Structural changes in tetracyanoethylene at high pressures: neutron diffraction study

We report on structural changes in monoclinic tetracyanoethylene, C₂(CN)₄ as studied by in situ high-pressure (0-5 GPa) neutron powder diffraction experiments. Structural parameters were obtained by Rietveld profile refinement of the diffraction pattern up to P = 2.5 GPa. Above this pressure the width parameter is found to diverge, indicating pressure-induced disordering at 2.5 GPa. The recovered sample, on release of pressure from 5 GPa, is found to have transformed to a graphite-like amorphous structure. The transformation to a graphite-like material has been verified by an independent high-pressure x-ray diffraction experiment.