Free Energy and Vibrational Entropy of Nanocrystalline bcc 57Fe and fcc Ni3Fe

Ranber Singh ； S. Prakash

《Chinese Journal of Physics》 40卷6期 (2002/12) Pp. 624-630

並列摘要

The free energy and vibrational entropy of nanocrystalline bcc 57Fe and fcc Ni3Fe are calculated in the harmonic approximation, using the vibrational density of states obtained from the Born-von Karman theory. For the nanophases, it is found that the vibrational entropy is higher and the free energy is lower than that of its bulk counterpart at all temperatures. The excessive vibrational entropy of the nanophase (excess as compared to that of the bulk phase) increases greatly with temperature at low temperatures but it is almost constant at higher temperatures (above about 200 K). The free energy difference of the nanophase and the bulk phase increases linearly with temperature. The results for the excessive vibrational entropy of nanophase are in good agreement with the experimental results at higher temperatures.