First principles study on structural and electronic properties and defect formation enthalpies of cubic [Hf.sub.3][N.sub.4] under high pressure

Using the self-consistent density functional method, we investigate the structural and electronic properties of cubic [Hf.sub.3][N.sub.4] with [Th.sub.3][P.sub.4] structure at ambient and high pressures. The lattice parameters, cell volume, bulk modulus, and pressure derivative at ambient pressure are obtained, which are in excellent agreement with the available measurements. The change of bond lengths for two different types of Hf-N bond with pressure suggests that the tetrahedral Hf-N bond is slightly less compressible than the octahedral ones, which agree well with the [Zr.sub.3][N.sub.4] and [Zn.sub.3][N.sub.2] results. The band gap pressure coefficient for c-[Hf.sub.3][N.sub.4] are fitted, which are 8.5 x [10.sup.-2] eV/GPa and -7.0 x [10.sup.-5] eV/[(GPa).sup.2], respectively. Based on the density of states analysis, band structure suggests that the investigated material can be used as a semiconductor optical material. Mulliken population analysis shows that the charge density of the Hf atom is less sensitive to pressure variation than that of the N atom. At last, the defect formation enthalpies of the cubic [Hf.sub.3][N.sub.4] are calculated. PACS Nos.: 62.50.-p, 71.15.Mb, 73.20.At. L'utilisation de la methode de la fonctionnelle de densite auto-coherente nous permet d'etudier les proprietes structurelles et electroniques du [Hf.sub.3][N.sub.4] cubique avec la structure [Th.sub.3][P.sub.4] a pression ambiante et haute. Nous obtenons les parametres du reseau, le volume de la cellule, le module de compression volumique et la derivee de la pression, le tout a pression ambiante et ces resultats sont en excellent accord avec les mesures disponibles. La variation avec la pression de la longueur de lien entre deux liens Hf-N differents suggere que le lien Hf-N tetraedrique est legerement moins compressible que l'octaedrique, ce qui agree avec les resultats pour [Zr.sub.3][N.sub.4] et [Zr.sub.3][N.sub.2]. Les coefficients de pression de la bande interdite de c-[Hf.sub.3][N.sub.4] sont alors ajustes numeriquement: 8.5 x [10.sup.-2] eV/GPa et -7.0 x [10.sup.-5] eV/GPa respectivement. Sur la base de l'analyse de la densite d'etats, la structure de bande suggere que ce materiau peut etre utilise comme semi-conducteur optique. L'analyse des charges de Mulliken montre que la densite de charge de l'atome Hf est moins sensible aux variations de pression que celle de l'atome N. Finalement, nous calculons l'enthalpie de formation de defauts dans [Hf.sub.3][N.sub.4] cubique. [Traduit par la Redaction]
1. Introduction Nitrides of transition metals that are used as hard materials have attracted great interest because of their high elastic moduli, ultrahardness, high melting points, and superconductivity [1-5]. Novel [...]