Theoretical elastic stiffness of quaternary crystal Y3Si5N9O by first-principles investigation

The theoretical elastic stiffness of Y3Si5N9O, the only Y-Si-O-N quaternary crystal that contains a framework of corner-sharing SiN4 and/or SiON3 tetrahedron in three dimensions, was investigated using the first-principles total energy calculations. The full set of second order elastic coefficients, polycrystalline bulk and shear moduli, and anisotropic elastic moduli were reported and further compared with those of Y2O3 and beta-Si3N4. The equation of state and compressibility of Y3Si5N9O were investigated at pressures up to 50 GPa. The crystal structure is stable up to 50 GPa and exhibits anisotropic compressibility under hydrostatic pressure. The relatively softer YN6 and/or YN5O polyhedra are more prone to distort or deform than the SiN4 and/or SiON3 tetrahedra. Therefore, although the crystal structure of Y3Si5N9O contains a Si-N-O framework similar to that in beta-Si3N4, it displays elastic stiffness between those of Y2O3 and beta-Si3N4.