Strengthening materials by changing the number of valence electrons

The elastic properties and electronic structures of transition metal compounds Cr₅B₃, Nb₅Si₃, Ta₅Si₃, Nb₅Ge₃, and Ta₅Ge₃, all having the Cr₅B₃-type structure, were studied using first-principles calculations. Because the chemical elements involved in the materials are from different groups and periods, the band widths and energy positions are different. However, all of them show very similar features in their electronic structure, in particular a pseudogap in the densities of states. The calculations show that all the materials can be strengthened by adjusting the number of valence electrons to 36 per formula unit, where the electronic states below the pseudogap are occupied and those above empty. The results indicate that the rigid band model can be applied to materials with the transition metal, the main-group element, or both are changed, suggesting a convenient way to design strong materials by changing the number of valence electrons.