WoS İndeksli Yayınlar Koleksiyonu
Permanent URI for this collectionhttps://hdl.handle.net/20.500.12573/394
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Article Pressure-Induced Polyamorphic Transition and Stepwise Ordering to Superhard B-Doped Diamond-like BC3(Elsevier Science SA, 2026-04) Durandurdu, MuratWe employ constant-pressure ab initio molecular dynamics simulations to investigate the pressure-induced phase transformations of amorphous BC3, which initially possesses a graphite-like layered structure. Our simulations reveal a first-order polyamorphic transition marked by a significant volume collapse and an increase in atomic coordination from a predominantly sp(2) network to a dense, tetrahedrally coordinated sp(3) network. Subsequent thermal annealing of the high-pressure phase uncovers a multi-step ordering process involving a metastable paracrystalline intermediate that bridges the high-density amorphous state and a thermally induced boron-doped diamond-like phase. All high-pressure phases are quenchable to ambient conditions, importantly retaining their semiconducting electronic structures across these transformations. Mechanical characterization demonstrates substantial stiffening, with bulk moduli ranging similar to 252 to 323 GPa. These findings illuminate novel and accessible routes to superhard semiconducting BC3 phases stabilized by pressure and temperature, with the boron-doped diamond-like phase identified as a metastable superhard semiconductor that is thermodynamically favored over the amorphous precursor but kinetically accessible only via the stepwise pathway described. This offers promising directions for advanced material design under extreme conditions.Article Densification-Induced Chemical Reorganization and Mechanical Enhancement in Amorphous Si2BC3N(Elsevier, 2026-02) Durandurdu, MuratThe atomistic mechanisms that govern the mechanical performance of amorphous silicon-boron carbonitride (SiBCN) ceramics remain insufficiently understood, particularly regarding the role of density. Here, we employ ab initio molecular dynamics simulations to elucidate the structural evolution and mechanical response of low-density (LDA, 2.20 g/cm3) and high-density (HDA, 2.53 g/cm3) amorphous Si2BC3N prepared via melt-quench. The HDA phase exhibits markedly higher atomic packing and network connectivity, accompanied by a nontrivial chemical reorganization. Densification significantly enhances heteronuclear bonding-especially Si-C coordination-while suppressing C-C and Si-Si homopolar bonds. These changes yield substantial mechanical strengthening: the HDA phase exhibits a 48% increase in bulk modulus (130 GPa vs. 88 GPa), along with elevated Young's (266 GPa) and shear (112 GPa) moduli. Our findings reveal a clear density-structure-property relationship in amorphous SiBCN, demonstrating that densification suppresses weak self-bonded motifs and promotes a robust, interconnected atomic network. This insight provides a pathway for designing high-performance amorphous SiBCN ceramics for extreme-environment applications.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 Citation - WoS: 3Citation - Scopus: 3Theoretical Investigation of Substituent Effects on the Relative Stabilities and Electronic Structure of [BnXn]2- Clusters(Springer, 2021-11-29) Tahaoglu, Duygu; Alkan, Fahri; Durandurdu, MuratIn this study, we provide a theoretical evaluation of relative stabilities and electronic structure for [BnXn](2-) clusters (n = 10, 12, 13, 14, 15, 16). Structural and electronic characteristics of [BnXn](2-) clusters are examined by comparison with the [B12X12](2-) counterparts with a focus on the substituent effects (X = H, F, Cl, Br, CN, BO, OH, NH2) on the electronic structure, electron detachment energies, formation enthalpies, and charge distributions. For the electronic structure and electron detachment energies, substituent effects on boron clusters are shown to follow a very similar trend to the mesomeric and inductive effects (+/- M and +/- I) of pi-conjugated systems, and the most stable derivatives in terms of HOMO/LUMO and electron detachment energies are calculated for CN and BO substituents due to strong -M effects. In the case of formation enthalpies for larger boron clusters (n >= 13), the icosahedral barrier is shown to increase with the halogen and CN substitution, whereas it is possible to reduce the icosahedral barrier for the cases of X = OH and NH2. It is shown that this reduction results from destabilizing the [B12X12](2-) cluster with electronic (+ M) and symmetry effects induced by OH and NH2 ligands.Article Citation - WoS: 5Citation - Scopus: 5Structural and Electronic Transformations of GeSe2 Glass Under High Pressures Studied by X-Ray Absorption Spectroscopy(Natl Acad Sciences, 2024-03-27) Mijit, Emin; Durandurdu, Murat; Rodrigues, Joao Elias F. S.; Trapananti, Angela; Rezvani, S. Javad; Rosa, Angelika Dorothea; Di Cicco, Andrea; Javad Rezvani, S.Pressure-induced transformations in an archetypal chalcogenide glass (GeSe2) have been investigated up to 157 GPa by X-ray absorption spectroscopy (XAS) and molecular dynamics (MD) simulations. Ge and Se K-edge XAS data allowed simultaneous tracking of the correlated local structural and electronic changes at both Ge and Se sites. Thanks to the simultaneous analysis of extended X-ray absorption fine structure (EXAFS) signals of both edges, reliable quantitative information about the evolution of the first neighbor Ge-Se distribution could be obtained. It also allowed to account for contributions of the Ge-Ge and Se-Se bond distributions (chemical disorder). The low-density to high-density amorphous-amorphous transformation was found to occur within 10 to 30 GPa pressure range, but the conversion from tetrahedral to octahedral coordination of the Ge sites is completed above similar to 80 GPa. No convincing evidence of another high-density amorphous state with coordination number larger than six was found within the investigated pressure range. The number of short Ge-Ge and Se-Se "wrong" bonds was found to increase upon pressurization. Experimental XAS results are confirmed by MD simulations, indicating the increase of chemical disorder under high pressure.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 Pressure-Induced Quenchable Superhard Tetrahedral Amorphous Phase of BC4N(Wiley, 2025-03-13) Durandurdu, MuratThe 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 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 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.