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Effect of antimony substitution on structural and electrical properties of LaFeO3
No full textFine crystalline LaFeO3 and antimony-substituted compounds have been prepared by coprecipitation
method. The as synthesized materials have been sintered at 1000 ◦C for
single-phase compound formation and evaluated for their electrical and structural properties.
TG/DTA studies ascribed that the precursor powders have undergone rapid changes
during the transformation of LaFeO3 and substituted compounds. XRD data reveal the presence
ofwell-defined sharp peaks, indicating the single-phase perovskite structure of LaFeO3
and polycrystalline structure of LaFeO3 and Sb2O3 compounds. The FT–IR spectra exhibit an
absorption band corresponding to Fe–O stretching vibration, which is shifted on the substitution
of Sb3+ ions. The temperature dependent d.c. conductivity shows the semiconducting
behavior of the synthesized materials. The band gap values are found to increase upto
x = 0.4 and decrease on further increase in concentrations of the Sb3+ ions. The decrease
in dielectric constant with increasing frequency explained the Maxwell–Wagner Interfacial
polarization model
Pulse plated zinc sulphide films and their characteristics
No full textZinc sulphide thin films were deposited by the
pulse plating technique using AR grade Zinc sulphate and
sodium thiosulphate precursors. The pH of the deposition
bath was adjusted to 2. The duty cycle was varied in the
range of 20–60%. Total deposition time was kept constant
as 60 min in all the cases. X-ray diffraction studies indicated
the formation of single phase cubic zinc sulphide
films. After heat treatment the crystal structure transformed
to hexagonal structure. Optical absorption measurements
indicated a band gap values in the range of 3.6–4.0 eV as
the duty cycle decreased. EDAX studies yielded a composition
of the films deposited at 50% duty cycle is
Zn = 48%, S = 52%. XPS studies indicated the formation
of ZnS. The Zn 2p and S 3p peaks are observed. AFM
studies indicated a rms value of surface roughness of
55 nm for the films deposited at a duty cycle of 60%
Electrochemical behaviour of nano-sized spinel LiMn2O4 and LiAlxMn2xO4(x ¼ Al: 0.00–0.40) synthesized via fumaric acid-assisted sol–gel synthesis for use in lithium rechargeable batteries
No full textPristine spinel LiMn2O4 and LiAlxMn2xO4 (x ¼ Al: 0.00–0.40) with sub-micron sized particles have been
synthesized using fumaric acid as chelating agent by sol–gel method. The synthesized samples were
subjected to thermogravimetric analysis (TGA), X-ray diffraction (XRD), Fourier transform infrared
spectroscopy (FTIR), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and
cyclic voltammetry (CV) and galvanostatic cycling studies. The TGA curve of the gel shows several
weight-loss regions stepwise amounting to 55% till 800 1C attributed to the decomposition of the
precursors. Calcination to higher temperatures (800 1C) yields pure-phase spinel (LiAlxMn2xO4), as it is
evident from the high-intensity XRD reflections matching to the standard pattern. SEM and TEM studies
confirm that the synthesized grains are of uniform regular surface morphology. FT-IR studies show
stretching and bending vibration bands of Li–O, Li–Al–Mn–O. LiAl0.1Mn1.90O4 spinel was found to deliver
discharge capacity of 139mA h/g during the first cycle with columbic efficiency of 97%. LiAl0.1Mn1.90O4
spinel exhibits the high cathodic peak current indicating better electrochemical performance. Low
doping (x ¼ 0.1) of Al is found to be beneficial in stabilizing the spinel structure
A photo-physical and electrochemical impedance spectroscopy study on the quasi-solid state dye-sensitized solar cells based on poly(vinylidene fluoride-co-hexafluoropropylene
No full textQuasi-solid state dye-sensitized solar cells (DSSCs) were fabricated with poly(vinylidene fluoride-cohexafluoropropylene)
(PVDF-HFP) in methoxy propionitrile (MPN) as gel polymer electrolyte (GPE),
tetrabutylammonium iodide (TBAI)/iodine (I2) as redox couple, 4-tertiary butyl pyridine (TBP) as additive
and silica nanoparticles as fillers. The energy conversion efficiency of the cell with 5 wt% PVDF-HFP is
comparable to that one obtained in liquid electrolyte system. Solar cell containing PVDF-HFP with 0.8M
of TBAI and 0.12Mof I2 shows maximum short-circuit current density (JSC). Further, tertiary butyl pyridine
(TBP) has little effect in improving the performance of the solar cell. Moreover, the addition of 1 wt% silica
nanoparticles is found to improve the at-rest durability and the performance of the solar cell. The transient
photovoltage and photocurrent measurements were employed to find out the electron lifetimes in TiO2
electrode with different weight percentages of PVDF-HFP, various concentrations of I2 and durability of
the cell storage at 70 ◦C. A photocurrent density of 14.04mAcm−2, an open-circuit voltage of 0.71V, a fill
factor of 0.598 and an overall conversion efficiency of 5.97% under 100mWcm−2 was observed for the
best performance of a solar cell in this work
A new SiO/C anode composition for lithium-ion battery
No full textA new anode composition comprising SiO and graphite(C) is prepared through a high-energy ball milling process. During the first cycle, the
anode delivers high discharge and charge capacity values of 1556 and 693 mAh g−1, respectively. The electrode shows a reversible charge capacity
value of 688 mAh g−1 at the 30th cycle with 99% Coulombic efficiency. X-ray diffraction analysis reveals that ball milling does not produce any
new compound, but only causes a reduction in particle size. The irreversible and reversible capacities appear to be interdependent
Electrochemical properties of doped lithium titanate compounds and their performance in lithium rechargeable batteries
No full textSeveral substituted titanates of formula Li4−xMgxTi5−xVxO12 (0≤x≤1) were synthesized (and investigated) as anode materials in rechargeable
lithium batteries. Five samples labeled as S1–S5 were calcined (fired) at 900 ◦C for 10 h in air, and slowly cooled to room temperature in a tube
furnace. The structural properties of the synthesized products have been investigated by X-ray diffraction (XRD), scanning electron microscope
(SEM) and Fourier transmission infrared (FTIR). XRD explained that the crystal structures of all samples were monoclinic while S1 and S3 were
hexagonal. The morphology of the crystal of S1 was spherical while the other samples were prismatic in shape. SEM investigations explained that
S4 had larger grain size diameter of 15–16 �m in comparison with the other samples. S4 sample had the highest conductivity 2.452×10−4 S cm−1.
