Revisiting Stabilities of Cubic Zincblende IV-IV Materials From Density Functional Theory

The electronic structure of cubic zincblende (ZB) IV-IV compounds are treated traditionally through first-principles models neglecting relativistic effects, regardless the presence of heavier atoms like Ge, Sn, or Pb. Applying relativistic first-principles plane wave pseudopotential methods, we revisit here the thermodynamic and dynamical stability of ZB-IV-IV materials: SiC, GeC, SnC, PbC, SiGe, SiSn, SiPb, GeSn, PbGe, and PbSn. Our results evince that except 3C-SiC, all other IV-IV compounds in the ZB phase exhibit positive formation enthalpy, thus manifesting thermodynamic instability. PbC, and SnC divulge huge thermodynamic instability, due to the high value of their elastic strain formation energy; whereas SiGe, GeSn, and PbSn show weak thermodynamic instability due to their insufficient chemical formation energy. Furthermore, except 3C-SiC, we found that all other ZB-IV-IV compounds are dynamically unstable.