Fig. 4: High-Pressure SPXRD measurements and structure analysis of C48H20.
From: Narrowing band gap chemically and physically: conductive dense hydrocarbon
a Selected in-situ high-pressure SPXRD profiles upon compression (top) and decompression (bottom). The experimental data at 0.3 GPa match the simulated SPXRD pattern of C48H20 collected at ambient conditions (CSD No. 1304527)36. b (a) Observed (red circles) and calculated (solid blue line) SPXRD profiles obtained from the Le Bail fit against the PXRD data of C48H20 at 0.3 GPa (top) and 23.0 GPa (bottom). The lower solid black line depicts the difference profiles. The solid blue and red vertical tick marks show the reflection positions of the monoclinic and triclinic C48H20 phases, respectively. The lower solid green lines indicate the fitted background contribution. c Zoomed-in look at the XRD patterns at the critical pressure points in comparative style serving as a signuatre of a crystal structure alteration. For clarity, background subtraction was applied. d Crystal packing of C48H20 at ambient conditions, viewed along a axis (left panel). Cell conventions for oligoacenes as used in literature47 (right panel). The index M stands for monoclinic cell, and T for triclinic cell. The characteristic distances are the layer thickness, h, and the long and short herringbone lengths x and y. e Schematic projection of the equatorial plane of point groups 2/m in the monoclinic phase and −1 in the triclinic phase during the structural transition triggered by hydrostatic pressure, in accordance with symmetry breaking and group-sub group relations.
