Browsing by Author "Yildiz, Tevhide Ayca"

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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.
Stoichiometric amorphous boron carbide (BC)
(SPRINGER, ONE NEW YORK PLAZA, SUITE 4600, NEW YORK, NY, UNITED STATES, 2020) Yildiz, Tevhide Ayca; Durandurdu, Murat; 0000-0001-5636-3183; AGÜ, Mühendislik Fakültesi, Malzeme Bilimi ve Nanoteknoloji Mühendisliği Bölümü
In 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.