铽改性铌酸锶钡晶体的介电谱研究

在5×10~2Hz 到5×10~8Hz 频率范围内测量了 Tb 改性的铌酸锶钡(SBN)晶体的室温介电常数,并以1×10~4Hz 的频率测量了这些介电常数从室温至居里温度以上的变化。对于 c 轴和 a 轴介电常数,都观测到了介电弛豫,但 c 轴介电弛豫频率明显低于 a 轴介电弛豫频率。对于不同的组份来说,介电弛豫频率随居里温度降低而降低。这些晶体的铁电—顺电相变是弥散性的,弥散程度随Tb 含量的增加而增高。     

DD3单晶镍基超合金高温力学性能

采用扫描电镜（ＳＥＭ）研究了单晶镍基高温合金ＤＤ３的高温蠕变性能和低应变速率下的拉伸行为。结果表明，ＤＤ３合金表现出良好的蠕变强度和较高的蠕变寿命；拉伸过程中合金的屈服强度在室温１１０３３Ｋ之间保持不变，当温度大于１０３３Ｋ后，屈服强度显著降低。断口分析表明，这类材料具有独特的断裂方式，断口为混合型，即包括韧性断裂和局部区域的解理断裂特征。     

PET/60PHB热致性液晶共聚酯的固相缩聚——影响表观反应速度的因素

本文将 PET/60PHB 热致性液晶共聚酯加热到玻璃化温度和熔融温度之间进行固相缩聚反应,研究了影响表观反应速度的主要因素——反应条件和预聚体的性质。在适当条件下固相缩聚反应,可将共聚酯的特性粘数[η]从0.690提高到1.083。     

Synthesis of few layer single crystal graphene grains on platinum by chemical vapour deposition

The present competition of graphene electronics demands an ef fi cient route which produces high quality and large area graphene. Chemical vapour deposition technique, where hydrocarbons dissociate in to active carbon species and form graphene layer on the desired metal catalyst via nucleation is considered as the most suitable method. In this study, single layer graphene with the presence of few layer single crystal graphene grains were grown on Pt foil via chemical vapour deposition. The higher growth temperature changes the surface morphology of the Pt foil so a delicate process of hydrogen bubbling was used to peel off graphene from Pt foil samples with the mechanical support of photoresist and further transferred to Si O2/Si substrates for analysis. Optical microscopy of the graphene transferred samples showed the regions of single layer along with different oriented graphene domains. Two type of interlayer stacking sequences, Bernal and twisted, were observed in the graphene grains.The presence of different stacking sequences in the graphene layers in fl uence the electronic and optical properties; in Bernal stacking the band gap can be tunable and in twisted stacking the overall sheet resistance can be reduced. Grain boundaries of Pt provides low energy sites to the carbon species, therefore the nucleation of grains are more at the boundaries. The stacking order and the number of layers in grains were seen more clearly with scanning electron microscopy. Raman spectroscopy showed high quality graphene samples due to very small D peak. 2D Raman peak for single layer graphene showed full width half maximum(FWHM) value of 30 cm-1. At points A, B and C, Bernal stacked grain showed FWHM values of 51.22, 58.45 and 64.72 cm-1, while twisted stacked grain showed the FWHM values of 27.26, 28.83 and 20.99 cm-1,respectively. FWHM values of 2D peak of Bernal stacked grain showed an increase of 20–30 cm-1 as compare to single layer graphene which showed its dispersive nature and con fi rmed Bernal sequence. On the other hand, the slightest decrease in FWHM values of 2D peak in twisted grain comparing to single layer con fi rmed the twisted sequence of grains. Atomic force microscopy analysis showed an increasing trend in grain height pro fi le with an increase in the number of layers.     

液晶Sc相的格胞模型

采用格胞模型，定义了Ｓｃ相分子相对格胞中心的取向序参量、质心位置序参量及两者耦合的序参量，得出平衡状态下分子质心作层状分布而分子取向的优先取向与层面法向倾斜．求出分子层厚度、指向矢倾斜角的表达式，并计算了它们随温度的变化，理论结果符合实验，     

关于胆甾相液晶选择反射特性的探讨

本文讨论了胆甾相液晶因分子排列的螺旋结构而具有的选择反射的光学特性,利用布喇格反射条件和电偶极子辐射模型,分别导出胆甾相液晶在反射时对入射光的波长和偏振状态的选择条件。     

HMX的晶体缺陷和酸值的关系

该文研究了奥克托今(HMX)的晶体缺陷和酸值(以醋酸计)之间的关系。在实验分析和显微照像基础上,提出在HMX晶体内形成母液包裹体的一种机制,即在晶体生长过程中出现了巨阶梯,进而形成包裹体,当HMX从强酸溶液中迅速成长时该包裹体由硝酸或汽泡充满。     

二维光子晶体中负折射现象的研究与仿真

使用光子晶体能带结构和等频面（EFS）方法对二维光子晶体中的负折射现象进了研究和仿真．得到了二维光子晶体中出现负折射率现象的频率范围．使用时域有限差分法（FDTD）对光波在二维光子晶体界面和晶体中的传播进行了数值仿真研究．由仿真结果发现在一定的频率范围内,在二维光子晶体中确实可以发现光波的负折射传播现象．     

工程陶瓷车削刀具磨损机理及理论模型的研究

通过二硅酸锂玻璃陶瓷的切削实验,依据摩擦学原理,结合犁沟效应从微观层面讨论了陶瓷材料对切削刀具磨损机理的影响.通过引入陶瓷晶体相关参数,揭示了陶瓷晶体的形貌和排布方式在车削过程中对刀具磨损量的影响,使磨损机理应用更具广泛性和直观性.结合几何学和运动学分析,建立了工程陶瓷材料车削刀具体积磨损量模型,并进行了实验验证.理论和实验结果均表明随切削路程的增大,刀具体积磨损量先表现为稳定增加,随后由于磨损面的不断增加以及热量堆积导致黏结磨损现象的出现,刀具磨损速度急剧加快,最终导致刀具刃缘崩碎而失效.     

二维光子晶体绝对带隙的研究

晶体中获得大的绝对带隙,可以通过降低格子对称性解除简并来实现。格子对称性的降低一般可以通过向晶体的原胞内引入不同半径的柱子的方法实现,在该方法基础上结合滑移操作,对二维正方形光子晶体结构进行了研究,发现这种联合方法用于打开绝对带隙特别有用,其相对带隙宽度约为“双柱子正方形格子”情况的2倍,同时还使绝对带隙出现的位置向低频处移动。