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The first-principles study of ferroelectric behaviours of PbTiO3/SrTiO3 and BaTiOn/SrTiO3 superlattices 下载免费PDF全文
We have performed the first-principles calculation to investigate the origins of ferroelectricities and different po- larization behaviours of superlattices BaTiO3/SrTiO3 and PbTiO3/SrTiO3. The density of state (DOS) and electronic charge profiles show that there are strong hybridizations between atoms Ti and O and between atoms Pb and O which play very important roles in producing the ferroelectricities of superlattices BaTiO3/SrTiO3 and PbTiO3/SrTiO3. Ow- ing to the decline of internal electric field in SrTiO3 (ST) layer, the tetragonality and polarizations of superlattices decrease with increasing the fraction of SrTiO3 in the superlattices. We find that the polarization of PbTiO3/SrTiO3 is largerthan that of BaTiO3/SrTiO3 at the same ratio of components, because the polarization mismatch between PbTiO3 and SrTiO3 is larger than that between BaTiO3 and SrTiO3. The polarization and tetragonality are en- hanced with respect to those of bulk tetragonal BaTiO3 in the superlattices BaTiO3/SrTiO3, while the polarization and tetragonality are reduced with respect to those of bulk tetragonal PbTiO3 in superlattices PbTiO3/SrTiO3. 相似文献
3.
本文提出了随机点场理论用于研究含有随机夹杂的统计非均匀介质。本文不同于其它作者,一般均将随机理论建立在Eshelby的等效夹杂原理之上,而这里是建立在Kunin的微结构理论基础之上。作为理论的一个应用,本文对复合材料的有效模量及夹杂内部及周围微观场进行了计算。 相似文献
4.
研究了基于互补色的高效聚合物白光器件,双色材料包括蓝绿光材料双(4,6-二氟苯基吡啶-N,C2)吡啶甲酰合铱(Firpic)和黄光材料三[3-(2,6-二甲基苯氧基)-6-(2-噻吩基)-哒嗪]铱(Fs-1),器件结构为ITO/PEDOT(40 nm)/PVK:OXD-7:Firpic:Fs-1(80 nm)/Ba(4 nm)/Al(120 nm).当发光层材料PVK∶OXD-7∶Firpic∶Fs-1质量比为63∶27∶10∶0.25时,用溶液加工方法得到高效白光器件,此时CIE色坐标为(0.30,0.39),最大电流效率为10.8 cd.A-1,亮度可达到4200 cd.m-2.在此基础上,引入水溶性电子注入材料聚[9,9-二(3′-N,N-二甲基胺基丙基-2,7-芴-2,7-交-(9,9-二辛基芴)](PFN)修饰阴极界面,使载流子注入和传输更平衡,当阴极为PFN(20 nm)/Al(120 nm)时,电流效率获得显著改善,达到13.1 cd.A-1,此时电流密度为4.9 mA.cm-2,亮度可达到6096 cd.m-2,白光器件的色坐标为(0.33,0.39),同时发光光谱稳定.另外通过电致发光(EL)、光致发光(PL)光谱及能级结构图分析了载流子俘获和能量转移在发光中的作用. 相似文献
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The non-singular and bounded terms for stresses near the crack tip were investigated. The crack problem in a transversely isotropic piezoelectric solid for the plane problem was dealt with. The principle of superposition and the Plemelj formulation were introduced. The non-singular terms are given by solving Rieman-Hilbert problem. It is shown that the non-singular terms are influenced by the elastic and electric constants. 相似文献
7.
In this paper, the dynamic interaction between two collinear cracks in a piezoelectric material plate under anti-plane shear
waves is investigated by using the non-local theory for impermeable crack surface conditions. By using the Fourier transform,
the problem can be solved with the help of two pairs of triple integral equations. These equations are solved using the Schmidt
method. This method is more reasonable and more appropriate. Unlike the classical elasticity solution, it is found that no
stress and electric displacement singularity is present at the crack tip. The non-local dynamic elastic solutions yield a
finite hoop stress at the crack tip, thus allowing for a fracture criterion based on the maximum dynamic stress hypothesis.
The project supported by the Natural Science Foundation of Heilongjiang Province and the National Natural Science Foundation
of China(10172030, 50232030) 相似文献
8.
An edge emitting laser with two symmetrical near-circular spots located far field (FF) is demonstrated using tapered double-sided Bragg reflection waveguides (BRWs). The BRWs consist of six pairs of top p-type and bottom n-type A10.Ga0.9 As/A10.3 Ga0.7As Bragg reflectors with a period thickness of 850 nm. The device has a 4° tapered angle configuration and exhibits two stable circular beams with a separation angle of 52°. Typical FF angles of 5.87° and 7.8° in the lateral and vertical directions, respectively, are achieved. The lateral FF angle in the ridged section is independent of the injection current (〉0.8 A) beeause of narrow ridge (-10 μm) confinement. By contrast, the FF angle in the tapered section shows an increase rate of 1.2 1.66°/A. The periodic modulation of the lasing wavelength is observed to be sensitive to self-heating effects. 相似文献
10.
电源变换系统中功率器件如MOSFET和IGBT开关管的高速切换将产生高幅值和宽频段的电磁干扰,是电动车辆最为常见也无法避免的电磁干扰源。同时,互连线缆是机电设备传递信号和能量的载体,是实现设备功能不可或缺的组成部分,线缆的天线效应使其成为设备产生电磁干扰的主要途径,是系统电磁兼容问题的主要根源之一。为了分析高压电源变换系统对低压控制系统的电磁耦合,以某典型地面装备电源变换系统IGBT开关管产生的脉冲宽度调制波(PWM波)作为电磁干扰源,以实装线缆作为分析对象,构建高低压线缆串扰模型,仿真分析不同线缆对地距离、线缆间距条件下单线、屏蔽线、双绞线等多类低压线缆的近端串扰电压,得出低压线缆的抗干扰性,为系统线缆的布线提供指导。 相似文献