Fig. 1: Structure and stability of NPG in different phases.
From: Understanding colossal barocaloric effects in plastic crystals
Crystal structure of NPG in (a) the monoclinic phase at low temperature and (b) cubic phase at high temperature. The light-yellow-shaded circle represents one NPG molecule. The green lines in (a) and green arrows in (b) demonstrate the stationarity and rotation of the NPG molecule, respectively. c Calculated volume dependence of total energy of NPG in monoclinic and cubic phases. Ef represent the formation energy as defined in the following paragraph. Black and red arrows indicate their corresponding experimental values17. d Schematic diagram indicates the existence of the energy barrier between monoclinic and cubic phases as shown by the red dash line, while the blue solid line marked by green arrows accounts for the entropy contributions to the total Gibbs free energy.
