Browsing by Author "Durandurdu, Murat"

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Ab initio study of boron-rich amorphous boron carbides
(WILEY, 2023) Yıldız, Tevhide Ayça; Durandurdu, Murat; 0000-0001-5636-3183; AGÜ, Mühendislik Fakültesi, Malzeme Bilimi ve Nanoteknoloji Mühendisliği Bölümü; Yıldız, Tevhide Ayça; Durandurdu, Murat
Amorphous boron carbide compositions having high B contents (BxC1−x, 0.50 ≤ x ≤ 0.95) are systematically created by way of ab initio molecular dynamics calculations, and their structural, electrical, and mechanical characteristics are inclusively investigated. The coordination number of both B and C atoms increases progressively with increasing B/C ratio and more close-packed materials having pentagonal pyramid motifs form. An amorphous diamond-like local arrangement is found to be dominant up to 65% B content, and beyond this content, a mixed state of amorphous diamond– and B-like structures is perceived in the models because sp3 hybridization around C atoms is still leading one for all compositions. The pentagonal pyramid motifs around C atoms are anticipated to appear beyond 65% content. The intericosahedral linear C–B–C chains do not form in any model. All amorphous boron carbides are semiconducting materials. The mechanical properties gradually increase with increasing B concentration, and some amorphous compositions are proposed to be hard materials on the basis of their Vickers hardness estimation.
Amorphous BC5 from first principles calculations
(ELSEVIER, 2022) Durandurdu, Murat; 0000-0001-5636-3183; AGÜ, Mühendislik Fakültesi, Malzeme Bilimi ve Nanoteknoloji Mühendisliği Bölümü; Durandurdu, Murat
A boron-substituted amorphous graphite (BC5) network is generated using a first principles molecular dynamics simulation and its atomic structure and electrical and mechanical properties are discussed in details. The network has a layered structure with primarily hexagonal (six membered) rings and its average coordination is about 3.0. The material is a solid solution having a minor amount of B-B homopolar bonds. It is structurally different from the BC5 crystal or monolayers proposed in the literature. The model is a semimetal material based on a generalized gradient approximation with the Hubbard correction (GGA+U) calculation. When its mechanical properties are concerned, they are comparable with those of graphite or amorphous graphite.
Amorphous boron arsenide
(ELSEVIER, RADARWEG 29, 1043 NX AMSTERDAM, NETHERLANDS, 2019) Durandurdu, Murat; 0000-0001-5636-3183; AGÜ, Mühendislik Fakültesi, Malzeme Bilimi ve Nanoteknoloji Mühendisliği Bölümü
The short-range order and electrical properties of amorphous boron arsenide (BAs) are evaluated by means of ab initio molecular dynamics simulations. The amorphous model is obtained from the fast solidification of the BAs melt and consists of B-rich and As-rich domains. The average coordination number of B- and As-atoms are found as 4.97 and 3.34, respectively. B-atoms have a tendency to form pentagonal pyramidal-like configurations as commonly seen in boron or boron rich materials. Yet B-12 molecules do not develop in the system but the formation of a B-10 cluster is perceived in the network. On the other hand, As-atoms have a trend to structure chain-like motifs and four-membered rings. Amorphization yield about 31% volume expansion in the amorphous network. All these findings reveal that the model shows strong chemical disorder and its short-range order is considerably different than that of the crystal. Amorphization-induced metallization is proposed for BAs.
Amorphous boron carbide from ab initio simulations
(ELSEVIER, RADARWEG 29, 1043 NX AMSTERDAM, NETHERLANDS, 2020) Yildiz, Tevhide Ayca; Durandurdu, Murat; 0000-0001-5636-3183; AGÜ, Mühendislik Fakültesi, Malzeme Bilimi ve Nanoteknoloji Mühendisliği Bölümü
An amorphous boron carbide (a-B4C) model is generated by means of ab-initio molecular dynamics calculations within a generalized gradient approximation and its structural, mechanical and electrical features are discussed in details. The mean coordination number of B and C atoms is estimated to be 5.29 and 4.17, respectively. The pentagonal pyramid-like motifs for B atoms, having sixfold coordination, are the main building units in a-B4C and some of which involve with the development of B-12 icosahedra. On the other hand, the fourfold-coordinated units are the leading configurations for C atoms. Surprisingly the formation of C-C bonds is found to be less favorable in the noncrystalline network, compared to the crystal. a-B4C is a semiconducting material having an energy band gap considerably less than that of the crystal. A noticeably decrease in the mechanical properties of B4C is observed by amorphization. Nonetheless a-B4C is categorized as a hard material due to its high Vickers hardness of about 24 GPa.
