纤锌矿氮化硼及其应用的研究（Ⅱ）——纤锌矿型氮化硼的等温状态方程

 使用两种不同的高压在位X光衍射法，研究了用爆炸法合成的纤锌矿型氮化硼（wBN）在室温下的等温状态方程。一种方法是用转靶X光角色散粉末衍射法，研究了它在0~40 GPa压力范围内的等温压缩行为。结果表明，wBN在0~40 GPa的压力范围内是稳定的，没有发生结构相变。通过p-V数据对Murnaghan方程拟合，得到wBN在p=0时的等温体模量B₀=(335±34) GPa及其对压力的一阶导数B₀'=4.21；另一种是用同步辐射X光能量色散衍射法，研究了它在0~25 GPa压力范围内的等温状态方程。实验中，使用了改进的自动加压的DAC高压装置，此装置保证了实验中衍射角θ₀固定不变。将获得的p-V数据仍用Murnaghan方程拟合，得到wBN在p=0时等温体模量B₀=(280±56) GPa，及其B₀'=4.39。     

高压导致纳米TiO2形变的电子显微研究

α-PbO₂相TiO₂高压相具有适宜的带隙能和可见光范围的光催化能力,是一种适用于可见光、高效且环保的光催化材料.本文使用金刚石对顶压砧对锐钛矿纳米球进行加压-卸压处理得到了α-PbO₂相TiO₂高压相.利用透射电子显微镜对比初始样品和卸压样品,观察结果表明晶粒发生了明显形变,高分辨图显示其晶粒中存在大量[100]方向层错和形变孪晶,其中亚微米级晶粒中形成了透镜形片层结构的形变孪晶带;纳米级晶粒中形成了扇形多重形变孪晶.研究表明高压下锐钛矿TiO₂可以发生明显的形变,其形变的微观机制与金属类似,主要为形变孪晶和层错滑移,形变孪晶的形成存在明显的尺寸效应.这些结果为TiO₂高压相变的尺寸效应研究提供了一个新的切入点,同时还为制备孪晶α-PbO₂相TiO₂高压相提供了方法.     

First-Principles Studies on Properties of Boron-Related Impurities in c-BN

We investigate, by first-principles calculations, the pressure dependence of formation enthalpies and defective geometry and bulk modulus of boron-related impurities （VB, Cs, NB, and OB） with different charged states in cubic boron nitride （c-BN） using a supercell approach. It is found that the nitrogen atoms surrounding the defect relax inward in the case of CB, while the nitrogen atoms relax outward in the other cases. These boron-related impurities become much more stable and have larger concentration with increasing pressure. The impurity CB^＋1 is found to have the lowest formation enthalpy, make the material exhibit semiconductor characters and have the bulk modulus higher than ideal c-BN and than those in the cases of other impurities. Our results suggest that the hardness of c-BN may be strengthened when a carbon atom substitutes at a B site.     

聚丙烯酸的单分子应力-应变行为

利用原子力显微镜的一种新方法 单分子力谱技术 研究了聚丙烯酸单链的弹性性质，得到了聚丙烯酸链的拉力与拉伸曲线．其拉力与拉伸曲线可以通过修改的Ｌａｎｇｅｖｉｎ方程进行较好地拟合．结果表明聚丙烯酸链的弹性性质与长度线性成比例，聚丙烯酸链具有相同的Ｋｕｈｎ长度（０６４±００５ｎｍ）和链段弹性系数（１３０００±２０００ｐＮ／ｎｍ），充分表明我们位伸的是聚丙烯酸的单链，所测得的拉力 拉伸行为是聚丙烯酸单链的弹性行为     

Structural stability and electrical properties of AlB2-type MnB2 under high pressure

The structural stability and electrical properties of AlB2-type MnB2 were studied based on high pressure angledispersive x-ray diffraction, in situ electrical resistivity measured in a diamond anvil cell(DAC) and first-principles calculations under high pressure. The x-ray diffraction results show that the structure of AlB2-type MnB2 remains stable up to 42.6 GPa. From the equation of state of MnB2, we obtained a bulk modulus value of 169.9±3.7 GPa with a fixed pressure derivative of 4, which indicates that AlB2-type MnB2 is a hard and incompressible material. The electrical resistance undergoes a transition at about 19.3 GPa, which can be explained by a transition of manganese 3d electrons from localization to delocalization under high pressure.     

