The Study On Electronical Structure Of Layered Ternary Carbide Composites

New layered ternary carbides attract increasing interest owing to their unique properties, which combine unusual properties of both metals and ceramics. Like metals, it is good thermal and electrical conductors, relatively soft. Like ceramics, it is elastically stiff; exhibit excellent high temperature mechanical properties. It is resistant to thermal shock and unusually damage tolerant, and exhibit excellent oxidation resistance. Above all, unlike conventional carbides, they can be machined by using conventional tools without lubricant, which are of great technological importance for their application. Additionally, it is an exceptional solid lubricant with an ultra-friction. These excellent properties mentioned above make them another family of technically important materials. And layered ternary carbide composites exhibit more salient properties. For example, the density of Cu/ Ti₃SiC₂ composite become higher considerably compactness, then their electrical conductivity, hardness and mechanical properties are also improved. At the same time the hardness and strength of Ti₂AlC,Ti₃AlC₂ increase evidently after adding TiB₂ herein. Therefore, this layered ternary carbide composites will have extensive foreground.The relations between composition, structure, chemical bond and property of Ti₃SiC₂, Ti₃SiC₂/Al, Ti₂AlC/Si, Ti₃AlC₂/Si, Ti-Al-C/TiB₂, Ti₂AlN are studied using density function theory and discrete variation method (DFT-DVM).When Al element is added into Ti₃SiC₂, there is less difference of ionic bond, which doesn't play a leading role to influent the properties. After adding Al, the covalent bond of Al and the near Ti become somewhat weaker, but the covalent bond of Al and the Si in the same layer is obviously stronger than that of Si and Si before adding. Therefore, in preparation of Ti₃SiC₂, adding proper quantity of Al can promote the formation of Ti₃SiC₂. The density of state shows that there is mixed conductor character in both of Ti₃SiC₂ and Adding Al Element. Ti₃SiC₂ is with more tendencies to form a semiconductor. The total density of state near Fermi lever after adding Al is larger than that before adding, so the electric conductivity may increase after adding Al.The strengths of ionic and covalent bonds both decrease after doping Si into Ti₂AlC. The interaction between Si and Ti in doping Si into Ti₂AlC is obvious weaker than that between Al and Ti in Ti₂AlC. The ionic and covalent bonds in Ti₃AlC₂ are stronger than those in Ti₂AlC. Therefore, in synthesis Ti₂AlC, doping Si into it enhances the Ti₃AlC₂ content instead of Ti₂AlC. The total density of state (DOS) shows that there is mixed conductor (conductor and semi-conductor) character in Ti₂AlC, Ti₃AlC₂ and doping Si series. Ti₂Si_xAl_1-xC is with more obvious tendency to form a semiconductor than Ti₂AlC.In the composites of Ti-Al-C/TiB₂, there are strong ionic and covalent interactions among the interfaces of the composites. The interactions among the interfaces, the whole ionic and covalent bond of Ti₃AlC₂/TiB₂ are stronger than those of Ti₂AlC/TiB₂. The results are consistent with the result of experiment that the mechanics property of Ti₃AlC₂/TiB₂ is better than that of Ti₂AlC/TiB₂.The experiment show that the hardness of Ti₂AlN is larger that that of Ti₂AlC owing to the difference of covalent bond. There is a less difference of ionic bond in Ti₂AlC and Ti₂AlN, the covalent bond of Ti₂AlN is larger than that of Ti₂AlC. Analysis of the total density of states, the trend forming forbidden band of Ti₂AlC was more evident than that of Ti₂AlN, which made the conductivity of Ti₂AlN than Ti₂AlC.