Amorphous boron carbonitride (BC4N) from ab initio simulations
(ELSEVIER, 2024) Durandurdu, Murat; 0000-0001-5636-3183; AGÜ, Mühendislik Fakültesi, Malzeme Bilimi ve Nanoteknoloji Mühendisliği Bölümü; Durandurdu, Murat
This study utilizes ab initio molecular dynamics simulations to explore the structure and properties of amorphous boron carbonitride (a-BC4N). A 432-atom model, generated via a conventional melt-and-quench technique, exhibits a graphite-like structure with all elements possessing an average coordination number of about 3.0. C atoms dominate within individual layers, interspersed with distinct BN domains. This atomic arrangement deviates considerably from that proposed for crystalline BC4N structures. Despite this structural variation, the a-BC4N model is likely a narrow band gap semiconductor (0.15 eV), similar to its crystalline counterparts. In terms of mechanical properties, a-BC4N demonstrates similarities with various layered materials while exhibiting a notably larger bulk modulus.
Amorphous boron nitride at high pressure
(TAYLOR & FRANCIS LTD2-4 PARK SQUARE, MILTON PARK, ABINGDON OR14 4RN, OXON, ENGLAND, 2016) Durandurdu, Murat; 0000-0001-5636-3183; AGÜ, Mühendislik Fakültesi, Malzeme Bilimi ve Nanoteknoloji Mühendisliği Bölümü; Durandurdu, Murat
The 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.
Amorphous boron phosphide: An ab initio investigation
(ELSEVIERRADARWEG 29, 1043 NX AMSTERDAM, NETHERLANDS, 2021) Bolat, Suleyman; Durandurdu, Murat; AGÜ, Mühendislik Fakültesi, Malzeme Bilimi ve Nanoteknoloji Mühendisliği Bölümü; Durandurdu, Murat
We generate a structural model of amorphous boron phosphide (BP) by quenching the melt via ab initio molecular dynamics calculations and compare it structurally and electrically with the crystal. We find that both phases of BP have a significantly different short-range order. Namely, the amorphous network presents strong chemical disorder and structural defects. P-atoms form only undercoordinated defects while B atoms present both undercoordinated and overcoordinated defects. The mean coordination number of B and P atoms is 4.17 and 3.69, correspondingly. Some of overcoordinated B atoms with chemical disorder yield the formation of pentagonal-pyramid-like motifs and a cage-like B10 cluster in the amorphous network. About 13 % volume expansion is observed by amorphization, probably due to the low-coordinated structural defects. The amorphous configuration is semiconductor as in the crystal but has a smaller energy band gap.
Amorphous boron suboxide
(WILEY, 111 RIVER ST, HOBOKEN 07030-5774, NJ USA, 2019) Durandurdu, Murat; 0000-0001-5636-3183; AGÜ, Mühendislik Fakültesi, Malzeme Bilimi ve Nanoteknoloji Mühendisliği Bölümü
We study the atomic structure and the electronic and mechanical properties of amorphous boron suboxide (B6O) using an ab initio molecular dynamic technique. The amorphous network is attained from the rapid solidification of the melt and found to consist of boron and oxygen-rich regions. In the boron-rich regions, boron atoms form mostly perfect or imperfect pentagonal pyramid-like configurations that normally yield the construction of ideal and incomplete B-12 molecules in the model. In addition to the B-12 molecules, we also observe the development of a pentagonal bipyramid (B-7) molecule in the noncrystalline structure. In the oxygen-rich regions, on the other hand, boron and oxygen atoms form threefold and twofold coordinated motifs, respectively. The boron-rich and oxygen-rich regions indeed represent structurally the characteristic of amorphous boron and boron trioxide (B2O3). The amorphous phase possesses a small band gap energy with respect to the crystal. On the bases of the localization of the tail states, we suggest that the p-type doping might be more convenient than the n-type doping in amorphous B6O. Bulk modulus and Vickers hardness of the noncrystalline configuration is estimated are be 106 and 13-18 GPa, respectively, which are noticeably less than those of the crystalline structure. Such a noticeable decrease in the mechanical properties is attributed to the presence of open structured B2O3 glassy domains in the amorphous model.