ZnS:Eu纳米晶的高压相变研究

采用同步辐射能量色散X射线衍射技术和金刚石对顶砧高压装置,对ZnS:Eu纳米晶进行了原位高压X光衍射实验.最高压力为30.8Pa.当压力为11.5GPa时,ZnS:Eu发生了一次从纤锌矿到闪锌矿的结构相变.在压力为16.0GPa时,又发生了明显的结构相变,相变后的结构为岩盐矿,其相变压力较体材料高.得到了Birch-Murnaghan状态方程、ZnS:Eu纳米晶的体模量和压力导数.ZnS:Eu纳米晶的体模量高于体材料的值,表明纳米材料较体材料的硬度高.     

二次加热法制备单分散性CoFe2O4纳米晶及其磁性研究

本文分别以CoCl2·6H2O,FeCl3·6H2O,NaOH为原料,利用N(CH3)4OH (四甲基氢氧化铵)作为改性剂,对CoFe2O4纳米颗粒进行原位表面改性,采用二次加热法,制备单分散性CoFe2O4纳米晶.利用透射电子显微镜(TEM)、X射线衍射仪(XRD)、能量散射分析仪(EDS)和振动样品磁强计等测试手段对样品的形貌,粒径,结构,以及磁学性能等进行了表征.结果表明,单分散性CoFe2O4纳米晶仍具有较大的饱和磁化强度和矫顽力.     

含镧金属富勒烯不同溶剂的高温高压提取

将金属原子或离子置于以Ｃ６０、Ｃ８２为代表的富勒烯笼内形成金属富勒烯包合物是目前富勒烯研究的热点课题［１～３］．合成的金属富勒烯常伴随生成较难分离的空心富勒烯,传统的索氏提取法效率又较低,使得金属富勒烯的深入研究受到限制［１,２］．本文采用改进的高温...     

Study of high pressure structural stability of CeO2 nanoparticles

In situ high pressure XRD diffraction and Raman spectroscopy have been performed on 12 nm CeO₂ nanoparticles. Surprisingly, under quasihydrostatic conditions, 12 nm CeO₂ nanoparticles maintain the fluorite-type structure in the whole pressure range (0-51 GPa) during the experiments, much more stable than the bulk counterpart (P_T～31 GPa). In contrast, they experienced phase transition at pressure as low as 26 GPa under non-hydrostatic conditions (adopting CsCl as pressure medium). Additionally, 32-36 nm CeO₂ nanoparticles exhibit an onset pressure of phase transition at 35 GPa under quasihydrostatic conditions, and this onset pressure is much lower than our result. Further analysis shows both the experimental condition (i.e., quasihydrostatic or non-hydrostatic) and grain size effect have a significant impact on the high pressure behaviors of CeO₂ nanomaterials.     

氢化石墨纳米结构的合成及尺寸相关的荧光性质

在溶剂热反应条件下(180℃),利用还原剂金属钾对卤代苯(溴苯和二溴苯)中的C—Br键进行选择性裂解,而含氢的碳六元环仍稳定且之间可以发生聚合成键,成功合成了2种不同的氢化石墨纳米结构,获得的产物分别呈黄褐色和黑色.拉曼和红外光谱分析结果表明,黑色产物为尺寸约2 nm的氢化石墨纳米片,而黄褐色样品为尺寸更小的氢化碳纳米结构;X射线衍射分析结果表明,2种产物都具有菱方结构但结晶性较低.对合成的氢化石墨纳米结构的荧光性质分析发现,样品具有尺寸相关的荧光现象,同等激发条件下,尺寸较小的黄褐色样品的发光强度约为黑色样品的15倍.