  Graphite is the thermodynamically stable form of carbon, and yet is
remarkably difficult to synthesise. A key step in graphite formation is the
removal of defects at high temperature ($>$2300~$^{\circ}$C) that allow
graphenic fragments to rearrange into ordered crystallites. We find the
critical defect controlling graphitisation is a screw dislocation that winds
through the layers like a spiral staircase, inhibiting lateral growth of the
graphenic crystallites ($L_a$) and preventing AB stacking of Bernal graphite.
High-resolution transmission electron microscopy (HRTEM) identifies screws as
interdigitated fringes with narrow focal depth in graphitising polyvinyl
chloride (PVC). Molecular dynamics simulations of parallel graphenic fragments
confirm that screws spontaneously form during heating, with higher annealing
temperature driving screw annihilation and crystallite growth. The time
evolution of graphitisation is tracked via X-ray diffraction (XRD), showing the
growth of $L_a$ and reduction of the interlayer spacing consistent with
molecular dynamics of screw annihilation. This mechanistic insight raises
opportunities to lower the barrier for graphitisation as well as broadening the
range of carbonaceous materials that can turn into graphite, thereby lowering
the cost of synthetic graphite used in lithium-ion batteries, carbon fibre, and
electrodes for smelting.
