WoS İndeksli Yayınlar Koleksiyonu

Permanent URI for this collectionhttps://hdl.handle.net/20.500.12573/394

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Citation - WoS: 2
Citation - Scopus: 2
Amorphous Boron Carbonitride (BC4N) From Ab Initio Simulations
(Elsevier, 2024) Durandurdu, Murat
This study utilizes ab initio molecular dynamics simulations to explore the structure and properties of amorphous boron carbonitride (a-BC4N). A 432-atom model, generated via a conventional melt-and-quench technique, exhibits a graphite-like structure with all elements possessing an average coordination number of about 3.0. C atoms dominate within individual layers, interspersed with distinct BN domains. This atomic arrangement deviates considerably from that proposed for crystalline BC4N structures. Despite this structural variation, the aBC4N model is likely a narrow band gap semiconductor (0.15 eV), similar to its crystalline counterparts. In terms of mechanical properties, a-BC4N demonstrates similarities with various layered materials while exhibiting a notably larger bulk modulus.
Citation - WoS: 2
Citation - Scopus: 2
Amorphous Boron Phosphide: An Ab Initio Investigation
(Elsevier, 2021) Bolat, Suleyman; Durandurdu, Murat
We generate a structural model of amorphous boron phosphide (BP) by quenching the melt via ab initio molecular dynamics calculations and compare it structurally and electrically with the crystal. We find that both phases of BP have a significantly different short-range order. Namely, the amorphous network presents strong chemical disorder and structural defects. P-atoms form only undercoordinated defects while B atoms present both undercoordinated and overcoordinated defects. The mean coordination number of B and P atoms is 4.17 and 3.69, correspondingly. Some of overcoordinated B atoms with chemical disorder yield the formation of pentagonal-pyramid-like motifs and a cage-like B10 cluster in the amorphous network. About 13 % volume expansion is observed by amorphization, probably due to the low-coordinated structural defects. The amorphous configuration is semiconductor as in the crystal but has a smaller energy band gap.
Citation - WoS: 5
Citation - Scopus: 5
Amorphous Silicon Hexaboride at High Pressure
(Taylor & Francis Ltd, 2020) Durandurdu, Murat
We investigate the pressure-induced structural phase transformation of amorphous silicon hexaboride (a-SiB6) using a constant pressure first principles approach. a-SiB6 is found to undergo a gradual phase transformation to a high-density amorphous phase (HDA) in which the average coordination number of both B and Si atoms is about 6. The HDA phase consists of differently coordinated motifs ranging from 4 to 8. B-12 icosahedra are found to persist during compression of a-SiB6 and the structural modifications primarily occur around Si atoms and in the regions linking pentagonal pyramid-like configurations to each other. Upon pressure release, an amorphous structure, similar to the uncompressed one, is recovered, indicating a reversible amorphous-to-amorphous phase change in a-SiB6. When the electronic structure is considered, the HDA phase is perceived to have a wider forbidden band gap than the uncompressed one.
Citation - WoS: 3
Citation - Scopus: 3
Amorphous Silicon Hexaboride: A First-Principles Study
(Taylor & Francis Ltd, 2018) Durandurdu, Murat
We report for the first time the atomic structure, electronic structure and mechanical properties of amorphous silicon hexaboride (a-SiB6) based on first-principles molecular dynamics simulation. The a-SiB6 model is generated from the melt and predominantly consists of pentagonal pyramid-like configurations and B-12 icosahedral molecules, similar to what has been observed in most boron-rich materials. The mean coordination number of B and Si atoms are 5.47 and 4.55, respectively. The model shows a semiconducting behaviour with a theoretical bandgap energy of 0.3eV. The conduction tail states are found to be highly localised and hence the n-type doping is suggested to be more difficult than the p-type doping for a-SiB6. The bulk modulus and Vickers hardness of a-SiB6 are estimated to be about 118 and 13-17GPa, respectively.
