First-principles studies of phase transition and structural stability of SrC2 under pressure

Abstract

Pressure-induced phase transitions in SrC 2 are investigated using the first-principles plane wave pseudopotential method within the generalized gradient approximation. The phase transition from monoclinic phase ( CaC 2-II-type, space group C2/c) to trigonal ( CaC 2-VII-type, space group [Formula: see text]) structure is predicted to occur at 10.4 GPa. The high-pressure phase is thermodynamic, mechanically and dynamically stable, as verified by the calculations of its formation energy, elastic stiffness constants and phonon dispersion. Further the electronic analysis predicates this high-pressure phase to be an insulator. When increasing pressure, the ionic bond between C and Sr is strengthened, as well is the covalent bond between C and C , however, the increase of the ionic interaction between Sr and C preponderates over that of the covalent bond interaction, so the gap is narrowed.