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: 6Tetrahedral Amorphous Boron Nitride: A Hard Material(Wiley, 2019-09-25) Durandurdu, MuratWe 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.Editorial Citation - WoS: 4Citation - Scopus: 5Hydrogenated Amorphous Boron Nitride: A First Principles Study(Elsevier, 2018-12) Uchoyuk, Tevhide Ayca; Durandurdu, MuratThe influence of hydrogenation on the atomic structure and electronic properties of amorphous boron nitride (alpha-BN) is investigated by using an ab-initio molecular dynamics technique. The structural evaluation of alpha-BN and the hydrogenated (alpha-BN:H) models with four different hydrogen concentrations reveals that although their short-range order is mainly similar to each other, hydrogenation yields some noticeable amendments on the local structure of alpha-BN. Hydrogenation suppresses the formation of twofold coordinated chain-like structures and tetragonal-like rings and leads to more sp(2) and even sp(3) hybridizations. It is also observed that the formation of N-H bonding is more favorable than that of the B-H bonding in the alpha-BN:H configurations. Furthermore hydrogenation is found to have an insignificant impact on the electronic structure of alpha-BN.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: 8Citation - Scopus: 8Hard Boron Rich Boron Nitride Nanoglasses(Wiley, 2017-12-21) Cetin, Aysegul O.; Durandurdu, MuratBoron-rich amorphous boron nitride (BxN1-x, 0.55x0.95) alloys are generated by means of abinitio molecular dynamics simulations and their local structure, mechanical properties and electronic structure are exposed. BN:B phase separations are perceived in all amorphous networks, suggesting that these materials can serve as nanoglass ceramics. The sp(2) hybridization is the main building unit in the BN-rich regions for low boron concentrations, and the models carry locally the signature of the two-dimensional hexagonal BN structure. The amorphous states having both sp(2) and sp(3) hybridizations form for boron contents between 70% and 80%. At higher boron concentrations, sp(3) hybridization with a fraction of similar to 90%-98% is detected as seen in the cubic or wurtize BN crystals. In the boron rich regions, the ideal and defective pentagonal pyramids emerge at 60% boron content, and the first complete B-12 molecule develops at 70% boron concentration. In addition to the B-12 icosahedron, the formation of a cage-like B-16 molecule is, for the first time, discovered in some amorphous alloys. The isolated B-16 molecule is, however, found to be unstable. The Vickers harness calculations reveal that some of these amorphous alloys can serve as hard materials. When their electron properties are considered, all amorphous materials are predicted to be semiconducting.Article Citation - WoS: 7Citation - Scopus: 7Amorphous Boron Nitride at High Pressure(Taylor & Francis Ltd, 2016-05-18) Durandurdu, MuratThe pressure-induced phase transformation in hexagonal boron nitrite and amorphous boron nitrite is studied using ab initio molecular dynamics simulations. The hexagonal-to-wurtzite phase transformation is successfully reproduced in the simulation with a transformation mechanism similar to one suggested in experiment. Amorphous boron nitrite, on the other hand, gradually transforms to a high-density amorphous phase with the application of pressure. This phase transformation is irreversible because a densified amorphous state having both sp(3) and sp(2) bonds is recovered upon pressure release. The high-density amorphous state mainly consists of sp(3) bonds and its local structure is quite similar to recently proposed intermediate boron nitrite phases, in particular tetragonal structure (P4(2)/mnm), rather than the known the wurtzite or cubic boron nitrite due to the existence of four membered rings and edge sharing connectivity. On the basis of this finding we propose that amorphous boron nitrite might be best candidate as a starting structure to synthesize the intermediate phase(s) at high pressure and temperature (probably below 800 degrees C) conditions.