Formation of one-dimensional quantum crystals of molecular deuterium inside carbon nanotubes

Crystallization under stringent cylindrical confinement leads to novel quasi-one-dimensional materials. Substances with strong cohesive interactions can eventually preserve the symmetries of their bulk phase compatible with the restricted geometry, while those with weak cohesive interactions develop qualitatively different structures. Frozen molecular deuterium (D-2), a solid with a strong quantum character, is structurally held by weak dispersive forces. Here, the formation of one-dimensional D-2 crystals under carbon nanotube confinement is reported. In contradiction with its weak cohesive interactions, their structures, scrutinized using neutron scattering, correspond to definite cylindrical sections of the hexagonal close-packed bulk crystal. The results are rationalized on the grounds of numerical calculations, which point towards nuclear quantum delocalization as the physical mechanism responsible for the stabilization of such outstanding structures. (C) 2020 Elsevier Ltd. All rights reserved.

Automated summary

Crystallization under stringent cylindrical confinement leads to the formation of quasi-one-dimensional structures, with substances exhibiting strong cohesive interactions preserving the symmetries of their bulk phase compatible with the restricted geometry. However, substances with weak cohesive interactions can develop qualitatively different structures under the same confinement conditions. In the case of frozen molecular deuterium held by weak dispersive forces, the formation of one-dimensional crystals under carbon nanotube confinement has been reported, with the structures corresponding to definite cylindrical sections of the hexagonal close-packed bulk crystal. The stabilization of these structures is attributed to nuclear quantum delocalization based on numerical calculations.