Theoretical calculations and experimental measurements of the structure of Ti5Si3 with interstitial additions

The equilibrium structural parameters, enthalpies of formation and partial densities of state for Ti5Si3 and Ti5Si3Z0.5 (Z= B, C, N or O) were calculated based on first-principle techniques. Enthalpy of formation calculations suggest that of the known structures for transition metal (TM) silicide compounds containing TM5Si3 (D88, D8l and D8m) the D88 structure is the most stable form of Ti5Si3, and the stability of the structure increases as Z atoms are added. The theoretically determined structural trends as a function of interstitial element, Z, agreed well with experimentally determined values. Both indicate bonding between Ti and Z atoms based on contraction of Ti–Z separations. The calculated partial densities of state suggest that p(Si)–d(Ti) and d(Ti)-d(Ti) interactions are responsible for most of the bonding in pure Ti5Si3, which agrees with previous studies. As Z atoms are added, p(Z)–d(Ti) interactions become significant at the expense of weakening some of the d(Ti)–d(Ti) interactions.