amirullah mamedov | Bilkent University (original) (raw)

Papers by amirullah mamedov

Applied Physics A, Mar 1, 2017

major fields in acoustics. Sonic crystals (SCs) are defined as structured materials formed by a p... more major fields in acoustics. Sonic crystals (SCs) are defined as structured materials formed by a periodic distributions of acoustic scatterers embedded in a host material, with strong periodic modulations in their density and elastic coefficients between the constituent materials. The periodicity of the scatterers in a surrounding material gives rise to the appearance of sonic band gaps, a range of frequencies for which sound propagation is forbidden inside the crystal. These stop bands were observed at frequencies depending on the lattice constant of the array in the band structures of crystals with various lattice geometries [3-5]. The SCs have induced several application proposals and enabled development of many new technologies. Recent studies in this field have attracted a great interest due to the splendid application prospects, such as acoustic filters [6, 7], shield devices [8-10], defect states for acoustic filters and wave guides [11], and so on. Recently, an increased attenuation at low frequencies has been achieved by the locally resonant sonic materials formed by soft and rigid elements [12]. Several theoretical methods have been used to study the elastic/acoustic band structures, such as, the plane-wave expansion (PWE) method [13, 14], the finite difference time domain (FDTD) method [15], the extended plane wave expansion (EPWE) method [16, 17], the multiple scattering theory (MST) [18], perturbative approach [19], and variational method [20]. Among them, the PWE is the most widely used method for calculating the band structures. In the literature, acoustic band gaps of various two-dimensional sonic crystal structures were investigated and these structures mostly consist of circular cross-section scatterers in square, triangular, rectangular lattices, the constituent being either both solids or fluids, or mixed solid-fluid [21]. Practically, band gaps properties of sonic crystal structures or the acoustic dispersion of the branches can be controlled by the lattice filling factor, the constituent Abstract The propagation of acoustic waves in twodimensional sonic crystals (SC) is studied theoretically. Effects of elliptical rod orientations on the acoustic band gaps in periodic arrays of rigid solid rods embedded in a polar liquid are investigated. We have found that the pass bands and forbidden bands of the sonic crystals can be changed by utilizing the rotational anisotropy of the structure factor at different rotation angles of the scatterers. The plane wave expansion (PWE) method is used to calculate the band structure. The variation of the absolute band gap was also investigated as a function of any filling fraction at a fixed orientation of the elliptical columns. The gap-tuning effect can be controlled by the rotational asymmetry and eccentricity of the scatterers.

Physica status solidi, Jul 16, 1980

Optics and Spectroscopy, Jul 1, 1982

Izvestiya Vysshikh Uchebnykh Zavedenij, Fizika, 1986

Physica Status Solidi (a), 1980

Electrical Properties of Electron (2 MeV) Irradiated p-CdSiAs2 and p-ZnSiAs2 Crystals BY V.N. BRU... more Electrical Properties of Electron (2 MeV) Irradiated p-CdSiAs2 and p-ZnSiAs2 Crystals BY V.N. BRUDNYI (a), M.A. KRIVOV (a), A. MAMEDOV (b), A.I. POTAPOV (a), V.D. PROCHUKHAN (b), and YU.V. RUD (b) 'Up to date the ternary semiconducting CdSiAs2 and ZnSiAs2 compounds a r e

Physica B+C, 1984

In the present paper the near-normal incidence reflectance for BaxSr~-xNb206 (0.25 ~< x ~< 0.75) ... more In the present paper the near-normal incidence reflectance for BaxSr~-xNb206 (0.25 ~< x ~< 0.75) and Ba2NaNbsOt5 has been measured in the energy region 1.0 to 35.0 eV. The optical constants for the region 0 to 35.0 eV have been derived from a Kramers-Kronig analysis. In the energy region 3.0 to 12.0 eV all the data obtained can be explained as the result of interband transitions from the valence band formed by O 2p orbitals to Nb 4d conduction band splitted in this case into two sub-bands (de, dy) with a distance of about 5 eV between them. In the high energy region (~>15 eV), however, the extrema in the e2 spectra are attributed to the transitions from core levels (O2s, Sr4p, Ba5p3/2, Ba5pv2) to the conduction band. In this region the spin-orb~ital splitting of the Sr 4p core level, A = 0.6 eV, is also observed. On the base of the data obtained, the energy transition diagram of the crystals investigated has been drawn up. The BO6 oetahedron is shown to be prominent in the formation of the band structure of these crystals.

