Theoretical Prediction of the Structure and Properties of Cubic Spinel Nitrides

Abstract

The structure and properties of cubic spinel nitrides were investigated based on first-principles theoretical calculations. The lattice constants, bulk moduli, band structures, electronic bonding, and lattice stability of thirty-nine single and double nitrides were studied. The single spinel nitrides of the form c-A 3 N 4 (where A is a Group IVA element), except c-Hf 3 N 4 , are all semiconductors with band gaps ranging from an indirect gap of 0.07 eV in c-Ti 3 N 4 to a direct gap of 3.45 eV in c-Si 3 N 4 . For double nitrides of the form c-AB 2 N 4 (where A and B are Group IVA (Ti, Zr, Hf) or IVB (C, Si, Ge, Sn) elements), both metallic and insulating band structures are possible. The stability of the double spinel nitrides, relative to single nitrides, is dependent on the optimal cation radii and polyhedral volumes at the tetrahedral A sites and the octahedral B sites. Of the thirty-two double nitrides, only nine are predicted to be energetically favorable. Among the potentially stable phases, the most interesting ones are c-CSi 2 N 4 (which has an exceptionally strong covalent bonding and large bulk modulus), c-SiGe 2 N 4 (which has an energetically favorable direct band gap of 1.85 eV), and c-SiTi 2 N 4 (which is metallic).

Recent Advances in New Hard High‐Pressure Nitrides

“…For the Si 3 N 4 -Ge 3 N 4 system such experiments have been performed in a LH-DAC at pressures of around 20 GPa and temperatures ranging up to T > 2300 K. [47] Starting with [ 47] This result implies that at the chosen synthesis conditions solid solutions of the high-pressure spinel phases of the Si 3 N 4 -Ge 3 N 4 system are not stable. The observation of c-(Si 0.59 -Ge 0.41 ) 3 N 4 , which can be approximated as c-Si 2 GeN 4 , contradicts theoretical formation energy calculations, [48] which predict that c-Si 2 GeN 4 should be unstable or metastable while c-SiGe 2 N 4 should be stable. While the theoretical result is in line with the general understanding that Si being the smaller ion should prefer the tetrahedral A site, and Ge being the larger ion should prefer the octahedral B site, the experimental observation of the mixed phase appears to be counterintuitive.…”

“…[48] Of all the potential compounds, only the fol- The first three of these compounds have been shown to be insulators with small gaps, whereas the rest are all metals. [48] Obviously, the participation of 3d or 4d electrons from group IVB elements in interatomic bonding tends to make these compounds metallic. None of these materials have been synthesized so far.…”

“…[13,45] This has not prevented theoretical calculations on other binary and ternary spinel nitrides and on a large number of spinel nitrides with cations belonging both to group IVA and IVB elements. [48,100] In several reports, the structure and properties of Ti 3 N 4 and Zr 3 N 4 have been studied theoretically in considerable detail. [107,108] On the experimental side, Tanaka et al have presented ELNES spectra of c-Si 3 N 4 for samples fabricated by the shock-compression method.…”

“…To a large extent these experimental data can be satisfactorily explained by theoretical calculations. [9,36,48,97,100,102,111] Theoretical calculations also provide elastic constants from which other bulk elastic properties can be derived. A more systematic study is necessary in order to fully understand the underlying mechanism that leads to the superb mechanical properties of this class of compounds.…”

Novel binary and ternary phases in the Si-C-N system

“…Ching et al 65), 66) suggested that only γ -Si2CN4 is stable with respect to decomposition to γ -Si3N4 and γ -C3N4. These works have shown that bulk moduli for all considered dense structures increase with increase of carbon content and reach the maximum value for binary C3N4 compound.…”