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Transition Metal Nitrides and Their Solid Solutions: A First-Principles Approach with Cluster Expansion Computational Predictive Models

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2017, Doctor of Philosophy, University of Toledo, Physics.
This dissertation is a computational exploration of transition metal nitrides, a group of materials that have myriad applications in the hard coatings industry. We aim to explore their structural, mechanical, electronic and thermodynamic properties and their solid solutions, discovering trends and correlations of their bonding nature and cause of superior stability and hardness. Here are the major work and results: 1. We performed first-principles calculations with density functional theory on six cubic structural prototypes, zincblende, rocksalt, cesium-chloride, NbO, fluorite and pyrite. We observed a few compounds with Vickers hardness higher than 20 GPa, such as rocksalt-structure ScN, TiN, cesium-chloride-structure VN, NbO-structure CrN, MoN, WN, and pyrite-structure MnN2, PtN2. (Chapter 4, Chapter 5 and Chapter 6) 2. We established an anti-correlation between metallic compounds’ total electronic density of states at the Fermi energy level, an indicator of metallicity and their shear-related mechanical properties, such as elastic constant C44, shear modulus, Pugh’s ratio and Vickers hardness. (Chapter 4, Chapter 5 and Chapter 6) 3. Beyond single-cation phases, we further studied the phase equilibria of three ceramic quasibinary systems, Ti1-xZrxN, Ti1-xHfxN and Zr1-xHfxN. We analyzed the asymmetry of composition-dependent formation energy curves through two energetically partially canceling processes. We concluded that the absence of experimental observations of phase separation, as predicted by our calculations in Ti1-xZrxN and Ti1-xHfxN is probably due to a combined effect of insufficient undercooling, inadequate atomic diffusivity, and the initial energy barrier for chemical exchange with constrained lattices. (Chapter 8) 4. We also showed that mixing nitrides of same group transition metals does not lead to hardness increase from an electronic origin, but through solution hardening mechanism, a plastic phenomenon difficult to catch with first-principles modeling methods. (Chapter 8) As demonstrated in this dissertation, the toolset surrounding density functional theory has evolved to a level of maturity, capable of handling more dimensions in the material property space. They are rapidly being developed and perfected, and great research opportunities are emerging.
Sanjay Khare (Committee Chair)
Jacques Amar (Committee Member)
Nikolas Podraza (Committee Member)
Bo Gao (Committee Member)
Daniel Georgiev (Committee Member)
165 p.

Recommended Citations

Citations

  • Liu, Z. (2017). Transition Metal Nitrides and Their Solid Solutions: A First-Principles Approach with Cluster Expansion Computational Predictive Models [Doctoral dissertation, University of Toledo]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1492525178190092

    APA Style (7th edition)

  • Liu, Zhi. Transition Metal Nitrides and Their Solid Solutions: A First-Principles Approach with Cluster Expansion Computational Predictive Models. 2017. University of Toledo, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=toledo1492525178190092.

    MLA Style (8th edition)

  • Liu, Zhi. "Transition Metal Nitrides and Their Solid Solutions: A First-Principles Approach with Cluster Expansion Computational Predictive Models." Doctoral dissertation, University of Toledo, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1492525178190092

    Chicago Manual of Style (17th edition)