Citation - WoS: 1
Citation - Scopus: 1
Atomic Structure and Properties of Amorphous Boron Carbon Nitride (BC2N): An Ab Initio Study
(Elsevier Science SA, 2025) Durandurdu, Murat
This 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.
Citation - WoS: 7
Citation - Scopus: 7
Atomic Structure of Amorphous CDO from First Principles Simulations
(Elsevier Science Bv, 2015) Durandurdu, Murat
Amorphous CdO (a-CdO) is obtained by cooling the liquid at a sufficiently fast cooling rate using first-principles simulations. The topology of the amorphous model is examined using a variety of analyzing techniques. The local structural arrangement of a-CdO is found to be partially similar to that of crystalline phase. The model is chemically ordered but consists of a significant amount of coordination defects. a-CdO is predicted to be a semiconductor with a band gap energy less than the crystalline state. It is likely that a-CdO might serve as a novel electronic material. (C) 2015 Elsevier B.V. All rights reserved.
Boron-Rich Amorphous Boron Oxides From Ab Initio Simulations
(Elsevier, 2023) Karacaoglan, Aysegul Ozlem Cetin; Durandurdu, Murat
Amorphous 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.
Citation - WoS: 2
Citation - Scopus: 2
A First Principles Study of Amorphous and Crystalline Silicon Tetraboride
(Elsevier Science SA, 2021) Karacaoglu, Ayseguel Ozlem; Durandurdu, Murat
Using first principles simulations, we generate an amorphous silicon tetraboride (SiB4) network from the melt and compare it structurally, mechanically and electrically with the crystal. Surprisingly the amorphous form is found to be energetically more favourable than the crystal. In both phases, the average coordination number of B atoms is comparable but that of Si atom is considerably different. Si atoms have a trend to structure in higher coordinated motifs in the amorphous configuration compared to the crystal. A close examination reveals that pentagonal pyramid-like arrangements are the leading units for B atoms in the noncrystalline state as in the crystal and some of which involve B12 and B11Si type molecules. Both phases exhibit a semiconducting character but have a significantly different band gap value (0.16 eV vs 0.88 eV). The Bulk modulus and Vicker's hardness are predicted to be similar to 151 GPa and 16.1-17.4 GPa for the amorphous network and to be similar to 161 GPa and 18.1-20.2 GPa for the crystal, correspondingly.
Citation - WoS: 3
Citation - Scopus: 3
High-Pressure Phase Transitions of TiN: An Ab Initio Constant Pressure Study
(Taylor & Francis Ltd, 2015) Durandurdu, Murat
An ab initio constant pressure molecular dynamics technique is carried out to explore the behaviour of rock salt-structured titanium nitride (TiN) under pressure. Two successive phase transformations are successfully observed in the dynamical simulations. The first one is an isostructural phase transition accompanied by an anomalous volume compression without any symmetry breaking. The second one is a reconstructive phase transformation into a CsCl-type structure. For the first time, the previously proposed two-phase transformations for TiN are confirmed through the simulations.
Irreversible Changes in Amorphous C3n4 Under Pressure: Loss of Chemical Order and Graphite-Like Character
(Taylor & Francis Ltd, 2025) Durandurdu, Murat
The high-pressure behavior of triazine-based amorphous C3N4, initially exhibiting a chemically ordered, graphite-like structure, was investigated using ab initio molecular dynamics simulations. Our study reveals a pressure-induced transition to a high-density amorphous (HDA) phase characterized by increased coordination number for carbon (3.88) and nitrogen (2.93) atoms. This transition occurs gradually over a broad pressure range, initiated by the breakdown of chemical ordering and the formation of homopolar C-C and N-N bonds, which persist in both the HDA and recovered phases. The recovered phase retains elevated coordination numbers (C: 3.25, N: 2.46) but loses its initial graphite-like topology, evolving into a three-dimensional network structure. Electronic structure analysis reveals semiconducting behavior in the HDA phase and n-type semiconductor characteristics in the recovered phase.
