Yazar "Palaz, Selami" seçeneğine göre listele

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    Band gap and optical transmission in the Fibonacci type one-dimensional A5B6C7 based photonic crystals
    (Wiley-V C H Verlag Gmbh, 2015) Simsek, Sevket; Koc, Husnu; Palaz, Selami; Oltulu, Oral; Mamedov, Amirullah M.; Ozbay, Ekmel
    In this work, we present an investigation of the optical properties and band structure calculations for the photonic crystal structures (PCs) based on one-dimensional (1D) photonic crystal. Here we use 1D A(5)B(6)C(7) (A:Sb; B:S, Se; C:I) based layers in air background. We have theoretically calculated photonic band structure and optical properties of A(5)B(6)C(7) (A:Sb; B:S, Se; C:I) based PCs. In our simulation, we employed the finite-difference time domain (FDTD) technique and the plane wave expansion method (PWE) which implies the solution of Maxwell equations with centered finite-difference expressions for the space and time derivatives.
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    Complete photonic band gaps in Sn2P2X6 (X = S, Se) supercell photonic crystals
    (Taylor & Francis Ltd, 2020) Simsek, Sevket; Palaz, Selami; Koc, Husnu; Mamedov, Amirullah M.; Ozbay, 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.
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    Complex Band Structure and Dispersion Relation of Acoustic Waves in Piezoelectric Based Topological Phononic Crystals
    (META Conference, 2019) Palaz, Selami; Ozer, Zafer; Simsek, Sevket; Koc, Husnu; Mamedov, Amirullah M.; Ozbay, Ekmel
    In present work, the acoustic band structure of a 2D phononic crystal (PC) containing piezoelectric materials (Bi12XO20, X=Si, Ge, Ti; LiTaO3) were investigated by the finite element method. 2D PC with triangular and honeycomb lattices composed of piezoelectric cylindrical rods are in the air and liquid matrix. The existence of stop bands are investigated for the waves of certain frequency ranges. This phononic band - forbidden frequency range - allows sound to be controlled in many useful ways in structures. These structure can be used as sonic filters, waveguides or resonant cavities. The calculated phonon dispersion results indicate the existence of full acoustic modes in the proposed structure along the high symmetry points. We have also calculated the band structures of the different types of unit cells that are yielded by space group symmetry operations of the triangular resonators. The results show that these acoustic metamaterials with Helmholtz resonators can be used successfully to reduce the Dirac cone frequencies. Dirac cone frequency decreases gradually with increasing filling ratio, which indicates a possible way to control wave propagation on the subwavelength scale. Numerical simulation results show that acoustic metamaterials can behave like zero-refractive-index media and can be applied to acoustic tunneling. © 2019, META Conference. All rights reserved.
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    Elastic and optical properties of sillenites: First principle calculations
    (Taylor & Francis Ltd, 2020) Koc, Husnu; Palaz, Selami; Simsek, Sevket; Mamedov, Amirullah M.; Ozbay, 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.
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    Electronic and elastic properties of the multiferroic crystals with the Kagome type lattices -Mn3V2O8 and Ni3V2O8: First principle calculations
    (Taylor & Francis Ltd, 2019) Koc, Husnu; Palaz, Selami; Mamedov, Amirullah M.; Ozbay, 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) E-g 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.
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    Electronic properties of spin excitation in multiferroics with a spinel structure: first principles calculation
    (Taylor & Francis Ltd, 2019) Koc, Husnu; Palaz, Selami; Mamedov, Amirullah M.; Ozbay, 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 E-g=1.87 eV for spin up and E-g=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.
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    Electronic, mechanical, and optical properties of Ruddlesden-Popper perovskite sulfides: First principle calculation
    (Taylor & Francis Ltd, 2018) Koc, Husnu; Palaz, Selami; Ugur, Gokay; Mamedov, Amirullah M.; Ozbay, Ekmel
    In the present paper we have investigated the electronic structure of some orthorhombic A(3)X(2)S(7) (X = Ti, Zr, and Hf) compounds based on the density functional theory. Then we extend the RuddlesdenPopper (RP) A(3)X(2)S(7) sulfides and examine how ferroelectricity is induced by coupled octahedral rotation modes. The mechanical and optical properties 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 A(3)X(2)S(7) can be understood from the nature of their electronic structures. The obtained electronic band structure for Ba3Hf2S7 and Ba3Hf2S7 compounds are semiconductor in nature, and the Ba3Hf2S7 compound is also semi-metal. Similar to ferroelectric oxides, there is a pronounced hybridization of electronic states between X-site cations and anions in A(3)X(2)S(7). Based on the obtained electronic structures, we further calculate the frequency-dependent dielectric function and other optical functions in different phases.
