Browsing by Author "Mamedov, Amirullah M."

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Open Access
2D anisotropic photonic crystals of hollow semiconductor nanorod with liquid crystals
(2013) Karaomerlioglu F.; Şimsek, Şevket; Mamedov, Amirullah M.; Özbay, Ekmel
Photonic crystals (PCs) have many applications in order to control light-wave propagation. A novel type of two-dimensional anisotropic PC is investigated band gap and optical properties as a hollow semiconductor nanorod with nematicliquid crystals (LC). The PC structure composed of an anisotropic nematicLC in semiconductor square hollow nanorod is designed using the plane wave expansion (PWE) method and finite-difference time-domain (FDTD) method. It has been used 5CB (4-pentyl-4'-cyanobiphenyl) as LC core, and Tellurium (Te) as square hollow nanorod material.The PC with hollow Tenanorod with nematicLC is compared with the PC with solid Tenanorodand the PC with hollow Tenanorod. © (2013) Trans Tech Publications, Switzerland.
Open Access
6th International Conference on Competitive Materials and Technology Processes and 2nd European Conference on Silicon and Silica Based Materials
(Institute of Physics, 2022) Whittingham, M. Stanley; Kulkov, Sergey N.; Beck, Uwe; Sekino, Tohru; Eshtiaghi, Nicky; Fiore, Saverio; Sadowski, Tomasz; Yang, Jun; Nagasawa, Shigeru; Contreras Garcia, M.E.; Srdic, Vladimir V.; Mamedov, Amirullah M.; Itatani, Kiyoshi; Stupina, Alena; Lecomte-Nana, Gizéle; Kotova, Olga; Rauwel, Erwan; Chen, Soo; Urakov, Aleksandr; Gömze, Ludmila; Kovács, A. Tünde; Jeon, Jae-Ho; Avetissov, Igor; Toyama, Takeshi; Panesar, Daman; Mori, Takao; Chemam, Abdelbaki; Ewais, Emad; Nguyen, Quang Chinh; Kocserha, A. István; Khramchenkov, Maxim; Kurovics, Emese; Knyazeva, Anna; Arinstein, Arkadi; Bursikova, Vilma; Shevchenko, Vladimir; Gömze, László A.; Iwayama, Tsutomu; Mahnicka-Goremikina, Ludmila; Chang, Jeong-Ho; Pytel, Zdzislaw; Hussainova, Irina; Kocserha, István; Amato, Rosaria D.; Ibrahim, Jamal Eldin F.M.; Mezinskis, Gundars; Sedlacik, Michal; Lederer, Gr. Martin; Krenek, Tomas
The aims of the 2nd European Conference on Silicon and Silica Based Materials (ec-siliconf2) and the 6th International Conference on Competitive Materials and Technology Processes (ic-cmtp6) are the followings: • Promote new methods and results of scientific research in the fields of material, chemical, physical, biological, environmental, healts as well as processing and technology sciences. • Change information between the theoretical and applied sciences and promote their technical and technological implantations. • Improve the communication between the scientist of different nations, countries, and continents. Among the major fields of interest are traditional and advanced materials with increased physical, chemical, biological, medical, thermal and mechanical properties, including their crystalline and nano-structures, phase transformations as well as methods of their technological processes, tests and measurements. Multidisciplinary applications of material science and technological problems encountered in sectors like metallic and non-metallic materials and composites, including metal-alloys, ceramics, polymers, glasses, thin films, etc. Mashinery, IT tools, aerospace, automotive and marine industry, electronics, energy, construction materials, medicine, biosciences, and environmental sciences are of particular interest. List of The International Scientific Advisory Board (ISAB), The International Organizing committee (IOC), The International Scientific Advisory Board (ISAB), The International Organizing committee (IOC), The Session of ic-cmtp6, The Session of ec-siliconf2 and Acknowledgement are available in this pdf.
