Scopus İndeksli Yayınlar Koleksiyonu
Permanent URI for this collectionhttps://hdl.handle.net/20.500.12573/395
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Article Citation - WoS: 6Citation - Scopus: 6Two Successive Amorphous-to Phase Transformations in TiO2(Wiley, 2017-05-22) Durandurdu, MuratBased on constant pressure ab initio simulations, we propose, for the first time, two successive amorphous-to-amorphous phase transformations for TiO2. The first one is a gradual phase transformation from a low-density amorphous phase to a high-density amorphous phase, whereas the second one is a first-order phase transformation from the high-density amorphous phase to a very high-density amorphous phase. The low-density amorphous to high-density amorphous phase change is irreversible, whereas the high-density amorphous to very high-density amorphous phase transformation is reversible. The high-density amorphous and very high-density amorphous phases consist of differently coordinated configurations. The sevenfold and ninefold-coordinated arrangements formed in amorphous TiO2 under pressure are similar to the main building motif of the baddeleyite and cotunnite polymorphs of TiO2, respectively, while the eightfold-coordinated configuration is different from the local structure of the cubic TiO2 phase. The electronic structure calculations suggest that both dense amorphous phases present a semiconducting character with a band gap energy less than that of the original low-density amorphous phase.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: 1Citation - Scopus: 1Pressure-Induced Phase Transformations in Amorphous Arsenic(Elsevier Science Bv, 2016-04) Durandurdu, MuratThe atomic structure of amorphous arsenic and its response to high pressure are explored using a constant pressure ab initio molecular dynamics technique. Different analyzing techniques reveal that amorphous arsenic has a local structure close to that of the crystalline phase. The model also presents some twofold and fourfold coordination defects. The existence of a possible amorphous to amorphous phase transition for arsenic is proposed on the bases of the observation of a gradual coordination increase with the application of pressure. Further compression of the amorphous state yields a transformation into a simple cubic crystal. (C) 2016 Elsevier B.V. All rights reserved.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: 5Citation - Scopus: 4Densification of Amorphous Boron Under Pressure(Elsevier, 2017-09) Durandurdu, MuratThe densification mechanism of amorphous boron under pressure is investigated using a constant pressure ab initio technique and found to be associated with two consecutive amorphous-to-amorphous phase transformations. Amorphous boron gradually transforms into a high density amorphous phase, followed by a first order phase transformation into another high density amorphous state. The high density amorphous phases of boron are not quenchable to ambient pressure. Most quasimolecular B-12 icosahedra in the model are found to be stable at the highest the theoretical pressure of 280 GPa reached in the present work and thus the phase transformations are principally due to the re-structural arrangements in the parts of the model connecting B-12 icosahedra.