Synthesis and Crystal Structures of Ca4SiN4 and New Polymorph of Ca5Si2N6

Elastic, electronic, chemical bonding and thermodynamic properties of the ternary nitride Ca4TiN4: Ab initio predictions

In order to shed light on the unexplored properties of the ternary nitride Ca₄TiN₄, we report for the first time the results of an ab initio study of its structural, electronic, elastic, chemical bonding and thermodynamic properties. Calculated equilibrium structural parameters are in excellent concordance with available experimental data. Electronic properties were explored through the calculation of the energy band dispersions and density of states. It is found that Ca₄TiN₄ has an indirect band gap (Z-Γ) of 1.625 (1.701) eV using LDA (GGA). Nature of the chemical bonding was studied via Mulliken population analysis and charge density distribution map. It is found that the Ca-N bond is dominantly ionic, whereas the Ti-N one is dominantly covalent. Elastic properties of both single-crystal and polycrystalline phases of the title compound were explored in details using the stain-stress approach. Analysis of the calculated elastic moduli reveals that the title compound is mechanically stable, ductile and elastically anisotropic. Temperature and pressure dependencies of the unit-cell volume, bulk modulus, heat capacities, volume thermal expansion coefficient, Grüneisen parameter and Debye temperature were investigated based on the quasiharmonic Debye model.

Low-Dimensional Nitridosilicates Grown from Ca/Li Flux: Void Metal Ca8In2SiN4 and Semiconductor Ca3SiN3H

Reactions of indium and silicon with lithium nitride in Ca/Li flux produce two new nitridosilicates: Ca₈In₂SiN₄ (orthorhombic, Ibam; a = 12.904(1) Å, b = 9.688(1) Å, c = 10.899(1) Å, Z = 4) and Ca₃SiN₃H (monoclinic, C2/c; a = 5.236(1) Å, b = 10.461(3) Å, c = 16.389(4) Å, β = 91.182(4)°, Z = 8). Ca₈In₂SiN₄ features isolated [SiN₄]^8- units and indium dimers surrounded by calcium atoms. Ca₃SiN₃H features infinite chains of corner-sharing SiN₄ tetrahedra and distorted edge-sharing H@Ca₆ octahedra. Optical properties and band structure calculations indicate that Ca₈In₂SiN₄ is a void metal with calcium and indium states at the Fermi level and Ca₃SiN₃H is a semiconductor with a band gap of 3.1 eV.