Journal of Engineering Physics, 1977

Using water and toluene as examples, it was established that the ratio between the coefficients o... more Using water and toluene as examples, it was established that the ratio between the coefficients of thermal conductivity and dynamic viscosity at high state parameters was proportional to the density to the power ~.

International Symposium Innovative Technologies Engineering and Science, Sep 29, 2017

Metamaterials are artificial materials that possess unusual physical properties that are not usua... more Metamaterials are artificial materials that possess unusual physical properties that are not usually found in natural materials. Phononic crystals (PnC) can be constructed by periodic distribution of inclusions embedded in a matrix with high contrast in mechanical properties. They can forbid the propagations of acoustic waves in certain frequencies by creating band gaps. Such band gaps may be independent of the direction of propagation of the incident wave. In present work the acoustic band structure of a two-dimensional phononic crystal consisting of square-shaped rods embedded in air matrix are studied to find the existence of stop bands for the waves of certain energy. The wave band structures of acoustic waves in 2D air/solid phononic structure are investigated theoretically by Finite Element (FE) simulations. A time harmonic analysis of the acoustic wave propagation is performed using the acoustics package of the FE software Comsol Multiphysics v5.3. Phononic band diagrams ω=ω(k) for a 2D PnC were plotted versus the wavevector k along the M-Г-X-M path in the first Brillouin zone. The calculated phonon dispersion results indicate the existence of full acoustic modes in the proposed structure along the high symmetry points.

World Journal of Condensed Matter Physics, 2015

In this work, we have investigated the electronic and optical properties of the technologically i... more In this work, we have investigated the electronic and optical properties of the technologically important rare earth oxide compounds-X2O3 (X: Gd, Tb) using the density functional theory within the GGA. The band structure of X2O3 have been calculated along high symmetry directions in the first brillouin zone. The real and imaginary parts of dilectric functions and the other optical responses such as energy-loss function, the effective number of valence electrons and the effective optical dielectric constants of the rare earth sesquioxides (Gd2O3 and Tb2O3) were calculated.

Ferroelectrics, May 19, 2019

We present band structure results for elastic waves in periodic composite materials consisting of... more We present band structure results for elastic waves in periodic composite materials consisting of a spiral scatterer shape embedded in a uniform silicon matrix. The material of the scatterer is tungsten as a high density material. The phononic band structure of two-dimensional solid phononic crystal is studied numerically by finite element method to obtain dispersion relations. We find full band gaps at relatively low frequencies for a low filling ratio. Due to spatial inhomogeneity, the unique structural characteristics of the spiral structure lead to localized modes. Hence, the proposed model geometry introduces a phononic crystal to cover a wide range of stopbands starting from low frequencies. The results could give a possibility to design effective filters for the low frequency range.

International Journal of Scientific and Technological Research, 2015

In this work, we have investigated the electronic and optical properties of the technologically i... more In this work, we have investigated the electronic and optical properties of the technologically important rare earth oxide compound-Dy2O3 using the density functional theory within the GGA. The band structure of Dy2O3 has been calculated along high symmetry directions in the first Brillouin zone. The real and imaginary parts of dilectric functions and the other optical responses such as energy-loss function, the effective number of valence electrons and the effective optical dielectric constants of the rare earth sesquioxide-Dy2O3 were calculated.

arXiv (Cornell University), May 7, 2013

In this report we present an investigation of the optical properties and band structure calculati... more In 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 LiNbO 3 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.

