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运用第一性原理研究0~40GPa下B2相NiTi合金的机械性能、电子性质以及热力学性能。计算发现,几何优化后NiTi晶体的晶格常数与实验值和其他文献提供的数值大体一致,表明随着压力的增加该型合金力学稳定且没有相变产生。NiTi合金的体模量B、剪切模量G和杨氏模量E以及B/G的值随压力增大呈线性增加,表明压力使其抗体积变形能力、抗剪变能力及塑性增强。研究发现,压力也会使NiTi合金的各向异性发生改变。对NiTi合金态密度的研究表明,该合金同时显现出共价性与离子性,并且压力对其电子性质无明显影响。此外,本文还研究了不同温度和压力下NiTi合金的热力学性能,包括德拜温度Θ_D,热容C_v和C_p的变化,为今后实验提供理论数据。
The first-principles theory is used to study the mechanical properties, electronic properties and thermodynamic properties of B2 NiTi alloy at 0-40GPa. Calculations show that the lattice constants of the NiTi crystal after geometric optimization are in good agreement with the experimental values and those provided by other literatures, indicating that the alloy is mechanically stable with no phase change as the pressure increases. The values of bulk modulus B, shear modulus G, Young’s modulus E and B / G of NiTi alloy increase linearly with the increase of pressure, which shows that the pressure can increase the resistance to volume deformation, shear resistance and plasticity. The study found that pressure can also change the anisotropy of the NiTi alloy. The study of state density of NiTi alloy shows that the alloy shows covalency and ionicity at the same time, and the pressure has no obvious influence on the electronic properties. In addition, the thermodynamic properties of NiTi alloys at different temperatures and pressures, including Debye temperature Θ_D, heat capacity C_v and C_p, were also studied in this paper, providing theoretical data for future experiments.