Figure 2. Theoretically predicted characteristics of Ca₂ZnN₂ and CaZn₂N₂.

(a) Ca–Zn–N ternary phase diagram at 0 K and 0 GPa, showing the stable region of Ca₂ZnN₂ and CaZn₂N₂ in the chemical potential space. The chemical potentials Δμ_i (i=Ca, Zn and N) are relative to those at the standard states, which are taken to be the Ca and Zn metals, and the N₂ molecule. The Zn₃N₂ phase is metastable and indicated in parenthesis. Chemical potential conditions I–IV are considered in the discussion of point-defect energetics. On the left and right sides of panel are the crystal structures of Ca₂ZnN₂ and CaZn₂N₂, respectively. The frames represent the conventional unit cells (I4/mmm (tetragonal) and (trigonal), respectively). The Ca atoms (green) and Zn atoms (white) are coordinated by five and two N atoms (yellow), respectively, in Ca₂ZnN₂, whereas by six and four N atoms in CaZn₂N₂; only Zn–N bonds are illustrated for easy visualization. (b) Electronic band structures. (c) Total and site-projected electronic densities of states per formula unit. (d) Absorption spectra (α: absorption coefficient; hν: photon energy). For b–d, the left and right sides of each panel show results for Ca₂ZnN₂ and CaZn₂N₂, respectively.