Size dependences of the lattice parameter and thermal expansion coefficient of C60 fullerite nanoparticles

Using the statistical theory of structural, dynamic and thermodynamic properties of anharmonic crystals and small particles, we investigate size effects in C60fullerite nanoparticles with fcc lattice. The intermolecular potential derived by Girifalco is utilized. We have considered three highly symmetrical forms of particles: cubical, spherical and octahedral, and calculated size dependences of their mean lattice parameters a and thermal expansion coefficients α. Influences of the surface tension and of the lattice relaxation near surfaces have been taken into account. For all three forms of nanoparticles, both a and α increase with decreasing size; that is a consequence of the anharmonicity. This effect is appreciably enhanced when the temperature increases. We also note a dominant contribution of the lattice relaxation to the size dependences. © 1997 Acta Metallurgica Inc.