Structural and vibrational properties of the van derWaals compound (N$_2$)$_{11}$He up to 135 GPa

S. Ninet (1, 2) , G. Weck (2) , P. Loubeyre (2) , F. Datchi (1)

1 IMPMC - Institut de minéralogie et de physique des milieux condensés
2 DPTA - Département de Physique Théorique et Appliquée

The structural and vibrational properties of the van der Waals compound (N$_2$)$_{11}$He have been measured up to 175 GPa. The structure, as determined at 14.5 GPa using single-crystal x-ray diffraction, is hexagonal ($P6_3/m$) with seven nonequivalent atoms: 6 N and 1 He. The N$_2$ molecule centered at (0,0,0) is orientationally disordered. A close relationship with the ε structure of pure solid N$_2$ is observed. A phase transition to a hexagonal superstructure occurs at 28 GPa, which is attributed to the ordering of these disordered N$_2$ molecules, driven by quadrupole-quadrupole interaction. A transition to an amorphous state then takes place at 135 GPa. Strong similarities in the structural evolution under pressure of the (N$_2$)$_{11}$He compound and of ε-N$_2$ are discussed.

Domaines: Science des matériaux [cond-mat.mtrl-sci]; Cristallographie

S. Ninet, G. Weck, P. Loubeyre, F. Datchi. Structural and vibrational properties of the van derWaals compound (N$_2$)$_{11}$He up to 135 GPa. Physical Review B, 2011, 83 (13), pp.134107. ⟨10.1103/PhysRevB.83.134107⟩. ⟨hal-00595299⟩