Growth mechanism of tantalum silicides by interdiffusion

Abstract

Interdiffusion studies were conducted to understand the atomic mechanism of the diffusing species and the growth mechanism of the phases. Integrated diffusion coefficients and the ratio of tracer diffusion coefficients were estimated for these analyses. The activation energies for the integrated diffusion coefficients were calculated as 550 ± 70 and 410 ± 39 kJ/mol in the TaSi2 and Ta5Si3 phases, respectively. In the TaSi2 phase, Ta has a slightly lower but comparable diffusion rate with respect to Si, although no Ta–Ta bonds are present in the crystal. In the Ta5Si3 phase, Si has a higher diffusion rate, which is rather unusual, if we consider the atoms in the nearest-neighbour positions for both the elements. The ratio of Si to Ta tracer diffusion coefficients is found to be lower in the Si-rich phase, TaSi2, compared to the Si-lean phase, Ta5Si3, which is also unusual. This indicates the type of structural defects present. An analysis on the growth mechanism of the phases indicates that duplex morphology and the Kirkendall marker plane should only be present in the TaSi2 phase. This is not present in the Ta5Si3 phase due to the very high growth rate of the TaSi2 phase, which consumes most of the Ta5Si3 phase layer. The problems in the calculation method used previously by others in this system are also explained.