Structural, elastic, thermal and lattice dynamic properties of new 321 MAX phases

Abstract A new series of the MAX family designated as 321 phases are recently reported with Nb 3 As 2 C, V 3 As 2 C, Nb 3 P 2 C and Ta 3 P 2 C. Most of physical properties of these new MAX phase compounds are unexplored and the present study aims to investigate their structural, elastic, thermal and lattice dynamic properties. Though all the phases are elastically anisotropic and brittle in nature, Nb 3 As 2 C is the most anisotropic and Ta 3 P 2 C is the most brittle. V 3 As 2 C compared to Nb 3 As 2 C and Ta 3 P 2 C compared to Nb 3 P 2 C should exhibit superior mechanical properties, as they possess larger elastic constants and moduli. Shear strength, bond covalency as well as the average bond strength and materials’ brittleness are predicted to follow: Ta 3 P 2 C > Nb 3 P 2 C > V 3 As 2 C > Nb 3 As 2 C. The estimated Debye temperature and lattice thermal conductivity are highest for Nb 3 As 2 C. Lattice dynamical features are investigated in detail and the infrared and Raman active modes are identified. The high melting temperatures of these compounds are beneficial for their potential applications at elevated temperatures.