Research On The Stability And Electronic Structure Of Ti、Nb、Sn Metal And Its Binary Alloys

At present, the Ti alloy plays an important role in many fields, due to its character of high strength, moreover, the outstanding corrosion resistance, and the characteristics of stable thermal stability. In recent years, people gradually change the Ti alloy from the industry areas to the medicine direction, but Al and V in the Ti-Al-V are harmful to human bodies, and Nb, Sn elements do not have a harm to human bodies, what’s more, Nb can also improve the stability of β-type Ti. Therefore, the theoretical research on Ti?Nb and Ti?Sn may promote the development of the Ti alloy in the medical direction.Nowadays, in the simulation calculation field of the materials study, the first principle method has already developed well. In the paper, we use the VASP package, which is based on the first principle, to analysis the stability and the electronic structure of Ti, Nb, Sn and its binary alloys, and provide data support for interatomic potential. First, use two different approximate methods(LDA and GGA) to calculate the lattice constants and the cohesive energy of Ti, Nb, Sn and its binary alloys. Next, we calculate and analysis the electronic structures of β Ti?Nb, Ti?Sn, Nb?Sn alloys. We obtain the conclusions finally:(1) For hcp?Ti, bcc?Nb and α?Sn, the lattice constants are a=2.92?(2.95?)、c=4.63?(4.68?);a=3.33?(3.30?);a=6.47?(6.48?), compared with the standard values, the agreement is very good for the lattice constant calculation. The error range(lattice constant a, for example) are 1.02%, 0.91% and 0.15% respectively. We find that the more the proportion of Nb in the whole system, the larger the lattice constant are for the β Ti?Nb alloys. There are six configurations of the Ti?Sn alloys( αTi6Sn5,βTi6Sn5, Ti2Sn1, Ti2Sn3, Ti3Sn1 and Ti5Sn3). Compared with the literature value, the error range of the lattice constant for them are 2.36%, 0.43%, 1.93%, 0.50%, 0.51% and 0.37%, respectively. As the same, the error range of the lattice constant for Nb?Sn are: 0.20%, 0.95% and 1.97%.(2) The results show that: for bcc, hcp and fcc of Ti, the relation of the cohesive energy is Ehcp>Efcc>Ebcc, hcp?Ti is the most stable. For Nb, bcc?Nb is more stable than fcc?Nb. For two configurations of Sn, Eα>Ebcc. In the β Ti?Nb alloy, with the increase of the proportion of Nb, its cohesive energy are increased linearly, as well as its stability. However, in the Ti?Sn alloys, as the proportion of Sn, the stability becomes worse, for the six kinds of configurations, that is the most stable structure is Ti3Sn1(4.97 e V), and the worst one is Ti2Sn3(4.30 e V). In the Nb?Sn alloy, the cohesive energy are 4.65 e V( Nb1Sn2), 6.29 e V( Nb3Sn1) and 5.49 e V( Nb6Sn5) respectively, namely E(Nb3Sn1)>E(Nb6Sn5)>E(Nb1Sn2). And the cohesive energy of LDA is generally larger than the calculated value of GGA, the difference about 0.5 e V.(3) The band structure show that: three binary alloys have some bands across the Fermi level, which shows the metal properties. To analysis the electronic density of states, three binary alloys exist the orbits hybridization, namely the systems contain covalent bonds. The density of states for β Ti?Nb system mainly comes from the contribution of d-orbitals electronic of Ti and Nb, and it mainly comes from Ti d and Sn p、s electronic in the Ti?Sn alloys, the density of state is mainly from Nb d and Sn p, s electronic contribution in the Nb?Sn alloy.