Distinct liquid phase in metal-cluster superlattice solids

Variable temperature x-ray diffraction and differential scanning calorimetry experiments on the superlattice solids of alkanethiol protected silver nanoclusters show that the translational periodicity collapses around 398 K resulting in a liquid phase, which upon cooling, reverts into the parent crystalline phase. This reversibility is seen in a narrow temperature window of 400--448 K. If the heating is done above 473 K, the reversibility is lost, and the liquid in the cooling cycle freezes into a disordered phase. The stability of different phases, encountered in the experiments, is discussed in terms of a phenomenological free energy.