Browsing by Subject "Ferroelectric materials"
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Item Open Access Dynamic nonlinear optical processes in some oxygen-octahedra ferroelectrics: first principle calculations(Taylor & Francis Inc., 2015) Simsek S.; Koc, H.; Palaz S.; Oltulu, O.; Mamedov, A. M.; Özbay, EkmelThe nonlinear optical properties and electro-optic effects of some oxygen-octahedra ferroelectrics are studied by the density functional theory (DFT) in the local density approximation (LDA) expressions based on first principle calculations without the scissor approximation. We present calculations of the frequency- dependent complex dielectric function and the second harmonic generation response coefficient over a large frequency range in tetragonal and rhombohedral phases. The electronic linear electro-optic susceptibility is also evaluated below the band gap. These results are based on a series of the LDA calculation using DFT. The results for are in agreement with the experiment below the band gap and those for are compared with the experimental data where available. © 2015 Taylor & Francis Group, LLC.Item Open Access Ferroelectric based microgyroscope for inertial measurement unit: Modeling and simulation(IEEE, 2012) Ozer, Z.; Mamedov, Amirullah M.; Özbay, EkmelThis 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.Item Open Access Linear and non-linear optical properties of AgBO3(B=Nb, Ta): First principle study(IEEE, 2013) Şimşek, Şevket; Mamedov, Amirullah M.; Özbay, EkmelThe 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.Item Open Access Low-temperature photoluminescence spectra of TlInxGa1-xS2 layer mixed crystals(Pergamon Press, 1995) Allakhverdiev, K. R.; Gasanly, N. M.; Aydınlı, AtillaLow-temperature photoluminescence spectra of TlInS2, TlIn0.95Ga0.05S2 and TlIn0.8Ga0.2S2 layer crystals were studied in the temperature range 14-220 K. The temperature dependencies of bands 2.374 eV (A), 2.570 eV (E) and 2.576 eV (F) for TlInS2 are interpreted by supposing that the crystal undergoes structural phase transitions. Band A is considered to come from a donor-acceptor recombination channel. © 1995.Item 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, EkmelThis 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.Item Open Access Optical properties of the narrow-band ferroelectrics: first principle calculations(Taylor & Francis Inc., 2015) Koc, H.; Simsek S.; Mamedov, A. M.; Özbay, 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 and 0.359. 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. © 2015 Taylor & Francis Group, LLC.Item Open Access Topological Insulators: Electronic Band Structure and Spectroscopy(Institute of Physics Publishing, 2017) Palaz S.; Koc, H.; Mamedov, Aamirullah M.; Özbay, EkmelIn this study, we present the results of our ab initio calculation of the elastic constants, density of states, charge density, and Born effective charge tensors for ferroelectric (rhombohedral) and paraelectric phases (cubic) of the narrow band ferroelectrics (GeTe, SnTe) pseudopotentials. The related quantities such as bulk modulus and shear modulus using obtained elastic constants have also been estimated in the present work. The total and partial densities of states corresponding to the band structure of Sn(Ge)Te(S,Se) were calculated. We also calculated the Born effective charge tensor of an atom (for instance, Ge, Sn, Te, etc.), which is defined as the induced polarization of the solid along the main direction by a unit displacement in the perpendicular direction of the sublattice of an atom at the vanishing electric field. © Published under licence by IOP Publishing Ltd.Item Open Access Two-dimensional ferroelectric photonic crystals: Optics and band structure(Taylor & Francis Inc., 2013-09-20) Simsek S.; Mamedov, A. M.; Özbay, EkmelIn this report we present an investigation of the optical properties and band structure calculations for the photonic structures based on the functional materials- ferroelectrics. A theoretical approach to the optical properties of the 2D and 3D photonic crystals which yields further insight in the phenomenon of the reflection from different families of lattice planes in relation to the presence of photonic gaps or photonic bands. We calculate the photonic bands and optical properties of LiNbO3 based photonic crystals. Calculations of reflection and transmission spectra show the features correspond to the onset of diffraction, as well as to additional reflectance structures at large values of the angle of incidence. © 2013 Copyright Taylor and Francis Group, LLC.