铪基超高温陶瓷的变成分晶体结构预测与熔化行为研究

Hafnium has several types of valences from +1 to +4, which could bond with boron (B), carbon (C) and nitrogen (N) such non-metallic elements to form ultra-high temperature ceramics with melting points exceeding 3000 centigrade, therefore serving as preferable materials in extreme high temperature environment. Molten structure of the material is quite different from that of the solid and gaseous phases. To determine the melting point of the material is critical to investigate the solid-liquid transition temperature as well as to reveal the melting mechanism of the material. The melting point of the material is closely related with its element type, element ratio, crystal structure and the environmental pressure. This project uses HfzX(1-z) (X = B, C, and N, 0<z<1) as the example ultra-high temperature ceramics, to search their crystal structures with variable compositions under normal and high pressures based on first-principles and evolutionary algorithms, to find out the stable crystal structures according to criteria such as energy, mechanical property and lattice dynamics characteristics. First-principles molecular dynamics will be applied to study the limit temperature of HfzX(1-z), i.e. the melting point, under high temperature and high pressure environment. The effects of element type, the ratio of X to Hf, and the initial crystal structure on the solid-liquid transition temperature will be revealed. This study realizes the ratioal design and evaluation from composition/structure to melting property for hafnium-based ultra-high temperature ceramics, which is also useful for the innovative design of the other ultra-high temperature materials.

铪元素（Hf）具有+1～+4多种化合价，它可以与硼（B）、碳（C）和氮（N）等非金属元素形成熔点超过3000 摄氏度的超高温陶瓷，成为极端高温环境的优选材料。材料的熔态结构与固态和气态截然不同，确定材料的熔点是获得固液转变温度以及揭示材料熔化机理的关键。材料的熔点与其元素类型、元素比例、晶体结构以及环境压力密切相关。本项目针对HfzX(1-z)（X=B、C和N, 0<z<1）超高温陶瓷，基于第一性原理和进化算法搜索其在常压和高压下的变成分晶体结构，并利用能量判据、力学判据和晶格动力学判据筛选出能够稳定存在的材料，进而应用第一性原理分子动力学研究HfzX(1-z)在高温高压环境下的使用极限温度即熔点，揭示元素类型、比例以及初始晶体结构对材料固液转变温度的影响规律，实现铪基超高温陶瓷材料"成分/结构-熔化性质"的理性设计与评价，对其它超高温材料的创新设计也具有普适意义。

针对HfZX1-ZX=B、C和N，0<z<1）超高温陶瓷，基于第一性原理和进化算法发现了一系列HfZX1-Z在常压和高压下的变成分晶体结构，并利用了能量判据、力学判据和晶格动力学判据筛选出能够稳定存在的晶体结构。基于第一性原理分子动力学研究了HfZX1-Z在高温高压环境下的使用极限温度即熔点，揭示了元素类型、比例及初始晶体结构对铪基超高温陶瓷固液转变温度的影响规律，实现了铪基超高温陶瓷材料“成分/结构-熔化性质”的理性设计与评价，合成出了Hf-C-N超高温陶瓷，为新型超高温陶瓷材料的创新设计提供了科学依据。. 本项目的研究成果已成功应用于Ti-N、H-Cl等材料的晶体结构预测，验证了此基础研究的普适性。. 本项目发表学术论文22篇，其中SCI 收录22篇，EI收录5 篇。两名博士、6名硕士和2名本科生受此项目资助。