Pair interaction energies and local structures of titanium and nickel atom-pairs in beta-Sn type silicon

摘要

Pair interaction energies (PIEs) of Ti-Ti, Ti-Ni and Ni-Ni pairs and optimized local structures around these pairs beta-Sn type Si are studied by first principles calculation to elucidate typical local structures of transition-metal (TM) atoms in Si-rich amorphous silicides or alloys. In the calculations, TM pairs are located at substitutional sites along a long axis of cuboid Si-432(TM2Si430) supercell (6x3x6 unit cells of beta-Sn type Si) to calculate interatomic distance dependences of PIEs up to 6 angstrom-distance (up to the 12th nearest neighboring (NN) distance). We find that interatomic distances of Ti-Ti and Ti-Ni pairs with largely negative PIEs agree with those in Si-rich ordered silicides such as TiSi2 and Ti4Ni4Si7, and that the optimized local structures around Ti-Ti and Ti-Ni pairs commonly have Si-hexagons, which typically appear in early-TM silicides, and thus expected to be observed in the amorphous Si-rich silicides or alloys. On the contrary, Ni-Ni pair in beta-Sn type Si indicates no significant feature in PIE profile or in local structures. Properties of Ni-Ni or Ni-Si bonding in Si-rich silicides may be governed by sp(3)-like Si lattices.