Open Access
Ab initio modeling of elastic and optical properties of Sb and Bi sesquioxides
(Institute of Physics Publishing, 2018) Koc, H.; Akhundov, C. G.; Mamedov, Amirullah M.; Özbay, Ekmel
First-principle calculations performed the structural, mechanical, electronic, and optical properties of Sb2O3 and Bi2O3 compounds in monoclinic (claudetite and α-Bi2O3) and orthorhombic (valentinite) structures. Local density approximation has been used for modeling exchange-correlation effects. The lattice parameters, bulk modulus, and the first derivate of bulk modulus (to fit to the Murnaghan's equation of state) of considered compounds have been calculated. The second-order elastic constants have been calculated, and the other related quantities have also been estimated in the present work. The electronic bands structures and the partial densities of states corresponding to the band structures are presented and analyzed. The real and imaginary parts of dielectric functions and energy-loss function are calculated. Our structural estimation and some other results are in agreement with the available experimental and theoretical data.
Open Access
Band structure and transmission spectra in multiferroic based Sierpinski-carpet phononic crystal
(EDP Sciences, 2020-06) Özer, Z.; Palaz, S.; Mamedov, Amirullah M.; Özbay, Ekmel
In this study, the band structure and transmission spectra in multiferroic based Sierpinski-carpet phononic crystal are investigated based on finite element simulation. In order to obtain the band structure of the phononic crystal (PnC), the Floquet periodicity conditions were applied to the sides of unit cell. The square lattice PnC consists of various piezoelectric inclusion in a rubber matrix with circular and triangular cross section.
Open Access
Band Structure of Phononic Crystal Consist of Hollow Aluminum Cylinders in Different Media; Finite Element Analysis
(IOP, 2019) Özer, Z.; Demir, M.; Mamedov, Amirullah M.; Özbay, Ekmel
In this study, we investigated band structure of a 2D Phononic Crystal (PnC) which was consist of hollow aluminum cylinders in different media. To validate the finite element predictions, we made a square lattice PnC which has lattice constant a=14mm, outer radius r1=5mm and inner radius r2=4mm of cylinders. In our experimental measurement, by using a signal generator software, we sent 100 Hz-20kHz sine signal for 5 seconds duration from speaker to the PnC where placed 1m away from. With the help of a microphone, we recorded the sound in front of the PnC (Pin) and backside the PnC (Pout). Then we were converted our recording into frequency domain by standard FFT algorithm, we calculated the Transmission Loss value according to the formula TL = 20*log10 (Pout / Pin) and obtained the experimental Transmission Loss. After experimental validation, we conducted band structure analysis of different combination of the 2D PnC by finite element method.
Open Access
Band structures of metacomposite based phononic crystals in quasi-Sierpinski fractals
(Scientific Society of the Silicate Industry, 2021-05-29) Oltulu, Oral; Özer, Zafer; Mamedov, Amirullah M.; Özbay, Ekmel
In this paper, we investigated the bandgaps of two-dimensional phononic crystals with quasiSierpinski carpet unit cells in a metacomposite based solid–solid phononic crystal. Finite element method was used to analyze the properties of two-dimensional phononic bandgaps (2D PBGs) in a quasi-fractal structure. Two new types of quasi-Sierpinski fractal unit cells whose constituents are homogeneous and isotropic were proposed to obtain larger full bandgaps. The results show that the PBGs of the proposed quasi-Sierpinski fractals are suitable to tune the PBG’s without changing the size of the phonic crystal. The new quasi-Sierpinski fractals also retain the selfsimilarity as in the third-order Sierpinski fractal unit cell. The investigated quasi-fractals can be easily modified to increase the filling fraction of the constituents, which can be effectively used to enlarge existing PBG by preserving degree of self-similarity structure.
Open Access
BaTiO3 based photonic time crystal and momentum stop band
(Taylor & Francis, 2020-04) Özer, Z.; Mamedov, Amirullah M.; Özbay, Ekmel
Temporally periodic photonic crystals develop an ω-k dispersion relation with momentum band gaps. While conventional photonic crystals induce forbidden bands in the frequency spectrum of photons, photonic time crystals create forbidden regions in the momentum spectrum of photons. This effect allows for enhanced control over many optical processes that require both photonic energy and momentum conservations such as nonlinear harmonic generation. The simulation results show that more intensive scatter fields can obtained in photonic space time crystal. Also, we investigate topological phase transitions of photonic time crystals systems.
