Scopus İndeksli Yayınlar Koleksiyonu
Permanent URI for this collectionhttps://hdl.handle.net/20.500.12573/395
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Article Citation - WoS: 3Citation - Scopus: 3Stoichiometric Amorphous Boron Carbide (BC)(Springer, 2020-07-17) Yildiz, Tevhide Ayca; Durandurdu, MuratIn this work, a stoichiometric amorphous boron carbide (a-BC) network is constructed via an ab initio molecular dynamics approach. Its structural, electrical and mechanical features are reconnoitered in details and compared with those of turbostratic BC and some important graphite-like amorphous materials. Our computer-generated structure exhibits strong chemical disorder as seen in turbostratic BC. However, it has mixed sp(2) and sp(3) hybridizations and the average coordination number of B and C atoms is projected to be similar to 3.22 and 3.46, correspondingly. Consequently, a-BC appears to be structurally different from turbostratic BC and graphite-like amorphous systems. a-BC is semiconductor having a theoretical band gap of similar to 0.20 eV. The bulk, Young's and shear moduli are estimated as similar to 105, 142 and 56 GPa, respectively. Its Vickers hardness is calculated to be about 7-8.5 GPa. a-BC is anticipated to be electronically and mechanically parallel to amorphous boron carbonitride.Article Citation - WoS: 1Citation - Scopus: 1Quenchable Amorphous Diamond: A Novel High-Pressure Route to Tetrahedral Amorphous Carbon(Wiley-VCH Verlag GmbH, 2025-05-03) Durandurdu, MuratThis study presents a groundbreaking theoretical prediction: the high-pressure transformation of amorphous graphite into a high-fraction sp3-bonded amorphous diamond phase. Employing ab initio molecular dynamics simulations, it is demonstrated that under extreme pressures, amorphous graphite undergoes an irreversible transition to an amorphous diamond phase. Thermodynamic analysis confirms the first-order nature of this sp2-to-sp3 transformation, with the transition predicted to occur at approximate to 33 GPa under experimental conditions. This transformation offers a novel pathway toward the synthesis of amorphous carbon with a high fraction of sp3 bonding, a long-standing challenge in materials science. This work expands understanding of carbon's high-pressure behavior and provides a compelling theoretical foundation for future experimental investigations aimed at synthesizing and characterizing this novel material.Article Citation - WoS: 29Citation - Scopus: 31Pressure-Induced Amorphization, Mechanical and Electronic Properties of Zeolitic Imidazolate Framework (ZIF-8)(Elsevier Science SA, 2020-01) Erkartal, Mustafa; Durandurdu, MuratAb initio molecular dynamics (AIMD) simulations are carried out to probe the high-pressure behavior of ZIF-8 over wide pressure-range. Under compression, the enormous distortions in the ZnN4 tetrahedral units lead to a crystal-to-amorphous phase transition at around 3 GPa. During the amorphization process, the Zn-N coordination is retained. No other phase change but a possible fracture of the system is proposed above 10 GPa. Depending on released pressures, amorphous states with different densities are recovered. Yet when the applied pressure is released just before the amorphization, the rotations of imidazolate linkers (swing effect) cause an isostructural crystal-to-crystal phase transition, in agreement with experiments. In the tensile regime, no phase transition is perceived up to -2.75 GPa at which point the structural failure is observed. The crystal-amorphous phase transitions are also discovered at around 4 GPa under uniaxial compressions. The amorphous structures formed under uniaxial stress are about 20% denser than the one formed under the hydrostatic pressure. The average Young's modulus and Poisson's ratio of ZIF-8 are estimated to be around 5.6 GPa and 0.4, respectively. Interestingly, the tensile strength of ZIF-8 is found to be about 50% greater than its compressive strength. This paper shows that the experimentally observed phase transitions can be successfully reproduced with a clear explanation about the transition mechanism(s) at the atomistic level and all mechanical properties can be accurately calculated for a given ZIF structure by using AIMD simulations.Article Citation - WoS: 3Citation - Scopus: 3New High-Pressure