WoS İndeksli Yayınlar Koleksiyonu
Permanent URI for this collectionhttps://hdl.handle.net/20.500.12573/394
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Article Citation - WoS: 4Citation - Scopus: 4Very Low Density Amorphous Phase of Zircon(Elsevier Science Bv, 2019-06) Bolat, Suleyman; Durandurdu, MuratUsing 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: 1Citation - Scopus: 1Solute Aggregation in Ca72Zn28 Metallic Glass(Elsevier Science Bv, 2018-11) Tahaoglu, Duygu; Durandurdu, MuratSolidification of the Ca72Zn28 melt is achieved by using both the thermal quenching and rapid pressurizing techniques in ab initio molecular dynamics simulations within a generalized gradient approximation. A chemical segregation process is perceived in the Ca72Zn28 system and hence the resulting configurations show nanosized glassy domains with different compositions. The structural and mechanical properties of both Ca72Zn28 metallic glasses have been probed by using various analyzing methods. Although the mean coordination number of the both models is found to be fairly close to each other, a careful investigation exposes that they have a different short-range order around Zn atoms. It appears that pressurizing significantly affects the environment of Zn atom, suppresses the occurrence of Zn-centered ideal icosahedral polyhedrons and retains the Zn centered tri-capped trigonal prism like configurations. On the other hand, the impact of pressure on the environment of Ca atoms is found to be not too drastic. The computer-generated models represent slightly different mechanical properties. The model obtained using the rapid pressurizing technique is stiffer than the one produced using the thermal quenching technique.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 Citation - WoS: 4Citation - Scopus: 4Permanent Densification of Amorphous Zinc Oxide Under Pressure: A First Principles Study(Elsevier Science Bv, 2018-02) Tahaoglu, Duygu; Durandurdu, MuratAb initio simulations within a generalized gradient approximation are carried out to investigate the densification mechanism of amorphous zinc oxide (a-ZnO) under hydrostatic pressure. In contrast to the crystalline ZnO, the densification of a-ZnO is found to proceed gradually and is associated with a structural modification from a low density amorphous state to a high density amorphous state. Accompanied by the phase transformation, the mean coordination number increases from similar to 4.0 to similar to 5.5. The high-density amorphous form of ZnO has a local structure, partially comparable with that of the rocksalt type ZnO crystal and presents a semiconducting behavior. The phase change is irreversible because upon pressure release, an amorphous model largely consisting of fivefold coordination is recovered. The decompressed model can be, therefore, classified as an intermediate phase between the wurtzite-like and the rocksalt-like amorphous configurations.Article Citation - WoS: 3Citation - Scopus: 2Local Structure of As2O3 Glass From First Principles Simulations(Elsevier Science Bv, 2016-03) Durandurdu, MuratWe model As2O3 glass from the liquid state using ab initio molecular dynamics simulations and probe its atomic structure using various analyzing techniques. The model is almost free from coordination and chemical defects and has an average coordination number of 238. The AsO3 pyramids are randomly connected via corner sharing to form the glass state. The glass network presents six membered hexagonal-like rings similar to those formed in the As4O6 molecules but isolated or complete As4O6 molecules do not exist. The glass state mainly consists of layer-like and incomplete As4O6-like structures. (C) 2016 Elsevier B.V. All rights reserved.Article Citation - WoS: 17Citation - Scopus: 17Hexagonal Nanosheets in Amorphous BN: A First Principles Study(Elsevier Science Bv, 2015-11) Durandurdu, MuratAmorphous boron nitrite is modeled by means of first principles molecular dynamics simulations and found to be almost chemically ordered in a stark contrast to the previous predictions. Its average coordination number is 2.97. The main building unit of the amorphous network is hexagonal rings as in the most stable boron nitrite phase but chain-like structures and tetragonal-like rings also exist in amorphous network. The model consists of partially hexagonal nanosheets and hence it is not entirely disordered. Amorphous boron nitrite has a band gap energy of about 2.0 eV. (C) 2015 Elsevier B.V. All rights reserved.Article Citation - WoS: 7Citation - Scopus: 7Atomic Structure of Amorphous CDO from First Principles Simulations(Elsevier Science Bv, 2015-03) Durandurdu, MuratAmorphous 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.