Ferroelectrics, Mar 11, 2020

In this study, the band structure and transmission in multiferroic based Sierpinski carpet phonon... more 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.

Physica status solidi, May 5, 2015

IOP conference series, Feb 1, 2017

In this study, we present the results of our ab initio calculation of the elastic constants, dens... more In 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.

Ferroelectrics, Jan 2, 2019

In the present study, the structural, electronic, optical, and mechanical properties of the Ruddl... more In the present study, the structural, electronic, optical, and mechanical properties of the Ruddlesden-Popper type oxide compounds are investigated by means of density functional theory. In our calculation, spin polarized electron band structures and density of the state were identified by adding to the spin contribution of the Mn-atom. For A 3 Mn 2 O 7 compounds, the real and imaginary parts of the dielectric function and other optical properties, such as energy loss function, effective number of valence electrons, and effective optical dielectric constant, were calculated accordingly. In addition, the bulk modules, shear modules, Young's modulus and Poisson ratios, anisotropy factors, sound velocities, and Debye temperatures for these compounds were calculated too.

Integrated Ferroelectrics, Oct 13, 2021

In present paper, the structural, mechanical, and electronic properties of the Sn2P2S6 compound u... more 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 (x) and the second harmonic generation response coefficient v (2) (À2x, x, x) over a large frequency range. The electronic linear electro-optic susceptibility v (2) (Àx, x, 0) is also evaluated below the band gap. These results are based on a series of the LDA calculation. The results for v (2) (Àx, x, 0) are in agreement with the experiment below the band gap and those for v (2) (Àx, x, 0) are compared with the experimental data where available.

Cogent Physics, Apr 11, 2016

In the present work, the acoustic band structure of a two-dimensional phononic crystal (PC) conta... more In the present work, the acoustic band structure of a two-dimensional phononic crystal (PC) containing an organic ferroelectric (PVDF-polyvinylidene fluoride) and topological insulator (SnTe) was investigated by the plane-wave-expansion (PWE) method. Two-dimensional PC with square lattices composed of SnTe cylindrical rods embedded in the PVDF matrix is studied to find the allowed and stop bands for the waves of certain energy. Phononic band diagram ω = ω(k) for a 2D PC, in which non-dimensional frequencies ωa/2πc (c-velocity of wave) were plotted vs. the wavevector k along the Г-X-M-Г path in the square Brillouin zone shows five stop bands in the frequency range between 10 and 110 kHz. The ferroelectric properties of PVDF and the unusual properties of SnTe as a topological material give us the ability to control the wave propagation through the PC over a wide frequency range of 10 3-10 6 Hz. SnTe is a discrete component that allows conducting electricity on its surface but shows insulator properties through its bulk volume. Tin telluride is considered as an acoustic topological insulator as the extension of topological insulators into the field of "topological phononics".

Ferroelectrics, May 18, 2016

Electronic structure and optical properties of the CdXO 3 and ZnXO 3 (XHGe, Sn) compounds have be... more Electronic structure and optical properties of the CdXO 3 and ZnXO 3 (XHGe, Sn) compounds have been investigated based on density functional theory. According to the predictive results, reveal that the CdXO 3 and ZnXO 3 would be candidates for a high performance lead free optical crystal, which will avoid the environmental toxicity problem of the lead-based materials.

arXiv (Cornell University), Apr 18, 2012

The electronic structures of ABO 3 ferroelectrics are calculated within the density functional th... more The electronic structures of ABO 3 ferroelectrics are calculated within the density functional theory, and their evolution is analyzed as the crystal-field symmetry changes from cubic to rhombohedral via tetragonal phases. Electronic structure fingerprints that characterize each phase from their electronic spectra are identified. We carried out electron-energy loss spectroscopy experiments by using synchrotron radiation and compared these results to the theoretical spectra calculated within DFT-LDA. The dominant role of the BO 6 octahedra in the formation of the energy spectra of ABO 3 compounds was demonstrated. Anomalous behavior of plasmons in ferroelectrics was exhibited by the function representing the characteristic energy loss in the region of phase transition.

