We have measured the specific heat between 0.5 and 20 K for three different solid phases of ethanol: the stable monoclinic crystal, the structural (amorphous) glass, and an orientationally disordered cubic crystalline phase (also named as orientational glass or “glassy crystal”). We have therefore extended previous experiments on ethanol down to temperatures low enough as to investigate the region typically dominated in glasses by two-level-systems excitations or tunneling states. It is found that the orientational glass (i.e., a disordered crystal) of ethanol exhibits the same linear-term coefficient in the specific heat, and hence the same density of tunneling states, than the true, structural glass (i.e., an amorphous solid). In addition, combining specific-heat measurements in both deuterated and hydrogenated ethanol has allowed us to study the isotopic effect on these universal glassy properties, as well as on the Debye coefficients.

• Received 17 January 2002

DOI:https://doi.org/10.1103/PhysRevB.66.012201