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Recently, ferroelectric materials have attracted considerable research attention. In particular, two dimensional (2D) ferroelectric materials have been considered as most crucial for next-generation circuit designs because of their application as novel electric memory devices. However, a 2D ferroelectric material is very rare. The ferroelectric materials with the form ABP2X6 (A = Ag, Cu; B = Bi, In; X = S, Se) are of interest because of their ferroelectric property maintained in their ultrathin structures. Within the ABP2X6 monolayer, the P―P bonds form the pillars that hold the top and bottom X planes, while the off-center A―B atoms between the X layers induce a spontaneous ferroelectric polarization. If the two off-center A―B sites are equally aligned, this would lead to the appearance of the paraelectric state. Such intriguing structures must impart novel mechanical properties to the materials. Until now, there has been no report on the mechanical properties of monolayer ABP2X6. Based on first-principles calculations, we studied the structural, electronic, mechanical as well as the electromechanical coupling properties of monolayer ABP2X6 (A = Ag, Cu; B = Bi, In; X = S, Se). We found that they are all semiconductors with wide bandgaps of 2.73, 2.17, 3.00, and 2.31 eV for CuInP2Se6, CuBiP2Se6, AgBiP2S6, and AgBiP2Se6, respectively, which are calculated based on the Heyd-Scuseria-Ernzerhof (HSE) exchange correlation functional model. The conduction band minimum is mainly from p orbitals of X and B atoms, whereas the valence band maximum is due to the hybridization of the p orbital of X atoms and the d orbital of A atoms. Moreover, there are three short and three long A/B―X bonds due to the A―B off-center displacement. Together with the d-p orbital hybridization, the main reason for the distorted ferroelectric structure in ABP2X6 monolayers is the Jahn-Teller effect. ABP2X6 monolayers are predicted to be a new class of auxetic materials with an out-of-plane negative Poisson's ratio, i.e., the values of the negative Poisson's ratio are in the order AgBiP2S6 (−0.805) < AgBiP2Se6 (−0.778) < CuBiP2Se6 (−0.670) < CuInP2S6 (−0.060). This is mainly due to the tensile strain applied in the x/y direction enlarging the angle between P―P bonds and top layer X atoms, thereby enhancing the bucking height of monolayer ABP2X6. Moreover, external strain has a significant impact on the A―B off-center displacement, rendering an out-of-plane piezoelectric polarization. The values of e13 for CuInP2S6, CuBiP2Se6, AgBiP2S6 , AgBiP2Se6 monolayers are calculated to be −3.95 × 10−12, −5.68 × 10−12, −3.94 × 10−12, −2.71 × 10−12 C∙m−1, respectively, which are comparable to the only experimentally confirmed 2D out-of-plane piezoelectric Janus system (piezoelectric coefficient = −3.8 × 10−12 C∙m−1). This unusual auxetic behavior, ferroelectric polarization, and the electromechanical coupling in monolayer ABP2X6 could potentially lead to enormous technologically important applications in nanoelectronics, nanomechanics, and piezoelectrics. 相似文献
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研究了V型三能级原子玻色-爱因斯坦凝聚体与双模压缩相干态光场相互作用系统中的光场压缩的特性.数值计算结果表明:光场的正交分量呈现周期性压缩,其周期与原子间相互作用密切相关,而最大压缩量与持续时间与初始光场的压缩因子有关. 相似文献
186.
低磁控溅射率MCP防离子反馈膜工艺研究 总被引:1,自引:1,他引:0
为消除反馈正离子对三代微光夜视器件光阴极的有害轰击,提高微光像增强器的工作寿命,开展了低磁控溅射率法沉积微通道板(MCP)Al2O3防离子反馈膜的工艺研究。通过优化制备工艺,获得了制备MCP防离子反馈膜的最佳沉积条件:溅射电压1000V,溅射气压(4~5)×10-2 Pa,沉积速率0.5nm/min等。研究结果表明:在此工艺条件下,能够制备出均匀、致密且通孔满足质量要求的MCP防离子反馈膜。如果偏离这一最佳工艺条件,制备出的MCP防离子反馈膜膜层疏松、不连续,且通孔不能满足要求。 相似文献
187.
提出一种基于OpenCV图像库的运动目标处理算法仿真方法,介绍了OpenCV库的特点和VC6环境下的配置,通过调用库中的视频读写函数、图像特征计算和光流计算函数,得到运动目标的光流场,为运动目标状态分析和跟踪提供了基础,仅在图像库的基础上编写了少量代码就使算法得以实现,提高了编程效率。 相似文献
188.
研究地层压力变化对渗流特征的影响,对低渗透储层、碳酸盐岩储层,或其他致密性储层的油气开采和储层改造都具有重要意义.在考虑渗流压力梯度平方项存在的前提下,运用摄动法求解的相关理论,将渗透率随压力的变化融入到渗流问题的求解过程中,有效地求解了该类压敏型储层的非线性渗流问题.结果表明,在实际应用中,尤其是在储层压敏性较弱的情况下,可考虑直接用0阶摄动解即可满足较好的计算精度;储层的压敏性越强,越适宜通过用摄动解的修正,来达到精确求解的目的. 相似文献
189.
ANNIHILATION OF VERTICAL-BLOCH-LINE CHAINS IN THE WALLS OF ORDINARY HARD BUBBLES SUBJECTED TO JOINT STATIC BIAS FIELD AND IN-PLANE FIELD
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For the ordinary hard bubbles(OHBs) of garnet bubble films, the annihilation of the vertical-Bloch line (VBL) chains in their walls subjected to joint static bias field Hb and in plane field Hip was experimentally studied. The curves of two critical in-plane fields, H(1)ip and H′ip, vs Hb were measured. By means of the so-called "head-cut" and "tail-cut" experiments designed in this work, it was verified that for the OHBs subjected to Hip, their VBL chains with different lengths lose VBLs and become shorter simultaneously. It was also verified that the critical in-plane fields H(1)ipand H′ip correspond to the break down of the shortest and longest VBL chains of OHBs, respectively. 相似文献
190.
STABILITY OF SECOND KIND OF DUMBBELL DOMAINS SUBJECTED TO AN IN-PLANE FIELD AT DIFFERENT BIAS FIELDS
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The softening process of the second kind of dumbbell domalns(liDs) in garnet bubble films subjected to an in-plane field Hip at different static bias field Hb was studied experimentally. It was found that when Hb is larger, the remaining percentage of IID, RIID, drops sharply at a certain Hip, and with the increase of Hb the drop occurs at lower Hip and becomes more intensive. We have confirmed that this is related to the "spontaneous-shrink" 0f IIDs, which plays an important role for the breakdown oF vertical Bloeh line chains of lids subjected to joint fields Hip and Hb . 相似文献