EFFECT OF DEFECTS AND TEMPERATURE ON THE MECHANICAL AND ELECTRONIC PROPERTIES OF NbC AND NbN: A FIRST-PRINCIPLES STUDY

Abstract

Transition metal carbides and nitrides (TMCNs) are materials that have attracted a lot of attention for both theoretical and experimental studies. This is largely attributed to their excellent physical and electronic properties that makes them ideal candidates for technological and industrial applications. This study focuses on the structural, mechanical and electronic properties of Niobium carbide (NbC) and Niobium Nitride (NbN). Also, owing to their fascinating properties, this study investigated the effects of defects and temperature on the mechanical properties of NbC and NbN from first principles. The study also investigated the effects of defects on the properties of the two materials with concentration ranging between (1.56% − 12.5%) and temperature ranging between 300 K – 1500 K. This is crucial since there exist no perfect materials in nature and the materials are used under extreme conditions such as high temperatures and high pressure. The calculations are performed on the rocksalt (RS), zinc blende (ZB) and wurzite (WZ) structures of the two compounds through the density functional theory formalism using generalized gradient functional approximation for the exchange correlation potential. The obtained results show that the pristine NbC and NbN have high values of elastic constants and mechanical properties in the range of 71 GPa – 815 GPa. The values of the mechanical properties among them bulk moduli, shear moduli, Vicker’s hardness as well as Young’s modulus decrease with increasing defect concentration (1.56 % - 12.5 %) and temperature (300 K - 1500 K). The results obtained show that defect concentration of up to 12.5 % does not compromise the structural properties of the materials and hence, they can still be used in various industrial applications. Further, the temperature range of 300 K – 1500 K considered show that the materials are still mechanically stable and can be suitable candidates in harsh environments of high temperature. Consequently, control of defects and temperature especially during synthesis of these materials is important in evaluating their mechanical response that can drive them to be ideal for super-hard and other related applications