Hg_2CuTi型Heusler合金Mn_2NiB马氏体相变微观机理的研究

The study of microcosmic mechanism of martensitic transformation in Hg_2Cu Ti- type Heusler alloy Mn_2NiB

运用基于密度泛函理论的第一性原理方法,研究了Hg2Cu Ti型Heusler合金Mn2Ni B马氏体相变的微观机理.研究表明:伴随着Mn2Ni B马氏体相变的发生,产生了拉长型八面体的畸变.此畸变先是由中心离子Mn的t2g轨道电子的非均匀占据而导致的弱Jahn-Teller效应来驱动.随着畸变的进行,Mn离子的孤对电子由dx2-y2轨道转移到dxy轨道,x、y方向的配体受到的推斥力减小而内移,进一步加剧这一畸变过程,使得dx2-y2和dxy轨道受到配体的推斥力增加,能级升高,而dz2、dyz和dxz受到的推斥力减少,能级降低,从而消除eg能级和降低t2g能级的简并,体系能量降低,最终体系畸变到一个稳定的马氏体相.

The microcosmic mechanism of martensitic transformation in Hg2 Cu Ti- type Heusler alloy Mn2 Ni B is researched by first- principles method based on the density functional theory. The results show that it generates the distortion of elongated octahedron with martensitic transformation in Mn2 Ni B. This distortion is first driven by a weak Jahn- Teller effect involving non- uniform occupation of electrons of t2 gorbit in center ionic Mn. This is creating further the distortion as the ligands pointing to x and y directions move inward originated from the reduced repulsive force due to unpaired electrons transfering to dxyorbit from dx2- y2 orbit in ionic Mn,this can lead to the eliminate degeneracy of energy level derived from the rising of energy levels of dx2- y2 and dxy,and the lowering of energy levels of dz2,dyzand dxz,and thus the system changes to stabilized martensitic phase as a result of the decrease of system energy in the end.