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Phase C2/m and three new phases of CaC2. The big and small balls represent calcium and carbon atoms, respectively. One-dimensional armchair carbon chains along c-axis direction observed in Cmcm. One-dimensional carbon ribbons and 2D graphene sheets observed in Immm and P6/mmm phases, respectively. In Immm, calcium atoms construct cylinder with hexagon cross-section, which is arranged periodically, centered by 1D carbon ribbon (Left of D).
