First-principles investigations of crystal structures and physical properties of jadeite under various pressures

The crystal structures, electronic, elastic properties, hardness and phase transition of jadeite under various pressures from 0 to 70 GPa are investigated by using the first-principles calculations based on plane-wave pseudopotential density functional theory within the generalized gradient approximation (GGA). The calculated lattice parameters a, b and c were found perfectly agree with the available experimental data below 10 GPa. They all present linear responses to pressure until 60 GPa, lattice parameters present nonlinear variations. The calculation results show compression along a-axis is more difficult than that along b-axis or c-axis which can be explained by the alternative arrangement of SiO tetrahedron and AlO octahedron along a-axis. The elastic constants, bulk modulus, shear modulus, Young's modulus, B/G, Poisson's ratio, hardness and electronic properties are further investigated as a function of pressure which all present anomaly at 60 GPa. The generalized Born's mechanical stability criterion present jadeite is mechanical unstable above 62 GPa. The calculation results all present phase transition of jadeite occurs above 60 GPa, which agree with the available experimental data and other theoretical results.