Ta-C化合物物理性质的第一性原理研究

First-principles Calculations of the Physical Properties of Ta-C Compounds

关键词:  第一性原理  弹性常数  电子结构  热物理性质

Key words:  first-principles calculations  elastic constants  electronic structure  thermo-physical properties

摘要:

[目的]难熔金属碳化物具有优异的物理化学性能,可在众多领域中广泛使用。[方法]利用基于密度泛函的第一性原理方法对Ta-C二元体系中的TaC、Ta₂C、Ta₄C₃ 3个金属间化合物的热力学、力学性质以及电子结构进行计算研究。[结果]本研究晶格常数计算值和实验值一致,形成焓以及弹性常数计算值和其他理论值吻合。弹性模量计算值表明TaC具有最高的体积模量、剪切模量和杨氏模量,也即其脆性最大;而Ta₂C各个模量最小,其延展性最大。电子结构和电荷密度差显示Ta的d态电子和C的p态电子有杂化的现象,并且Ta-C之间呈现离子键特征。利用德拜模型得到了3个化合物在高温高压下的热物理性质,随着温度的增加,体积模量减小,而热容以及热膨胀系数增大,其中热容在1 000 K以上变化越来越小,最后接近杜隆-珀蒂极限值。随着压强的增加,体积模量增大,而热容和热膨胀系数减小。[结论]在3个化合物中,TaC的强度最高,脆性最大,而Ta₂C的强度最低,延展性最好。

Abstract:

[Objective] Refractory metal carbides have excellent physical and chemical properties, and which can be widely used in many fields.[Methods] The thermodynamic, mechanical and electronic properties of TaC、Ta₂C、Ta₄C₃ three intermetallics of Ta-C binary system were investigated by using the first-principles calculations based on density functional theory.[Results] The results showed that the calculated lattice constants were in good agreement with the experimental data.The calculated formation enthalpies and elastic constants were all coincide with the other theoretical data.The modulus of elasticity TaC had the highest bulk, shear and Young's modulus, and it was also the most brittle.Meanwhile,the bulk, shear and Young's modulus of Ta₂C were the smallest, and it had the maximum ductility.The difference between the electronic structure and the charge density showed that the strong hybridization between Ta-d states and C-p states,and the bond between Ta-C was ionic bond. By using Debye model,the thermos-physical properties of Ta-C compounds had been estimated with high temperature and high pressure. With the increasing temperature,the bulk modulus decreased and the heat capacities and the thermal expansion coefficients decreased,the heat capacity changed smaller and smaller above 1 000 K, and finally approaching the Dulong-Petit limited value.With the increasing pressure, the bulk modulus increased and the heat capacities and thermal expansion coefficients decreased.[Conclusion] Among the three compounds, TaC had the largest strength and brittleness, and Ta₂C had the lowest strength and the best ductility.