Defense of the dissertation of Omarkhan Aitolkyn for the degree of Doctor of Philosophy (PhD) in the specialty «8D05323 - Technical Physics»

At the L.N. Gumilyov Eurasian National University Omarkhan Aitolkyn Shayakhmetkhankyzy will defend the dissertation work for the degree of Doctor of Philosophy (PhD) on the topic Quantum chemical study of stable manganese borides and nitrides and their mechanical properties at extreme pressures under the educational program «8D05323 – Technical Physics».

The dissertation was carried out at the «Technical Physics education department» of L.N. Gumilyov Eurasian National University.

The language of defense is russian

Official reviewers:

Daulet Sergeev – Candidate of Physical and Mathematical Sciences, Associate Professor, Lieutenant Colonel, Head of the Department of Design and Operation of Radio-Electronic Equipment at the Republican State Institution “T. Ya. Begeldinov Military Institute of the Air Defense Forces” of the Ministry of Defense of the Republic of Kazakhstan, Aktobe, Republic of Kazakhstan;

Gulbanu Kaptagay – PhD, Associate Professor of the Department of Physics, Kazakh National Women’s Teacher Training University, Almaty, Republic of Kazakhstan.

Temporary members of the Dissertation Council:

Anuar Aldongarov – Doctor of Philosophy (PhD), Associate Professor of the Department of Technical Physics, L.N. Gumilyov Eurasian National University, Astana, Republic of Kazakhstan;

Zhanturina Nurgul – Doctor of Philosophy (PhD), Associate Professor, Aktobe Regional State University named after K.Zhubanov, Aktobe, Republic of Kazakhstan;

Kalytka Valeriy - Candidate of Physical and Mathematical Sciences, PhD, Associate Professor, Acting Professor of the Department of Energy Systems, Karaganda Technical University named after Abylkas Saginov, Karaganda, Republic of Kazakhstan.

Scientific advisors:

Abdirash Akilbekov – Candidate of Physical and Mathematical Sciences, Professor, Department of Technical Physics, L. N. Gumilyov Eurasian National University, Astana, Republic of Kazakhstan

Tatyana Bekker – Doctor of Geological and Mineralogical Sciences, Professor of the Russian Academy of Sciences, Leading Researcher at the V. S. Sobolev Institute of Geology and Mineralogy, Siberian Branch of the Russian Academy of Sciences, Novosibirsk, Russian Federation

The defense will take place on May 02, 2026, at 02:00 PM in the Dissertation Council for the training direction «8D053 – Physical and chemical sciences» in the specialty «8D05323 – Technical Physics» of L.N. Gumilyov Eurasian National University. The dissertation council meeting will be held in offline and online formats.