Amorphous carbon nitride (C3N4)
(ELSEVIER, 2024) Durandurdu, Murat; 0000-0001-5636-3183; AGÜ, Mühendislik Fakültesi, Malzeme Bilimi ve Nanoteknoloji Mühendisliği Bölümü; Durandurdu, Murat
This detailed investigation employs an ab initio approach to explore the atomic structure and electronic properties of an amorphous carbon nitride (C3N4) model. The model, designed with an exact 3:4 ratio, is based on an amorphous boron nitride configuration. The study reveals crucial insights into the mean coordination number for C and N atoms within the amorphous structure. With values of 2.95 for C atoms and 2.21 for N atoms, these coordination numbers closely resemble those observed in graphite-like crystals. The local structure of the amorphous network exhibits similarities to the triazine-based graphitic C3N4 crystal and is notably devoid of homopolar bonds. The estimated band gap for the amorphous C3N4 model is 1.2 eV, representing a significant reduction compared to the crystal structure, which exhibits a band gap of about 2.93 eV as determined through GGA+U calculations.
Amorphous GaN: Polyamorphism and crystallization at high pressure
(ELSEVIER, 2024) Durandurdu, Murat; 0000-0001-5636-3183; AGÜ, Mühendislik Fakültesi, Malzeme Bilimi ve Nanoteknoloji Mühendisliği Bölümü; Durandurdu, Murat
Employing constant pressure ab initio simulations, we have shed light on the previously unknown high-pressure behavior of amorphous gallium nitride. Our findings reveal a two-step transformation sequence under pressure. The initial transition involves a polyamorphic transformation from a low-density amorphous (LDA) phase to a high-density amorphous (HDA) phase with an average coordination number of 5.4. Upon pressure release, the HDA state partially reverts to a denser amorphous network with a higher coordination number (4.34) compared to the original LDA phase. Further pressurization triggers the crystallization of the HDA state into a rocksalt structure. Remarkably, the electronic structure of the amorphous forms of GaN exhibits insignificant sensitivity to changes in coordination number, maintaining a band gap of approximately 1.7–2.0 eV across all phases.
Amorphous magnesium silicide
(ELSEVIER, RADARWEG 29, 1043 NX AMSTERDAM, NETHERLANDS, 2018) Durandurdu, Murat; 0000-0001-5636-3183; AGÜ, Mühendislik Fakültesi, Malzeme Bilimi ve Nanoteknoloji Mühendisliği Bölümü
A first principles molecular dynamics technique is employed to generate an amorphous magnesium silicide (Mg2Si) model from its liquid state and its structural, electrical and mechanical features are disclosed for the first time. Si atoms form predominantly the standard square dodecahedron-like and the tri-capped trigonal prism-like configurations while Mg atoms arrange themselves primarily in higher coordinated crystal-like and icosahedrallike polyhedrons. The mean coordination number of Mg and Si is estimated to be similar to 12.84 and similar to 8.2, respectively. Si-Si homopolar bonds are also presented in the amorphous network, in contrast to the crystal. Based on our findings, we propose that the amorphous model has a short-range order, quite different than that of the anti fluorite Mg2Si crystal but similar to that of metallic glasses. The different local structure of the amorphous state yields distinct electronic and mechanical properties, relative to the crystal. Within the known limitation of DFT-GGA simulations, the amorphous Mg2Si is found to be semimetal though the anti-fluorite structure is semiconductor. Furthermore, amorphous Mg2Si is predicted to be less brittle than the crystal structure. Since the potential use of the Mg2Si crystal as a biodegradable implant material is hindered because of its brittle behavior, here we propose that amorphous or nanoglass forms might eliminate this limitation of Mg2Si and hence it can serve as an implant material in near future.
