Pressure-induced structural phase transition in the Bechgaard-Fabre salts

The crystal structures of the quasi-one-dimensional organic salts (TMTTF)${}_2$PF${}_6$ and (TMTSF)${}_2$PF${}_6$ were studied by pressure-dependent x-ray diffraction up to 10 GPa at room temperature. The unit-cell parameters exhibit a clear anomaly due to a structural phase transition at 8.5 and 5.5 GPa for (TMTTF)${}_2$PF${}_6$ and (TMTSF)${}_2$PF${}_6$, respectively.