共查询到20条相似文献,搜索用时 93 毫秒
1.
2.
3.
4.
5.
采用拉曼散射技术,从声子角度研究了Ga3PO7晶体的非弹性振动特性,主要内容为:采用位置对称性法从理论上计算了晶体的晶格振动模式,判定了晶体共有27个拉曼活性模,其振动模式为Γ=7Al+10E,可看作由PO43-集团形成的晶体的内振动模和由PO43-集团、O和Ga原子形成的晶体的外振动模组成;通过室温拉曼光谱实验观测到了晶体的16个拉曼活性模,包括8个外振动模和6个内振动模,并对各模进行了指认,其中高波段的声子模主要为PO4四面体的内振动模.由于晶体结构缺陷和某些内、外振动模的耦合等原因,观测到的振动模数量明显少于理论预测值. 相似文献
6.
固-流结构声子晶体中弹性波能带的色散研究 总被引:6,自引:1,他引:5
推导出弹性波斜入射固-流结构声子晶体的转移矩阵和色散公式.利用色散公式研究了弹性波在固-流结构声子晶体中的能带特性.结果表明,介质厚度固定时,弹性波中会出现多级禁带,禁带的频率中心随入射角的增加而向高频方向移动,入射角增加到一定值后会分裂出新的禁带,分裂出的禁带频率宽度随级数的增加而增大.入射角固定时,禁带的频率宽度随介质厚度近似成反比变化,分裂出的禁带频率宽度随介质厚度的增加而减小. 相似文献
7.
8.
本文采用中频感应提拉法成功生长了LaAlO3和Ce3+:LaAlO3晶体.沿生长方向即α轴方向切割、抛光后得到实验样品.测试了氢气退火前后纯LaAlO3和Ce3+:LaAlO3从190nm到2500nm的吸收谱和透过谱.测试结果表明:纯LaAlO3晶体在196~220nm处出现宽带吸收,氢气退火后此一波段的吸收系数明显降低;未退火的Ce:LaAlO3晶体在196~209nm,246nm,314nm出现明显的吸收波段,氢气退火后其吸收谱发生显著变化,在198,206,214,246和314nm处出现对应于Ce3+的4f-5d的跃迁吸收;Ce:LaAlO3晶体较之纯LaAlO3晶体在红外区的透过率要高;氢气退火后,Ce:LaAlO3晶体和纯LaAlO3晶体在红外区的透过率下降. 相似文献
9.
在KNSBN晶体中掺进CuO,采用硅钼棒作加热体,以Czochralski技术生长Cu:KNSBN晶体.以二波耦合光路,测试晶体的衍射效率和记录时间,计算折射率变化值Δn.Cu:KNSBN晶体的衍射效率,记录速度和折射率变化值皆高于Fe:LiNbO3晶体.尤其记录速度比Fe:LiNbO3晶体高一个数量级以上.测试Cu:KNSBN晶体位相共轭反射率R和自泵浦位相共轭反射率RC.Cu:KNSBN晶体的自泵浦位相共轭反射率RC值达到64;,是纯KNSBN晶体的二倍.以Cu:KNSBN晶体自泵浦位相共轭镜进行消畸变实验.实验结果表明:输出光波确系输入探测光波的位相共轭光波. 相似文献
10.
11.
The characteristics in the plastic deformation of silicon crystals are first reviewed. Such characteristics have been interpreted quantitatively on the basis of some models on the velocity and the multiplication of dislocations during deformation. The results of the in-situ observations of silicon crystals deformed at elevated temperatures in a HVEM are presented. The slowness and the smoothness in the dislocation motion, the dynamic pile-up as a general mode of the collective motion of dislocations, the formation processes of multiplication centers of dislocations observed during the deformation all support the validity of the models adopted. Dislocation dipoles and Lomer-Cottrell sessiles are observed not to act as strong obstacles which play important roles in the work hardening of the crystals. 相似文献
12.
. Barta P. M. Silvestrova N. A. Moiseeva J. U. V. Pisarevskij 《Crystal Research and Technology》1980,15(7):843-848
Sections through the surfaces of phase and group velocities of propagation of acoustic waves in Hg2Cl2, Hg2Br2 and Hg2I2 were ascertained. The relations between the directions of energy propagation and the directions of phase velocities were also established. It was found that the energy flux deviates from the A-plane towards the [001] direction. The direction of the smallest velocity of propagation of acoustic waves in the A-plane was found, too. The results of this study are interesting especially with respect to the practical utilization of some new types of acoustic and acousto-optic elements. 相似文献
13.
