We first consider the electronic properties of the phases which form in nature, noting that although they have been identified experimentally, they may not necessarily be stable £¨equilibrium£© structures. The atomic geometry of rocksalt TaN is shown in Fig. 1£¨a£©, along with the electron density of states £¨DOS£© [Fig. 1£¨b£©] which shows clearly that TaN is metallic. The calculated equilibrium volume is 1.0% smaller than experiment. The Ta4N5 phase, depicted in Figs. 1(c)and 1(d), also has the rocksalt structure, but contains an ordered arrangement of Ta vacancies. There are 18 atoms in the unit cell. The calculated equilibrium volume of Ta4N5 is 1.2% smaller than the experimental value. The corresponding DOS
[Fig. 1(e)] exhibits a noticeable dip at EF, suggesting a greater stability as compared to TaN. The electronic structure of these phases was presented and discussed in more detail in our earlier publication (Ref. 10). |