Anomalous heat capacity of nanoparticles

Abstract

It was shown experimentally that the specific heat of nanosized particles was higher than that of macroscopic particles of the same nature. It was also found that the heat capacity increased as the size of nanoparticles decreased. We analyzed the reasons for the anomalous behavior of the heat capacity of nanoparticles. For this purpose, we considered nanoparticles with a simple cubic lattice and an arbitrary external geometric shape. The simplest harmonic interaction potential between the nearest neighbor particles was used. Qualitative agreement with experimental data was obtained. The main factor responsible for the anomalous behavior of small particles was phonon spectrum softening compared with bulk material when free boundary conditions were used. The lower frequencies make a larger contribution to heat capacity. It was found that, apart from particle size, the geometric shape and defect structure of nanoparticles influenced their heat capacity: given the same number of particles, an increase in asymmetry and disorder caused an increase in heat capacity.