Proportional correlation between heat capacity and thermal expansion of atomic, molecular crystals and carbon nanostructures

Abstract

Correlation between thermal expansions $\beta(T)$ and heat capacity $C(T)$ of atomic and molecular crystals, amorphous materials with a structural disorder, carbon nanomaterials (fullerite C$_{60}$, bundles SWCNTs of single-walled carbon nanotubes) was analyzed. The influence of the contribution to the coefficient of linear thermal expansion $\alpha_\textrm{Xe}(T)$ of Xe atoms adsorbed on the SWCNTs bundles is considered. The proportional correlation was found between the contribution to the coefficient of linear thermal expansion $\alpha_\textrm{Xe}(T)$ and the normalized to the gas constant heat capacity $C_\textrm{Xe}(T)/R$ of Xe atoms adsorbed on the SWCNTs bundles. The proportional correlation $(\beta/\beta^*) \sim (C_\textrm{V}/R)$ with the parameter $\beta^*$ for the bulk thermal expansion coefficient for cryocrystals is proposed. In the case of atomic crystals such as Xe and Ar, the proportional correlation $(\beta/\beta^*) \sim (C_\textrm{V}/R)$ is observed in the temperature range from the lowest experimental to temperatures where $C_\textrm{V}/R \approx 2.3$. The correlation is not observed in the temperatures where $2.3<C_V/R<3$ (classical Dulong-Petit law). It was found that the universal proportional correlation is also observed for molecular crystals with linear symmetry, such as CO$_{2}$, CO, and N$_{2}$O if the normalized heat capacity below the values $C_\textrm{V}/R \approx 3 \div 3.5$.