Applied Physics A, Mar 1, 2017

major fields in acoustics. Sonic crystals (SCs) are defined as structured materials formed by a p... more major fields in acoustics. Sonic crystals (SCs) are defined as structured materials formed by a periodic distributions of acoustic scatterers embedded in a host material, with strong periodic modulations in their density and elastic coefficients between the constituent materials. The periodicity of the scatterers in a surrounding material gives rise to the appearance of sonic band gaps, a range of frequencies for which sound propagation is forbidden inside the crystal. These stop bands were observed at frequencies depending on the lattice constant of the array in the band structures of crystals with various lattice geometries [3-5]. The SCs have induced several application proposals and enabled development of many new technologies. Recent studies in this field have attracted a great interest due to the splendid application prospects, such as acoustic filters [6, 7], shield devices [8-10], defect states for acoustic filters and wave guides [11], and so on. Recently, an increased attenuation at low frequencies has been achieved by the locally resonant sonic materials formed by soft and rigid elements [12]. Several theoretical methods have been used to study the elastic/acoustic band structures, such as, the plane-wave expansion (PWE) method [13, 14], the finite difference time domain (FDTD) method [15], the extended plane wave expansion (EPWE) method [16, 17], the multiple scattering theory (MST) [18], perturbative approach [19], and variational method [20]. Among them, the PWE is the most widely used method for calculating the band structures. In the literature, acoustic band gaps of various two-dimensional sonic crystal structures were investigated and these structures mostly consist of circular cross-section scatterers in square, triangular, rectangular lattices, the constituent being either both solids or fluids, or mixed solid-fluid [21]. Practically, band gaps properties of sonic crystal structures or the acoustic dispersion of the branches can be controlled by the lattice filling factor, the constituent Abstract The propagation of acoustic waves in twodimensional sonic crystals (SC) is studied theoretically. Effects of elliptical rod orientations on the acoustic band gaps in periodic arrays of rigid solid rods embedded in a polar liquid are investigated. We have found that the pass bands and forbidden bands of the sonic crystals can be changed by utilizing the rotational anisotropy of the structure factor at different rotation angles of the scatterers. The plane wave expansion (PWE) method is used to calculate the band structure. The variation of the absolute band gap was also investigated as a function of any filling fraction at a fixed orientation of the elliptical columns. The gap-tuning effect can be controlled by the rotational asymmetry and eccentricity of the scatterers.

Physica status solidi, Jul 16, 1980

Optics and Spectroscopy, Jul 1, 1982

Izvestiya Vysshikh Uchebnykh Zavedenij, Fizika, 1986

Physica Status Solidi (a), 1980

Electrical Properties of Electron (2 MeV) Irradiated p-CdSiAs2 and p-ZnSiAs2 Crystals BY V.N. BRU... more Electrical Properties of Electron (2 MeV) Irradiated p-CdSiAs2 and p-ZnSiAs2 Crystals BY V.N. BRUDNYI (a), M.A. KRIVOV (a), A. MAMEDOV (b), A.I. POTAPOV (a), V.D. PROCHUKHAN (b), and YU.V. RUD (b) 'Up to date the ternary semiconducting CdSiAs2 and ZnSiAs2 compounds a r e

Physica B+C, 1984

In the present paper the near-normal incidence reflectance for BaxSr~-xNb206 (0.25 ~< x ~< 0.75) ... more In the present paper the near-normal incidence reflectance for BaxSr~-xNb206 (0.25 ~< x ~< 0.75) and Ba2NaNbsOt5 has been measured in the energy region 1.0 to 35.0 eV. The optical constants for the region 0 to 35.0 eV have been derived from a Kramers-Kronig analysis. In the energy region 3.0 to 12.0 eV all the data obtained can be explained as the result of interband transitions from the valence band formed by O 2p orbitals to Nb 4d conduction band splitted in this case into two sub-bands (de, dy) with a distance of about 5 eV between them. In the high energy region (~>15 eV), however, the extrema in the e2 spectra are attributed to the transitions from core levels (O2s, Sr4p, Ba5p3/2, Ba5pv2) to the conduction band. In this region the spin-orb~ital splitting of the Sr 4p core level, A = 0.6 eV, is also observed. On the base of the data obtained, the energy transition diagram of the crystals investigated has been drawn up. The BO6 oetahedron is shown to be prominent in the formation of the band structure of these crystals.

