K. Ephraim Babu

First-Principles Study of Electronic Structure and Optical Properties of Cubic Perovskite CsCaF3

Electronic, structural and optical properties of the cubic perovskite CsCaF3 are calculated by using the full potential linearized augmented plane wave (FP-LAPW) plus local orbitals method with generalized gradient approximation (GGA) in the framework of the density functional theory. The calculated lattice constant is in good agreement with the experimental result. The electronic band structure shows that the fundamental band gap is wide and indirect at (Γ–R) point. The contribution of the different bands is analyzed from the total and partial density of states curves. The charge density plots show strong ionic bonding in Cs-F, and ionic and weak covalent bonding between Ca and F. Calculations of the optical spectra, viz., the dielectric function, optical reflectivity, absorption coefficient, real part of optical conductivity, refractive index, extinction coefficient and electron energy loss, are performed for the energy range 0–30 eV.

Investigation of optoelectronic properties of cubic perovskite LaGaO3

The structural, electronic, bonding and optical properties of cubic perovskite LaGaO3 have been calculated using the full-potential linearized augmented plane wave (FP-LAPW) method in the density functional theory (DFT) as embodied in WIEN2k code. The modified Becke-Johnson (mBJ) potential is applied for the calculation of electronic and optical properties. The calculated lattice constant is in good agreement with the experimental result. The predicted band structure shows an indirect (M-X) band gap of 4.22 eV. The bonding in the material is of mixed covalent and ionic nature. Optical properties like dielectric function, refractive index, reflectivity, conductivity and absorption coefficient are presented.

First-principles study of electronic and optical properties of cubic perovskite CsSrF3

We present first principles calculations of the electronic, structural and optical properties of the cubic perovskite CsSrF3 by using the full potential linearized augmented plane wave (FP-LAPW) plus local orbitals method with generalized gradient approximation (GGA) in the frame work of density functional theory. The calculated lattice constant is in a good agreement with the experimental result. The electronic band structure shows that the fundamental band gap is wide and direct at Γ point. The contribution of the different bands was analyzed from the total and partial density of states curves. The charge density plots show strong ionic bonding in Cs-F, ionic and weak covalent bonding between Sr and F. The calculated optical spectra viz., the dielectric function, optical reflectivity, absorption coefficient, real part of optical conductivity, refractive index, extinction coefficient and electron energy loss, are presented for the energy range of 0–30 eV.

Structural, electronic and elastic properties of KCaF3 and RbCaF3 for vacuum-ultraviolet-transparent lens materials

The first principles calculation within the full potential linearized augmented plane wave (FP-LAPW) method is applied to study the structural, electronic and elastic properties of cubic perovskite-type compounds KCaF3 and RbCaF3. The exchange correlation effects are included through the LDA, GGA and modified Becke-Johnson (mBJ) exchange potential. The calculated structural properties such as equilibrium lattice constant, the bulk modulus and its pressure derivative are in good agreement with the available data. KCaF3 and RbCaF3 have wide and indirect band gaps and they agree with experimental values. The elastic properties such as elastic constants, anisotropy factor, shear modulus, Young’s modulus and Poisson’s ratio are obtained for the first time. KCaF3 and RbCaF3 are elastically anisotropic and the B/G ratio indicate that these are ductile materials.

Structural and conductivity studies of LiNi0.5Mn0.5O2 cathode materials for lithium-ion batteries

Abstract Layered oxide LiMO2 (Ni, Co, Mn) have been proposed as cathode materials for lithium-ion batteries. Mainly LiNiO2 is accepted as an attractive cathode material because of its various advantages such as low cost, high discharge capacity, good reversibility. The LiNi0.5Mn0.5O2 powders are synthesized by a sol-gel method using citric acid as a chelating agent. The structure of the synthesized material is analyzed by using XRD, FT-IR and the microstructures of the samples are observed by using FESEM. The intensities and positions of the peaks are in a good agreement with the previous results. The morphological changes are clearly observed as a result of manganese substitution. The Fourier transform infrared (FT-IR) spectra obtained with KBr pellet data reveal the structure of the oxide lattice constituted by LiO6 and NiO6 octahedra. The conductivity studies are characterized by (EIS) in the frequency range of 42 Hz to 1 MHz at room temperature to 120 °C. The dielectric properties are analyzed in the framework of complex dielectric permittivity and complex electric modulus formalisms. It indicates that the conductivity increases with increasing temperature. The fitting data of EIS plots replicate the non-Debye relaxation process with negative temperature coefficient of resistance (NTCR) behavior.

Synthesis and structural characterization of LiNi0.92Mg0.08O2 and LiNi0.92Co0.06Mg0.02O2 cathode materials

At present three major layered structured oxides (LiCoO2, LiNiO2, and LiMnO2) are used for cathode materials. In the present study we synthesis LiNi0.92Mg0.08O2 and LiNi0.92Co0.06 Mg0.02O2 cathode materials in solid state reaction method at high temperature. The crystalline powders are characterized for their phase identification using x-ray diffraction analysis (XRD). All two synthesized samples possessed the α-NaFeO2 structure of the rhombohedral system (space group, R3¯m) with no evidence of any impurities. The morphological features of the powders are characterized by field effect scanning electron microscopy (FESEM). The Fourier Transform infrared (FT-IR) spectroscopic data reveals the structure of the oxide lattice constituted by LiO6 and NiO6 octahedra.

Structural and optoelectronic properties of cubic perovskite RbPbF3

Abstract.The structural and optoelectronic properties of cubic perovskite RbPbF3 are calculated using all electrons full potential linearized augmented plane wave (FP-LAPW) method. The calculated lattice constant is in good agreement with the experimental result. The calculated band structure shows a direct band gap of 3⋅07 eV. The contribution of different bands is analysed from the total and partial density of state curves. We identified hybridization of Pb s, Pb p states with F p states in the valence bonding region. Calculations of the optical spectra, viz., the dielectric function, optical reflectivity, absorption coefficient, real part of optical conductivity, refractive index, extinction coefficient and electron energy loss are performed for the energy range of 0–30 eV. Based on the direct bandgap, as well as other optical properties of the compound, it is predicted that this material is useful for vacuum-ultraviolet-transparent (VUV-transparent) applications.

Elastic and Optoelectronic Properties of KCdF3: ab initio Calculations through LDA/GGA/TB-mBJ within FP-LAPW Method

Ab initio calculations are performed on the electronic, structural, elastic and optical properties of the cubic per-ovskite KCdF3. The Kohn—Sham equations are solved by applying the full potential linearized augmented plane wave (FP-LAPW) method. The exchange correlation effects are included through the local density approximation (LDA), generalized gradient approximation (GGA) and modified Becke-Johnson (mBJ) exchange potential. The calculated lattice constant is in good agreement with the experimental result. The elastic properties such as elastic constants, anisotropy factor, shear modulus, Youngs modulus and Poissons ratio are calculated. KCdF3 is ductile and elastically anisotropic. The calculations of the electronic band structure, density of states (DOS) and charge density show that this compound has an indirect energy band gap (M—Γ) with a mixed ionic and covalent bonding. The contribution of the different bands is analyzed from the total and partial density of states curves. Optical response of the dielectric functions, optical reflectivity, absorption coefficient, real part of optical conductivity, refractive index, extinction coefficient and electron energy loss, are presented for the energy range of 0–40 eV. The compound KCdF3 can be used for high-frequency optical and optoelectronic devices.