Elastic stability and electronic structure of pyrite type PtN2: A hard semiconductor

The elastic properties and electronic structure of PtN2 with the pyrite structure [PtN2(C2)] were studied with first-principles calculations. The crystal structure is demonstrated to be elastically stable with a lower energy than the metastable fluorite structure proposed before. The calculated shear modulus of 214 GPa suggests that PtN2(C2) is harder than some well-known hard materials such as TiN and SiC. The high elastic moduli are attributed to a stacking of corner-shared PtN6 octahedra bonded by strong N-N covalent bonding. In contrast to the metallic fluorite-type phase, PtN2(C2) is semiconducting with an indirect band gap.