First-principles investigation on the elastic stability and thermodynamic properties of Ti2SC
First-principles investigation on the elastic stability and thermodynamic properties of Ti2SC
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DOI：
10.1088/1674-1056/21/5/056301
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发表时间：
2012-05
影响因子：
1.7
通讯作者：
Ze-Jin 则金 Yang 杨;Y. Guo 郭;Rong-Feng 狐荣锋 Linghu 令;X. Cheng 程;X. Yang 杨
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文献类型：
--
作者：
Ze-Jin 则金 Yang 杨;Y. Guo 郭;Rong-Feng 狐荣锋 Linghu 令;X. Cheng 程;X. Yang 杨
在密度泛函理论（DFT）框架下，采用广义梯度近似（GGA）下的范德比尔特型平面波超软赝势，研究了高温高压下Ti 2SC的晶体结构、弹性和热力学性质.计算的晶格体积的压力依赖性与实验结果非常一致。计算的结构参数的Ti原子经历了一个微妙的增加与施加的压力和增加暂停在较高的压力。弹性常数的计算表明，晶格仍然是稳定的高达200 GPa。对弹性性质的研究表明，c轴比a轴更硬，这与纵向弹性常数（C33，C11）相对于横向弹性常数（C44，C12，C13）更大相一致。泊松比的研究证实，较高的离子或较弱的共价键的贡献，在原子内的Ti 2SC应假定和离子的性质增加压力。体弹性模量（B）和剪切模量（G）的比值（B/G）以及B/C44表明Ti 2SC在环境条件下是脆性的，并且脆性随压力而降低。在不同的压力下，等温和绝热体积模量表现出相反的温度依赖性。我们再次观察到，德拜温度和格吕奈森参数相对于热膨胀系数、熵和热容表现出弱的温度依赖性，从中可以清楚地看到压力效应。
Using Vanderbilt-type plane-wave ultrasoft pseudopotentials within the generalized gradient approximation (GGA) in the frame of density functional theory (DFT), we have investigated the crystal structures, elastic, and thermodynamic properties for Ti2SC under high temperature and high pressure. The calculated pressure dependence of the lattice volume is in excellent agreement with the experimental results. The calculated structural parameter of the Ti atom experienced a subtle increase with applied pressures and the increase suspended under higher pressures. The elastic constants calculations demonstrated that the crystal lattice is still stable up to 200 GPa. Investigations on the elastic properties show that the c axis is stiffer than the a axis, which is consistent with the larger longitudinal elastic constants (C33, C11) relative to transverse ones (C44, C12, C13). Study on Poisson's ratio confirmed that the higher ionic or weaker covalent contribution in intra-atomic bonding for Ti2SC should be assumed and the nature of ionic increased with pressure. The ratio (B/G) of bulk (B) and shear (G) moduli as well as B/C44 demonstrated the brittleness of Ti2SC at ambient conditions and the brittleness decreased with pressure. Moreover, the isothermal and adiabatic bulk moduli displayed opposite temperature dependence under different pressures. Again, we observed that the Debye temperature and Grüneisen parameter show weak temperature dependence relative to the thermal expansion coefficient, entropy, and heat capacity, from which the pressure effects are clearly seen.