Citation - WoS: 2
Citation - Scopus: 2
MgCu Metallic Glass
(Taylor & Francis Ltd, 2018) Durandurdu, Murat
We generate an amorphous MgCu model using the rapid solidification of the melt through a first-principles molecular dynamics approach within a generalised gradient approximation and reveal, for the first time, its structural features and mechanical properties in details. The liquid and glassy MgCu are found to acquire slightly distinct local structures. Yet in both forms of MgCu, most Cu atoms have a tendency to form the ideal and defective icosahedrons while Mg atoms are arranged in complex configurations. The mean coordination number of Cu and Mg at 300 K is 11.31 and 13.73, respectively. The short-range order of MgCu glass is projected to be different than the known crystalline MgCu and Mg2Cu phases. The mechanical properties of MgCu glass and the CsCl-type MgCu crystal are computed and compared. On the basis of the enthalpy analyses, a possible pressure-induced crystallisation of the MgCu glass into a CsCl-type structure is proposed to occur at around 11 GPa.
Citation - WoS: 2
Citation - Scopus: 2
Possible Boron-Rich Amorphous Silicon Borides From Ab Initio Simulations
(Springer, 2023) Karacaoglan, Aysegul Ozlem Cetin; Durandurdu, Murat
ContextBy means of ab initio molecular dynamics simulations, possible boron-rich amorphous silicon borides (BnSi1-n, 0.5 <= n <= 0.95) are generated and their microstructure, electrical properties and mechanical characters are scrutinized in details. As expected, the mean coordination number of each species increases progressively and more closed packed structures form with increasing B concentration. In all amorphous models, pentagonal pyramid-like configurations are observed and some of which lead to the development of B-12 and B11Si icosahedrons. It should be noted that the B11Si icosahedron does not form in any crystalline silicon borides. Due to the affinity of B atoms to form cage-like clusters, phase separations (Si:B) are perceived in the most models. All simulated amorphous configurations are a semiconducting material on the basis of GGA+U calculations. The bulk modulus of the computer-generated amorphous compounds is in the range of 90 GPa to 182 GPa. As predictable, the Vickers hardness increases with increasing B content and reaches values of 25-33 GPa at 95% B concentration. Due to their electrical and mechanical properties, these materials might offer some practical applications in semiconductor technologies.MethodThe density functional theory (DFT) based ab initio molecular dynamics (AIMD) simulations were used to generate B-rich amorphous configurations.
Pressure-Induced Quenchable Superhard Tetrahedral Amorphous Phase of BC4N
(Wiley, 2025) Durandurdu, Murat
The high-pressure behavior of an amorphous boron carbon nitride (BC4N) composition is investigated using constant-pressure ab initio molecular dynamics simulations. A first-order phase transformation into a tetrahedral amorphous phase with a high fraction of sp3 bonding is observed. This tetrahedral phase is quenchable and exhibits ultra-high incompressibility and a high Vickers hardness (46 GPa), placing it firmly in the category of superhard materials, comparable to tetrahedral amorphous carbon. Tetrahedral amorphous BC4N demonstrates semiconducting behavior with a narrow bandgap of 0.4 eV, making it suitable for applications requiring both mechanical robustness and moderate electronic conductivity. Thermodynamic analyses confirm the likelihood of a first-order sp2-to-sp3 transition, suggesting that such a transformation could occur around 29 GPa under experimental conditions.
Quenchable Amorphous Diamond: A Novel High-Pressure Route to Tetrahedral Amorphous Carbon
(Wiley-VCH Verlag GmbH, 2025) Durandurdu, Murat
This 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.
Tuning Properties of Amorphous Boron Via Hydrogenation: An Ab Initio Study
(Elsevier, 2026) Durandurdu, Murat
Ab 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.

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