高温高压下利用非金属元素硒和碲作触媒合成金刚石的行为规律及其触媒机理研究

In this project, the behavior rules and mechanism of diamond synthesis would be systematically researched in the systems of selenium-carbon and Tellurium-carbon under high pressure and high temperature (HPHT) conditions. It includes: research on spontaneous nucleation and growth characteristics of diamond crystal under a much wider range of pressure and temperature as well as its relationship with hold time, determine the distribution in the high pressure phase diagram of carbon; clarify the effection of sample assembly type and adding proportion on spontaneous nucleation and growth, obtain the optimal environmental conditions of the diamond synthesis; detect and analyze the characteristics and differences of diamond crystal in structure, morphology ,composition and physical properties using Se and Te as catalyst; explore the growth of diamond seed crystal to synthesis of large single crystal (≥2mm) by the temperature gradient method; analyze in depth the kinetics and catalytic mechanism of graphite-diamond phase transition in Se-C and Te-C systems under HPHT conditions. In this study, the synthetic diamond used inorganic non-metallic catalyst of Se and Te is an ultimate functional material with extremely wide application, a large number of experimental data and theoretical analysis would deepen our understanding of catalyst mechanism for diamond synthesis using elements of the oxygen group as catalyst, it is of great academic significance in the development of artificial diamond science and technology.

本项目拟深入系统地研究Se-C(硒-碳)、Te-C（碲-碳）体系在高温高压下合成金刚石的行为规律及其触媒作用机理。内容包括：在宽广的压力温度幅度下，研究两体系金刚石晶体成核与生长的特征及其与合成时间的关系，确定它们在碳元素高压相图上的分布规律；弄清楚样品组合方式及添加比例对晶体自发成核和生长的影响，获得最优化的金刚石晶体生长环境条件；检测分析用Se、Te作触媒合成的金刚石在结构、形貌、成分和物理性能方面的特征和差异；探索利用温度差法对放置的金刚石晶种进行生长大颗粒单晶（≥2mm）的实验；深入系统分析Se-C、Te-C体系高温高压下石墨向金刚石相变的动力学及触媒作用机理。本研究利用无机非金属触媒Se、Te合成的金刚石是一种应用价值极为广泛的极限功能材料，大量实验数据与理论分析将加深理解氧族元素在合成金刚石过程中的触媒作用机理，在人造金刚石的科学技术发展中具有极为重要研究价值和学术意义。

高压科学技术的发展为新材料合成、结构物性研究提供了的重要支撑，本项目建立在六含八大腔体压力实验技术上，先后开发并完善了一级压砧校准、八面体制作与组装等方法；利用金属Bi、半导体ZnTe、ZnS分别对14/8，11/5系统进行了压力标定，而温度标定结果表明斜孔组合方式保温效果更好。分别以Se、Te为触媒与石墨共存体系进行了高温高压实验，结果表明金刚石是在熔融状态的触媒液相环境中生长的，合成的金刚石晶体经历了溶解析出的过程；通过对不同体系下高压离解能的计算，加深了对氧族元素作为触媒合成金刚石的相变规律和具体过程的认识，特别是对非金属单质Se、Te触媒机理的认识：元素（O、S、Se、Te）在高温高压下与碳发生化合反应，生成碳化物（CX或CX2）, 热力学计算表明，碳化物处于不稳定状态，不断进行分解，在金刚石的热力学稳定区，分解析出的碳原子以金刚石结构的形式成核和生长，使得晶体不断得到长大。也可以理解为：氧族元素的存在降低了石墨向金刚石转变的势垒，通过化合和分解反应的方式顺利实现了金刚石的成核和生长。利用非金属单质Se、Te作触媒合成金刚石及其机理分析研究将在金刚石科学和技术的发展中具有重要的意义。