Fachbereich 11 - Physik
Institut für Materialphysik
Diffusion in Metals, Intermetallics, Silicides, Quasicrystals and Metallic Glasses

Diffusion in Silicides

Diffusion of germanium and molybdenum self-diffusion in molybdenum-disilicide single crystals grown by a floating zone technique at Kyoto University were carried out using the radiotracer method in combination with sputter sectioning for determination of diffusion penetration profiles. The isotope ⁷¹Ge was used to simulate Si self-diffusion, since Si has only a fairly short-lived radioisotope. Diffusivities were determined for the two principal directions of the tetragonal structure of molybdenum disilicide. Germanium diffuses is five to six orders of magnitude faster than molybdenum. This indicates that diffusion in the Si and Mo sublattice is decoupled. The diffusion anisotropy is remarkable. Diffusion perpendicular to the tetragonal axis is significantly faster than parallel to that axis for both Ge and Mo. The activation enthalpies for both principal directions were determined. In recent experiments with the short-lived tracer ³¹Si (half-life time: 2.6 hours), which we carried out at the IGISOL accelerator in Jyväskylä (Finnland), demonstrated that Si and Ge diffusion is indeed fairly similar.

Diffusion of silicon and germanium was studied in the D0₃ phase of the binary Fe-Si alloy system. The stable isotopes ³⁰Si and ⁷⁴Ge were used as tracers and diffusion profiles were analyses by secondary ion mass spectroscopy (SIMS). The experiments confirm the strong asymmetry between the diffusion of the major components of Fe₃Si, which was already deduced from tracer experiments of ⁵⁹Fe and ⁷¹Ge performed earlier at our laboratory. The present study confirms that germanium and silicon diffuse at similar rates and much slower than iron.

Drittmittelgeber:

Deutsche Forschungsgemeinschaft

Beteiligte Wissenschaftler:

Prof. Dr. G. Borchardt (TU Clausthal), Dr. K. Freitag (Universität Bonn), Dr. K. Ito (Kyoto University, Japan), Prof. Dr. H. Mehrer (Leiter), Dipl.-Phys. M. Salamon, Dr. B. Sepiol (Universität Wien), Dr. M. Wellen (TU Clausthal), Prof. Dr. M Yamaguchi (Kyoto University, Japan)

Veröffentlichungen:

Salamon, M., K. Ito, M. Yamaguchi, K. Freitag, H. Mehrer: Diffusion of ⁷¹Ge in molybdenum disilicide, Defect and Diffusion Forum 194 - 199, 523 - 529 (2001)

Salamon, M., H. Mehrer: Diffusion of ⁷¹Ge and ⁹⁹Mo in molybdenum disilicide, Defectand Diffusion Forum 216 -217, 161 -168 (2003).

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 Fe ₃Si: ion implantion and SIMS studies, Defect and Diffusion Forum 194 - 199, 499 - 504 (2001)