Strain effects on structural, electronic, and optical properties of BeO by DFT (original) (raw)
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Accurate Electronic, Transport, and Related Properties of Wurtzite Beryllium Oxide (w-BeO)
Journal of Modern Physics, 2017
We report details of our ab-initio, self-consistent density functional theory (DFT) calculations of electronic and related properties of wurtzite beryllium oxide (w-BeO). Our calculations were performed using a local density approximation (LDA) potential and the linear combination of atomic orbitals (LCAO) formalism. Unlike previous DFT studies of BeO, the implementation of the Bagayoko, Zhao, and Williams (BZW) method, as enhanced by the work of Ekuma and Franklin (BZW-EF), ensures the full physical content of the results of our calculations, as per the derivation of DFT. We present our computed band gap, total and partial densities of states, and effective masses. Our direct band gap of 10.30 eV, reached by using the experimental lattice constants of a = 2.6979 A and c = 4.3772 A at room temperature, agrees very well the experimental values of 10.28 eV and 10.3 eV. The hybridization of O and Be p states in the upper valence bands, as per our calculated, partial densities of states...
Atomic Structure of Highly StrainedBiFeO3Thin Films
Physical Review Letters, 2012
We determine the atomic structure of the pseudotetragonal T-phase and the pseudorhombohedral R-phase in highly strained multiferroic BiFeO3 thin films by using a combination of atomic-resolution scanning transmission electron microscopy and electron energy-loss spectroscopy (EELS). The coordination of the Fe atoms and their displacement relative to the O and Bi positions are assessed by direct imaging. These observations allow us to interpret the electronic structure data derived from EELS and provide evidence for the giant spontaneous polarization in strained BiFeO3 thin films.
2019
CuBO2 (B=Y, Sc) has great interest nowadays, because it has a wide-range of application in solar cells, flat panel displays, gas sensors, biosensors and touch panels. Structural, electronic and optical properties of CuBO2 under axial strain were investigated by using full potential linearized augmented plane-wave (FP-LAPW) method based on density functional theory (DFT) within GGA and TB-mBJ(Tran-Blaha modified Beck-johnson) functional. The computed structural lattice parameters are in good agreement with the previous simulated and experimental results. The energy band structures, density of states, charge densities, bond lengths and optical properties are calculated and analyzed with and without strain. The results show that, by increasing the tensile strain, the band gap of CuBO2 oxide decrease as compared to unstrained copper oxide. From optical properties, it is noted that in visible energy region the CuYO2 have more transparent behavior as compared to CuScO2. The wide band-gap ...
First-principles study of the optical properties of BeO in its ambient and high-pressure phases
Journal of Physics and Chemistry of Solids, 2009
Optical properties such as the dynamic dielectric function, reflectance, and energy-loss function of beryllium oxide (BeO) in its ambient and high-pressure phases are reported for a wide energy range of 0–50eV. The calculations of optical properties employ first-principles methods based on all-electron density functional theory together with sum over states and finite-field methods. Our results show subtle differences in the
Strain induced Jahn-Teller distortions in BaFeO3 : A first-principles study
arXiv: Materials Science, 2017
The effect of epitaxial strain on structural, magnetic and electronic properties of BaFeO 3 per- ovskite oxide are investigated from first principles calculations, using the Density Functional The- ory (DFT) plus the Hubbard approach (DFT+U) within the Generalized Gradient Approximation (GGA). Hybrid functional calculations, based on mixed exact Hartree-Fock (HF) and DFT exchange energy functionals, are also performed. For the ground state calculations,the DFT+U is found more suitable to describe the half metallic and ferromagnetic state of cubic BaFeO 3 . The possible oc- curence of oxygen octahedra rotations, Jahn-Teller distortions and charge orderings through biaxial strain are explored. The obtained results reveal that the Jahn-teller distortion is induced under tensile biaxial strain while the oxygen octahedra rotations and breathing are unusualy not observed. Then, the strained BaFeO 3 is considered as a particular Jahn-Teller distorted perovskite with excep- tional propertie...
Physica Status Solidi (a), 2007
We present results of a theoretical study of the electronic band structure of wurtzite InN films under biaxial strain in the C -plane (0001) and in planes that correspond to non-polar orientations such as the A -plane (110) and the M -plane (100). The calculations are performed under the k · p perturbation theory approach using the Bir–Pikus Hamiltonian. The results show that the fundamental bandgap of InN shifts by 30 meV (14 meV) for isotropic tensile (compressive) strain in the C -plane with out-of-plane contraction (dilation) of 0.2%. For films of non-polar orientations, the c-axis lies in the film plane and the strain is expected to be different between directions parallel and perpendicular to c. Such anisotropic strain give rise to valence band mixing which results in dramatic changes in the optical polarization properties as evidenced by the calculated oscillator strengths of the interband transitions. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
Optical response of BiFeO3 films subjected to uniaxial strain
Physical Review Materials
The impact of single-axis lattice expansion on the optical response of BiFeO 3 films is examined. Low-energy He implantation is used to tailor morphotropic phases of BiFeO 3 films and study changes in their optical spectra with continuously increasing lattice expansion. He ion implantation of epitaxial rhombohedral (R)and tetragonal (T)-like BiFeO 3 films induces uniaxial out-of-plane strain that, on R-like films, eventually leads to a complete R-T phase transition. This approach allows us to provide insights into the optical response of BiFeO 3 films. Strain doping of T-like films leads to a significant redshift of the optical absorption spectra that is theoretically explained by a lowering of Fe 3d t 2g states. R-like films, on the other hand, show a less-pronounced sensitivity to uniaxial strain and a blueshift of about 250 meV at the strain-induced R-T transition. The results demonstrate that strain doping allows a deeper examination of the optical properties of epitaxial phases that are otherwise impossible to access by standard epitaxy.
Lattice dynamics of beryllium oxide: Inelastic x-ray scattering andab initiocalculations
Physical Review B, 2008
The phonon-dispersion relations of the lightest wurtzite structure compound BeO have been determined from inelastic x-ray scattering ͑IXS͒ measurements and analyzed by ab initio calculations. Experimental data and calculations show good agreement and reconcile the existing controversies. The phonon linewidth of the longitudinal-optical phonon along ⌫-A reveals a marked q dependence, which can be correlated with the two-phonon density of states, thus pointing toward a strong anharmonic behavior.
Pressure- and Strain-Dependent Quasiparticle Energies of Cubic, Wurtzite and Hexagonal BN
physica status solidi (b), 2000
The electronic excitation energies of boron nitride in the layered hexagonal (h-BN), zincblende (c-BN), and wurtzite (w-BN) structures under applied pressure and lattice stretching have been studied. Hydrostatic pressure applied on denser phases c-BN and w-BN has been considered, on the other hand for h-BN both hydrostatic pressure and compression along the c-axis have been studied. Pressure-and strain-dependent electronic excitation energies have been calculated using a DFT-GW method including quasiparticle corrections in GW approximation. The model we introduced to reproduce the dielectric screening of the system under study depends both on lattice parameters of the crystal and on its dielectric constant. Excitation spectra for the three phases under positive or negative stresses up to $ 0X01 Mbar show the same fundamental gap ordering found at equilibrium. On the other hand for h-BN our DFT-GW results predict, at about 197 c-axis enlarging, a minimal gap crossover that may play an important role when the material is intercalated.