Revisiting The Disorder-Order Transition In 1-X-Adamantane Plastic Crystals: Rayleigh Wing, Boson Peak, And Lattice Phonons

In this paper, we revisit the disorder-order transition in 1-chloro-adamantane and present new data on 1-bromo-adamantane. Rayleigh scattering and Raman-active optical lattice phonons are used to easily characterize the phase change. Unlike Cl-derivative, the Br-derivative shows a semiordered structure in the vicinity of ambient P,T conditions, which is peculiar of this compound and seems to be due to a more reduced rotational disorder of the Br-derivative with respect to the other halogen-adamantanes. The semiordered phase is briefly discussed in terms of its Rayleigh Wing and Boson peak.