Extended Data Fig. 2: Synchrotron XRD patterns collected at different locations of the argon NDCs sample.

a, Synchrotron XRD pattern (black circles) of the NDC containing high-pressure argon synthesized at ~49.0 GPa and ~2100 K (the same sample with Fig. 3a but collected at a different ___location with a different XRD intensity ratio between argon and diamond) and the Rietveld refinement (red curve). The x-ray wavelength was 0.3738 Å. The refined lattice parameters of diamond and argon are 3.57 Å and 4.21 Å, respectively. b, Two XRD patterns from the same NDC sample (blue curve from a and black curve from Fig. 3a) compared with that of pure nanocrystalline diamond (pink curve from Ref. ³⁴). The XRD pattern in Fig. 3a is from an argon-rich region while the pattern here in a is from another relatively argon-poor region with a much weaker argon signal. A comparison of the three XRD patterns further supports the non-uniform argon-ND composite feature of the NDCs sample.