At a voltage plateau located at about 1.55V (vs. Li +), S4 cell exhibited an initial specific discharge capacity of 198 mAh g−1. The results of cyclic
voltammetry for Li4−xMgxTi5−xVxO12 showed that the electrochemical reaction was based on Ti4+/Ti3+ redox couple at potential range from 1.5 to
1.7V. There is a pair of reversible redox peaks corresponding to the process of Li+ intercalation and de-intercalation in the Li–Ti–O oxides
Thermal and electrochemical behaviour of C/LixCoO2 cell during safety test
No full textThermal and electrochemical processes in a 1000 mAh lithium-ion pouch cell with a graphite anode and a LixCoO2 cathode during a safety
test are examined. In overcharge tests, the forced current shifts the cell voltage to above 4.2V. This causes a cell charged at the 1C rate to lose
cycleability and a cell charged at the 3C rate to undergo explosion. In nail penetration and impact tests, a high discharge current passing through the
cells gives rise to thermal runaway. These overcharge and high discharge currents promote joule heat within the cells and leads to decomposition
and release of oxygen from the de-lithiated LixCoO2 and combustion of carbonaceous materials. X-ray diffraction analysis reveals the presence
of Co3O4 in the cathode material of a 4.5V cell heated to 400 ◦C. The major cathode product formed after the combustion process cells abused
by forced current is Co3O4 and by discharge current the products are LiCoO2 and Co3O4. The formation of a trace quantity of CoO through the
reduction of Co3O4 by virtue of the reducing power of the organic solvent is also discussed
A preliminary investigation into the new class of lithium intercalating LiNiSiO4 cathode material
No full textA unique attempt to exploit silicate chemistry for a possible enhancement of the
electrochemical properties of a lithium ion system via exploration of the novel category lithium
intercalating LiNiSiO4 cathode has been made through the present study. A novel citric acid
assisted modified sol–gel method (CAM sol–gel) has been adopted to synthesize the title
compound with a formation temperature positioned well below 500 ◦C, as derived from thermal
studies. A powder x-ray diffraction (PXRD) pattern evidenced the absence of undesirable peaks
and confirmed the formation of a hexagonal lattice structure with enhanced crystallinity and
phase purity, and the presence of uniformly distributed particles of ∼200 nm size with well
defined grain boundaries is obvious from the scanning electron microscopy (SEM) image of
LiNiSiO4 material. Further, magic angle spinning (MAS) 7Li nuclear magnetic resonance
(NMR) results from LiNiSiO4 confirmed the presence of a layered type of crystal arrangement.
A cyclic voltammetry (CV) study performed on a LiNiSiO4 cathode revealed an excellent
reversibility without any change in the peak position upon extended cycling, thus substantiating
the structural stability upon progressive cycling
Growth mechanism and optoelectronic properties of nanocrystalline In2O3 films prepared by chemical spray pyrolysis of metal-organic precursor
No full textThin films of indium oxide, In2O3, were deposited by chemical spray pyrolysis technique, using aqueous alcoholic solutions of indium
acetylacetonate (In-acac) precursor, on glass substrates kept at temperatures between 300 and 500 1C. The structural, optical, and
electrical properties have been investigated as a function of deposition temperature, precursor concentration, carrier gas pressure, and
substrate-to-nozzle distance. X-ray diffraction studies showed that the formation of nanocrystalline In2O3 films is preferentially oriented
along (2 2 2) plane. The surface morphological modifications with substrate temperature were observed using scanning electron and
atomic force microscopic studies. Optical transmittance behavior of the films in the visible and IR region was strongly affected by the
deposition parameters. The optical band gap values observed are between 3.53 and 3.68 eV. The long wavelength limit of refractive index
is 1.83. The Hall mobility is found to vary from 23 to 37 cm2/V s and carrier density is found nearly constant at about 1020 cm�3
Magnetic phase stability and spin-dependent transport in CeNi4M (M=Sc, Ti, V, Cr, Mn, Fe, and Co): First-principles study
No full textof a set of intermetallic compounds CeNi4M �M=Sc-Co� are investigated. All the compounds are
considered to be in the orthorhombic phase, in which a transition metal atom M substitutes for one of the Ni
atoms in the parent hexagonal CeNi5 structure. The optimized lattice constants are shown to be in good
agreement with the corresponding experimental data. The volume of CeNi4M turns out to decrease with
changing the M component from Sc to Co. Our calculations reveal that the ferromagnetic state is energetically
more favorable for the compounds with M=Sc, Mn, Fe, and Co, while for CeNi4Cr, the structure is found to
be antiferromagnetic. Except for CeNi4Sc, the magnetism in these compounds originates mainly from M
atoms. The ferromagnetic coupling is mediated through the indirect d-d and d-f exchange interactions. The
spin-dependent transport calculations show that the spin polarization in the diffusive regime is significantly
higher than that in the ballistic one for these intermetallic compound