First-principle Studies Of Ion Doping And Graphene Adsorbing On The Surface Of BiF₃

In this paper, first-principles calculations based on density function theory have been implemented. Firstly, we investigated the effect of S doping on the Bi F3 under the consideration of charge defect and neutral charge. By calculating the formation energy, we obtained the most stable structure of S doped Bi F3. On this basis, we analyzed the geometry structure, electronic structure and electrochemical properties of S doped Bi F3 with different S doping concentration. Then we further analyzed the defect of Sn doping. By calculating the formation energy, we obtained the most stable defect structure. On this basis, we investigated the influence of Sn doping on the geometry structure, magnetism, electronic structure and electrochemical properties of Bi F3. Lastly, we investigated the microstructure and physical mechanism of graphene adsorbing on the Bi F3(111) surface and discussed Al modified Bi F3(111) surface and its adsorption mechanism with graphene. The calculated results were summarized as follows:(1) The effect of S doping on the Bi F3: Firstly, under the consideration of charge defect and two kinds of F vacancy, by calculating the formation energy, it is obtained that the system of S doped Bi F3 has the lowest formation energy at the point h8 when F atom is displaced by S atom at the state of neutral charge. By structural optimizing and the calculated cohesive energy, the stability of S doped Bi F3 decreases and the volume of crystal swells with the increase of S doping concentration. Then, according to the calculated result of DOS, it can be obtained that the total magnetic moment of the systems of S doped Bi F3 become more and more larger with the increase of S doping concentration and they all exhibit the character of half-metallic. Lastly, by calculating the capacity and voltage of Bi F3 and S doped Bi F3, it is found that the capacity decreases with the increase of S doping concentration while voltage increase with the increase of S doping concentration, and the capacity and voltage of S doped Bi F3 both are better than those of pure Bi F3.(2) The effect of Sn doping on the Bi F3: Firstly, under the consideration of the charge defect and three kinds of typical vacancies(12-BiV 、22-BiV and0FV), calculated formation energies indicate that the Sn1/32Bi30/32F3 with vacancy is the easiest to be fabricated at point J due to Sn4+ doping. Here, J(SnDm,BiDm,FDm) is(-5.82 e V,0,-1.61 e V). Then by crystal optimizing, it can be obtained that in the Sn1/32Bi30/32F3, the Bi-F bonds around Sn and12-Bi V have increased and the expand degree decreases with the increase of the distance from them. In addition, the volume swells with the increasing distance of Bi-F bond. What’s more,by calculating the state density and Bader charge of Sn1/32Bi30/32F3, it is found that Sn4+ doping can improve the electrical conductivity of Bi F3. Meanwhile, the charge transfer between Sn and F ions is larger than that between Bi and F ions, which means Sn-F bond can present much stronger ionic bond. On the other hand, the charge transfer between Bi-F bond has reduced, which means Sn4+ doping with12-Bi V weaken the ionic bond between Bi and F atoms. Lastly, according to the calculated results of average theoretic capacitance and voltage,it is concluded that Sn4+ doping with12-Bi V can improve the electrochemical property of Bi F3.(3) We calculated the properties of Bi F3(111) surface and the mechanism of graphene adsorbing on the surface of Al modified Bi F3(111). Firstly, based on the calculated surface energy, it is found that Bi F3(111) with F termination( labeled as Bi F3(111)-F) is more stable than Bi F3(111) with Bi termination(labeled as Bi F3(111)-Bi), Moreover the relaxation of the three topmost atomic layers on the surface is more obvious. Then the mechanism of Al adsorbing on the Bi F3(111)-F is further analyzed according to the calculated results of adsorption energy, it is found that the Top site is the most stable adsorption site. On this basis,we investigated the mechanism of action of Al between the graphene and Bi F3(111)-F by calculating the adsorbing energy, DOS and total charge density. The calculated results show that the adsorption of graphene on the Bi F3(111)-F can be strenghthed by Al atom. What’s more, the electrical conductivity of Bi F3(111)-F can be improved obviously by adsorbing graphene.