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    Incommensurate Phase Transition and Electronic Properties of BaMnF4
    (Iop Publishing Ltd, 2019) Palaz, Selami; Simsek, Sevket; Koc, Husnu; Babayeva, Rena; Mamedov, Amirullah M.; Ozbay, 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 t(2g) bands and occupied lower-Hubbard e(g) 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.
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    Mechanical, electronic, and optical properties of the A4B6 layered ferroelectrics: ab initio calculation
    (Wiley-V C H Verlag Gmbh, 2015) Koc, Husnu; Simsek, Sevket; Palaz, Selami; Oltulu, Oral; Mamedov, Amirullah M.; Ozbay, Ekmel
    We have performed a first principles study of the structural, elastic and electronic properties of orthorhombic SnS and GeS compounds using the density functional theory within the local density approximation. The second-order elastic constants have been calculated, and the other related quantities such as the Young's modulus, shear modulus, Poisson's ratio, anisotropy factor, sound velocities, Debye temperature, and hardness have also been estimated in the present work. All of the calculated modulus and Poisson's ratio for SnS were less than the same parameters for GeS. Our calculations have discovered the large anisotropy of elastic parameters in the (100) and (010)-planes for both compounds. The band structures of orthorhombic SnS and GeS have been calculated along high symmetry directions in the first Brillouin zone (BZ). The calculation results for the band gap of Sn(Ge) S gave E-g=0.256 eV (0.852 eV) and has an indirect character for an interband transition. The real and imaginary parts of dielectric functions and (by using these results) the optical constant such as energy-loss function, the effective number of valance electrons and the effective optical dielectric constant were calculated. All of the principal features and singularities of the dielectric functions for both compounds were found in the energy region between 2 eV and 20 eV.
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    Optical, electronic, and elastic properties of some A5B6C7 ferroelectrics (A=Sb, Bi; B=S, Se; C=I, Br, Cl): First principle calculation
    (Taylor & Francis Ltd, 2017) Koc, Husni; Palaz, Selami; Mamedov, Amirullah M.; Ozbay, Ekmel
    In present paper, we focus on the structural, mechanical, electronic, and optical properties for the A(5)B(6)C(7)(A = Sb, Bi; B = Te, Se; S; C = I, Br, Cl) compounds using the density functional methods in generalized gradient approximation. The lattice parameters, mechanical properties, electronic bands structures and the partial densities of states corresponding to the band structures, and optical properties are presented and analysed. Our structural estimation and some other results are in agreement with the available experimental and theoretical data.
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    Slater Insulator Phase of X2 (X = Na, Li)IrO3: First Principles Calculation
    (Taylor & Francis Ltd, 2021) Koc, Husnu; Palaz, Selami; Mamedov, Amirullah M.; Ozbay, Ekmel
    In the present work, the structural, electronic and mechanical properties of Na2IrO3 and Li2IrO3 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 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 X2IrO3 (X = Na, Li) compounds for both spin up and spin down states are indirect wide gap semiconductor in nature. Considering the spin states from the electronic band structure and density of the state (DOS) of the Na (Li)(2)IrO3 compounds, it has been identified that E-g=1.824 (2.315) eV for spin up and E-g=1.558 (2.019) 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.
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    Sn2P2X2 (X=S, Se) as novel materials for phononic crystals
    (META Conference, 2019) Palaz, Selami; Ozer, Zafer; Simsek, Sevket; Koc, Husnu; Mamedov, Amirullah M.; Ozbay, Ekmel
    [No abstract available]
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    The Mechanical, Electronic and Optical Properties of Sn2P2S6 Compound in Different Phases
    (Taylor & Francis Ltd, 2021) Koc, Husnu; Palaz, Selami; Simsek, Sevket; 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 (omega) and the second harmonic generation response coefficient chi ((2)) (-2 omega, omega, omega) over a large frequency range. The electronic linear electro-optic susceptibility chi ((2)) (-omega, omega, 0) is also evaluated below the band gap. These results are based on a series of the LDA calculation. The results for chi ((2)) (-omega, omega, 0) are in agreement with the experiment below the band gap and those for chi ((2)) (-omega, omega, 0) are compared with the experimental data where available.