A high-resolution neutron scattering study of the hydrogen-driven metal-insulator phase transition in KC8Hx

Neutron diffraction studies on hydrogen chemisorbed into the stage-1 graphite intercalation compound KC8 are presented, including time-resolved scans across the hydriding transition to the saturated compound KC8H0.67. This transition involved a hydrogen-driven structural change taking place over 11.5 h. The Rietveld-refined structure of KC8 was confirmed to be Fdd2 using GSAS. Proposed structures for the stage-2 saturated compound were fitted, the most successful being a tri-layer C12/m1 structure with a reduced χ2 value of 1.940. A partial resolution of the in-plane structure is thus achieved, but further refinement is required to elucidate the hydrogen siting and the diffusion process.