Electronic and elastic properties of metastable Zr₃N₄: a joint experimental and theoretical study

The electronic structures and elastic properties of metastable Zr₃N₄ 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 Zr₃N₄ phases (including orthorhombic, spinel and Th₃P₄-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 Zr₃N₄ 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 Zr₃N₄ 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 Zr₃N₄ and ZrN phases have been calculated. The theoretical hardness values of ZrN and orthorhombic Zr₃N₄ 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.