3 results
Search Results
Now showing 1 - 3 of 3
Article Citation - WoS: 8Citation - Scopus: 9Experimental and Theoretical Investigation of the Mechanical Characteristics of Sillenite Compound: Bi12geo20<(Elsevier Science Sa, 2021) Surucu, Gokhan; Isik, Mehmet; Gencer, Aysenur; Gasanly, NizamiThe present study reports the mechanical and elastic characteristics of Bi12GeO20 (BGO) compound by experimental nanoindentation measurements and density functional theory (DFT) calculations. X-ray diffraction pattern of BGO was plotted and revealed diffraction peaks were associated with Miller indices of cubic crystalline structure with lattice constant of a = 10.304 angstrom. Two- and three-dimensional representations of Young's modulus, linear compressibility, shear modulus and Poisson's ratio were presented according to DFT calculations. The calculated elastic constants pointed out the mechanically stable and anisotropic behavior of the BGO. The hardness and Young's modulus ranges of the BGO calculated from DFT studies were found as 3.7-6.3 GPa and 61.7-98.9 GPa, respectively. Hardness and Young's modulus of BGO single crystal were also obtained by analyzing force-dependent nanoindentation experimental data. It was observed that hardness and Young's modulus decrease with increase of load in the low applied loads and then reaches saturation in the high applied loads. This behavior is known as indentation size effect. True hardness value was determined from proportional specimen resistance model as 4.1 GPa. The force independent region presented the Young's modulus as 114 GPa. (C) 2021 Elsevier B.V. All rights reserved.Article Citation - WoS: 48Citation - Scopus: 50Lattice Dynamical and Thermo-Elastic Properties of M2alb (m = V, Nb, Ta) Max Phase Borides(Elsevier Science Sa, 2020) Surucu, Gokhan; Gencer, Aysenur; Wang, Xiaotian; Surucu, OzgeThe structural, electronic, dynamic, and thermo-elastic properties of M2AlB (X = V, Nb, Ta) MAX phase borides were investigated using first principle calculations as implemented in the Vienna Ab-initio Simulation Package (VASP) with the generalized gradient approximation (GGA). The obtained structural properties and formation energies showed the thermodynamic stability and synthesizability of M2AlB. The electronic band structures were determined and they revealed that these compounds had a metallic character. The dynamic stability of M2AlB compounds were investigated with phonon dispersion curves and these compounds were found to be dynamically stable. The elastic constants were also calculated to determine the mechanical stability and to obtain the polycrystalline properties such as bulk modulus, shear modulus, etc. The thermo-elastic properties (thermal expansion coefficient, heat capacity, entropy, and free energy) were studied in a temperature range in between 0 and 1000 K and a pressure range in between 0 and 30 GPa. In addition, the direction dependent sound wave velocities were studied in three dimensions. Moreover, the minimum thermal conductivities and the diffusion thermal conductivities of these compounds were determined. This work is the processor study for the investigation of the main physical properties of M2AlB (M = V, Nb, Ta) ceramic compounds to date. (C) 2019 Elsevier B.V. All rights reserved.Article Citation - WoS: 29Citation - Scopus: 34Enhanced Hydrogen Storage of a Functional Material: Hf2cf2< Mxene With Li Decoration(Elsevier, 2021) Gencer, Aysenur; Aydin, Sezgin; Surucu, Ozge; Wang, Xiaotian; Deligoz, Engin; Surucu, GokhanIn this paper, the hydrogen storage properties of the Li-decorated stable Hf2CF2 MXene layer, obtained by the exfoliation of Al from Hf2AlC and F-termination, are considered by using first-principles calculations based on Density Functional Theory. First, the stability characteristics of the host structure (Hf2CF2 layer) are examined by investigating bulk Hf2AlC. To enhance the adsorbed number of H-2 molecules, the well-defined initial H-2 coordinates are constructed by CLICH (Cap-Like Initial Conditions for Hydrogens) and Monte Carlo-based algorithms. After the geometry optimizations of the designed H-2 systems on the Li/Hf2CF2 layer, the adsorption energies of nH(2)/Li/Hf2CF2 n = 1-10, 15, 20 and 25 systems are calculated, and the suitable values (0.2-0.6 eV/H-2) are obtained up to 15H(2). For n = 20 and 25 systems, which have adsorption energies of 0.15 eV/H-2 and 0.16 eV/H-2, respectively. The structural properties and adsorption geometries of these molecules are analyzed. Additionally, the partial density of the states, electron density difference maps, and Mulliken atomic charges are presented to identify the actual binding mechanism of the systems. The results reveal that the Li-decorated Hf2CF2 MXene layer can be preferred for the hydrogen storage applications due to its stable nature and the convenient adsorption characteristics.
