K. Vijaya Babu

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.

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.

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.

Effect of Nb substitution on structural, electrical and electrochemical properties of LiTi2(PO4)3 as electrolyte materials for lithium ion batteries

ABSTRACT The NASICON (Na Super Ionic CONductors)-type materials are good ionic conductors when serving as solid electrolytes for lithium–ion batteries. In this paper, Nb-doped LiTi2(PO4)3 has been synthesized by solid-state reaction method and the structural, vibrational and dielectric studies are systematically investigated. The X-ray diffraction conforms that the Nb-doped LiTi2(PO4)3 compound has NASICON structure, i.e. rhombohedral with space group R-3c. The average crystallite size and lattice constant are increased with dopant concentration. The grain sizes of the synthesized compounds are investigated by scanning electron microscope and it is found to be in the range of 5 μm. From Fourier-transform infrared spectroscopy spectra, stretching vibrations of P-O-P bond are identified in the region of 700–750 cm−1. AC electrical study is carried out by exploiting the impedance and dielectric spectroscopy. The activation energy increases with dopant concentration since ion diffusion becomes easy as the volume fraction of the grain increases. Non-Debye behavior of conductivity relaxation is reflected in the modulus analysis.

Dielectric and impedance analysis of Li0.5La0.5Ti1-xZrxO3(x = 0.05 and 0.1) ceramics as improved electrolyte material for lithium-ion batteries

Abstract The most attractive property of Li0.5La0.5TiO3 (LLTO) electrolytes is their high ionic conductivity. Studies have shown that LLTO is capable of existing in a state with an ionic conductivity of 10-3 S/cm, which is comparable to liquid electrolytes. In addition to the high ionic conductivity of the material, LLTO is electrochemically stable and able to withstand hundreds of cycles. So, the studies of the solid electrolyte material are very important for the development of lithium-ion batteries. In the present paper, Li0.5La0.5Ti1-xZrxO3 (x = 0.05 and 0.1) have been prepared by a solid-state reaction method at 1300 °C for 6 hours to improve electrolyte materials for lithium-ion batteries. The phase identified by X-ray diffractometry and crystal structure corresponds to pm3m (2 2 1) space group (Z = 1). The frequency and temperature dependence of impedance, dielectric permittivity, dielectric loss and electric modulus of the Li0.5La0.5Ti1-xZrxO3 (x = 0.05 and 0.1) have been investigated. The dielectric and impedance properties have been studied over a range of frequency (42 Hz to 5 MHz) and temperatures (30 °C to 100 °C). The frequency dependent plot of modulus shows that the conductivity relaxation is of non-Debye type.

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.