Investigations on structural,elastic, thermodynamic and electronic properties of TiN,Ti2N and Ti3N2 under high pressure by first-principles |
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| Institution: | 1. School of Physics and Optoelectronic Engineering, Xidian University, Xi’an, Shaanxi 710071, PR China;2. National Supercomputing Center in Shenzhen, Shenzhen 518055, PR China;1. Center of Advanced Studies in Physics (CASP), GC University, Lahore, 54000, Pakistan;2. Department of Physics, Bahauddin Zakariya University, 60800, Mulatan, Pakistan;1. School of Chemistry and Materials Science, Ludong University, Yantai 264025, China;2. School of Chemical Engineering, Nanjing University of Science and Technology, Nanjing 210094, China;3. Institute of Chemical Materials, China Academy of Engineering Physics (CAEP), Mianyang 621900, China;1. School of Mechanical and Electrical Engineering, Henan Institute of Science and Technology, Xinxiang 453003, China;2. AECC Shenyang Liming Aero. Engine CO.,LTD., Shenyang 110043, China;3. Laboratory for Corrosion and Protection of Metals, Institute of Metal Research, No.62 Wencui Road, Shenyang 110016, China;4. Shenyang National Laboratory for Materials Science, Northeastern University, No. 3-11 Wenhua Road, Shenyang 110819, China |
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| Abstract: | The lattice parameters, cell volume, elastic constants, bulk modulus, shear modulus, Young's modulus and Poisson's ratio are calculated at zero pressure, and their values are in excellent agreement with the available data, for TiN, Ti2N and Ti3N2. By using the elastic stability criteria, it is shown that the three structures are all stable. The brittle/ductile behaviors are assessed in the pressures from 0 GPa to 50 GPa. Our calculations present that the performances for TiN, Ti2N and Ti3N2 become from brittle to ductile with pressure rise. The Debye temperature rises as pressure increase. With increasing N content, the enhancement of covalent interactions and decline of metallicity lead to the increase of the micro-hardness. Their constant volume heat capacities increase rapidly in the lower temperature, at a given pressure. At higher temperature, the heat capacities are close to the Dulong–Petit limit, and the heat capacities of TiN and Ti2N are larger than that of c-BN. The thermal expansion coefficients of titanium nitrides are slightly larger than that of c-BN. The band structure and the total Density of States (DOS) are calculated at 0 GPa and 50 GPa. The results show that TiN and Ti2N present metallic character. Ti3N2 present semiconducting character. The band structures have some discrepancies between 0 GPa and 50 GPa. The extent of energy dispersion increases slightly at 50 GPa, which means that the itinerant character of electrons becomes stronger at 50 GPa. The main bonding peaks of TiN, Ti2N and Ti3N2 locate in the range from −10 to 10 eV, which originate from the contribution of valance electron numbers of Ti s, Ti p, Ti d, N s and N p orbits. We can also find that the pressure makes that the total DOS decrease at the Fermi level for Ti2N. The bonding behavior of N–Ti compounds is a combination of covalent and ionic nature. As N content increases, valence band broadens, valence electron concentration increases, and covalent interactions become stronger. This is reflected in shortening of Ti–N bonds. |
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| Keywords: | Titanium nitrides First-principles calculations High pressure Physical properties |
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