Scopus İndeksli Yayınlar Koleksiyonu
Permanent URI for this collectionhttps://hdl.handle.net/20.500.12573/395
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Article Tuning Properties of Amorphous Boron Via Hydrogenation: An Ab Initio Study(Elsevier, 2026-01) Durandurdu, MuratAb initio simulations are employed to investigate the structural, mechanical, and electronic properties of hydrogenated amorphous boron (a-B:H) across a range of hydrogen concentrations (approximate to 6-21 at.%). The results indicate that pentagonal-like boron clusters constitute the primary structural motifs. The bonding environment consists of both B-H terminal bonds and B-H-B bridging bonds, with the fraction of bridging bonds ranging from 10 % to 16 %. Increasing the hydrogen content leads to a reduction in density and bulk modulus, accompanied by a systematic widening of the electronic band gap. These results demonstrate that hydrogen incorporation profoundly modifies the atomic structure, softens the network, and enhances the semiconducting character of a-B:H, highlighting the tunability of properties in boron-based amorphous materials.Article Pressure-Driven Structural Evolution of Amorphous InN(Elsevier, 2025-02) Durandurdu, MuratThrough constant-pressure ab initio simulations, we have uncovered high-pressure phase transformations in amorphous indium nitride for the first time. Our results reveal a distinct two-step progression under compression. Initially, a polyamorphic transition occurs, where the low-density amorphous (LDA) phase transforms into a high-density amorphous (HDA) phase. This HDA structure remains stable in some pressure range and then crystallization initiates, leading to a rocksalt configuration. Upon decompression, the HDA phase reverts to an amorphous network with a slightly higher density and coordination number than the initial LDA state.Article Citation - WoS: 10Citation - Scopus: 11Liquid Boron and Amorphous Boron: An Ab Initio Molecular Dynamics Study(Elsevier, 2015-06) Durandurdu, MuratThe atomic structure of liquid and amorphous boron is investigated using an ab initio molecular dynamics technique. Liquid and amorphous states are found to have notably different microstructures and an average coordination number. Ideal and defective pentagonal pyramidal polyhedrons are the primary building unit of liquid boron but B-12 icosahedra do not exist in the liquid state. During the rapid solidification, more ideal pentagonal pyramids develop progressively, resulting into a gradual formation of B-12 icosahedra. On the basis of our findings, the atomic packing of pure amorphous boron is proposed to be somewhat close to that of the alpha-rhombohedral phase in contrast to the previous suggestions. (C) 2015 Elsevier B.V. All rights reserved.Editorial Citation - WoS: 4Citation - Scopus: 5Hydrogenated Amorphous Boron Nitride: A First Principles Study(Elsevier, 2018-12) Uchoyuk, Tevhide Ayca; Durandurdu, MuratThe influence of hydrogenation on the atomic structure and electronic properties of amorphous boron nitride (alpha-BN) is investigated by using an ab-initio molecular dynamics technique. The structural evaluation of alpha-BN and the hydrogenated (alpha-BN:H) models with four different hydrogen concentrations reveals that although their short-range order is mainly similar to each other, hydrogenation yields some noticeable amendments on the local structure of alpha-BN. Hydrogenation suppresses the formation of twofold coordinated chain-like structures and tetragonal-like rings and leads to more sp(2) and even sp(3) hybridizations. It is also observed that the formation of N-H bonding is more favorable than that of the B-H bonding in the alpha-BN:H configurations. Furthermore hydrogenation is found to have an insignificant impact on the electronic structure of alpha-BN.Article Boron-Rich Amorphous Boron Oxides From Ab Initio Simulations(Elsevier, 2023-03) Karacaoglan, Aysegul Ozlem Cetin; Durandurdu, MuratAmorphous boron oxide (BxO1-x, 0.5 <= x <= 95) configurations are simulated by means of an ab initio molecular dynamics technique and their microstructure and mechanical properties are revealed in details. With increasing B content, the average B-coordination noticeably increases from 3.18 to 5.62 whereas the O-coordination, sur-prisingly, remains almost null, about 2.0. The formation of complete B12 molecules is observed after 80% B concentrations. Chemical segregation is witnessed in most models and hence the resulting configurations show B: B2O3 phase separations. The mechanical properties (bulk, shear and Young moduli, Vickers hardness and microhardness) substantially increase with increasing B content. The amorphous materials (BxO1-x, x >= 80) are classified as hard materials. Within the limitations of DFT calculations and approaches used, we speculate that there is a ductile-to-brittle transition at around 70-75% B contents.Article Citation - WoS: 3Citation - Scopus: 4An In-Depth Investigation of Mg-Zn Metallic Glasses: A First Principles Study(Elsevier, 2018-10) Erkartal, Mustafa; Durandurdu, MuratThe atomic structures, glass forming evolutions, mechanical properties and high pressure behavior of Mg75Zn20Ca5 and Mg60Zn35Ca5 bulk metallic glasses, which are promising candidates for biomedical implants, have been examined by using ab initio molecular dynamics simulations. The pair-distribution function and coordination number analyses show that increasing Zn content in the alloy results in a decrease in several bond distances and an increase in the total coordination number of each species due to the atomic size