掺杂5d过渡金属、C、N对ReB2和WB4的热、力学性能影响的研究

超硬材料在科学、技术和工业领域具有非常重要的价值。高温高压合成的金刚石和立方氮化硼的应用都受到很大限制。与它们相比，常压下合成的超硬材料ReB2和WB4更具有市场竞争力，实验报道少量Re掺入WB4中，虽然可提高硬度，但相应成本也提高了。掺杂引起硬度变化的内在微观机理不清楚。掺杂对ReB2和WB4各种性质影响的研究还很少。.本项目拟研究掺杂5d 过渡金属、C、N对超硬材料ReB2和WB4的结构、相稳定性和力学性质影响的内在微观机理。探讨常压及高压下掺杂化合物的热、力学性质以及相变；利用从生成焓-压强关系以及能量凸包之间的关系的角度和化学势能的角度来判定相稳定性的两种方法，寻找基态结构；探讨电子结构与力学性质，如体模量、剪切模量、理想强度、硬度等之间的关系等。研究哪些规律是特定体系的特殊行为，哪些是普遍规律。从得到的普遍规律中抽象出物理模型，指导实验合成和预测新型高硬度材料。

Superhard materials are of considerable importance for science, technology and industrial applications. Diamond and cubic boron nitride must be synthesized at high tempreture and pressure, and their applications are generally limited by cost. Compared with them, ReB2 and WB4 synthesized at ambient pressure are even more competitive on the market. Moreover, WB4 with a small amount of Re increased hardness, although the cost is increased. The precise mechanism for the increased hardness by the addition of Re is not yet understood in detail. The investigation on effect of doping on various properties of ReB2 and WB4 are scare. .In this project, we study effect of the 5d transitional metal, C and N doping on crytal structure, phase stability and mechanical property of superhard ReB2 and WB4. It is discussed that the thermodynamic and mechanical properties,and phase transformation of doping compounds at ambient and high pressures. Using two methods of idetifying the phase stability from enthalpy pressure relationship and convex hulls, and chemical potentials, to search the ground state phase. Moreover, we discuss the correlation between electronic structure and mechanical properties, such as bulk and shear moduli, hardness, strength. It is studied that what is the special behaviour of a particular system, which is a universal law. From the universal law, we extract the physical models, and guide synthesis and prediction of new materials with high hardness.