Study of the Lattice Dynamics of Iron Nanocrystals by Mossbauer Spectroscopy

ABSTRACTThe vibrational properties of iron particles with nanometer sizes in Fe-SiO2 and Fe-A12O3 granular materials are studied by Mössbauer spectroscopy. The spectra include contributions from metallic Fe atoms at the core of the particles and apparently from surface and oxidized Fe atoms, which are analyzed separately. The temperature dependences of the recoilless fractions are analyzed using the Debye model. The Mossbauer Debye temperature ΘM for metallic Fe is found to decrease dramatically with smaller grain sizes, indicative of a “softening” of the phonon spectrum.