Phase of MgH2: An Ab Initio Constant-Pressure Study(IOP Publishing Ltd, 2014-02-01) Durandurdu, MuratThe stability of magnesium hydride (MgH2) at high pressure is studied using a constant-pressure ab initio technique. Two phase transformations are successfully observed through the simulations. The rutile structure undergoes a phase transformation into a CaCl2-type phase. Further increase in pressure results into a first-order phase transition into an orthorhombic state within Pbcm symmetry. This phase can be considered as a distorted CsF2-type crystal and does not correspond to the previously proposed MgH2 phases. The transformation mechanism of the CaCl2-Pbcm phase change at the atomistic level is successfully characterized and it is found that the CaCl2-to-Pbcm phase change proceeds via an ideal CaF2-type intermediate phase. These phase transformations are also analyzed using total energy-volume calculations.Copyright (C) EPLA, 2014Article Citation - WoS: 1Citation - Scopus: 1Atomic Structure and Properties of Amorphous Boron Carbon Nitride (BC2N): An Ab Initio Study(Elsevier Science SA, 2025-03) Durandurdu, MuratThis study investigates the atomic structure and properties of amorphous boron carbon nitride (a- BC2N) using ab initio molecular dynamics simulations. Structural analysis reveals a layer-like topology with varied bonding environments. Unlike the ordered alternating C-C and B-N layers found in the lowest-energy crystalline BC2N structure, a-BC2N features a solid-solution-like arrangement, with B, C, and N atoms randomly distributed within each layer. This randomness gives rise to small, distinct C-rich and BN-rich domains and irregular short zigzag chains of C-C and B-N bonds within each layer. Electronic structure analysis suggests that a-BC2N is likely a semiconductor. Mechanically, a-BC2N displays properties typical of layered materials but with an enhanced bulk modulus.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: 1Citation - Scopus: 1Amorphous Zircon at High Pressure(Pergamon-Elsevier Science Ltd, 2021-06) Bolat, Suleyman; Durandurdu, MuratThe high-pressure behavior of a very low-density amorphous zircon model having Zr (Si) coordination of 5.6 (4.02) is explored by ab initio simulations. Two consecutive pressure-induced phase modifications are proposed for this material. The first transition is from a very low-density amorphous state to a dense amorphous state having Zr (Si) coordination of 7.3 (4.5). The second one is from the dense phase to a high-density amorphous structure with Zr and Si coordination numbers of about 8 and 5.5, correspondingly. Both phase changes proceed progressively. The first phase transformation is irreversible whist the second one is reversible. The Voronoi polyhedron analysis reveals the presence of polyhedron of the zircon crystal (<0,4,4,0>), the zirconia baddaliyette phase (<1,3,3,0>) and the zirconia cotunnite state (<0,3,6,0>) around Zr atoms in the amorphous states formed on both compression and decompression, meaning that the amorphous configurations consist of a mixed state of them.Article Amorphous Silicon Nanoparticles and Silicon Nanoglasses From Ab Initio Simulations(Springer, 2024-04-26) Bolat, Suleyman; Durandurdu, MuratThe structural and electrical characteristics of spherical amorphous silicon nanoparticles (Si-NPs) with radii ranging from 9 to 15 & Aring;, and silicon nanoglasses (Si-NGs) formed by compressing identical-sized Si-NPs, are being investigated for the first-time using ab initio simulations. Analysis reveals predominantly fourfold coordination within Si-NPs, accompanied by noticeable coordination defects. The prevalence of fourfold coordination increases with increasing Si-NP size. Si-NGs, while exhibiting similar dominant fourfold coordination, possess a small fraction of coordination defects (5-8%) primarily concentrated at the interfaces of compressed Si-NPs. Si-NGs are found to have a more open structure compared to amorphous Si. This structural variation, along with observed distortions within Si-NGs, is hypothesized to contribute to a significant narrowing of their band gaps relative to amorphous Si.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.Correction Amorphous Boron Carbide From Ab Initio Simulations(Elsevier, 2023-01) Yildiz, Tevhide Ayca; Durandurdu, Murat