Fig. 2: Evolution of the XRD pattern during the pressure-driven phase transition.

Reciprocal space maps parallel to the 03l-plane (a–f), the -15l-plane (g–l) and the 04l-plane (m–r) (integration thickness perpendicular to the plane: Δh = 0.04) in the pressure range 0.2 GPa to 1.26 GPa at 300 K. The indexation corresponds to the hexagonal setting (cf. Fig. 3). The diffuse stripes along the l-direction observable in (h–j) and (m–r) are a hallmark of stacking faults. The intensity shift along the l-direction in (g–l) is representative of all reflections with h − k = 3n (n integer and h, k ≠ 3n) and reveals the rearrangement of the Cl—Ru—Cl sandwich layers from a cubic to a hexagonal closed chlorine packing. While the diffuse stripes along the l-direction fulfilling the condition h − k = 3n ± 1 (with n integer) as depicted in (m–r) signal the disordered stacking of the Ru honeycomb nets over the entire pressure range.