Amorphous silicon hexaboride at high pressure
(TAYLOR & FRANCIS LTD, 2-4 PARK SQUARE, MILTON PARK, ABINGDON OR14 4RN, OXON, ENGLAND, 2020) Durandurdu, Murat; 0000-0001-5636-3183; AGÜ, Mühendislik Fakültesi, Malzeme Bilimi ve Nanoteknoloji Mühendisliği Bölümü
We investigate the pressure-induced structural phase transformation of amorphous silicon hexaboride (a-SiB6) using a constant pressure first principles approach. a-SiB6 is found to undergo a gradual phase transformation to a high-density amorphous phase (HDA) in which the average coordination number of both B and Si atoms is about 6. The HDA phase consists of differently coordinated motifs ranging from 4 to 8. B-12 icosahedra are found to persist during compression of a-SiB6 and the structural modifications primarily occur around Si atoms and in the regions linking pentagonal pyramid-like configurations to each other. Upon pressure release, an amorphous structure, similar to the uncompressed one, is recovered, indicating a reversible amorphous-to-amorphous phase change in a-SiB6. When the electronic structure is considered, the HDA phase is perceived to have a wider forbidden band gap than the uncompressed one.
Amorphous silicon hexaboride: a first-principles study
(TAYLOR & FRANCIS LTD, 2-4 PARK SQUARE, MILTON PARK, ABINGDON OR14 4RN, OXON, ENGLAND, 2018) Durandurdu, Murat; 0000-0001-5636-3183; AGÜ, Mühendislik Fakültesi, Malzeme Bilimi ve Nanoteknoloji Mühendisliği Bölümü
We report for the first time the atomic structure, electronic structure and mechanical properties of amorphous silicon hexaboride (a-SiB6) based on first-principles molecular dynamics simulation. The a-SiB6 model is generated from the melt and predominantly consists of pentagonal pyramid-like configurations and B-12 icosahedral molecules, similar to what has been observed in most boron-rich materials. The mean coordination number of B and Si atoms are 5.47 and 4.55, respectively. The model shows a semiconducting behaviour with a theoretical bandgap energy of 0.3eV. The conduction tail states are found to be highly localised and hence the n-type doping is suggested to be more difficult than the p-type doping for a-SiB6. The bulk modulus and Vickers hardness of a-SiB6 are estimated to be about 118 and 13-17GPa, respectively.
Amorphous Silicon Nanoparticles and Silicon Nanoglasses from Ab Initio Simulations
(SPRINGER LINK, 2024) Bolat, Süleyman; Durandurdu, Murat; 0000-0001-5636-3183; AGÜ, Mühendislik Fakültesi, Malzeme Bilimi ve Nanoteknoloji Mühendisliği Bölümü; Durandurdu, Murat
The structural and electrical characteristics of spherical amorphous silicon nanoparticles (Si-NPs) with radii ranging from 9 to 15 Å, and silicon nanoglasses (Si-NGs) formed by compressing identical-sized Si-NPs, are being investigated for the first-time using ab initio simulations. Analysis reveals predominantly fourfold coordination within Si-NPs, accompanied by noticeable coordination defects. The prevalence of fourfold coordination increases with increasing Si-NP size. Si-NGs, while exhibiting similar dominant fourfold coordination, possess a small fraction of coordination defects (5–8%) primarily concentrated at the interfaces of compressed Si-NPs. Si-NGs are found to have a more open structure compared to amorphous Si. This structural variation, along with observed distortions within Si-NGs, is hypothesized to contribute to a significant narrowing of their band gaps relative to amorphous Si.
Amorphous silicon triboride: A first principles study
(ELSEVIER, RADARWEG 29, 1043 NX AMSTERDAM, NETHERLANDS, 2020) Ozlem, Aysegul; Karacaoglan, Cetin; Durandurdu, Murat; 0000-0001-5636-3183; AGÜ, Mühendislik Fakültesi, Malzeme Bilimi ve Nanoteknoloji Mühendisliği Bölümü
Using ab initio molecular dynamics simulations, an amorphous silicon triboride (a-SiB3) network is generated and its atomic structure, electronic features and mechanical properties are compared with those of the crystal. The average coordination number of B and Si atoms in a-SiB3 is found as 5.8 and 4.6, correspondingly, close to 6.0 (B atom) and 5.0 (Si atom) in the crystal. A careful investigation reveals partial structural similarities around B atoms but not around Si atoms in both phases of SiB3. The presence of B-12, B11Si and B-10 molecules is witnessed in a-SiB3. The last two molecules, however, do not exist in the crystal. a-SiB3 is a semiconducting material. The bulk modulus of the ordered and disordered structures is projected to be 151 GPa and 131 GPa, respectively. The Vickers hardness of a-SiB3 is calculated to be similar to 13-15 GPa, less than similar to 20-25 GPa estimated for the crystal.
