The effect of the noncentral impurity-matrix interaction upon the thermal expansion and polyamorphism of solid CO-C60 solutions at low temperatures

TL;DR

This study investigates how noncentral interactions between CO molecules and C60 affect thermal expansion and phase transitions in CO-C60 solutions at very low temperatures, revealing a first-order phase transition around 4-6 K.

Contribution

It provides new insights into the role of noncentral impurity-matrix interactions on low-temperature thermal properties and phase behavior of CO-C60 solutions compared to N2-C60 solutions.

Findings

First-order phase transition at 4-6 K evidenced by hysteresis and thermal expansion maxima

Noncentral CO-C60 interactions influence thermal expansion and phase transition behavior

Comparison with N2-C60 solutions clarifies the specific effects of CO molecules

Abstract

Orientational glasses with CO molecules occupying 26% and 90% of the octahedral interstitial sites in the C60 lattice have been investigated by the dilatometric method in a temperature interval of 2.5 - 23 K. At temperatures 4 - 6 K the glasses undergo a first-order phase transition which is evident from the hysteresis of the thermal expansion and the maxima in the temperature dependences of the linear thermal expansion coefficients, and the thermalization times of the samples. The effect of the noncentral CO-C60 interaction upon the thermal expansion and the phase transition in these glasses was clarified by comparing the behavior of the properties of the CO-C60 and N2-C60 solutions.