共查询到20条相似文献,搜索用时 125 毫秒
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基于传输矩阵法研究了一维压电Fibonacci类准周期声子晶体的传输特性, 比较了一维Fibonacci序列压电准周期声子晶体与非压电准周期声子晶体以及压电周期性声子晶体的透射性. 计算结果表明:弹性波通过一维准周期结构压电声子晶体时与周期性声子晶体一样会有带隙的出现, 且发现具有压电性的Fibonacci序列准周期声子晶体禁带宽度发生了展宽. 进一步讨论了入射角度对固定频率下声子透射系数的影响,结果表明一维压电Fibonacci序列准周期结构声子透射性依赖于入射角度的选取. 相似文献
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室温下记录了有机非线性光学晶体二苯甲酮三种不同偏振的红外反射光谱(200-4000cm^-1)。利用K-K变换确定了晶格振动模的模,纵频率。根据由K-K变换得到的介电常数和折射率的色散曲线外推得到晶体的静态介电常数,高频介电常数和近红外波段的折射率。还对反射带进行了认定。研究表明该晶体二苯甲酮分子间不存在氩键,只以弱的范德华键相结合。结合晶体结构对强反射带出现的原因作了解释。 相似文献
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采用无序元素孤立位移模型(REI mode),建立了三元混晶AB1-xCx品格动力学的Born—Huang方程,并由此出发讨论了几种三元混晶晶格振动的介电常数和远红外反射谱。理论计算结果表明,这个模型适用于三元混晶的所有情况:(1)单模情况——在整个成分比例区域内(0≤x≤1)有1支横光学声子(TO)和1支纵光学声子(LO);(2)双模情况——在整个成分比例区域内(0≤x≤1),有2支横光学声子和2支纵光学声子;(3)第3种情况——部分区域为单模而另外区域为双模。结果显示,单模晶体只有1个反射带;双模晶体有2个反射带;第3种类型的晶体在部分区域有1个反射带而在另外的区域有2个反射带。该理论模型提供了一个理解三元混晶光学性质的可能的途径,依此为基础可以讨论电子一声子相互作用等其他问题。 相似文献
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当ZnO-SiO2-Si结构中的ZnO薄膜C轴取向偏离基片法向时,将对声表面波传播速度,机电耦合系数等参量产生影响。本文对此问题进行了理论分析和数值计算;同时还讨论了本结构中影响声表面波束偏的一些参数。 相似文献
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分别在77K、100K、200K和300K温度下测量了钨酸铅(PbWO4,PWO)晶体的红外反射谱,观察到8个反射峰;实验表明PWO晶体在低温77~300K范围内结构稳定.利用Kramers-Kronig(K-K)关系对样品的红外反射谱进行数据处理,获得了不同温度下各振动模的横光学(TO)声子频率ωTO,从而得到了PWO晶体各振动模的温度变化特性,研究表明:Pb2+离子的平动模频率随温度降低发生蓝移,主要是晶格的热膨胀影响;WO42-离子团的振动模频率随温度降低发生红移,主要是非简谐耦合作用影响. 相似文献
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根据尘埃等离子体理论,考虑到尘埃粒子的充放电过程,研究了尘埃冰晶粒子吞噬效应对极区中层电子浓度分层结构及电导率和介电常数的影响。结果表明,尘埃冰晶粒子的吞噬效应造成了极区中层80~90km高度范围内电子浓度的分层结构,并进而导致这一区域尘埃等离子体电导率、介电常数沿高度出现明显的分层,为解释和研究极区中层夏季回波现象提供参考。 相似文献
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J Iwicki E Ludwig J Buck M Kall?ne F K?hler R Herges L Kipp K Rossnagel 《J Phys Condens Matter》2012,24(39):394011
In?situ ultraviolet photoelectron spectroscopy is used to study the growth of ultrathin films of azobenzene-based functional molecules (azobenzene, Disperse Orange 3 and a triazatriangulenium platform with an attached functional azo-group) on the layered metal TiTe(2) and on the layered semiconductor HfS(2) at liquid nitrogen temperatures. Effects of intermolecular interactions, of the substrate electronic structure, and of the thermal energy of the sublimated molecules on the growth process and on the adsorbate electronic structure are identified and discussed. A weak adsorbate-substrate interaction is particularly observed for the layered semiconducting substrate, holding the promise of efficient molecular photoswitching. 相似文献
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《Phase Transitions》2012,85(4):282-296
The structure–property correlation has been systematically investigated by the modification of the central core part of the dichiral materials so that the chiral and/or non-chiral issue having an effect on the formation of the layered or inter-connected structure can be studied. The central phenyl core of the dichiral compound showing the inter-connected ordered smectic Q phase has been modified in the following three ways: introduction of the substituent in the central phenyl core, introduction of the alkyl spacers between the central phenyl core and the peripheral mesogenic groups, and replacement of the central phenyl ring by the alkyl spacer. It has been found that (1) a symmetric structure stabilizes the tilted molecular ordering and the inter-connected structure, whereas the non-symmetric structure stabilizes the smectic A ordering; (2) a flexible molecular structure stabilizes the layered phase rather than the inter-connected; (3) increase in the degree of the segregation in the molecular assemblies stabilizes the anticlinic layered ordering; (4) increase in the local liquid-crystallinity stabilizes the layered structure; and (5) the ordered inter-connected structure is more sensitive to the chirality of the system than the disordered inter-connected structure. 相似文献
