First-principles study of the structural and elastic properties of Cr{sub 2}AlX (X=N, C) compounds

• Published in: Journal of solid state chemistry Vol. 191
• Main Authors: Cui Shouxin, School of Physics Science and Information Technology, Liaocheng University, Liaocheng 252059, College of Life Science and Biotechnology and Research Center on New Aeronautics and Astronautics, Shanghai Jiaotong University, Shanghai 200240, Wei Dongqing, Hu Haiquan, Feng Wenxia, Gong Zizheng
• Format: Journal Article
• Language: English
• Published: United States 15.07.2012
• Subjects: BONDING; BRITTLENESS; CARBON COMPOUNDS; CHEMICAL BONDS; CRYSTALS; DENSITY; DENSITY FUNCTIONAL METHOD; DISTRIBUTION; DUCTILITY; ELASTICITY; HARDNESS; INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; MATERIALS SCIENCE; PRESSURE RANGE GIGA PA; STABILITY
• ISSN: 0022-4596; 1095-726X
• DOI: 10.1016/J.JSSC.2012.03.014

The structural, electronic and elastic properties of Cr{sub 2}AlX, with X=N, C, have been investigated at the density functional theory level by applying a plane-wave pseudopotential approach. The band structure and density of states reveal the metallic features of Cr{sub 2}AlX. The total and projected density of states indicate that the bonding is achieved through a hybridization of Cr 3d states with Al and X-atom p states. The Cr 3d-X2p bonds are lower in energy and are stiffer than Cr 3d-Al 3p bonds. The charge density distributions indicate that there exist soft Cr-Al and relatively strong Cr-X covalent bonds, which might be responsible for their hardness. The elastic constants were obtained in the pressure range 0-100 GPa, and satisfy the stability conditions for hexagonal crystal, which indicates that these two compounds are stable in the pressure regime studied. By analyzing bulk modulus to shear modulus ratio and Cauchy pressure, Cr{sub 2}AlC is predicted to be brittleness and Cr{sub 2}AlN is ductile. The Debye temperature was obtained from the average sound velocity. - Graphical abstract: The heterogeneity of chemical bonds in Cr{sub 2}AlX (X=N, C) is observed: soft Cr-Al and relatively strong Cr-X covalent bonds might be contributed to their hardness. Highlights: Black-Right-Pointing-Pointer Cr 3d-X2p (X=N, C) bonds are lower in energy and stiffer than Cr 3d-Al 3p bonds for Cr{sub 2}AlX. Black-Right-Pointing-Pointer The hardness of Cr{sub 2}AlX might be ascribed to soft Cr-Al and relatively strong Cr-X covalent bonds. Black-Right-Pointing-Pointer The predicted brittleness of Cr{sub 2}AlC and ductility of Cr{sub 2}AlN originated from their novel structure.