It is shown that the so-called ordinary electromagnetic waves (the waves whose group velocity is parallel to the wave normal) cannot propagate outside the planes parallel to the principal planes of the permittivity tensor in transparent optically biaxial crystals. For each of the three such planes, the waves of one of the two independent branches are ordinary irrespectively of the direction of their propagation, whereas the waves of the other branch are ordinary only if they propagate along two mutually orthogonal directions of the corresponding eigenvectors of the permittivity tensor. 相似文献
14.
The dispersion equation for quasi-Rayleigh acoustic modes in transversely isotropic sandwich-type structures (an elastic layer between two substrates) has been obtained in the analytical form. The equation is analyzed for three types of structures—a layer between two soft substrates, a layer between a soft and a hard substrate, and a structure consisting of two contacting substrates with markedly different values of hardness. Eigenmodes are determined for all three structures. Depending on the combination of the material parameters in these structures, these eigenwaves are either Rayleigh-type waves localized at interfaces in the substrates and accompanying a Lamb wave in the interlayer (in the absence of an interlayer, forming a Stoneley wave) or the leaky modes characterized by a small imaginary addition to the phase velocity and the presence of bulk partial waves of leakage providing some energy removal from the interfaces. Without any calculations, simple criteria were established that allow one to predict the existence of a leaky mode in the given structure and the number of leakage fluxes it contains. The resonance reflection is analized for the case where the incidence angle of the wave in the substrate corresponding to the velocity v of the wave-front propagation along the interface is close to the value of the real part of the phase velocity of the leaky mode. 相似文献
15.
本文采用第一性原理计算了La3Ga5-xSiAlxO14 (LGAS)压电晶体几何结构、能带和态密度.并研究了其在X、Y和Z切型的声表面波速度、机电耦合系数及能流角.当x=0.5时,构建了La3Ga4.5SiAl0.5O14晶体的1×1×2超晶胞结构,发现A1原子替代2d四面体位置的Ga原子时体系总能量最低,体积最小,因此是最稳定的状态.与石英相比,LGAS具有声表面波速度较低、机电耦合系数较大且存在能流角为零的切型等优点.掺Al元素降低了成本但对结构和声表面波特性影响不大.Y切0是较好的切型,可用于制备声表面波器件. 相似文献
16.
Semicircular crystals of Pb were grown from the melt by a rotational operation so as to change the orientation of the solid-liquid interface during crystallization. In pure Pb, specimens grew as polycrystals with grain boundaries developed transversely to the growth direction. According to the decrease in purity, the grown crystals consisted of several long grains along the circular arc. A competitive growth between grains was inhibited by a small amount of impurity and then the mode of growth approached to the complete adhesive one. 相似文献
17.
GaPO4晶体弹性与压电性能的研究 总被引:4,自引:2,他引:2
本文首先绘制了GaPO4晶体在(100),(010),(001)三个主晶面内慢度分布曲线,计算了声速的最大值,并与水晶进行了比较,发现GaPO4晶体的声速普遍小于水晶的声速;其次还探讨了GaPo4晶体压电系数d11及机电耦合系数k11随空间方向变化的规律,得到了GaPO4晶体d11,k11的最大值及其方向,并分别和水晶进行了比较,发现GaPO4晶体的d11和k11都远大于水晶的。这些结果将对GaPO4晶体在压电器件和声光器件的设计,开发及利用等方面具有一定的理论指导作用。 相似文献
18.
为衰减中低频振动噪声,本文设计了一种非严格对称的开口圆环类声子晶体结构,基于有限元法和弹性波理论分析了其禁带特性和各方向的振动衰减性能;结合系统的振动模态解释了带隙打开和关闭的原因,并分析了几何参数对带隙宽度的影响规律。结果表明:由于晶体的非严格对称,仅ΓX方向的传输损耗和禁带特性吻合,且衰减性能优于MΓ方向,禁带内平均衰减27.8 dB,同比提升了5.5 dB。禁带内几乎没有产生位移变形量,而通带因无法抑制弹性波传播导致变形量显著增大;芯体的水平和旋转运动是带隙起始、截止的明显标志。以钨为芯体,能获得起始频率和带宽均为500 Hz的低频带隙,增大芯体的材料密度、填充率和晶格尺寸有助于获得较低频率的完整带隙。 相似文献
19.
Crystallography Reports - A formula for the propagation velocity of the regeneration surface front is derived under the assumption of equal growth rates of the polyhedral crystal faces and the... 相似文献
20.
A compact analytical representation for the dispersion equation, which determins the propagation velocity of surface polaritons in an arbitrarily oriented interface between an optically uniaxial crystal and isotropic medium, is proposed. The equation obtained is reduced to a rational fourth-order equation with respect to the square of velocity. The approximate form of this equation for the limiting case (the medium adjacent to a crystal is a metal with a high complex permittivity) coincides with the result following from the Leontovich impedance approximation. 相似文献