On the ionicity of carbon in Be2C. A theoretical investigation of its electronic structure

The role of beryllium in alloys, Zintl phases and intermetallic compounds

Although beryllium is widely used as alloying component in diverse light-weight alloys, the crystal chemistry of beryllium containing Zintl phases and intermetallic compounds is only scarcely developed and only few phase diagrams, mostly the industrially relevant ones, have been studied in detail. The present review summarizes the crystal chemical data of binary and ternary beryllium intermetallic compounds along with the results of the few documented physical property studies.

Ambient-Pressure Polymerization of Carbon Anions in the High-Pressure Phase Mg2C

Experimental and theoretical methods were employed to investigate the ambient-pressure, metastable phase transition pathways for Mg2C, which was recovered after high-pressure synthesis. We demonstrate that at temperatures above 600 K isolated C(4-) anions within the Mg2C structure polymerize into longer-chain carbon polyanions, resulting in the formation of the α-Mg2C3 (Pnnm) structure, which is another local energy minimum for the carbon-magnesium system. Access to the thermodynamic ground state (decomposition into graphite) was achieved at temperatures above ∼1000 K. These results indicate that recoverable high-pressure materials can serve as useful high-energy precursors for ambient-pressure materials synthesis, and they show a novel mechanism for the formation of carbon chains from methanide structures.