Formation of unusual Cr~(5+) charge state in CaCr_(0.5)Fe_(0.5)O_3 perovskite

A new oxide CaCr_(0.5)Fe_(0.5)O_3 was prepared under high pressure and temperature conditions. It crystallizes in a B-site disordered Pbnm perovskite structure. The charge combination is determined to be Cr~(5+)/Fe~(3+) with the presence of unusual Cr~(5+) state in octahedral coordination, although Cr~(4+) and Fe~(4+) occur in the related perovskites CaCrO_3 and CaFeO_3.The randomly distributed Cr~(5+) and Fe~(3+) spins lead to short-range ferromagnetic coupling, whereas an antiferromagnetic phase transition takes place near 50 K due to the Fe~(3+)–O–Fe~(3+) interaction. In spite of the B-site Cr~(5+)/Fe~(3+) disorder,the compound exhibits electrical insulating behavior. First-principles calculations further demonstrate the formation of CaCr_(0.5)~(5+)Fe_(0.5)~(3+)O_3 charge combination, and the electron correlation effect of Fe~(3+) plays an important role for the insulting ground state. CaCr_(0.5)Fe_(0.5)O_3 provides the first Cr~(5+) perovskite system with octahedral coordination, opening a new avenue to explore novel transition-metal oxides with exotic charge states.     

Room-Temperature Magnetism Realized by Doping Fe into Ferroelectric LiTaO3

We synthesize LiTal-x FexO3-σ （LTFO） remain single phase up to x = 0.09 ceramics by the conventional solid-state reaction method. The samples The magnetic measurements show that the doping of Fe successfully realizes ferromagnetism of LTFO at room temperature. The dielectric measurements indicate that LTFO is ferroelectric, similarly to LiTaO3 （LTO）, but its ferroelectric Curie temperature seems to decrease with the increasing Fe content. By means of doping Fe ions into LTO, the coexistence of spontaneous electric polarization and spontaneous magnetic moment is realized at room temperature.     

Misfit-layered compound PbTiS3 with incommensurate modulation： Transmission electron microscopy analysis and transport properties

The microstructural characteristic of the misfit-layered compound PbTiS3 has been studied with transmission electron microscopy. All the incommensurate modulation-induced satellite spots and main diffraction spots of basic sublattices can be indexed systematically with a superspace group method. Finally, the relationship between the electronic transport properties and the crystal structure is discussed.     

纳米材料及HfO_2基存储器件的原位电子显微学研究

总结了我们将原位技术和透射电子显微学分析方法相结合,针对纳米材料和器件的结构、形貌、成分以及电势分布等物理性质的动态行为所开展的综合物性表征和分析工作.主要成果有:揭示了C_(60)纳米晶须在焦耳热作用下的结构相变路径;观察到了电荷俘获存储器中的电荷存储位置以及栅极电压诱导的氧空位缺陷;研究了阻变存储器中氧空位通道的形成过程以及导电通道的开关机理.这些成果不但有助于深入理解纳米材料和器件相关功能的物理机理,改善其工作性能,更展示了透射电子显微学在微电子领域强大的研究能力.     

高压下ZnSe 纳米带的结构相变及拉曼散射研究

 利用高压原位角散X射线衍射实验研究了ZnSe纳米带的结构稳定性。发现样品在12.6 GPa 附近存在一个从立方闪锌矿型到立方岩盐矿型的结构相变,并且在相变点附近存在较大的体积收缩,相对体积变化率达13%。利用Birch-Murnaghan 状态方程拟合,得到了闪锌矿相的体弹模量约为56 GPa,略低于体材料的体弹模量（约67 GPa）;并得到其立方岩盐矿相的体弹模量约为116 GPa。高压拉曼散射实验结果表明,横光学声子模散射峰在5.5 GPa压力附近发生劈裂,纵光学声子模散射峰在12.8 GPa压力以上逐渐消失。根据角散实验的体弹模量数据,计算得到了闪锌矿相中对应不同声子模式的格林爱森常数。     

A-site ordered perovskite CaCu_3Cu_2Ir_2O_(12-δ) with square-planar and octahedral coordinated Cu ions

A novel CaCu_3Cu_2Ir_2O_(12-δ) polycrystalline sample was synthesized at 8 GPa and 1373 K.Rietveld structural analysis shows that this compound crystallizes in an AA'_3B_4O_(12)-type A-site ordered perovskite structure with space group Im-3.Xray absorption spectra reveal a +2-charge state for both the square-planar and octahedral coordinated Cu ions,and the valence state of Ir is found to be about +5.Although the A-site Ca and the A'-site Cu~(2+) are 1:3 ordered at fixed atomic positions,the distribution of B-site Cu~(2+) and Ir~(5+) is disorderly.As a result,no long-range magnetic ordering is observed at temperatures down to 2 K.Electrical transport and heat capacity measurements demonstrate itinerant electronic behavior.The crystal structure is stable with pressure up to 35.7 GPa at room temperature.     

Zn2SnO4纳米线高压下的相变研究

 利用金刚石对顶压砧（DAC）对具有反尖晶石结构的透明导体氧化物Zn₂SnO₄（ZTO）纳米线进行了原位高压同步辐射角散X射线衍射（ADXRD）研究。结果发现：在压力为12.9 GPa附近,晶体的对称性降低,并发生晶体结构相变,产生中间过渡相;当压力为32.7 GPa时,发生高压相变,形成高压相。在样品加压前后,纳米线的形貌发生了很大的变化。通过Birch-Murnaghan方程,拟合得到B′₀=4时的体弹模量B₀ =(168.6±9.7) GPa。     

关于中学数学教学的目的任务的一些意見

明确中学数学教学的目的任务是提高教学貭量的先决条件。在教育大革命之前有些数学教师是不重視数学教学的目的任务的。例如:部分教师在备課时并不考虑怎样貫彻目的任务;有的教师在課时計划里虽然写出“教学目的”一項,但是并沒有本着目的要求讲这节課。有的教师說:“把书教好就行了,目的任务有甚么用?”我們认为沒有明确的目的任务,也就沒有“把书教好”的标准了。另外,教学无目的也正是“为教育而教育”的旧教育思想的反映。我們不能认为讲完了課,批改了作业,就算完成了教学任务,我們必須有明确的奋斗目标才能培养出合乎国家要求的人材。数学教学的目的任务是数学教学的指南,所以怎样根据教育方針、本科特点和普通中学性质来确定数学教学的目的任务问题是当前改进教学的重要问题之一。在探討目的任务之前对于以下几个问题有必要取得一致的认识是 (一)确定目的任务的根据。关于确定目的任务的根据我們是从以下三个方面来考虑的: 1.教育方針:党的教育方針是教育为无产阶級政治服务、教育与生产劳动相結合,毛主席指出我們的教育目的是培养有社会主义觉悟有文化的劳动者,这是确定数学教学目的任务首先应該考虑的問题。我們曾經对教育方針的理解有些片面性,认为教育方針只包括“加强政治,联系生产”,对于传授系統的巩固的科学知識的重要意义体会不足。 2.数学的特点:我們认为数学有如下几点特点:(1)数学是自然科学,它沒有阶級性,但含育着辯証唯物主义思想因素;(2)数学是基础課,有应用上的广泛性;(3)数学是反映客观实际的,但有高度的抽象性;(4)数学有精确性和邏輯上的严密性。 3.普通中学的性质:普通中学是与小学和大学相