Title: Insights into the predicted Hf2SN and Ti2CdN in comparison with their synthesized carbide counter parts

Abstract

In this study, density functional theory (DFT) methods are employed to explore some physical properties (structural, elastic, electronic charge density distribution, Fermi surface topology, Mulliken bond overlap population, thermal conductivity, Vickers hardness and optical properties) of the two predicted nitride MAX phases Hf2SN and Ti2CdN to reveal their few macroscopic behaviours. The obtained results are compared with those calculated for their carbide counterparts Hf2SC and Ti2CdC. The lattice constants a and c of both nitride phases are smaller compared to their carbide counterparts. All the elastic constants and moduli of Ti2CdN are larger than those of Ti2CdC while the maximum elastic constants (except C12 and C13) and all moduli of Hf2SN are smaller than those of Hf2SC. The nitride phase Hf2SN is ductile while the carbide phase Hf2SC is brittle in nature. Conversely, the nitride phase Ti2CdN is brittle in nature while the carbide phase Ti2CdC lies on the broader line between ductility and brittleness. Investigation of phase stability via enthalpy calculations shows that the predicted nitrides are stable. Between the two predicted nitride MAX phases, Ti2CdN is structurally more stable than Hf2SN since the Fermi level of Ti2CdN is closer to the pseudogap compared to Hf2SN. Both sets of MAX phases may be used as coating materials to minimize solar heating. Due to ductility (i.e., machinability) the predicted phase Hf2SN seems to be more useful than its carbide counterpart Hf2SC in some technological applications. Again, the predicted phase Ti2CdN appears to be more useful than the already synthesized Ti2CdC in several engineering applications since it is found to be stiffer than Ti2CdC. But the Cd containing phases should preferably be used under controlled environment in possible technological devices. The predictions will hopefully stimulate the experimentalists to synthesize Hf2SC and Ti2CdN.

Biography

A.K.M. Azharul Islam is Professor Emeritus and former Vice-Chancellor of International Islamic University Chittagong, Bangladesh. He successfully pursued DIC from Imperial College of Sci. & Tech., London in the year 1969. He was awarded Ph. D. in 1972 from London University. He is a Fellow of the Institute of Physics (UK) as well as Bangladesh Academy of Sciences. His field of research was Elementary particle physics during 1967-1978. His research interest now spans the fundamental aspects of Condensed matter, which include Superconductivity, defects of solids, electronic structure of materials, MAX phases, nanomaterials. He has received several national and international awards for his research activities.