Research On The First-principles Calculations Of Binary Rare Earth Compound In Ag-Cu-Ni-Ce Alloy

The study for new electrical contact materials proceeds deeply with the performancerequirements of the electrical equipment constantly improving and the shape tending tosmall and complicated in recent years. AgCuNiRE alloys are compound layer silver alloyof new expensive/inexpensive composite electrical contact materials developed by ouruniversity collaborating with Chongqing Chuanyi metallic functional materials Co., LTD.Because of their good electrical and thermal conductivity, stable contact resistance, goodmechanical performance, wear and electric corrosion resistance they have been used in theactual production application. Through the experiment study it has been known that rareearth plays a major role in improving the microstructure and mechanical properties of alloy.This is closely related to the rare earth compounds in the alloy. But the in-depth sutdy ofthe compounds properties are not enough, which influences its further application. Thereare many difficulties on experimental research. Therefore the theoretical research on thebasic physical properties of rare earth compounds in the silver alloy are studied by usingthe first-principles method. The aim is to study the structure and mechanical properties ofcompounds, which has good theoretical guidance value to the application of rare earthelements in the silver alloy.In this article the electronic structure (energy band diagram and the density of states)and the mechanical properties (lattice constant, binding energy and the elastic constants) ofthe intermetallic compounds in the Ag-Ce, Cu-Ce, Ni-Ce binary alloy are respectivelycalculated by using CASTEP module which is based on density functional theory.Comparing the heat formation and binding energy of intermetallic compounds, theformation ability and structure stability can be analyzed. Analyzing electronic structure ofthe compounds can indicate the bond characteristics and orbital contribution. Comparingthe elastic modulus value would analyz the mechanical properties of rare earth compounds.At last the basic physical properties would be summarized. The results are as follows.In the binary system of Ag-Ce, the formation enthalpy calculation results of AgCe,Ag2Ce and Ag4Ce compounds are-0.372,-0.201and-0.771ev/atom. They all can beformed on the thermodynamics and the strongest formation ability is Ag4Ce phase. Thecalculation value of binding energy of AgCe,Ag2Ce and Ag4Ce are respectively-4.761,-4.387and-4.793ev/atom. The stability of Ag4Ce is best. Density of state figures show that the bonding electrons near Fermi level of total state is mainly composed of Ce f and dorbitals and a small amount Ag p orbital, which verifies the stability of AgCe phase isbetter than Ag2Ce and Ag4Ce. The bulk modulus of AgCe and Ag4Ce is59.198and109.005respectively, the shear modulus is22.702and34.652, young’s modulus is60.385and221.559, poisson’s ratio is0.330and0.394, the elastic anisotropic coefficient is1.936and1.388. The results of analysis is that the hardness and the average valence bondstrength of Ag4Ce phase are better. And the plastic of AgCe is better.In the binary system of Cu-Ce, the formation enthalpy value of CuCe, Cu2Ce, Cu4Ce,Cu5Ce and Cu6Ce compounds is0.056,-0.082,0.060,-0.097and-0.022ev/atomrespectively, which shows that CuCe and Cu4Ce can not be easily formed in the system,and the formation ability of Cu5Ce is the strongest. The binding energy value of CuCe,Cu2Ce, Cu4Ce, Cu5Ce and Cu6Ce is-4.886,-5.006,-4.849,-5.001and-4.924ev ev/atom,The crystal structure stability of Cu2Ce and Cu5Ce is better. The analysis of density of statediagram showes that the bonding electrons near Fermi level of total state is mainlycomposed of Ce f and d orbitals and a small amount Cu p orbital. It can also be confirmedthat the crystal structure stability of Cu5Ce and Cu2Ce is higher, which is the same as theresult of the binding energy.The calculation results of Ni-Ce binary system show that the formation enthalpy ofNi2Ce, Ni3Ce, Ni7Ce2, Ni5Ce and Ni3Ce7compounds is respectively-3.032,-3.785,-4.011,-4.576and-0.185ev/atom, which indicates that the formation ability of Ni5Ce is the best.The calculated value of their binding energy is-7.291,-7.952,-4.67,-8.651å'Œ-4.85ev/atom. The structures of all the compounds is stable and the structure stability of Ni5Ceis the best. From the analysis of density of state diagram, it can be known that the mainvalence electrons of the system is composed by Ce f, Ce d orbit, a small amount of Ni pand d orbit,which also verifies the stability of Ni5Ce phase is more better. The bulkmodulus of Ni2Ce and Ni5Ce is146.042and218.798respectively, the shear modulus is36.316and83.216, the young’s modulus is100.609and221.559, poisson’s ratio is0.385and0.331, the elastic anisotropic coefficient is1.34and1.30. The stability, hardness andthe average valence bond strength of Ni5Ce is better and the plastic of Ni2Ce is better thanNi5Ce.