Open Access
Complete photonic band gaps in Sn2P2X6 (X = S, Se) supercell photonic crystals
(Taylor & Francis, 2020-04) Şimşek, Ş.; Palaz, S.; Koç, H.; Mamedov, Amirullah M.; Özbay, Ekmel
In this work, we present an investigation of the optical properties and band structures for the photonic crystal structures (PCs) based on Sn2P2X6: X = S, Se) with Fibonacci superlattices. The optical properties of PCs can be tuned by varying structure parameters such as the lengths of poled domains, filling factor, and dispersion relation. In our simulation, we employed the finite-difference time domain technique and the plane wave expansion method, which implies the solution of Maxwell equations with centered finite-difference expressions for the space and time derivatives.
Open Access
Elastic and optical properties of sillenites: First principle calculations
(Taylor & Francis, 2020-04) Koç, H.; Palaz, S.; Şimşek, Ş.; Mamedov, Amirullah M.; Özbay, Ekmel
In the present paper, we have investigated the electronic structure of some sillenites - Bi12MO20 (M = Ti, Ge, and Si) compounds based on the density functional theory. The mechanical and optical properties of Bi12MO20 have also been computed. The second-order elastic constants have been calculated, and the other related quantities have also been estimated in the present work. The band gap trend in Bi12MO20 can be understood from the nature of their electronic structures. The obtained electronic band structure for all Bi12MO20 compounds is semiconductor in nature. Similar to other oxides, there is a pronounced hybridization of electronic states between M-site cations and anions in Bi12MO20. Based on the obtained electronic structures, we further calculate the frequency-dependent dielectric function and other optical functions.
Open Access
Elastic, electronic, and optical properties of NaSnX (X=Sb, Bi, As): first principle calculations
(IOP, 2019) Koç, H.; Mamedov, Amirullah M.; Özbay, Ekmel
In the present work, the structural, mechanical, electronic and optical properties of NaSnX (X=Sb, B, As) compounds have been investigated by means of first principles calculations. The generalized gradient approximation has been used for modeling the exchangecorrelation effects. It has been observed that the calculated lattice parameters are in good agreement with the experimental and theoretical lattice parameters. Bulk modulus, shear modulus, Young's modulus Poisson's ratio, sound velocities and the Debye temperatures using the calculated elastic constants for NaSnSb, NaSnBi and NaSnAs compounds have been obtained. The electronic band structure and the projected density of states corresponding to the electronic band structure have calculated.and interpreted. The obtained electronic band structure for NaSnSb and NaSnBi compounds are metallic in nature, and the NaSnAs compound is also a narrow semiconductor. Based on the obtained electronic structures, we further calculated the frequency-dependent dielectric function, the energy-loss function, optical conductivity, and reflection along the x- and z- axes.
Open Access
Electronic and elastic properties of the multiferroic crystals with the Kagome type lattices -Mn3V2O8 and Ni3V2O8: First principle calculations
(Taylor & Francis, 2019-08-16) Koç, H.; Palaz, S.; Mamedov, Amirullah M.; Özbay, Ekmel
The electronic, mechanical, and optical properties of the Kagome staircase compounds, Mn3V2O8 and Ni3V2O8, have been investigated using the VASP (Vienna ab-initio Simulation Program) that was developed within the density functional theory (DFT). The spin polarized generalized gradient approximation has been used for modeling exchange-correlation effects. The electronic band structures for both compounds and total and partial density of states corresponding to these band structures have been calculated. Spin up (spin down) Eg values for Mn3V2O8 and Ni3V2O8 compounds are 0.77 eV indirect (3.18 direct) and 1.58 eV indirect (0.62 eV) direct, respectively. The band gaps of both compound is in the d-d character. Bulk modulus, shear modulus, Young's modulus, Poisson's ratio, anisotropic factors, sound velocity, and Debye temperature were calculated and interpreted.
