碱土金属掺杂六硼化镧对热电子发射性能调控机制的研究

The cathode is the heart of all kinds of modern vacuum electronic devices, which is widely used for national defense and civil fields. Among the cathodes, lanthanum hexaboride(LaB6) demonstrates important theoretical significance and applicable value. Low working temperature and high current density is a new requirement for the development of the LaB6-based cathode materials development. Emission performance can be improved by a structure regulation via alkaline-earth metals doping LaB6, which provides a new pathway for development of cathode materials. Considering that most of the features and underlying mechanism of the alkaline-earth metals doping on structure and performance remain unclear, in this project the first principle calculation based on density function theory, combined with the boron thermal reduction, neutron powder diffraction and emitting performance testing techniques will be employed to get the relationship relations between composition, crystal structure, and work function. Moreover, scanning electron microscopy and X-ray photoelectron spectroscopy are supposed to characterize the surface states of cathodes, to investigate the emission mechanism and explore the action mechanism of regulating the thermal emission properties via alkaline-earth metals doping LaB6. We will predict the effective way to achieve high emission performance, and we are strongly convinced that these studies will provide important theoretical base for preparing high-performance thermionic cathodes.

阴极是各种现代真空电子设备的心脏器件，在国防军工和民用等多个领域有广泛的应用。其中，六硼化镧（LaB6）热阴极具有重要理论研究意义和应用价值。低温、高电流密度是当前对LaB6基阴极材料发展的新要求。新近发现的通过碱土金属掺杂调控LaB6结构提高发射性能为阴极发展提供了一种新途径。然而碱土金属掺杂LaB6固溶体对结构与性能影响的物理机理及其特性等基础性研究才刚刚起步，亟待深入探讨。本课题拟采用基于密度泛函理论的第一性原理计算，结合硼热还原制备、中子粉末衍射、发射性能测试等实验分析方法，系统研究碱土金属掺杂LaB6的组分、晶体结构与发射性能之间的关系规律。此外，综合采用X射线光电子能谱、扫描电镜等技术对阴极表面状态进行研究，探讨热电子发射机理，阐明碱土金属掺杂对LaB6发射性能的调控机制。探索提高发射性能的有效方法和途径，为制备高性能热阴极提供重要理论参考依据。

阴极是各种现代真空电子设备的心脏器件，在国防军工和民用等多个领域有广泛的应用。六硼化镧（LaB6）是性能优异的热阴极材料，具有大电流发射密度、长寿命、抗中毒、化学稳定性高、耐离子轰击等优点，有重要研究意义和应用价值。低温、高电流密度是当前对LaB6基阴极材料发展的新要求。本项目研究发现，通过碱土金属掺杂调控LaB6结构提高发射性能为阴极发展提供了一种新途径。本课题采用基于密度泛函理论的第一性原理计算，结合硼热还原制备、中子粉末衍射、发射性能测试等实验分析方法，系统研究了碱土金属掺杂LaB6的组分、晶体结构与发射性能之间的关系规律。综合采用X射线光电子能谱、扫描电镜等技术对阴极表面状态进行研究，探讨热电子发射机理，初步阐明了碱土金属掺杂对LaB6发射性能的调控机制。探索提高发射性能的有效方法和途径，为制备高性能热阴极提供重要理论参考依据。制备的(La0.9Ca0.1)B6固溶体阴极经热电子发射测试可知，在1673 K、1773 K和1873 K温度下饱和发射电流密度值分别达47.93 A/cm2、70.41 A/cm2和83.47 A/cm2；制备的（La0.6Sr0.6）B6阴极在1773 K和1873 K温度下，饱和发射电流密度值分别达53.16A/cm2和69.71 A/cm2，说明该材料具有很好的发射性能。可广泛应用于空间站、深空探测、高低轨地球卫星轨道控制、电子束焊接等航空航天、国防和民用高科技领域，具有十分重要的社会、经济效益和广阔的应用前景。