High pressure crystallography and chemistry of new carbides of alkali and alkali earth metals.*

With experimental data it has been demonstrated that under high-pressure conditions (above 5 GPa and 1300 K) thermodynamically stable Mg-C compounds are indeed possible. The new compounds synthesized, Mg₂C and β-Mg₂C₃, crystallizes in the monoclinic C2/m space group, and contains rare allene-derrived C₃^4- anions that are isoelectronic with CO₂.
Graphite intercalation compounds (GIC) with metals such as Li, Na and K form different compositions (and crystal structures) produced by stacking along c-axis of metal (Me) and n carbon (A, B or C) layers. The n number indicate the stage of intercalation. Typically ordered compounds are obtained for n = 1 to 6 with various stacking sequences depending on metals: n = 1 for MeAMeB, n = 2 for MeABMeBAMeCA, n = 3 for MeABCMeBCAMeCAB, etc. Both high pressure and high temperature leads to increasing n. Here we will discuss the structural features of GIC, the XRD, Raman and other structurally related data, as well as corresponding “diamond intercalation compounds” (DIC) structurally related to GIC .