Structure and mechanical properties of tungsten mononitride under high pressure from first-principles calculations

The first-principles study on the structure and mechanical properties of tungsten mononitride (WN) with WC-, NiAs-, and NaCl-structure phases are reported using the pseudopotential plane wave method within the generalized gradient approximation. The obtained equilibrium structure parameters and ground state mechanical properties are in good agreement with the experimental and other theoretical results. The formation enthalpy and elastic stability criteria indicate that NiAs-type WN is always the most energy favorable and mechanical stable phase under current studied pressure range, while the WC-type WN should be metastable which is different from the experimental result. The mechanical properties show that the predicted NiAs-type WN is an ultra-incompressible and hard material among the considered phases. In addition, the calculated B/G ratio indicated that WC-type WN possesses ductility nature and NiAs-type WN has brittle nature in the pressure range of 0-80 GPa. The elastic anisotropic factors for three phases of WN suggest that they are elastically highly anisotropic and strongly dependent on the propagation direction. (C) 2013 Elsevier B. V. All rights reserved.