First low-spin carbodiimide, Fe2(NCN)3, predicted from first-principles investigations

The structural stability and physical properties of the Fe(III) carbodiimide Fe2(NCN)3 were studied by use of density functional theory. The results indicate that Fe2(NCN)3 (space group R 3 ‾ c $R‾{3}c$ ) is stable both thermodynamically and mechanically. The electronic structure in combination with the phonon dispersion relations suggest that the title compound should be ferromagnetic and half-metallic, and that the Fe3+ ions are in the low-spin state.

Chiral triclinic metamaterial crystals supporting isotropic acoustical activity and isotropic chiral phonons

Recent work predicted the existence of isotropic chiral phonon dispersion relations of the lowest bands connected to isotropic acoustical activity in cubic crystalline approximants of three-dimensional (3D) chiral icosahedral metamaterial quasi-crystals. While these architectures are fairly broadband and presumably robust against fabrication tolerances due to orientation averaging, they are extremely complex, very hard to manufacture experimentally, and they show effects which are about an order of magnitude smaller compared with those of ordinary highly anisotropic chiral cubic metamaterial crystals. Here, we propose and analyse a chiral triclinic metamaterial crystal exhibiting broadband isotropic acoustical activity. These 3D truss lattices are much less complex and exhibit substantially larger effects than the 3D quasi-crystals at the price of being somewhat more susceptible to fabrication tolerances. This susceptibility originates from the fact that we have tailored the lowest two transverse phonon bands to exhibit an ‘accidental’ degeneracy in momentum space.

Theory of renormalized phonon group velocity in high-temperature superconductors

The expressions for the renormalized phonon group velocity (RPGV) has been developed from renormalized phonon dispersion relations obtained with the help of impurity-induced anharmonic quantum dynamics of phonons via Green’s functions. It is observed that RPGV shows dependence on doping, phonon frequency, temperature, and anharmonicity. The [Formula: see text] superconductor has been taken for model calculations to successfully apply the new results of RPGV.

First-Principles Calculation for the Influence of C and O on the Mechanical Properties of γ-TiAl Alloy at High Temperature

The elastic constants of temperature dependence, thermal expansion coefficient and phonon dispersion relations of γ-TiAl doped with C/O have been investigated using first-principles calculations in order to gain insight into the mechanical performance of γ-TiAl in cases of high temperature. This study shows that γ-TiAl maintains stability at high temperatures introduced by C or O atoms. Importantly, the hardness increases and retains excellent resistance to external pressure. The results indicate that even if the TiAl alloy is doped with C or O atoms, it can also exhibit excellent mechanical properties at a high temperature.