金属间化合物TM-Zn(TM=Ni,Pd,Pt,Cu,Ag,Au)四方变形结构稳定性的第一性原理研究

金属间化合物的结构和结构稳定性显著影响材料的性能. 本文基于第一性原理，利用“Exact Muffin-Tin Orbitals”(EMTO)方法及全电荷密度(Full Charge Density)处理技术，精确计算了TM10(Ni, Pd, Pt)-Zn和TM11(Cu, Ag, Au)-Zn两类金属间化合物体系能量，确定了体系的结构稳定性；使用“The Vienna ab initio package”(VASP)软件，采用投影缀加平面波赝势和PBE交换-关联泛函进行了全弛豫计算，模拟了TM-Zn金属间化合物的四方变形过程；通过分析金属间化合物在四方变形过程中电子态密度，揭示了其结构稳定性机理，并使用VESTA软件可视化了电子局域化函数，获得了金属键的特征；利用YPHON软件并结合线性响应理论计算了金属间化合物沿高对称点的声子色散曲线. 研究结果表明：TM10-Zn倾向于CuTi型结构稳定，而TM11-Zn倾向于CsCl型结构稳定；在费米能级附近的电子简并轨道劈裂，诱发TM10-Zn金属间化合物体系产生Jahn-Teller效应，Jahn-Teller效应使得其在四方变形过程中能量降低，因此其四方结构更加稳定，而在TM11-Zn金属间化合物体系并不存在Jahn-Teller效应，因此 CuTi型AgZn和AuZn结构不稳定；TM10-Zn的金属键强度大于TM11-Zn，且CsCl型结构的金属键强度大于CuTi型结构.

The structure stability of tetragonal distortion for TM-Zn (TM = Ni, Pd, Pt, Cu, Ag, Au) intermetallic compounds by first-principles calculations

The material properties depend essentially on its structure and structural stability. Based on first-principles calculations, the Exact Muffin-Tin Orbital (EMTO) method in combination with the full charge density (FCD) technique was employed to study the structural stability of TM10 (Ni, Pd, Pt)-Zn and TM11(Cu, Ag, Au)-Zn intermetallic compounds by calculating the total energy accurately. The Vienna ab initio package (VASP) in conjunction with projector augmented wave (PAW) pseudopotentials within PBE was applied to calculate the total energy of crystal structure under full-relaxed condition thus the tetragonal distortion of TM-Zn intermetallic compounds were simulated. Based on the analysis of electron density of state, the mechanism of structural stability was revealed. The VESTA software was employed to visualize the electronic localization functions (ELF) and obtain the characters of TM-Zn chemical bonds. The YPHON code was applied to calculate the phonon frequencies by the linear-response theory. The results showed that CuTi-type TM10-Zn intermetallic compounds were stable, while the CsCl-type TM11-Zn intermetallic compounds were stable. The separation of degenerate orbitals around Fermi-level induced the Jahn-Teller effect, which can explain the energy decreasing of TM10-Zn intermetallic compounds during the process of lattice distortion. While there was no Jahn-Teller effect for the TM11-Zn intermetallics. So the lattices of AgZn and AuZn with CuTi-type structure were unstable. The strength of TM10-Zn metallic bond was larger than TM11-Zn metallic bond, and the bond strength of CsCl-type structure was larger than that of CuTi-type structure.