| Nowadays, the interfacial properties play an increasing significant role in industrial applications. The crystal structure and electronic properties with different interface are calculated by the method of ab initio calculation. In recent years, some special natures of the interface have been explored deeply using first-principles.Based on the density functional theory, using the first principle, the physical features of W/ZrB2system were calculated, including the comparison of TiB2, ZrB2block features, the stability properties of W three low index crystal face (001),(110),(111),W/ZrB2interface system deepen and the according theoretical explanation about some experiments conclusions. All calculations using the generalized gradient approximation to the plane-wave ultrasoft pseudopotential method, ranging from lattice energy to geometry optimization, thereby getting the ground-state equilibrium model, and the crystal band structure, density of States, state density and the electronic population of different models were calculated. And these calculation results were analyzed, thus revealing some special nature of the interface structure. The main research contents and results are as follows:1. Based on Density Functional Theory (DFT), using first-principles pseudopotential plane wave method, elastic properties and electronic structure of TiB2and ZrB2were calculated. The elastic constants of these compounds were calculated by Voigt-Reuss-Hill method. The results show that the elastic modulus of TiB2and ZrB2are594and520GPa, and the shear modulus are268and229GPa, respectively. Pugh empirical criterion and Poisson’s ratio show that the two compounds are very brittle, and the brittleness of TiB2is higher than ZrB2. Finally, the differences in elastic properties between TiB2and ZrB2result from their electronic structures.2. Surface relaxation, surface energy and Density of States (DOS) of metal W on low index surfaces (001),(110) and (111) were calculated. The results showed that: the relaxation and surface energy were|△14(110)|<|△14(111)|<|△14(001)|and Esurf(110)<ESurf(111)<Esurf(001), respectively. The surface relaxation and surface energy of W (110) were both minimum, which proved that W(110) was the most stable surface. According to Density of States, the essence of the distinct stability of W (001), W (110) and W (111) was discussed.3. The optimal electronic structure of W(110)/ZrB2(001) interface was investigated. The ideal work of adhesion (Wad) and interface energy (γ) were calculated for six different interfacial structures, taking into account both Zr-and B-terminations of the boride. The interfacial electronic structure including charge density distribution, states of density (DOS), and Mulliken population was simulated to determine the nature of metal/boride bonding. The results showed that the most stable interface geometry is B-termination, in accord with other theoretical observations. Meanwhile, the adhesion strength of the metal/ceramic interfaces is closely related to the atomic type at the surface layer of the ceramic.4. Through the analysis of W (110)/ZrB2(001) optimal interface, combining the B-termination surface with W form the most stable interface, thus using density of States of this surface to analyze the XRD trends as well as the multilayer film superhard phenomenon of W (110)/ZrB2(001) multilayer system.Based on the above results, some special properties of surface and interface play a certain explanation role of experiments on a multilayer superhard effect. |
PDF Full Text Request