Self-diffusion of boron in TiB[sub 2]

Schmidt, H.; Borchardt, G.; Schmalzried, C.; Telle, R.; Weber, S.; Scherrer, H.
January 2003
Journal of Applied Physics;1/15/2003, Vol. 93 Issue 2, p907
Academic Journal
Self-diffusion studies of boron in polycrystalline TiB[sub 2] were carried out as a function of temperature, using a specially designed experiment with stable [sup 10]B tracers, [sup 11]B-enriched TiB[sub 2] samples, and secondary ion mass spectrometry for depth profiling. The diffusivities were extracted from the isotope depth profiles in the range between 950 and 1600 °C. They obey an Arrhenius behavior with an activation enthalpy of about ΔH=2.2 eV and a preexponential factor of D[sub 0]=4 × 10[sup -12] m²/s. Interpolation of the diffusivities to the melting point of 3225 °C reveals a very low value of about D(T[sub m])≈10[sup -15]m²/s, which reflects the covalent bonds present in the material. A possible explanation for the low values obtained for D[sub 0] and ΔH is the assumption of a diffusion mechanism via vacancies, where in addition to thermal vacancies a substantial concentration of structural vacancies are present. The possible influence of grain boundaries and of the anisotropic crystal structure on the results is discussed together with crystallographic diffusion paths.


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