Open Access
Electronic band structure of rare-earth ferroelastics: theoretical investigations
(National Institute of Optoelectronics, 2018) Şimşek, Ş.; Uğur, G.; Uğur, Ş.; Mamedov, Amirullah M.; Özbay, Ekmel
In the present work, the electronic band structure and optical properties of RE2(MoO4)3 are investigated. The ground state energies and electronic structures were calculated using density functional theory (DFT) within the generalized-gradient approximation (GGA). The real and imaginary parts of dielectric functions and hence the optical functions such as energy-loss function, the effective number of valance electrons and the effective optical dielectric constant were also calculated. The main structure element in all our of compounds is the MoO4 tetrahedron. The presence of the MoO4 tetrahedra in the lattice of Gd2(MoO4)3, the similarity of the band structure and optical spectra of Gd2(MoO4)3 to those other tetraoxyanions of molybdenium demonstrate an important role of the MoO4 tetrahedra in the formation of the energy spectrum of Gd2(MoO4)3and other RE2(MoO4)3 compounds. This means that the MoO4 tetrahedra determine the lower edge of the conduction band and the upper edge of the valence band, and the conduction band is split into two subbands. The optical properties of RE2(MoO4)3 are in good agreement with this conclusion and previous experimental data.
Open Access
Electronic properties of spin excitation in multiferroics with a spinel structure: first principles calculation
(Taylor & Francis, 2019-06-04) Koç, H.; Palaz, S.; Mamedov, Amirullah M.; Özbay, Ekmel
In the present work, the structural, electronic and mechanical properties of LiVCuO4 and LiCu2O4 spinel type multiferroics have been investigated by means of first principles calculations. The spin polarized generalized gradient approximation has been used for modeling exchange-correlation effects. The structural optimization of these multiferroics compounds has been performed by using VASP-code, and the lattice parameters and magnetic moments have been calculated. From our calculation, it has been determined that the LiVCuO4 compound is a narrow band gap semiconductor, while the LiCu2O4 compound is metallic in nature. Considering the spin states from the electronic band structure and density of the state (DOS) of the LiVCuO4 compound, it has been identified that Eg=1.87 eV for spin up and Eg=0.37 eV for spin down. The second-order elastic constants have been calculated, and the other related quantities have also been estimated in the present work.
Open Access
Electronic structure of conventional slater type antiferromagnetic insulators: AIrO3 (A=Sr, Ba) perovskites
(Institute of Physics, 2022) Koc, Husnu; Mamedov, Amirullah M.; Özbay, Ekmel
The structural, mechanical, and electronic properties of Perovskite BaIrO3 and SrIrO3 compounds based on the density functional theory (DFT) have been examined in four different structures (C2/c, R-3m, P6_3/mmc and Pm-3m) and Pnma structure, respectively. The spin polarized generalized gradient approximation has been used for modeling exchange-correlation effects. As a result of spin polarized calculations, it has been observed that BaIrO3 compound showed magnetic properties in C2/c and R-3m structures, but not in Pm-3m and P6_3/mmc structures. SrIrO3 compound also shows magnetic properties in Pnma structure. The elastic constants have been calculated using the strain-stress method and the other related quantities (the bulk modulus, shear modulus, Young's modulus, Poisson's ratio, anisotropy factor, sound velocities, and Debye temperature) have also been estimated. In electronic band structure calculations, while Pm-3m and P6_3/mmc structures of NaIrO3 compound are metallic and semiconductor (Eg = 1.190 eV indirect), respectively, while C2/c and R-3m structures showing magnetic properties are metallic in spin down state and semiconductor (Eg=0.992 eV indirect and Eg=0.665 eV direct, respectively) in the spin up state. The Pmna structure in the SrIrO3 compound is a semiconductor in both spin states (Eg=0.701 eV “0.632 eV” indirect in the spin up “spin down”). © 2022 Institute of Physics Publishing. All rights reserved.
Open Access
Ferroelectric based fractal phononic crystals: wave propagation and band structure
(Taylor & Francis, 2020-04) Palaz, S.; Özer, Z.; Mamedov, Amirullah M.; Özbay, Ekmel
In this study, the band structure and transmission in multiferroic based Sierpinski carpet phononic crystal are investigated based on finite element simulation. In order to obtain the band structure of the phononic crystal (PnC), the Floquet periodicity conditions were applied to the sides of the unit cell. The square lattice PnC consists of various piezoelectric inclusion in a rubber matrix with square and circular cross section.
Open Access
Ferroelectric based microgyroscope for inertial measurement unit: Modeling and simulation
(IEEE, 2012) Ozer, Z.; Mamedov, Amirullah M.; Özbay, Ekmel
This paper present the design and modeling of the micro-electromechanical systems (MEMS) on the ternary ferroelectric compounds (PZT and Ba xSr 1-xTiO 3) based by using finite element model (FEM) simulation. © 2012 IEEE.
