Electronic and elastic properties of metastable Zr 3 N 4 : a joint experimental and theoretical study.

The electronic structures and elastic properties of metastable Zr3 N4 phases have been investigated using the first-principles calculations with the Heyd-Scuseria-Ernzerhof (HSE06) hybrid functional, in comparison with those of the stable ZrN phase. All three metastable Zr3 N4 phases (including orthorhombic, spinel and Th3 P4 -type phases) are found to be semiconducting with bandgaps of 1.72-1.94 eV. In particular, the computationally indirect bandgap of 1.72 eV of orthorhombic Zr3 N4 is consistent with the experimental value of 1.8 eV. The detailed analyses of the electronic structures reveal that the change of electrical conductivity from metallic ZrN to semiconducting Zr3 N4 is mainly due to the electron transfer from Zr to N atoms, which weakens the Zr-Zr interactions and reduces the proportion of metallic bonding. In addition, the elastic properties of Zr3 N4 and ZrN phases have been calculated. The theoretical hardness values of ZrN and orthorhombic Zr3 N4 are 18.06 and 6.98 GPa, respectively, agreeing well with the experimental values of 19.26 and 7.90 GPa. This work may further promote the understanding of the promising Zr-N material system.