Electronic structure, mechanical properties and anisotropy of thermal conductivity of Y-Si-O-N quaternary crystals

The electronic structure, mechanical and thermal properties of Y-Si-O-N quaternary crystals have been investigated by local-density approximation (LDA) and further have been verified by the experimental results. It was found that the calculated band gap of YSiO2N, Y2Si3O3N4, Y3Si5ON9, Y4Si2O7N2 and Y10(SiO4)6N2 compounds are that of typical insulators with occupied valence band (VB) and unoccupied conduction band (CB) states separated by a wide band-gap. The bottom of the CB is dominated by 3p orbitals of Si atoms and the 4d orbitals of Y atoms, while the top of the VB is mainly dominated by 2p orbitals of N and 2p orbitals of O atoms orbital for all quaternary crystals. The minimum thermal conductivity of Y-Si-O-N quaternary crystals at high temperature was evaluated by Clarke's model and Cahill's model. According to Clarke's model, the minimum thermal conductivity of YSiO2N, Y2Si3O3N4, Y3Si5ON9, Y4Si2O7N2 and Y10(SiO4)6N2 are 1.50, 1.81, 1.91, 1.37 and 1.38 W m−1 K−1, respectively. The calculated results also show that these phases have the anisotropic minimum thermal conductivity, medium elastic properties and hardness.