V. Veeraiah

Structural and dielectric studies of LiNiPO4 and LiNi0.5Co0.5PO4 cathode materials for lithium-ion batteries

Abstract Olivine-type LiNiPO4 has been considered as a most competitive positive electrode active material for lithium-ion batteries. In the present paper, the LiNiPO4 and Co-doped LiNi0.5Co0.5PO4 are synthesized by solid-state reaction method under air atmosphere. All the X-ray diffraction peaks of both the compounds are indexed and it is found that the samples are well crystallized in orthorhombic olivine structure belonging to the space group Pnma. The crystallite size is calculated from the Scherrer formula and it is found to be 6.918 and 4.818 nm for pure and doped samples, respectively. The surface morphology and grain sizes of the materials are investigated through scanning electron microscope. Presence of preferred local cation environment is understood from Fourier transform infrared spectroscopy (FTIR) studies. The conductivity and dielectric analysis of the samples are carried out at different temperatures and frequencies using the complex impedance spectroscopy technique. The electrical conductivity of LiNi0.5Co0.5PO4 is higher than that of pure LiNiPO4.

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.

Effect of strontium on Nd doped Ba1−xSrxCe0.65Zr0.25Nd0.1O3−δ proton conductor as an electrolyte for solid oxide fuel cells

Graphical abstract

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.

Effect of magnesium substitution on structural and dielectric properties of LiNiPO4

Abstract The aim of this paper is to study the effect of Mg2+ doping in place of Ni in LiNiPO4 compounds synthesized by solid state reaction method. As Mg is a relatively light and cheap, and is expected to stabilize the structure, it has been considered as a substituent for Ni. The structural and conductivity studies of the substituted phases are discussed in comparison with LiNiPO4. In this study, we have proposed cation-substituted compounds, LiNi1–xMgxPO4 (x = 0, 0.05, 0.1 and 0.15) where a part of the divalent state of Ni2+ is replaced with the corresponding amount of Mg2+ and where the charge compensation is maintained by lithium deficiency. It is possible to obtain the mentioned compounds because the pristine LiNiPO4 compound is stable in ambient atmosphere, which differs considerably from the LiCoPO4 compound.

Effect of Strontium the phase structure of Ba1−xSrxCe0.65Zr0.2Y0.15O3−δ (0 ≤ x ≤ 0.25) proton conductor by citrate–EDTA complexing sol–gel method

Abstract Proton conducting oxides Ba1−xSrxCe0.65Zr0.2Y0.15O3−δ (0 ≤ x ≤ 0.25) are prepared using the citrate–EDTA complexing sol–gel method. The effect of strontium and yttrium doping on the material properties is systematically investigated. The phase formation, thermal analysis, morphology, stability and conductivity measurements are performed on the sintered powders through TG–DTA, XRD, SEM, EDAX, FTIR, Raman and LCR measurements. The results indicated a single-phase orthorhombic system. Strontium incorporation helped in increasing the grain size up to 20% of strontium doping while reducing the lattice parameters and unit cell volume. The ionic conductivities of the Ba1−xSrxCe0.65Zr0.2Y0.15O3−δ sintered oxides increased with increase in the concentration of Sr2+ along with the co-doping strategy of trivalent Y3+ in the B site. Among the synthesized samples, Ba0.8Sr0.2Ce0.65Zr0.2Y0.15O3−δ pellet with orthorhombic structure showed highest conductivity with a value of 2.35 × 10−1 S/cm and 2.41 × 10−1 S/cm at 500 °C due to its smaller lattice volume, larger grain size and lower activation energy that led to excessive increase in conductivity. All pellets exhibited good chemical stability when exposed to air and H2O atmospheres. These results indicate that this composition can be used as a potential electrolyte if synthesis conditions and temperature are well maintained.

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 impedance studies of doped LLT materials for electrolytes of lithium-ion batteries

In order to attain high conductivity, we have to investigate the structural and conductivity studies of novel polycrystalline Lithium Lanthanum Titanate with doping of pentavalent Niobium. The compound Li0.5-xLa0.5NbxTi1-xO3 (x = 0, 0.05, 0.1 and 0.15) (LLTN) having perovskite Cubic structure synthesized by ceramic technology. The crystalline phase identification and determination of lattice parameters of each sample were carried out by X-ray diffraction (XRD) analysis. The Raman Spectra were performed to understand the bonding nature of these materials. The lithium-ion conductivity and dielectric constant of the compound have been determined with AC impedance spectroscopy.