of Tac with c/a in the region from 11.0 to 13.0 K phase B was independent of the c/a ratio with a Tbc = 10.8 ± 0.2 K. 相似文献