6 research outputs found
Dynamics in the ordered and disordered phases of barocaloric adamantane
High-entropy order–disorder phase transitions can be used for efficient and eco-friendly barocaloric
solid-state cooling. Here the barocaloric effect is reported in an archetypal plastic crystal, adamantane.
Adamantane has a colossal isothermally reversible entropy change of 106 J K1 kg1
. Extremely low
hysteresis means that this can be accessed at pressure differences less than 200 bar. Configurational
entropy can only account for about 40% of the total entropy change; the remainder is due to vibrational
effects. Using neutron spectroscopy and supercell lattice dynamics calculations, it is found that this
vibrational entropy change is mainly caused by softening in the high-entropy phase of acoustic modes
that correspond to molecular rotations. We attribute this difference in the dynamics to the contrast
between an ‘interlocked’ state in the low-entropy phase and sphere-like behaviour in the high-entropy
phase. Although adamantane is a simple van der Waals solid with near-spherical molecules, this
approach can be leveraged for the design of more complex barocaloric molecular crystals. Moreover,
this study shows that supercell lattice dynamics calculations can accurately map the effect of
orientational disorder on the phonon spectrum, paving the way for studying the vibrational entropy,
thermal conductivity, and other thermodynamic effects in more complex materials