Structure And Structure Stabilities Of Transition Metal Atoms Doped Materials

Transition metal elements have been used in many important fields for different applications, such as alloy steel, high temperature ceramic, semiconductor industry and so on. In this thesis, we have studied the structures and structure stabilities of transition metal atom doped materials, such as yttrium stabilized cubic zirconia and iron doped carbon nanotubes for examples.In this thesis, we have studied how the yttrium atoms and oxygen vacancies affect the structure stabilities of yttrium stabilized cubic zirconia. We find that the yttrium atoms assembling and forming yttrium chains are beneficial to stabilize the doped structures of cubic zirconia with high yttrium concentration. When the oxygen atoms diffuse along the directions of yttrium atoms assembling, the diffusion barrier is much lower than that of other directions. Thus, the diffusion barrier of oxygen atoms in this structure is anisotropy. We suggest that new devices with high oxygen iron conductivity on a certain direction could be produced by using this structure.We have also studied the structure stabilities of iron doped carbon nanotubes. For the adsorption of Fe atoms in the nanotubes, when the diameter of the nanotube is small, the nanotube could bedeformed by the adsorbing of atoms. This deformation changes theπbonding of the nanotubes and has significant effect on the interaction between the adsorbed atoms and the nanotube.We find that a single Fe atom bonds stably with carbon nanotubes, while Fe chains do not bond stably with carbon nanotubes. We have proposed a physical mechanism and show that the transfer energy of spin-up electrons in a half-filled d orbital to the spin-down electrons in another half-filled d orbital in Fe atoms determines the ability of the bonding of single Fe atoms and Fe chains with carbon nanotubes. The results can explain the experiment that Fe nanowires are easy to move inside the nanotubes. Our results also have important implication to the catalysis mechanism of Fe clusters in the growth of carbon nanotubes. Moreover, the electron transfer enhances the spin polarization of the Fe chains near the Fermi level, which has potential application to the high spin polarization nano-devices.