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

Pair interaction energies (PIEs) of Ti-Ti, Ti-Ni and Ni-Ni pairs and optimized local structures around these pairs in β-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 Si432(TM2Si430) supercell (6×3×6 unit cells of β-Sn type Si) to calculate interatomic distance dependences of PIEs up to 6 Å-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 β-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 sp3-like Si lattices.