First principles study on the elastic properties and electronic structures of (Fe, Cr)3C

First principles calculations are performed to investigate the elastic properties and electronic structures of Cr doped Fe₃C carbides, the obtained results are compared with Cr₃C and Fe₃C. The calculated bulk modulus of Fe₁₁CrC₄ and Fe₁₀Cr₂C₄ is 260GPa and 270GPa, respectively, larger than Fe₃C. So the hardness of Fe₃C phase can be enhanced by doped with an appropriate amount of Cr, however, the calculated formation enthalpy and defect formation enthalpy of Fe₁₁CrC₄ and Fe₁₀Cr₂C₄ are positive. On the other hand, the electronic calculations reveal that the ground states of Fe₁₁CrC₄ and Fe₁₀Cr₂C₄ are ferromagnetic. The evaluated local magnetic moments of Fe at 4c sites are larger than that of 8d sites, which is analogous to Fe₃C. Milliken population results indicate that the stabilities of Fe₁₁CrC₄ and Fe₁₀Cr₂C₄ are reduced mainly due to the strong repulsive bonds among metal atoms.     

Nb_2O_5对碲铅铋铌系玻璃结构和性能的影响

采用熔融法制备不同Nb2O5含量的TeO2-PbO-Bi2O3-Nb2O5系玻璃粉,研究了Nb2O5的加入量对TeO2-PbO-Bi2O3-Nb2O5系玻璃热膨胀系数、软化温度和热稳定性的影响。利用傅里叶变换红外光谱仪检测玻璃粉的结构,通过热机械分析仪和综合热分析分别测试玻璃的膨胀系数和析晶温度,采用场发射扫描电镜观察太阳能电池Ag/Si接触界面。结果表明,随着Nb2O5含量的增加,玻璃的热膨胀系数和软化温度逐渐降低,玻璃化温度和析晶温度逐渐升高,玻璃的热稳定性逐渐增强。添加Nb2O5的玻璃粉所对应的太阳能电池正面电极中,Ag/Si接触界面存在大量的纳米银粒子,这将更有利于晶硅太阳能电池的光电子传导。     

合金元素对 Nb2Mo2Si合金相平衡及Nb2 Nb 5Si 3共晶组织形态的影响

采用电弧熔炼法制备了 Nb220Si210Mo、Nb220Si210Mo23M (M = Cr , Al , Ti) (原子分数) 四种 Nb2Mo2Si基超高温合金。利用 SEM、EDS、XRD等实验技术对铸造合金的相组成与组织形态进行了观察和分析。Nb220Si210Mo 合金由铌固溶体 (Nb SS) 与βNb 5Si 3化合物两相构成 , 其铸造组织包含大量片层状共晶 (Nb SS 2βNb 5Si 3) 组织。少量合金元素 Cr (3 at %) 能够改变 Nb220Si210Mo 合金的相平衡关系 , Nb220Si210Mo23Cr 的铸造组织中不仅存在 Nb SS和βNb 5Si 3 , 而且还出现少量 Cr 2Nb相 ; 而添加合金元素 Al、Ti (3 at %) 并不改变 Nb220Si210Mo 合金的相平衡关系。添加 Cr 使 Nb SS 2 βNb 5Si 3共晶组织失去了平直片层特征 ; Al 有利于共晶组织中片层状共晶形成 ; 添加 Ti使共晶组织呈现羽毛状特征。合金化使 Nb与βNb 5Si 3的晶格常数发生变化 : Nb的晶格常数均变小; Nb220Si210Mo23Cr合金中βNb 5Si 3的 c/ a值减小 , 其它 3种合金中βNb 5Si 3的 c/ a值增大。     

沉积温度对a-C:F薄膜结构与热稳定性的影响

在不同的沉积温度下，利用CHF3和C2H2为气体源，在微波电子回旋共振等离子体化学气相沉积(ECR-CVD)系统中制备了氟化非晶碳(-C：F)薄膜，为了研究其热稳定性，薄膜在500℃的真空中作了退火处理。测量了退火前后其电学、光学性质的变化，使用FFIR、Raman、XPS方法考察了其结构随沉积温度的变化，分析了性质同结构之间的关联。结果表明，在高的沉积温度下制备的薄膜中的F／C比较低，CF2和CF3键成分较少而以CF键成分为主，其交联程度高，因而具有较好的热稳定性。     

The impact of diversifying and de novo firms on regional innovation performance in an emerging industry: a longitudinal study of the U.S. ethanol industry

There is growing interest among strategy scholars and policy makers regarding the influence of diversifying and de novo firms on regional innovation activities in emerging industries. This paper examines how the population, entry, and exit of diversifying and de novo firms in regions influence regional innovation output in an emerging industry. Using longitudinal data from the U.S. ethanol industry, we find that the local population and exit of diversifying and de novo firms have differing impacts on regional innovation output. Our findings contribute to the literature on firm heterogeneity, agglomeration, and regional innovation systems.