Effect of Impurities on the Oxygen Adsorption Properties on the NiTi(110) Surface
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DISORDER, AND PHASE TRANSITION IN CONDENSED SYSTEM
Effect of Impurities on the Oxygen Adsorption Properties on the NiTi(110) Surface A. V. Bakulina,* and S. E. Kulkovab aInstitute
of Strength Physics and Materials Science, Siberian Branch, Russian Academy of Sciences, Tomsk, 634055 Russia bNational Research Tomsk State University, Tomsk, 634050 Russia * e-mail: [email protected] Received February 25, 2019; revised March 5, 2019; accepted March 5, 2019
Abstract—The effect of 3d–5d elements on the oxygen adsorption energy on the NiTi(110) surface has been studied by the projector augmented-waves method within density functional theory. It is shown that almost all elements, except for a few elements of the end of d periods, lead to an increase in the adsorption energy if they substitute for nickel. On the contrary, the substitutional impurities in the titanium sublattice lower this energy. Based on the analysis of the electronic characteristics of the surface with impurities, it has been found that an increase/decrease in the oxygen adsorption energy on NiTi(110) correlates with a change in the ionic contribution to the mechanism of oxygen bonding with the surface. DOI: 10.1134/S1063776119070033
1. INTRODUCTION It is known that NiTi-based intermetallic alloys have unique mechanical properties, including shapememory effect and superplasticity. They are widely used in various branches of the modern industry as electrical switches, connecting elements, fuses, thermal sensors, temperature controllers, satellite antennas, etc. Pins, various clamps, dental and bone implants, wire from nitinol (the name derived from the addition of the elements of the alloy and the laboratory where it was first obtained) are widely used in medicine. The interaction between the material from which the implant is made and human tissues is the main problem in medical applications. The biocompatibility of NiTi is believed to be the result of the formation of a thin inert TiO2 film on its surface, which prevents the release of nickel [1]. Based on the experimental studies of NiTi wires with oxide layers of different thickness and thermodynamic analysis, Tian et al. [2] concluded that the appearance of Ni on the alloy surface can be prevented if the surface is fully oxidized. It is known that the interaction of titanium with oxygen may lead to the formation of several titanium oxides on the NiTi surface (Ti2O, TiO, Ti2O3, Ti3O5, TiO2), depending on the surface treatment methods [1]. In particular, it was shown in [2] that surface segregation of nickel in a thin oxide layer with oxygen deficiency is mainly due to atoms, although in thick oxide layers, surface segregation is dominated by metal particles. Earlier [3], we studied oxygen adsorption on the NiTi(110) surface and the atomic structure of the alloy–oxide interface using ab initio calculations,
which provided additional information on nickel segregation. In particular, it was shown that the formation of single Ni defects is preferable in TiO over those in TiO2, which confirms the conc
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