Amorphous zircon at high pressure
(PERGAMON-ELSEVIER SCIENCE LTDTHE BOULEVARD, LANGFORD LANE, KIDLINGTON, OXFORD OX5 1GB, ENGLAND, 2021) Bolat, Suleyman; AGÜ, Mühendislik Fakültesi, Malzeme Bilimi ve Nanoteknoloji Mühendisliği Bölümü; Durandurdu, Murat
The high-pressure behavior of a very low-density amorphous zircon model having Zr (Si) coordination of 5.6 (4.02) is explored by ab initio simulations. Two consecutive pressure-induced phase modifications are proposed for this material. The first transition is from a very low-density amorphous state to a dense amorphous state having Zr (Si) coordination of 7.3 (4.5). The second one is from the dense phase to a high-density amorphous structure with Zr and Si coordination numbers of about 8 and 5.5, correspondingly. Both phase changes proceed progressively. The first phase transformation is irreversible whist the second one is reversible. The Voronoi polyhedron analysis reveals the presence of polyhedron of the zircon crystal (<0,4,4,0>), the zirconia baddaliyette phase (<1,3,3,0>) and the zirconia cotunnite state (<0,3,6,0>) around Zr atoms in the amorphous states formed on both compression and decompression, meaning that the amorphous configurations consist of a mixed state of them.
Amorphous zirconia at high pressure
(WILEY, 111 RIVER ST, HOBOKEN 07030-5774, NJ USA, 2018) Durandurdu, Murat; 0000-0001-5636-3183; AGÜ, Mühendislik Fakültesi, Malzeme Bilimi ve Nanoteknoloji Mühendisliği Bölümü
We show, by means of ab initio calculations, that amorphous zirconia progressively transforms to a high-density amorphous phase with the application of pressure. The average coordination number of Zr and O atoms under pressure rises gradually to 8 and 4, respectively. The main building unit of the dense noncrystalline state is the eightfold-coordinated Zr atoms (62.5%). When the coordinated modification of Zr atoms in the zirconia crystal at high pressure and temperature conditions is considered, it can be perceived that amorphous zirconia follows a transformation mechanism similar to the one observed at high temperature but different than the one detected at high pressure. The dense disordered phase is indeed found to be locally comparable with the high-temperature tetragonal crystal. Upon decompression, some high-pressure arrangements are persevered in the model and a transformation into another amorphous state whose structure is intermediate between uncompressed and dense amorphous phases is observed in the simulations. The high-pressure amorphous structures are found to be semiconductors with a band gap smaller than that of the original model.
Amorphous zirconia: ab initio molecular dynamics simulations
(TAYLOR & FRANCIS LTD2-4 PARK SQUARE, MILTON PARK, ABINGDON OR14 4RN, OXON, ENGLAND, 2017) Durandurdu, Murat; AGÜ, Mühendislik Fakültesi, Malzeme Bilimi ve Nanoteknoloji Mühendisliği Bölümü
We investigate the short-range order of the liquid and amorphous zirconia using an ab initio molecular dynamics technique. Both forms of zirconia are projected to be structurally close to each other. The amorphous network has predominantly seven-fold coordinated Zr atoms (similar to% 65), and three-fold and four-fold coordinated O atoms (similar to 46%), and hence it resembles locally the monoclinic zirconia phase. Within the known limitations of the DFT-GGA calculation, the liquid state is predicted to be semi-metal, whereas the amorphous form is projected to be semiconductor having a band gap energy of similar to 3.5 eV. We find an asymmetry in localisation of the band tail states. On the basis of this finding, we discuss possible distinctions in n-type and p-type doping in amorphous zirconia.
Atomic structure and properties of amorphous boron carbon nitride (BC2N): An ab initio study
(ELSEVIER, 2025) Durandurdu, Murat; 0000-0001-5636-3183; AGÜ, Mühendislik Fakültesi, Malzeme Bilimi ve Nanoteknoloji Mühendisliği Bölümü; 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.
Atomic structure of amorphous CdO from first principles simulations
(ELSEVIER, 2015) Durandurdu, Murat; 0000-0001-5636-3183; AGÜ, Mühendislik Fakültesi, Malzeme Bilimi ve Nanoteknoloji Mühendisliği Bölümü; Durandurdu, Murat
Amorphous 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.