Density functional study of carbon vacancies in titanium carbide.

Title Density functional study of carbon vacancies in titanium carbide.
Authors M. Råsander; H.W. Hugosson; A. Delin
Journal J Phys Condens Matter
DOI 10.1088/1361-648X/aa9979

It is well established that TiC contains carbon vacancies not only in carbon-deficient environments but also in carbon-rich environments. We have performed density functional calculations of the vacancy formation energy in TiC for C- as well as Ti-rich conditions using several different approximations to the exchange-correlation functional, and also carefully considering the nature and thermodynamics of the carbon reference state, as well as the effect of varying growth conditions. We find that the formation of carbon vacancies is clearly favorable under Ti-rich conditions, whereas it is slightly energetically unfavorable under C-rich conditions. Furthermore, we find that the relaxations of the atoms close to the vacancy site are rather long-ranged, and that these relaxations contribute significantly to the stabilization of the vacancy. Since carbon vacancies in TiC are also experimentally observed in carbon-rich environments, we conclude that kinetics may play an important role. This conclusion is consistent with the experimentally observed high activation energies and sluggish diffusion of vacancies in TiC, effectively causing a freezing in of the vacancies.

Citation M. Råsander; H.W. Hugosson; A. Delin.Density functional study of carbon vacancies in titanium carbide.. J Phys Condens Matter. 2018;30(1):015702. doi:10.1088/1361-648X/aa9979

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See more Titanium products. Titanium (atomic symbol: Ti, atomic number: 22) is a Block D, Group 4, Period 4 element with an atomic weight of 47.867. The number of electrons in each of Titanium's shells is [2, 8, 10, 2] and its electron configuration is [Ar] 3d2 4s2. Titanium Bohr ModelThe titanium atom has a radius of 147 pm and a Van der Waals radius of 187 pm. Titanium was discovered by William Gregor in 1791 and first isolated by Jöns Jakob Berzelius in 1825. In its elemental form, titanium has a silvery grey-white metallic appearance. Titanium's properties are chemically and physically similar to zirconium, both of which have the same number of valence electrons and are in the same group in the periodic table. Elemental TitaniumTitanium has five naturally occurring isotopes: 46Ti through 50Ti, with 48Ti being the most abundant (73.8%). Titanium is found in igneous rocks and the sediments derived from them. It is named after the word Titanos, which is Greek for Titans.

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