New Crystal Structure Map for Intermetallic Compounds

在离散变分(DV)-Xα簇法计算电子结构的基础上，提出了新的晶体结构图。对于含过渡金属的铝化物和硅化物，我们使用了两个电子参数来构建这样的图。一个参数是键级，它是M和Al(或Si)原子之间共价键强度的量度。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与MAL、M3Al、MAL_3、MSi、M_3Si、MSi_2和M_5Si_3有关的结构图。每张地图上都有明显的晶体结构分离。研究发现，与已有的其他结构图(如Pettifor图)相比，这些新的结构图对预测化合物的晶体结构具有更高的准确性。此外，通过考虑三种元素在二元化合物中的取代位置，构建了甚至适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MAP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。结果表明，这些新的结构图对新的金属间化合物的设计和开发是有用的。

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.