Address: Astana, Kazhymukan Street, 13, auditorium No. 310 

Abstract (English):The aim of the dissertation research The purpose of the dissertation research is to identify stable structures of manganese borides and nitrides, as well as to evaluate the mechanical properties of stable structures. Research objectives 1. To carry out a theoretical search for stable crystal structures in Mn–B and Mn–N systems in the pressure range 0-200 GPa. 2. To determine the stability intervals of the detected structures of manganese borides and nitrides, taking into account spin polarization. 3. Calculate phonon dispersion curves and determine the dynamic stability of the found structures. 4. Calculate the phase P–T diagrams of the found borides and manganese nitrides. 5. Calculate the elastic constants Cij and use them to evaluate the mechanical properties of borides and manganese nitrides. Research methods In the present study, the calculation of the search for stable crystal structures was carried out using evolutionary algorithms implemented in the USPEX software package. All calculations were carried out within the framework of density functional theory using the VASP software package. Phonon dispersion curves were calculated using the supercellular method and the finite shift method implemented in the Phonopy program. The elastic constants Cij were calculated using the strain–stress ratio, and then the elastic modules were calculated using the Voigt-Reuss-Hill averaging. Vickers hardness was estimated using the empirical models of Chen and Tian. The main provisions (proven scientific hypotheses and other conclusions that are new knowledge) submitted for defense 1. In the Mn–B system, eight stable intermediates are present in the pressure range 0-200 GPa: Mn2B, MnB, Mn3B4, Mn2B3, MnB2, MnB3, MnB4 and MnB6. Six of these compounds are classified as solid materials. 2. Taking into account the influence of temperature on phase equilibria in the MnN system removes contradictions between previously published theoretical and experimental results. Thus, there are four thermodynamically stable MnN modifications in the pressure range 0-200 GPa: F4 ̅3m, I4/mmm, P63/mmc и Pnma. 3. In the Mn–N system, six stable intermediates are present in the pressure range 0-200 GPa: Mn3N, Mn5N2, Mn2N, MnN, MnN2 and MnN4. Four of these compounds are classified as solid materials. Description of the main results of the study In the thesis, a new structure in the Mn-N system was predicted for the first time, and dynamic stability was established for Mn-B and Mn-N systems by calculating phonon spectra. The stability fields of the MnxBy and MnxNy structures found are determined, which indicate which stoichiometries are stable over the entire pressure range of 0-200 GPa and which stoichiometries decompose into isochemical mixtures, being unstable at certain pressures. Substantiation of the novelty and importance of the results obtained The main results obtained by the author are new: 1. For the first time, all phase relationships of intermediates in Mn–B and Mn–N systems were calculated and corresponding P–T diagrams were constructed. 2. One new manganese nitride Mn5N2 was predicted, which stabilizes above 180 GPa and has a C2/m structure. 3. It was found that a new high-baric MnN phase recently experimentally synthesized above ~55 GPa should have a distorted structure of the NiAs type of rhombic symmetry (Pnma). 4. For the first time, the mechanical properties of all intermediate compounds in Mn–B and Mn–N systems were evaluated. Compliance with the directions of scientific development or state programs The dissertation work corresponds to the priority directions of science development that are being implemented in the Republic of Kazakhstan and contains new scientifically based theoretical results, the totality of which is important for the development of the studied scientific directions. Description of the Applicant’s Contribution to Each Publication All theoretical calculations presented in the dissertation were performed personally by the author, with the participation of staff members of the Laboratory of Experimental Geochemistry and Mantle Petrology of the Earth at Novosibirsk State University and the Laboratory of Phase Transformations and Phase Diagrams of Earth Materials at High Pressures of the V.S. Sobolev Institute of Geology and Mineralogy of the Siberian Branch of the Russian Academy of Sciences. Processing and analysis of the results were carried out jointly with the scientific advisors. Based on the materials of the dissertation research, three articles have been published in peer-reviewed scientific journals indexed in the international databases Web of Science and Scopus: 1.Sagatov N., Bazarbek A., Omarkhan S., Akilbekov A., Sagatova D. Structure searching and phase relationships in MnN up to 50 GPa: a DFT study. Physical Chemistry Chemical Physics, 2024, Vol. 26, p. 28947. (Q2 quartile) 2.Bazarbek A., Sagatov N., Omarkhan S., Sagatova D., Akilbekov A. High-pressure stability and mechanical properties of manganese nitrides: A DFT study. Computational Materials Science, 2025, Vol. 14 (8), 730, pp. 1–13. (Q2 quartile) 3. Bazarbek A., Sagatov N., Omarkhan S., Sagatova D., Bekker T., Akilbekov A. DFT investigation of Mn–B compounds under high pressures: Thermodynamic stability and mechanical properties. Vacuum, 2026, Vol. 243, p. 11843. (Q2 quartile) Approbation of the Dissertation The results of the dissertation research were presented in two abstracts and oral presentations published in the proceedings of international scientific conferences: – International Scientific Conference of Students and Young Scientists “Science and Education – 2023” (Astana, 2023); – International Scientific Conference of Students and Young Scientists “Farabi Alemi – 2023” (Almaty, 2023). Structure and Scope of the Dissertation The dissertation consists of an introduction, three chapters, a conclusion, and a list of references. The total length of the dissertation is 132 typewritten pages and includes 50 figures, 24 tables, and 236 references.

Dissertation

List of Scientific Works

Consultant's Review

Foreign Consultant's Review

Conclusion of the Research Ethics Committee

Official Reviewer's Review

Official Reviewer's Review