Journal of Engineering Physics, 1977

Using water and toluene as examples, it was established that the ratio between the coefficients o... more Using water and toluene as examples, it was established that the ratio between the coefficients of thermal conductivity and dynamic viscosity at high state parameters was proportional to the density to the power ~.

International Symposium Innovative Technologies Engineering and Science, Sep 29, 2017

Metamaterials are artificial materials that possess unusual physical properties that are not usua... more Metamaterials are artificial materials that possess unusual physical properties that are not usually found in natural materials. Phononic crystals (PnC) can be constructed by periodic distribution of inclusions embedded in a matrix with high contrast in mechanical properties. They can forbid the propagations of acoustic waves in certain frequencies by creating band gaps. Such band gaps may be independent of the direction of propagation of the incident wave. In present work the acoustic band structure of a two-dimensional phononic crystal consisting of square-shaped rods embedded in air matrix are studied to find the existence of stop bands for the waves of certain energy. The wave band structures of acoustic waves in 2D air/solid phononic structure are investigated theoretically by Finite Element (FE) simulations. A time harmonic analysis of the acoustic wave propagation is performed using the acoustics package of the FE software Comsol Multiphysics v5.3. Phononic band diagrams ω=ω(k) for a 2D PnC were plotted versus the wavevector k along the M-Г-X-M path in the first Brillouin zone. The calculated phonon dispersion results indicate the existence of full acoustic modes in the proposed structure along the high symmetry points.

World Journal of Condensed Matter Physics, 2015

In this work, we have investigated the electronic and optical properties of the technologically i... more In this work, we have investigated the electronic and optical properties of the technologically important rare earth oxide compounds-X2O3 (X: Gd, Tb) using the density functional theory within the GGA. The band structure of X2O3 have been calculated along high symmetry directions in the first brillouin zone. The real and imaginary parts of dilectric functions and the other optical responses such as energy-loss function, the effective number of valence electrons and the effective optical dielectric constants of the rare earth sesquioxides (Gd2O3 and Tb2O3) were calculated.

Ferroelectrics, May 19, 2019

We present band structure results for elastic waves in periodic composite materials consisting of... more We present band structure results for elastic waves in periodic composite materials consisting of a spiral scatterer shape embedded in a uniform silicon matrix. The material of the scatterer is tungsten as a high density material. The phononic band structure of two-dimensional solid phononic crystal is studied numerically by finite element method to obtain dispersion relations. We find full band gaps at relatively low frequencies for a low filling ratio. Due to spatial inhomogeneity, the unique structural characteristics of the spiral structure lead to localized modes. Hence, the proposed model geometry introduces a phononic crystal to cover a wide range of stopbands starting from low frequencies. The results could give a possibility to design effective filters for the low frequency range.

International Journal of Scientific and Technological Research, 2015

In this work, we have investigated the electronic and optical properties of the technologically i... more In this work, we have investigated the electronic and optical properties of the technologically important rare earth oxide compound-Dy2O3 using the density functional theory within the GGA. The band structure of Dy2O3 has been calculated along high symmetry directions in the first Brillouin zone. The real and imaginary parts of dilectric functions and the other optical responses such as energy-loss function, the effective number of valence electrons and the effective optical dielectric constants of the rare earth sesquioxide-Dy2O3 were calculated.

arXiv (Cornell University), May 7, 2013

In this report we present an investigation of the optical properties and band structure calculati... more In 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 LiNbO 3 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.

Ferroelectrics, Mar 11, 2020

In this study, the band structure and transmission in multiferroic based Sierpinski carpet phonon... more 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.

