Energetics of C11b, C40, C54, and C49 structures in transition-metal disilicides

Abstract

The relative energies of the related C11_b, C40, and C54 crystal structures of group IV–VII transition-metal disilicides are obtained by ab initio self-consistent band-structure calculations using the augmented-spherical-wave (ASW) method. The structural energy differences among these three structures correlate strongly with d-band filling, with C40 being stabilized relative to C54 and C11_b relative to C40 as the transition-metal d-electron count increases. The C40/C11_b energy difference is 2 and MoSi₂. Relative C11_b/C40/C54 energies are similar in magnitude to those obtained in previous studies of L1₂/D0₂₂/D0₂₃ competition in transition-metal aluminides.^1,2 Calculations of the C49/C54 energetic competition are inaccurate; the differences in atomic coordination in these two structures are probably too large for the computational method to handle accurately. The total-energy results are interpreted by a detailed analysis of the electronic density-of-states (DOS) distributions. The stable structures do not correlate as strongly with DOS effects in the vicinity of the Fermi level as in the aluminides.