RAgSb2金属间化合物的第一性原理研究

本文从理论计算的角度研究RAgSb_2(R=La-Sm,Gd-Er)合金的部分物理性质,为解释这些化合物的奇特物理性质提供理论依据。采用第一性原理计算方法研究RAgSb_2化合物的结构、机械性能、声子以及热力学性质。根据Birch-Murnagha方程拟合结果,发现LaAgSb_2无磁性,其余合金均表现磁有序,其中除了CeAgSb_2和GdAgSb_2外,其余的RAgSb_2合金的反铁磁态能量低于铁磁态。这些化合物的结合能计算数值均为负值,说明它们具有稳定的结构。而弹性模量的计算结果表明这些化合物具有稳定的机械性能。根据泊松比和B/G值,可以证实GdAgSb_2合金和TbAgSb_2合金具有韧性,而其余的合金表现为脆性。声子谱的计算结果显示这些合金具有稳定的热力学性质,其热容CV随着温度的升高,在低温下急剧增加并与T~3成正比,在较高温度下缓慢增加并趋向于Dulong-Petit极限,高温下的热容接近47.5cal·cell~(-1)·K~(-1)。

First-principles Study of RAgSb2 Inter-metallic Compounds

The partial physical properties of RAgSb₂ (R=La-Sm, Gd-Er) alloys was studied from the perspective of theoretical calculations to provide a theoretical basis for explaining the unusual physical properties of these compounds. First-principles calculation methods were used to study the structure, mechanical properties, phonons, and thermodynamic properties of RAgSb₂ compounds. According to the fitting results of Birch-Murnagha equation, it is found that except CeAgSb₂ and GdAgSb₂, RAgSb₂ shows that the energy of anti-ferromagnetic state is lower than that of ferromagnetic state. The calculated values of the cohesive energy of these compounds are all negative, indicating that they have stable structures. The calculated results of elastic modulus suggest that these compounds have stable mechanical properties. According to Poisson''s ratio and B/G value, it can be verified that the GdAgSb₂ and TbAgSb₂ alloys perform toughness,while the remaining alloys are brittle. The phonon spectrum calculation results show that these alloys have stable thermodynamic properties, and their heat capacity C_V increases with temperature and increases sharply at low temperatures and is proportional to T³, and slowly increases at higher temperatures and tends to Dulong-Petit limit. The heat capacity at high temperature is close to 47.5 cal·cell^-1·K^-1.