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A. N. Nikitin T. Lokajicek A. A. Kruglov R. N. Vasin I. Yu. Zel’ 《Journal of Surface Investigation: X-ray, Synchrotron and Neutron Techniques》2012,6(6):954-960
The results of measuring the velocities of quasi-longitudinal elastic waves propagating through two-phase layered model samples are presented. These samples are fabricated from powders of different crystalline minerals and epoxy. The influence of foliation and powder grain sizes on the elastic anisotropy of the samples is analyzed. It has been revealed that samples with muscovite and quartz fillers have different relations between the layered structure and the spatial distribution of the velocities of quasi-longitudinal elastic waves. 相似文献
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B.Ya. Shapiro 《Solid State Communications》1983,48(4):365-367
The theory of mixed state of the layered metals is presented. It is shown that the lattices of the superconductive states localized along the magnetic field arise in the layered metals systems. The magnetic moment, structure and energy of the lattices of the superconductive states are determined. 相似文献
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本文首先以刚度矩阵法为基础, 给出了ZnO薄膜/金刚石在四种不同激励条件下的有效介电常数计算公式. 然后以此为工具, 分别计算了多晶ZnO(002) 薄膜/多晶金刚石和单晶ZnO(002) 薄膜/多晶金刚石的声表面波特性, 并根据计算结果及设计制作声表面波器件的要求, 对ZnO膜厚的选择进行了详细地分析. 最后讨论了ZnO/金刚石/Si复合晶片可以忽略Si衬底对声表面特性影响时对金刚石膜厚的要求.
关键词:
声表面波
压电多层结构
有效介电常数
刚度矩阵法 相似文献
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层状材料一直是超导研究领域的热点材料, 陆续有数十种新型的层状超导材料被不断发现, 从至今为止超导转变温度最高的铜氧化物材料, 到铁基超导, 再到诸多新型的层状材料, 学者们关于超导微观机制的理解也在随之更新, 从取得成功的 Bardeen-Cooper-Schrieffer 经典理论到至今无法解释的非常规超导机制, 研究之路从未停止. 本文将研究利用助熔剂法合成的 LaO1 -xFxBiS2 材料的结构、 电阻、 磁化率等性质, 并与国际社会上已存在的研究成果进行对比, 同时从晶体结构、 压力效应、 体超导电性、 临界温度、 微观机制五个方面, 对近年发现的镧系铋硫基层状超导材料的研究情况进行讨论. 相似文献
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In this paper, dispersive behavior and band structure of SH waves in magnetic–electric (ME) periodically layered plate are investigated by the transfer matrix method. Two kinds of unit cell form, one is piezoelectric (PE)/piezomagnetic (PM)/PE, and the other is PM/PE/PM, are considered in detailed. A peculiar case of the generalized single-celled plate is first presented and then the multi-celled periodical layered plates for discussion on the propagation behaviors and the band characteristics of SH waves, respectively. The effects on dispersive curves of four kinds of ME boundary conditions at the free surface of plates are discussed. Numerical examples for phase velocities or frequencies all show that the zero-order mode is non-dispersive both for single-celled and multi-celled periodically layered plates. The high modes of dispersive curves tend to the shear wave velocity of the slower sub-layer as frequencies increase both for these two structures. The frequency pass-band and frequency band gaps appear in multi-layered ME periodically layered plates. Electrical and magnetic boundary conditions, respectively, determine the dispersive curves for SH waves in the PE/PM/PE and PM/PE/PM periodically layered plates. 相似文献