difference between Mg and Zn atoms. According to the Voronoi tessellation, bond pair and bond angle distribution analyzes, the fivefold geometrical arrangements (pentagonal-bipyramid) are the most predominant in the first coordination shell, indicating the stability of the amorphous states and their dense atomic packing. The most striking result emerged from the calculations of mechanical properties is that an increase of Zn (>= 30%) content in the alloy yields embrittlement in the alloys. Under uniaxial compressions, both compositions undergo structural failure between 6 and 8 GPa. Under hydrostatic pressure, a diminishing in fcc/hcp ordering and an enlargement of the ideal icosahedral ordering may indicate a more disordered structure. In our view, these results represent a good step toward understanding the atomic structures Mg-Zn-Ca bulk metallic glasses.Article Citation - WoS: 2Citation - Scopus: 2Amorphous Silicon Triboride: A First Principles Study(Elsevier, 2020-05) Ozlem, Aysegul; Karacaoglan, Cetin; Durandurdu, Murat; Çetin Karacaoğlan, Ayşegül ÖzlemUsing ab initio molecular dynamics simulations, an amorphous silicon triboride (a-SiB3) network is generated and its atomic structure, electronic features and mechanical properties are compared with those of the crystal. The average coordination number of B and Si atoms in a-SiB3 is found as 5.8 and 4.6, correspondingly, close to 6.0 (B atom) and 5.0 (Si atom) in the crystal. A careful investigation reveals partial structural similarities around B atoms but not around Si atoms in both phases of SiB3. The presence of B-12, B11Si and B-10 molecules is witnessed in a-SiB3. The last two molecules, however, do not exist in the crystal. a-SiB3 is a semiconducting material. The bulk modulus of the ordered and disordered structures is projected to be 151 GPa and 131 GPa, respectively. The Vickers hardness of a-SiB3 is calculated to be similar to 13-15 GPa, less than similar to 20-25 GPa estimated for the crystal.Article Citation - WoS: 1Citation - Scopus: 1Amorphous Magnesium Silicide(Elsevier, 2018-10) Durandurdu, MuratA first principles molecular dynamics technique is employed to generate an amorphous magnesium silicide (Mg2Si) model from its liquid state and its structural, electrical and mechanical features are disclosed for the first time. Si atoms form predominantly the standard square dodecahedron-like and the tri-capped trigonal prism-like configurations while Mg atoms arrange themselves primarily in higher coordinated crystal-like and icosahedrallike polyhedrons. The mean coordination number of Mg and Si is estimated to be similar to 12.84 and similar to 8.2, respectively. Si-Si homopolar bonds are also presented in the amorphous network, in contrast to the crystal. Based on our findings, we propose that the amorphous model has a short-range order, quite different than that of the anti fluorite Mg2Si crystal but similar to that of metallic glasses. The different local structure of the amorphous state yields distinct electronic and mechanical properties, relative to the crystal. Within the known limitation of DFT-GGA simulations, the amorphous Mg2Si is found to be semimetal though the anti-fluorite structure is semiconductor. Furthermore, amorphous Mg2Si is predicted to be less brittle than the crystal structure. Since the potential use of the Mg2Si crystal as a biodegradable implant material is hindered because of its brittle behavior, here we propose that amorphous or nanoglass forms might eliminate this limitation of Mg2Si and hence it can serve as an implant material in near future.Article Citation - WoS: 1Citation - Scopus: 1Amorphous GaN: Polyamorphism and Crystallization at High Pressure(Elsevier, 2024-05) Durandurdu, MuratEmploying constant pressure ab initio simulations, we have shed light on the previously unknown high-pressure behavior of amorphous gallium nitride. Our findings reveal a two-step transformation sequence under pressure. The initial transition involves a polyamorphic transformation from a low-density amorphous (LDA) phase to a high-density amorphous (HDA) phase with an average coordination number of 5.4. Upon pressure release, the HDA state partially reverts to a denser amorphous network with a higher coordination number (4.34) compared to the original LDA phase. Further pressurization triggers the crystallization of the HDA state into a rocksalt structure. Remarkably, the electronic structure of the amorphous forms of GaN exhibits insignificant sensitivity to changes in coordination number, maintaining a band gap of approximately 1.7-2.0 eV across all phases.Article Citation - WoS: 3Citation - Scopus: 3Amorphous Carbon Nitride (C3N4)(Elsevier, 2024-05) Durandurdu, MuratThis detailed investigation employs an ab initio approach to explore the atomic structure and electronic properties of an amorphous carbon nitride (C3N4) model. The model, designed with an exact 3:4 ratio, is based on an amorphous boron nitride configuration. The study reveals crucial insights into the mean coordination number for C and N atoms within the amorphous structure. With values of 2.95 for C atoms and 2.21 for N atoms, these coordination numbers closely resemble those observed in graphite -like crystals. The local structure of the amorphous network exhibits similarities to the triazine-based graphitic C3N4 crystal and is notably devoid of homopolar bonds. The estimated band gap for the amorphous C3N4 model is 1.2 eV, representing a significant reduction compared to the crystal structure, which exhibits a band gap of about 2.93 eV as determined through GGA+U calculations.