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Öğe Ab initio Modeling of Elastic and Optical Properties of Sb and Bi Sesquioxides(Iop Publishing Ltd, 2018) Koc, H.; Akhundov, Chingiz G.; Mamedov, Amirullah M.; Ozbay, EkmelFirst-principle calculations performed the structural, mechanical, electronic, and optical properties of Sb2O3 and Bi2O3 compounds in monoclinic (claudetite and alpha-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.Öğe 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, EkmelIn 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.Öğe 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, EkmelIn 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.Öğe 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, EkmelIn 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.Öğe Elastic and optical properties of sillenites: First principle calculations(Taylor & Francis Ltd, 2020) Koc, Husnu; Palaz, Selami; Simsek, Sevket; Mamedov, Amirullah M.; Ozbay, EkmelIn 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.Öğe Elastic, Electronic, and Optical properties of NaSnX (X=Sb, Bi, As): First principle calculations(Iop Publishing Ltd, 2019) Koc, Husnu; Mamedov, Amirullah M.; Ozbay, EkmelIn 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 exchange-correlation 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.Öğe 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, EkmelThe 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.Öğe 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, EkmelIn 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.Öğe Electronic Structure of Conventional Slater Type Antiferromagnetic Insulators: AIrO3 (A=Sr, Ba) Perovskites(Institute of Physics, 2022) Koc, Husnu; Mamedov, Amirullah M.; Ozbay, EkmelThe 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.Öğe 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, EkmelIn 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.Öğe Incommensurate Phase Transition and Electronic Properties of BaMnF4(Iop Publishing Ltd, 2019) Palaz, Selami; Simsek, Sevket; Koc, Husnu; Babayeva, Rena; Mamedov, Amirullah M.; Ozbay, EkmelWe 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.Öğe Mechanical, electronic, and optical properties of Bi2S 3and Bi2Se3 compounds: First principle investigations(Springer Verlag, 2014) Koc, Husnu; Ozisik, Haci; Deligöz, Engin; Mamedov, Amirullah M.; Ozbay, EkmelThe structural, mechanical, electronic, and optical properties of orthorhombic Bi2S3 and Bi2Se3 compounds have been investigated by means of first principles calculations. The calculated lattice parameters and internal coordinates are in very good agreement with the experimental findings. The elastic constants are obtained, then the secondary results such as bulk modulus, shear modulus, Young's modulus, Poisson's ratio, anisotropy factor, and Debye temperature of polycrystalline aggregates are derived, and the relevant mechanical properties are also discussed. Furthermore, the band structures and optical properties such as real and imaginary parts of dielectric functions, energy-loss function, the effective number of valance electrons, and the effective optical dielectric constant have been computed. We also calculated some non-linearities for Bi2S 3 and Bi2Se3 (tensors of elasto-optical coefficients) under pressure. © Springer-Verlag 2014.Öğe 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, EkmelWe 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.Öğe Optical Properties and Electronic Band Structure of Topological Insulators (on A25B36 Compound Based)(Taylor & Francis Ltd, 2013) Koc, H.; Mamedov, Amirullah M.; Ozbay, EkmelWe have performed a first principles study of structural, electronic, and optical properties of rhombohedral Sb2Te3 and Bi2Te3 compounds using the density functional theory within the local density approximation. The lattice parameters, bulk modulus, and its pressure derivatives of these compounds have been obtained. The linear photon-energy dependent dielectric functions and some optical properties such as the energy-loss function, the effective number of valance electrons and the effective optical dielectric constant are calculated and presented in the study.Öğe Optical Properties of the Narrow-Band Ferroelectrics: First Principle Calculations(Taylor & Francis Ltd, 2015) Koc, Husnu; Simsek, Sevket; Mamedov, Amirullah M.; Ozbay, EkmelBased on density functional theory, we have studied the electronic, and optical properties of narrow-band ferroelectric compounds - (Ge,Sn) Te. Generalized gradient approximation has been used for modeling exchange-correlation effects. The lattice parameters of the considered compounds have been calculated. The calculated electronic band structure shows that GeTe and SnTe compounds have a direct forbidden band gap of 0.742 ev and 0.359 eV. The real and imaginary parts of dielectric functions and therefore, the optical functions such as energy-loss function, as well as the effective number of valance electrons and the effective optical dielectric constant are all calculated. Our structural estimation and some other results are in agreement with the available experimental and theoretical data.Öğe 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, EkmelIn 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.Öğe Slater Insulator Phase of X2 (X = Na, Li)IrO3: First Principles Calculation(Taylor & Francis Ltd, 2021) Koc, Husnu; Palaz, Selami; Mamedov, Amirullah M.; Ozbay, EkmelIn 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.Öğe 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]Öğe Strain effects and electronic structures of narrow band P-R ferroelectrics: First principles calculation(Taylor & Francis Ltd, 2019) Bozdag, Nedim; Koc, Husnu; Simsek, Sevket; Mamedov, Amirullah M.; Ozbay, EkmelIn the present work, the structural, mechanical, electronic and optical properties of the Ruddlesden-Popper(RP) Ba3X2S7 (X = Zr, Hf, Ti) sulfides compounds have been investigated by means of first principles calculations. The generalized gradiend approximation has been used for modeling exchange-correlation effects. It has been observed that the calculated lattice parameters are in good agreement with the experimental values. Bulk modulus, shear modulus, Young's modulus Poisson's ratio, and Poisson's ratio from the calculated elastic constants for Ba3Zr2S7, Ba3Hf2S7, and Ba3Ti2S7 compounds, respectively have been obtained. The obtained electronic band structure for Ba3Zr2S7 and Ba3Hf2S7 compounds are semiconductor in nature, and the Ba3Ti2S7 compound also is metallic. Based on the obtained electronic structures, we further calculated the frequency-dependent dielectric function and other optical functions along the x- and z- axes.Öğe Structural, elastic, and electronic properties of topological insulators: Sb2Te3 and Bi2Te3(IEEE, 2013) Koc, Husnu; Mamedov, Amirullah M.; Ozbay, EkmelWe have performed a first principles study of structural, elastic, and electronic properties of rhombohedral Sb2Te3 and Bi2Te3 compounds using the density functional theory within the local density approximation. The lattice parameters of considered compounds have been calculated. 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, and Debye temperature have also been estimated in the present work. The calculated electronic band structure shows that Sb2Te3 and Bi2Te3 compounds have a direct forbidden band gap. Our structural estimation and some other results are in agreement with the available experimental and theoretical data.