Open Access
Incommensurate phase transition and electronic properties of BaMnF4
(IOP, 2019) Palaz, S.; Şimşek, Ş.; Koç, H.; Babayeva, R.; Mamedov, Amirullah M.; Özbay, Ekmel
We present the ab initio study the electronic, mechanical and structural properties of BaMnF4. We duscuss the trends in the electronic and mechanical properties of BaMnF4 under pressure up to 80 GPa. BaMnF4 belongs to the family of BaMF4-type fluorides (M = Mn, Fe, Co, Ni, Mg, Zn) which share the same orthorhombic structure. The main focus of this study is to elaborate the changes brought about in the electronic and the structural properties by applied pressure. The calculated lattice parameters have been in agreement with the available experimental and theoretical value. Band gap of BaMnF4 in our calculation is about 2.0 eV, separating the empty upper-Hubbard t2g bands and occupied lower-Hubbard eg bands. The total and partial DOS corresponding to the electronic band structure are calculated. Comparative analysis of the results of these calculations shows that the band-gap energy of BaMnF4 decreases with increasing pressure and has a minima value at a critical pressure (appr. 65 GPa), after which it increases again. Some fundamental physical parameters such as elastic constants, bulk modulus, Poisson’s ratio, sound velocities and Debye temperature were calculated and interpreted, too.
Open Access
Linear and non-linear optical properties of AgBO3(B=Nb, Ta): First principle study
(IEEE, 2013) Şimşek, Şevket; Mamedov, Amirullah M.
The linear and nonlinear optical properties of ferroelectrics AgBO 3 (B=Ta, Nb) are studied by density functional theory (DFT) in the local density approximation (LDA) expressions based on first principle calculations without the scissor approximation. Specially, we present calculations of the frequency-dependent complex dielectric function ε(ω), and the second harmonic generation response coefficient χ(2)(-2ω,ω,ω) over a large frequency range in rhombohedral phase for the first time. The electronic linear electrooptic susceptibility χ(2)(-ω,ω,0) is also evaluated below the band gap. These results are based on a series of the LDA calculation using DFT. © 2013 IEEE.
Open Access
The mechanical, electronic and optical properties of Sn2P2S6 compound in different phases
(Taylor & Francis, 2021-12-01) Koc, H.; Palaz, S.; Simsek, S.; Mamedov, Amirullah M.; Ozbay, Ekmel
In present paper, the structural, mechanical, and electronic properties of the Sn2P2S6 compound under different pressures by the density functional methods in the generalized gradient approximation have been examined in the ferroelectric (Pc) and paraelectric (P2_1/c) phases. The lattice parameters, mechanical properties, electronic bands structures and partial density of states for both phases are presented and analyzed. The nonlinear optical properties and electro-optic effects of Sn2P2S6-Pc have been studied by the density functional theory in the local density approximation. Our structural estimation and some other results are in agreement with the available experimental and theoretical data. We present calculations of the frequency-dependent complex dielectric function (ω) and the second harmonic generation response coefficient χ(2) (−2ω, ω, ω) over a large frequency range. The electronic linear electro-optic susceptibility χ(2) (−ω, ω, 0) is also evaluated below the band gap. These results are based on a series of the LDA calculation. The results for χ(2) (−ω, ω, 0) are in agreement with the experiment below the band gap and those for χ(2) (−ω, ω, 0) are compared with the experimental data where available.
Open Access
Modeling and simulation of the ferroelectric based micro gyroscope: FEM analysis
(Taylor and Francis, 2013-09-23) Ozer, Z.; Mamedov, Amirullah M.; Özbay, Ekmel
This paper presents the design and modeling of micro-electromechanical systems (MEMS) on the ternary ferroelectric compounds (PZT) based by using finite element model (FEM) simulation. The conceptual framework establishes five steps to perform the critical analysis: design a novel structure, define the failure mechanisms under the given conditions, analyze different vibrations, analyze the operation principle, and detect resonance modes. In addition, MEMS failure modes were analyzed under different scenarios and the obtained results discussed. Copyright © Taylor & Francis Group, LLC.