Physica status solidi, May 5, 2015

IOP conference series, Feb 1, 2017

In this study, we present the results of our ab initio calculation of the elastic constants, dens... more In 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.

Ferroelectrics, Jan 2, 2019

In the present study, the structural, electronic, optical, and mechanical properties of the Ruddl... more In the present study, the structural, electronic, optical, and mechanical properties of the Ruddlesden-Popper type oxide compounds are investigated by means of density functional theory. In our calculation, spin polarized electron band structures and density of the state were identified by adding to the spin contribution of the Mn-atom. For A 3 Mn 2 O 7 compounds, the real and imaginary parts of the dielectric function and other optical properties, such as energy loss function, effective number of valence electrons, and effective optical dielectric constant, were calculated accordingly. In addition, the bulk modules, shear modules, Young's modulus and Poisson ratios, anisotropy factors, sound velocities, and Debye temperatures for these compounds were calculated too.

Integrated Ferroelectrics, Oct 13, 2021

In present paper, the structural, mechanical, and electronic properties of the Sn2P2S6 compound u... more 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 (x) and the second harmonic generation response coefficient v (2) (À2x, x, x) over a large frequency range. The electronic linear electro-optic susceptibility v (2) (Àx, x, 0) is also evaluated below the band gap. These results are based on a series of the LDA calculation. The results for v (2) (Àx, x, 0) are in agreement with the experiment below the band gap and those for v (2) (Àx, x, 0) are compared with the experimental data where available.

Cogent Physics, Apr 11, 2016

In the present work, the acoustic band structure of a two-dimensional phononic crystal (PC) conta... more In the present work, the acoustic band structure of a two-dimensional phononic crystal (PC) containing an organic ferroelectric (PVDF-polyvinylidene fluoride) and topological insulator (SnTe) was investigated by the plane-wave-expansion (PWE) method. Two-dimensional PC with square lattices composed of SnTe cylindrical rods embedded in the PVDF matrix is studied to find the allowed and stop bands for the waves of certain energy. Phononic band diagram ω = ω(k) for a 2D PC, in which non-dimensional frequencies ωa/2πc (c-velocity of wave) were plotted vs. the wavevector k along the Г-X-M-Г path in the square Brillouin zone shows five stop bands in the frequency range between 10 and 110 kHz. The ferroelectric properties of PVDF and the unusual properties of SnTe as a topological material give us the ability to control the wave propagation through the PC over a wide frequency range of 10 3-10 6 Hz. SnTe is a discrete component that allows conducting electricity on its surface but shows insulator properties through its bulk volume. Tin telluride is considered as an acoustic topological insulator as the extension of topological insulators into the field of "topological phononics".

Ferroelectrics, May 18, 2016

Electronic structure and optical properties of the CdXO 3 and ZnXO 3 (XHGe, Sn) compounds have be... more Electronic structure and optical properties of the CdXO 3 and ZnXO 3 (XHGe, Sn) compounds have been investigated based on density functional theory. According to the predictive results, reveal that the CdXO 3 and ZnXO 3 would be candidates for a high performance lead free optical crystal, which will avoid the environmental toxicity problem of the lead-based materials.

arXiv (Cornell University), Apr 18, 2012

The electronic structures of ABO 3 ferroelectrics are calculated within the density functional th... more The electronic structures of ABO 3 ferroelectrics are calculated within the density functional theory, and their evolution is analyzed as the crystal-field symmetry changes from cubic to rhombohedral via tetragonal phases. Electronic structure fingerprints that characterize each phase from their electronic spectra are identified. We carried out electron-energy loss spectroscopy experiments by using synchrotron radiation and compared these results to the theoretical spectra calculated within DFT-LDA. The dominant role of the BO 6 octahedra in the formation of the energy spectra of ABO 3 compounds was demonstrated. Anomalous behavior of plasmons in ferroelectrics was exhibited by the function representing the characteristic energy loss in the region of phase transition.