Scopus İndeksli Yayınlar Koleksiyonu
Permanent URI for this collectionhttps://hdl.handle.net/20.500.12573/395
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Article Citation - WoS: 9Citation - Scopus: 9Unveiling the Multifaceted Properties of a 3D Covalent-Organic Framework: Pressure-Induced Phase Transition, Negative Linear Compressibility and Auxeticity(Elsevier, 2023-08) Erkartal, MustafaHigh-pressure behavior and mechanical properties of a three-dimensional covalent-organic framework (NPN-1) were investigated by using different types of first principles molecular simulations. An irreversible pressureinduced first-order isosymmetric phase transition was predicted at 0.14 GPa. The subunit of NPN-1 retains its rigidity under pressure thanks to the strong covalent bonds. However, compression leads to significant tilting of the nitrophenyl groups. The mechanical properties of frameworks are highly anisotropic. Remarkably, both phases exhibit not only negative linear compressibility along the c-axis but also negative Poisson's ratio in certain directions. Detailed structural analysis revealed that the origin of the phase transition and anomalous mechanical properties of both phases are the wine-rack motif and strut-hinge mechanism. To the best of our knowledge, this study is the first report of such behavior in COFs, opening up new avenues for the exploration of COFs as materials for many promising applications.Article Citation - WoS: 6Citation - Scopus: 7Extreme Flexibility and Unusual Piezomechanical Properties of Zinc-Alkyl Metal-Organic Frameworks: A First Principles Study(Elsevier, 2023-06) Erkartal, MustafaThe behavior of three Zn-alkyl-based MOFs, ZnGA (Zn-Glutarate), ZnAA (Zn-Adipate), and ZAG-4 (Zinc Alky Gate), under hydrostatic compression has been investigated using first-principles DFT simulation, which has proven its reliability in previous studies. Due to the lack of the high pressure experimental data for ZnGA and ZnAA, the reliability of the simulation parameters was tested by taking ZAG-4, whose structural flexibility has been previously reported experimentally and computationally, as a benchmark. All three structures were found to exhibit elastic deformation under pressure up to 15 GPa, due to the flexibility of the alkyl chains that allow the structures to move without disrupting the metal-ligand coordination. Interestingly, the structures exhibit different mechanical properties, with ZAG-4 showing negative linear compressibility (NLC), ZnGA showing positive linear compressibility (PLC), and ZnAA showing zero linear compressibility (ZLC). The NLC in ZAG-4 is attributed to the proton transfer between phosphonate oxygen and water in the structure as previously reported, while the ZLC in ZnAA is due to a dumbbell-like structural motif formed by substructures displaying both NLC and PLC.Article Citation - WoS: 1Citation - Scopus: 1Amorphous Zirconia at High Pressure(Wiley, 2018-06-08) Durandurdu, MuratWe 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.