Graphite-lithium-europium system: Modulation of the structural and physical properties of the lamellar phases as a consequence of their chemical composition

This paper summarizes the whole chemical, structural and magnetic properties collected in the graphite-lithium-europium system. The intercalation mechanisms which occur during reactions between graphite and lithium-europium liquid alloys have been identified. The investigation of the experimental parameters leads to the optimized conditions to isolate europium-based graphite intercalation compounds (GICs) denoted α-phase and γ-phase. The ion beam analysis has been carried out to simultaneously quantify the amount of carbon, lithium and europium in a same sample. The α-phase shows a homogeneous distribution of the elements laterally and in depth, with a Li0.2Eu2C6 chemical formula. The unexpected presence of lithium has been revealed in the γ-phase but the EuC6 GIC is clearly detected, in agreement with X-ray diffraction experiments. The structural properties of Li0.2Eu2C6 have been studied and a Li-Eu-Eu-Eu-Li poly-layered sheet intercalated between graphene planes has been showed along the c-axis, with c = 3.IC = 2400 pm. The presence of lithium allows the building of a poly-layered metallic structure leading to specific magnetic properties different from those of EuC6. In the latter case, lithium does not affect either the structural or the magnetic properties of the intercalation compound.