Abstract
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.
Highlights
A disorder−order phase transition is defined as the property of a material to undergo a transition, under pressure, or by lowering the temperature, from a phase where atoms/ molecules are arranged randomly with no long-range correlation to a phase in which the system shows a periodic pattern of atoms/molecules with long-range correlation.[1]
This phenomenon has been observed on several classes of materials: ionic salts, polymer nanoparticles, metal−organic framework (MOF), perovskite, perovskite−MOF, and liquid crystals.[2−9] These disorder−order phase transitions have gained renewed attention in the past couple of years, in connection with the flourishing research activity on hybrid lead halide perovskites
Molecular crystals may show two particular kinds of disorders, the most common being the ability of the molecules or parts of them to switch from one orientation to another within the lattice, while the second one refers to their capability to migrate with relative ease from one site to another.[13]
Summary
A disorder−order phase transition is defined as the property of a material to undergo a transition, under pressure, or by lowering the temperature, from a phase where atoms/ molecules are arranged randomly with no long-range correlation to a phase in which the system shows a periodic pattern of atoms/molecules with long-range correlation.[1].
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