New Crystal Structure Map for Intermetallic Compounds

利用离散变分(DV)- x α簇法计算电子结构，提出了新的晶体结构图。为了构建包含过渡金属M的铝化物和硅化物的图谱，使用了两个电子参数。一个是键序，它是M和Al（或Si）原子之间共价键强度的度量。另一个是d轨道能级，它与元素的原子大小和电负性有关。例如，利用这两个理论参数绘制了MAl、M_3Al、MAl_3、MSi、M_3Si、MSi_2和M_5Si_3相关的结构图。在每张地图上都有清晰的晶体结构分离。人们发现，这些新图谱在预测化合物的晶体结构方面比迄今为止开发的任何其他图谱（例如Pettifor图谱）都更准确。此外，考虑到二元化合物中第三元素的取代位，构建了甚至可用于三元化合物的结构图。利用TiAl、Nb_3Al、NiAl、FeAl和MoSi_2五种金属间化合物的图，研究了在二元化合物中加入第三元素改变其晶体结构的可能性。这些新的结构图对设计和开发新的金属间化合物具有重要意义。

New crystal structure maps were proposed based on the calculation of electronic structures by the discrete variational (DV)-Xalpha cluster method. Two electronic parameters were utilized in order to construct such a map for aluminides and silicides containing transition metals, M. The one was the bond order that is a measure of the covalent bond strength between M and Al(or Si) atoms. The other was d orbital energy level which correlated with the atomic size and electronegativity of elements. For example, structure maps pertinent to MAl, M_3Al, MAl_3, MSi, M_3Si, MSi_2 and M_5Si_3 were made using these two theoretical parameters. There was clear separation of crystal structures in every map. It was found that these new maps were more accurate in predicting the crystal structures of the compounds than any other structure maps so far developed (for example, the Pettifor map ).Furthermore, structure maps which are usable even for ternary compounds were constructed by taking into account the substitutional sites of third elements in binary compounds. Employing the maps for five intermetallic compounds, TiAl, Nb_3Al, NiAl, FeAl and MoSi_2, the possibility of changing their crystal structures was examined by the addition of third elements into binary compounds. It was concluded that these new structure maps were useful for the design and development of new intermetallic compounds.