First Principles Study on Structure Stability and Mechanical Properties of YNi2B2C and LuNi2B2C under Pressure

The pressure effects on the lattice parameters and elastic constants of the tetragonal RNi 2 B 2 C (R=Y, Lu) are investigated by means of the first principles. The predicted lattice constants and elastic constants of YNi 2 B 2 C and LuNi 2 B 2 C at 0 GPa agree well with the available data. By the elastic stability criteria under isotropic pressure, it is predicted that YNi 2 B 2 C and LuNi 2 B 2 C with tetragonal structure are not mechanically stable above 93 GPa and 50 GPa, respectively. Pugh’s modulus ratio, Poisson’s ratio, Vickers hardness, elastic anisotropy and Debye temperature of YNi 2 B 2 C in the pressure range of 0–100 GPa and LuNi 2 B 2 C in the pressure range of 0-60 GPa are further investigated. It is shown that the ductility and Debye temperature of tetragonal RNi 2 B 2 C (R=Y, Lu) increase with increasing pressure, and LuNi 2 B 2 C is more ductile and lower Debye temperature than YNi 2 B 2 C under different pressures.