Enthalpy of formation calculations on five-membered azaborolidine derivatives

Mechanical properties and electronic structure of Cu-doped tin: a first-principle study

Metal doping is an effective method for improving the toughness of ceramic materials and reducing coating fractures. In this study, first-principle calculations based on density functional theory were performed to study the formation energy, elastic constant, and electronic structure of Cu-doped TiN. The results reveal that Cu tends to replace the Ti sites in TiN crystal cells; with an increase in Cu concentration, the formation energy of the Cu-doped TiN system decreases. This indicates that the structural stability of Cu-doped TiN decreases. From the calculated elastic constant and the Voigt-Reuss-Hill approximation, it is evident that the bulk modulus B and shear modulus G decrease as the Cu concentration increases. However, G decreases more rapidly, thus increasing the B/G ratio. According to Paugh's ratio, the increase in B/G indicates an increase in the ductility of TiN. The results of the band structure, density of states, charge density, and Mulliken bond population analysis reveal that Cu doping reduces the covalent bond strength of TiN, enhances metallicity, and reduces the structural stability of the system, enhancing the toughness of TiN. The results of this study will provide theoretical and experimental guidance for improving the toughness of TiN coatings.

Evaluation of the Crystal Structure and Mechanical Properties of Cu Doped TiN Films

In this study, TiN films doped with different copper contents (TiCuN) were prepared by using direct current magnetron sputtering method. The effects of Cu doping on composition, structure, and mechanical properties of TiN films were studied by energy-dispersive spectroscopy (EDS), X-ray diffraction (XRD), a Vickers microhardnessmeter, and density functional theory (DFT). The results of experimental and DFT study showed that Cu mainly replaced Ti atoms in TiN to form replacement solid solution doping. When Cu replaced Ti in TiN, a weak Cu-N (bond population varied from 0.06 to 0.11) covalent bond formed; meanwhile, the bonding strength of Ti-N (bond population varied from 0.29 to 0.4) bond adjacent to Cu increased. When Cu content was low, a small number of weak Cu-N bonds were formed, with strengthened Ti-N bond near Cu atom, resulting in an increased hardness of Cu doped TiN films. According to the theory of weak bonds, when the Cu content was increased further, the number of weak Cu-N bonds increased and TiCuN hardness decreased. With an increase in Cu content, it was found the toughness of TiCuN also increased. The results of this study will provide a theoretical and experimental guidance for improving the toughness and deformation resistance of TiN, which has a potential application in the surface modification of medical devices.