Browsing by Author "Karacaoglan, Aysegul Ozlem Cetin"

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Citation - WoS: 1
Amorphous to Amorphous Phase Transformation in Boron-Rich Amorphous Silicon Borides: An Ab Initio Study
(Taylor & Francis Ltd, 2024) Karacaoglan, Aysegul Ozlem Cetin; Durandurdu, Murat
This study employs a constant-pressure ab initio approach to investigate the high-pressure behavior of five distinct boron-rich amorphous silicon borides. A unique amorphous-to-amorphous phase transition is exposed, providing insights into the structural resilience of these materials under extreme conditions. Our results reveal a gradual increase in the coordination number of both B and Si atoms under pressure, with subsequent densification upon pressure release. Yet the recovered amorphous phases closely resemble the uncompressed states, highlighting the reversibility of these phase changes. Significant structural modifications around Si atoms are observed, emphasizing their pivotal role in the observed phase transitions. Additionally, pressure-induced metallization is witnessed in these materials, indicating their distinctive electronic behavior under high pressure. This work significantly contributes to a deeper understanding of the high-pressure behavior of boron-rich amorphous silicon borides and opens avenues for exploring their potential applications in fields requiring exceptional structural stability and unique pressure-dependent properties.
Boron-Rich Amorphous Boron Oxides From Ab Initio Simulations
(Elsevier, 2023) Karacaoglan, Aysegul Ozlem Cetin; Durandurdu, Murat
Amorphous boron oxide (BxO1-x, 0.5 <= x <= 95) configurations are simulated by means of an ab initio molecular dynamics technique and their microstructure and mechanical properties are revealed in details. With increasing B content, the average B-coordination noticeably increases from 3.18 to 5.62 whereas the O-coordination, sur-prisingly, remains almost null, about 2.0. The formation of complete B12 molecules is observed after 80% B concentrations. Chemical segregation is witnessed in most models and hence the resulting configurations show B: B2O3 phase separations. The mechanical properties (bulk, shear and Young moduli, Vickers hardness and microhardness) substantially increase with increasing B content. The amorphous materials (BxO1-x, x >= 80) are classified as hard materials. Within the limitations of DFT calculations and approaches used, we speculate that there is a ductile-to-brittle transition at around 70-75% B contents.
Citation - WoS: 2
Citation - Scopus: 2
Possible Boron-Rich Amorphous Silicon Borides From Ab Initio Simulations
(Springer, 2023) Karacaoglan, Aysegul Ozlem Cetin; Durandurdu, Murat
ContextBy means of ab initio molecular dynamics simulations, possible boron-rich amorphous silicon borides (BnSi1-n, 0.5 <= n <= 0.95) are generated and their microstructure, electrical properties and mechanical characters are scrutinized in details. As expected, the mean coordination number of each species increases progressively and more closed packed structures form with increasing B concentration. In all amorphous models, pentagonal pyramid-like configurations are observed and some of which lead to the development of B-12 and B11Si icosahedrons. It should be noted that the B11Si icosahedron does not form in any crystalline silicon borides. Due to the affinity of B atoms to form cage-like clusters, phase separations (Si:B) are perceived in the most models. All simulated amorphous configurations are a semiconducting material on the basis of GGA+U calculations. The bulk modulus of the computer-generated amorphous compounds is in the range of 90 GPa to 182 GPa. As predictable, the Vickers hardness increases with increasing B content and reaches values of 25-33 GPa at 95% B concentration. Due to their electrical and mechanical properties, these materials might offer some practical applications in semiconductor technologies.MethodThe density functional theory (DFT) based ab initio molecular dynamics (AIMD) simulations were used to generate B-rich amorphous configurations.