NUKLEONIKA 2006, 51(2):101-104
Agata Jab³oñska1, Ludwik D¹browski1, Jan Suwalski1, Stoyko Neov2
1 Nuclear Methods of Solid State Physics Department,
Institute of Atomic Energy, 05-400 Otwock-Œwierk, Poland
2 Neutron Optics and Structure Analysis Laboratory,
Institute for Nuclear Research and Nuclear Energy, 72 Tzarigradsko chaussee Blvd., 1784 Sofia, Bulgaria
Martensite containing 0.87 wt.% carbon was studied by Mössbauer spectroscopy at temperatures,
T = 10, 15, 25, 40 and 78 K and by X-ray diffraction at T = 78 K in the course of 35 days.
Samples in the form of 30 mm thick foil of pure carbon martensite with
enhanced tetragonality were synthesized applying non-standard technology. The measured by X-rays
(c/a - 1) ratio varies within the limits 0.044-0.055 by pulsations with a period of
few hours. According to Kurdimov’s model any changes in tetragonality of martensite are fully
related to the passage of carbon atoms from Oc to Oa and Ob
octahedral sites or vice versa. Pulsations of the central and satellite sextets were observed
by Mössbauer spectroscopy. In accordance with the conventional interpretation of satellites,
these pulsations result from different spatial distribution of carbon around the Fe atoms in
the diffusion process. The data of (c/a - 1) pulsations were used to determine the
diffusion coefficient below 78 K. The measured diffusion coefficient of carbon in a-iron
below 78 K contradicts the classical approach to the observed temperature dependence.
As the temperature is lowered below 78 K, the diffusion constant approaches the nearly
temperature-independent value. The low temperature branch is apparently characteristic of
a quantum mechanical process dominated by tunnelling in the ground state.