Influence of the pressure on the low temperature (7K) crystal structure of the superconducting molecular salt (TMTSF)2ClO4

The anion ordering which occurs in (TMTSF)2ClO4 at 24 K is characterized by the appearance of b*/2 superlattice reflections, without any important change in the basic crystal structure. The intensities of these superlattice reflections have been measured at 7 K (ambient pressure). At the same temperature, these reflections do not appear under pressure (5 kbar). Thus, in the latter case, the anions remain disordered.