Scopus İndeksli Yayınlar Koleksiyonu

Permanent URI for this collectionhttps://hdl.handle.net/20.500.12573/395

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Start date: 2019Subject: search.filters.subject.Amorphous

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Now showing 1 - 10 of 26
  • Article
    Tuning Properties of Amorphous Boron Via Hydrogenation: An Ab Initio Study
    (Elsevier, 2026-01) 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.
  • Article
    Citation - WoS: 4
    Citation - Scopus: 4
    Very Low Density Amorphous Phase of Zircon
    (Elsevier Science Bv, 2019-06) Bolat, Suleyman; Durandurdu, Murat
    Using a reliable ab initio molecular dynamics method, we investigate the rapid solidification of the zircon melt. Accompanied by amorphization, a drastic volume expansion of 27% is perceived. This value is fairly larger than 18% observed in the metamict zircon. Such a large volume swelling leads to a significant decrease in the mean coordination number of Zr atoms, which is about 5.66 and the lowest one reported so far. On the other hand, the volume expansion is found to have almost no impact on the average coordination number of Si atoms i.e., they maintain their tetragonal coordination. As suggested by earlier investigations, the polymerization of SiO4 units is witnessed but our model shows the highest polymerization with respect to the previous simulations. Based on our findings, we propose that our model does not represent the metamict zircon but a very low density amorphous phase of zircon.
  • Article
    Citation - WoS: 6
    Citation - Scopus: 6
    Tetrahedral Amorphous Boron Nitride: A Hard Material
    (Wiley, 2019-09-25) Durandurdu, Murat
    We generate a tetrahedrally coordinated amorphous boron nitride (BN) model by means of first principles molecular dynamics calculations and report its mechanical and electrical properties in detail. The amorphous configuration is almost free from chemical disorder and consists of about 20% coordination defects, similar to tetrahedral (diamond-like) amorphous carbon. Its theoretical band gap energy is about 2.0 eV, less than 4.85 eV estimated for cubic BN. The bulk modulus and Vickers hardness of tetrahedral amorphous BN are computed as 206 GPa and 28-35 GPa, respectively. Based on these findings, we propose that tetrahedral noncrystalline BN can serve as electronic and hard materials as well.
  • Article
    Pressure-Induced Quenchable Superhard Tetrahedral Amorphous Phase of BC4N
    (Wiley, 2025-03-13) 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.
  • Article
    Pressure-Driven Structural Evolution of Amorphous InN
    (Elsevier, 2025-02) Durandurdu, Murat
    Through 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: 2
    Citation - Scopus: 2
    Possible Boron-Rich Amorphous Silicon Borides From Ab Initio Simulations
    (Springer, 2023-03-10) 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.
  • Article
    Citation - WoS: 1
    Citation - Scopus: 1
    Liquid and Amorphous States of Boron Subarsenide
    (Wiley, 2019-08-13) Durandurdu, Murat
    Ab initio molecular dynamics simulations are executed to probe the short-range order and the electrical features of the liquid and amorphous boron subarsenide (B12As2). A drastic volume swelling of similar to 40% is witnessed for the liquid state, relative to the crystal. The density of the melt is found to be close to that of liquid boron. As the temperature applied is gradually decreased, the volume progressively decreases and a glass-transition zone at around 1400 K is observed. About 14% volume expansion is perceived for the amorphous phase. Due to the drastic density (volume) difference between the liquid and amorphous forms, their atomic structure is found to be different from each other. In the liquid phase at 2500 K, the mean coordination number (CN) of B and As atoms is 4.4 and 2.5, correspondingly. During the solidification process, both average CNs steadily increase and reach values of 5.5 (B-atom) and 4.14 (As-atom) at 300 K. The pentagonal pyramid-like motifs barely survive at 2500 K but during the quenching process they develop progressively and some of which lead to the formation of B-12 clusters. In the amorphous state, the chain-like and A7-like As-As clusters are observed. Nonetheless, the noncrystalline state is proposed to be partially similar to the crystalline structure. The liquid state shows a metallic character while the amorphous form presents a semiconducting nature having an energy band gap much smaller than that of the crystalline phase.
  • Article
    Boron-Rich Amorphous Boron Oxides From Ab Initio Simulations
    (Elsevier, 2023-03) 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.
  • Article
    Citation - WoS: 1
    Citation - Scopus: 1
    Atomic Structure and Properties of Amorphous Boron Carbon Nitride (BC2N): An Ab Initio Study
    (Elsevier Science SA, 2025-03) 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.
  • Article
    Citation - WoS: 1
    Amorphous to Amorphous Phase Transformation in Boron-Rich Amorphous Silicon Borides: An Ab Initio Study
    (Taylor & Francis Ltd, 2024-05-24) Karacaoglan, Aysegul Ozlem Cetin; Durandurdu, Murat
    This study employs a constant-pressure ab initio approach to investigate the high-pressure behavior of five distinct boron-rich amorphous silicon borides. A unique amorphous-to-amorphous phase transition is exposed, providing insights into the structural resilience of these materials under extreme conditions. Our results reveal a gradual increase in the coordination number of both B and Si atoms under pressure, with subsequent densification upon pressure release. Yet the recovered amorphous phases closely resemble the uncompressed states, highlighting the reversibility of these phase changes. Significant structural modifications around Si atoms are observed, emphasizing their pivotal role in the observed phase transitions. Additionally, pressure-induced metallization is witnessed in these materials, indicating their distinctive electronic behavior under high pressure. This work significantly contributes to a deeper understanding of the high-pressure behavior of boron-rich amorphous silicon borides and opens avenues for exploring their potential applications in fields requiring exceptional structural stability and unique pressure-dependent properties.