Theoretical Prediction of Superconductivity in Boron Kagome Monolayer:MB3(M=Be,Ca,Sr) and the Hydrogenated CaB3

Using first-principles calculations, we predict a new type of two-dimensional(2D) boride MB₃(M = Be,Ca, Sr), constituted by boron kagome monolayer and the metal atoms adsorbed above the center of the boron hexagons. The band structures show that the three MB₃ compounds are metallic, thus the possible phononmediated superconductivity is explored. Based on the Eliashberg equation, for BeB₃, CaB₃, and SrB₃, the calculated electron–phonon coupli...     

无规聚丙烯腈纤维热处理过程相转变行为的同步辐射研究

使用在线同步辐射广角X射线衍射(WAXD)和原位变温傅里叶红外(FTIR)研究了无规聚丙烯腈(at-PAN)纤维热处理过程中晶区的相转变行为.研究发现,WAXD图像中由(110)晶面衍射形成的衍射弧在加热过程中其q值随温度的变化速率不完全一致,在110℃存在突变点,此温度下晶区的热膨胀率从4.15×10-4nm/K(α1)突变为1.13×10-3nm/K(α2),同时DSC曲线在110℃附近出现放热峰,说明发生了晶胞结构转变.通过升温FTIR测试发现1230 cm-1和1250 cm-1处吸收峰的相对强度随热处理过程也发生变化,两峰峰强分别对应纤维中31螺旋构象与平面锯齿构象的相对含量,通过C=I1250/I1230与热处理温度的关系发现C值在110℃突然急剧减小,说明at-PAN纤维晶区分子链在110℃附近发生了平面锯齿构象向31螺旋构象的剧烈转变,而正是由于这种转变导致晶区层间距的变化使得WAXD图像中衍射弧的位置随温度变化速率不一致,即相转变行为是由分子链构象的变化引起的.