Suprem R. Das

Structural and multiferroic properties of La-modified BiFeO3 ceramics

The coexistence of the magnetic and the electrical properties in lanthanum (La)-modified bismuth ferrite (Bi1−xLaxFeO3, x=0.05, 0.1, 0.15, and 0.2) ceramics was studied and compared with those of bismuth ferrite (BiFeO3). The presence of a small secondary phase of BiFeO3 (arises due to excess Bi2O3) was removed on La substitution at the Bi site, as observed in x-ray diffraction (XRD). The effect of La substitution on dielectric constant, loss tangent, and remnant polarization of the samples was studied in a wide range of temperature (77–400K) and frequency (1kHz–1MHz). The variation of magnetization, coercive field, and exchange bias with temperature (2–300K) and La concentration were investigated. These changes in the magnetic parameters with La doping along with those of the electron magnetic resonance parameters measured at 300K and 9.28GHz are understood in terms of increase in the magnetic anisotropy and magnetization. These results also show that stabilization of crystal structure and nonuniformity ...

Effect of La substitution on structural and electrical properties of BiFeO3 thin film

The effect of La substitution on the structural and electrical properties of multiferroic BiFeO3 thin films grown on Pt∕TiO2∕SiO2∕Si substrates by pulsed laser deposition has been reported. X-ray diffraction data confirmed the substitutions of La into the Bi site with the elimination of all of the secondary phases. The dielectric constant of the films was systematically increased from 165 to ∼350 and the films showed excellent dielectric loss behavior. We observed a gradual increase in the remnant polarization (2Pr) with lanthanum substitution obtaining a maximum value of ∼42μC∕cm2 at 20mol% La incorporation. The leakage current behavior at room temperature of the films was studied and it was found that the leakage current decreased from 10−4to10−7A∕cm2 for La-substituted films at a field strength of 50kV∕cm. The reduction of dc leakage current of La-substituted films is explained on the basis of relative phase stability and improved microstructure of the material.

Spinel LiMn2−xNixO4 cathode materials for high energy density lithium ion rechargeable batteries

The practical limitations of fully lithium ion insertion and extraction into LiMn2O4 cathode structure without any structural instability make it unsuitable in commercial Li-ion rechargeable batteries. In this work, we showed that those partially substituted by Ni, i.e., LiMn2−xNixO4 (0≤x≤0.5), prepared by sol-gel technique, could be used as a potential candidate for high energy density and high voltage Li-ion battery applications with superior rate capabilities. The improved structural stability of the cathode was probed by x-ray diffraction and micro-Raman spectroscopy. The density-functional theoretical calculations were employed to identify the minimum energy needed for Li+ diffusion pathway and activation energy in the spinel framework with different Ni ion concentrations. Our results showed significant enhancement in the properties with 25at.% of Ni solid-solution doping in LiMn2O4 host and the experimental results are in line with the theoretical computations.

Li-Ion Rechargeable Battery with LiMn1.5Ni0.46Rh0.04O4 Spinel Cathode Material

Limn 1.5 Ni 0.46 Rh 0.04 O 4 cathode material was synthesized by the sol-gel method and used in Li-ion coin cells. The structural and electrochemical studies were carried out using X-ray diffraction and X-ray photoelectron spectroscopy of the cathode material and charge-discharge characteristics of the assembled battery. The lattice parameter before and after charge-discharge cycles were found to be about 8.217 and 8.202 A, respectively. The initial discharge capacity was found to be about 153 mAh/g and the capacity retention was about 93.5% after 50 charge-discharge cycles.

Role of Rare-Earth Element Doping in the Cycleability of LiMn2O4 Cathodes for Li-ion Rechargeable Batteries

We have synthesized spinel LiMn 1.99 Nd 0.01 O 4 and LiMn 1.99 Ce 0.01 O 4 powder by chemical synthesis method. The synthesized powders were used to prepare cathodes for Li ion coin cells. The structural and electrochemical properties were investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), cyclic voltammetry and charge-discharge studies, respectively. The cyclic voltammetry of the cathodes revealed the reversible nature of Li-ion intercalation in the cell. The charge-discharge characteristics for LiMn1.99Ce0.01O4 were obtained in 3.5 V – 4.8 V voltage range, while for LiMn 1.99 Nd 0.01 O 4 the charge-discharge were carried out in 3.4 V – 4.4 V range. The initial discharge capacities of LiMn 1.99 Ce 0.01 O 4 and LiMn 1.99 Nd 0.01 O 4 were obtained as 134mAh/g and 149 mAh/g, respectively. The coin cells were tested for up to 25 charge-discharge cycles and after 25 cycles the discharge capacities were determined to 79.5 mAh/g and 132 mAh/g for LiMn 1.99 Ce 0.01 O 4 and LiMn 1.99 Nd 0.01 O 4 cathodes respectively. However, by doping with a small concentration of rare earth materials, like Ce and Nd reduces the capacity fading in pure LiMn 2 O 4 cathodes making it suitable for Li-ion battery applications.

Electrochemical Properties of Solution Synthesized Undoped and Aluminum Doped Lithium Manganate Thin Films

The spinel structured lithium manganate (LMO) is a promising cathode material for lithium ion rechargeable micro-batteries due to its higher energy density, environmentally benign nature, and low cost. To date, self-discharge and capacity fading (4 and 3V range), especially at elevated temperatures, still remains major research issues of LMO based cathodes. In the present work we have successfully synthesized lithium manganate thin films by a cost effective solution growth technique. These films exhibited excellent reversible lithium ion intercalation behavior with a discharge capacity of about 55.08:Ahcm −2 :m −1 at a load of 20:Acm −2 . The Li + diffusivity was found to increase by substituting a part of manganese with aluminum (Al) in LMO lattice. Al substituted LMO films exhibited better cycleability as compared to the undoped LMO films. Further studies are in progress to investigate the effect of Al substitution on the cycleability of the films.

Influence of Ta 2 O 5 , TiO 2 , and ZrO 2 Interfacial Layers on Structural and Electrical Properties of Laser Ablated Ba 0.5 Sr 0.5 TiO 3 Thin Films

Pulsed laser deposition technique was used to fabricate Ba 0.5 Sr 0.5 TiO 3 (BST) thin-films on Pt/TiO 2 /SiO 2 /Si substrates. The influence of thin interfacial layers of Ta 2 O 5 , TiO 2 , and ZrO 2 , on the structural and electrical properties of BST thin films was investigated. Insertion of interfacial layers does not affect the perovskite phase formation of BST thin films. Buffer layers helped to make uniform distribution of grains and resulted in a relative increase in the average grain size. The dielectric tunability of BST thin films was reduced with the presence of buffer layers. A BST thin film having a dielectric permitivity of 470 reduced to 337, 235 and 233 in the presence of Ta 2 O 5 , TiO 2 , and ZrO 2 layers, respectively. The reduction of the relative dielectric permittivity of BST films with the insertion of interfacial layers was explained in terms of a series capacitance effect, due to the low dielectric constant of interfacial layers. The TiO 2 layer did not show any appreciable change in the leakage current density. Deposition of thin Ta 2 O 5 and ZrO 2 interfacial layer on top of Pt reduced the leakage current density by an order of magnitude.