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Dissertation-PhD-Vijaya-Adhikari.pdf (2.59 MB)

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Transition Metal Nitrides in M4N structure and TiN-ScN and TiN-YN Alloy System: A Computational Investigation by First-Principles Approach

Adhikari, Vijaya
http://orcid.org/0000-0002-5144-0511
http://rave.ohiolink.edu/etdc/view?acc_num=toledo1627650177603629

Abstract Details

2021, Doctor of Philosophy, University of Toledo, Physics.
This dissertation is a systematic computational investigation of transition metal nitrides in M4N structure and in two alloy systems of Ti1-xScxN and Ti1-xYxN (0 ≤ x ≤ 1). Transition metal nitrides constitute a class of materials which have been broadly applied in the industry of hard coatings and cuttings. Our objective is to expand the currently existing database of these materials by exploring their structural, mechanical, magnetic, electronic, and thermodynamic properties, stability and hardness using the state-of-the-art first principles computational approach. Chapters 4 and 6 contain the main results and are summarized as follows. 1. We performed first-principles calculations with density functional theory on 28 metal rich cubic binary M4N structures. We provided a high through-put database of mechanical, electronic, magnetic, and structural properties for these compounds. We observed three compounds with Vickers hardness around or above 20 GPa, such as Re4N, Tc4N, and Mn4N (Chapter 4). We also identified 25 M4N compounds as mechanically stable while the remaining 3 (V4N, Nb4N, and Pt4N) as unstable. 2. We showed the relationship between the hardness and stability of these compounds and the density of states. We also calculated the magnetic properties of five magnetic compounds and exhibited that the consideration of electronic spin-polarization is very important in accurately calculating ground state energy and hence mechanical properties of these transition metal nitrides. 3. We also studied the phase stability, mechanical and electronic properties of two ceramic quasi-binary systems, Ti1-xScxN and Ti1-xYxN using density functional theory, cluster expansions and Monte Carlo simulations. We predicted strong exothermic mixing of TiN and ScN due to cationic similarity with the formation of 4 novel intermetallic compounds TiScN2, TiSc8N9, TiSc9N10, and Ti3Sc2N5 in the Ti1-xScxN system having hardness as high as 27.3 GPa. The phase diagram of Ti1-xScxN system showed an upper consolute temperature of 660 K, where the miscibility gap is closed, which is in close agreement to experimental observations (Chapter 6). We suggest Ti1-xScxN compounds for hard coating applications due to their enhanced hardness and stability. 4. We predicted endothermic mixing of TiN and YN due to their mismatched cationic properties leading to a very large consolute temperature of 7225 K in Ti1-xYxN system arising due to large structural distortion and positive strain energies. 5. We used projected density of states and Crystal Orbital Hamiltonian Populations graphs to analyze and explain the stability and enhanced hardness in Ti1-xScxN and also studied the case of random solid solutions with similar results. The hardness is found to be enhanced at the valence electron concentration of 8.4 – 8.6 in Ti1-xScxN system, which is a very useful result in tuning the mechanical properties through controlled electron concentration. As presented in this dissertation, the first principles computational approach based on density functional theory along with statistical methods based on cluster expansion and Monte Carlo simulation have been very efficient and successful in modeling, predicting, and designing the material’s property. These methods and techniques are being developed and enhanced rapidly and can speed up future computational research as a complement to experimental observation as well as prediction of new materials.
Sanjay Khare, Dr. (Committee Chair)
Jacques Amar, Dr. (Committee Member)
Richard Irving, Dr. (Committee Member)
Aniruddha Ray, Dr. (Committee Member)
Anju Gupta, Dr. (Committee Member)
131 p.
Physics
transition metals; nitrides; M4N; first-principles; mechanical properties; elastic constants; solid solutions; cluster expansion; phase diagrams; stability

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Citations

  • Adhikari, V. (2021). Transition Metal Nitrides in M4N structure and TiN-ScN and TiN-YN Alloy System: A Computational Investigation by First-Principles Approach [Doctoral dissertation, University of Toledo]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1627650177603629

    APA Style (7th edition)

  • Adhikari, Vijaya. Transition Metal Nitrides in M4N structure and TiN-ScN and TiN-YN Alloy System: A Computational Investigation by First-Principles Approach. 2021. University of Toledo, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=toledo1627650177603629.

    MLA Style (8th edition)

  • Adhikari, Vijaya. "Transition Metal Nitrides in M4N structure and TiN-ScN and TiN-YN Alloy System: A Computational Investigation by First-Principles Approach." Doctoral dissertation, University of Toledo, 2021. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1627650177603629

    Chicago Manual of Style (17th edition)

toledo1627650177603629
224
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