Analogies and differences between calcium-based and europium-based graphite intercalation compounds

Abstract

An original method using lithium-based liquid alloys has been developed, allowing studies on bulk graphite intercalation compounds with calcium and europium. We showed that binary and ternary compounds belonging to graphite-lithium-calcium and graphite-lithium-europium systems are synthesized in both cases for equivalent reaction conditions but amazingly with many different structural and physical properties. Concerning CaC6 and EuC6, even if their 2D unit cells are hexal, their c-axis stacking sequences lead to different symmetries. Regarding kinetical data, formation mechanisms of these graphite intercalation compounds appear comparable however different, with a first common step before differenciation in the intercalation mechanism. Obviously, their physical properties are strongly different due to the nature of the intercalated metallic element. So, the different ternary compounds from these systems also show very considerable differences concerning their electronic properties: complex magnetic ordering for Eu-based ternary GIC and superconducting behaviour for Ca-based ternary GIC. However, common points are highlighted.