Diffusion in iron silicides

Diffusion of silicon and germanium in the D0₃ phase of the system Fe-Si has been studied. As there is no radioactive Si isotope for detailed self-diffusion studies the rare stable isotope ³⁰Si was used. Tracer deposition was done by ion implantation. Profiles were analysed by means of secondary ion mass spectrometry (SIMS). In a preceding study the radioisotope ⁷¹Ge served as a substitute for Si. One experiment with the short-lived ³¹Si showed very similar diffusion rates for Si and Ge, so that the approach of using the homologous element seemed to be appropriate. As a check for this approach we also performed diffusion experiments with the stable isotope ⁷⁴Ge in analogy to those with ³⁰Si. The obtained data confirms the strong asymmetry between the diffusion of majority and minority constituents in D0₃ phases. The data also shows the homology of Ge and Si. Finally this demonstrates that radiotracer methods and SIMS technique can be successfully combined in order to cover a large temperature interval.

Self-diffusion of Fe and diffusion of Ge in the B20 phase FeSi have been studied as a function of temperature using the radiotracer method. Ge has been used to simulate Si self-diffusion. Both diffusivities are very small, and their values for Fe are about one to two orders of magnitude smaller than for Ge. This uncoupled diffusion may be explained by vacancy-based diffusion on the Fe and Si sublattices. Both diffusivities reach a value of about 10^-14m²s^-1 near the melting temperature which is more typical for semiconductors than for metals. Results are discussed in comparison with other diffusion data on phases of the Fe-Si system and on other transition metal silicides.

Drittmittelgeber:

Deutsche Forschungsgemeinschaft

Beteiligte Wissenschaftler:

Dr. H. Baumann (Universität Frankfurt), Prof. Dr. G. Borchardt (TU Clausthal), Dr. P. Fielitz (TU Clausthal), Prof. Dr. H. Mehrer (Leiter), Dipl.-Phys. M. Salamon, Dr. B. Sepiol (Universität Wien), Dr. S. Scherrer (École des Mines, Nancy/Frankreich), Dr. S. Weber (École des Mines, Nancy/Frankreich), Dr. M. Wellen (TU Clausthal)

Veröffentlichungen:

Salamon, M., H. Mehrer: Diffusion in the B20-type phase FeSi, Phil. Mag. A 79, 2137 - 2155 (1999)

Wellen, M., P. Fielitz, G. Borchardt, S. Weber, S. Scherrer, H. Mehrer, H. Baumann, B. Sepiol: Diffusion of Si and Ge in the intermetallic phase Fe₃Si: ion implantation and SIMS studies, Mat. Sci. Forum, in print