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Akhilesh Kumar Singh

Publications and source records attributed to Akhilesh Kumar Singh.

At least 19 recordsLinked to original sources
arXiv2026

Spinel Ferrite-Based Materials for Electrochemical Applications: Synthesis, Applications, and Future Perspectives

Spinel ferrites have shown wide range of applications in various fields, including supercapacitors, Li-ion batteries, water splitting, chemical sensors, catalytic activity, high-frequency magnetic devices, and biomedical, hyperthermia, drug delivery applications., etc. This review focuses on the latest progress and trends on design of spinel ferrites (MFe2O4; M = Divalent transition metal ion) based materials for electrochemical applications. Spinel ferrites exhibit good chemical stability, high surface area and excellent electrochemical behaviour with their multiple oxidation states, making them suitable for the detection of a wide range of gaseous analytes including volatile organic compounds, heavy metal ions, biomolecules, and environmental pollutants. It also makes spinel ferrites a great choice for efficient energy storage and utility in supercapacitors. The electrochemical performance of spinel ferrite-based electrode materials can be effectively tuned via morphology control, incorporation of carbon-based materials, compositional substitution, doping and forming composition systems, especially in nanostructured form. This review will serve as a comprehensive resource for researchers interested in the synthesis and various enhancement techniques for electrode material composition of electrochemical device applications specifically, gas sensors and supercapacitors, which are two of the highest emerging functional applications for the new sustainability directed world, utilizing these advanced materials.

cond-mat.mtrl-sci↗
arXiv2025

Image Classification Method using Dynamic Quantum Inspired Genetic Algorithm

This study presents a dynamic Quantum-Inspired Genetic Algorithm (D-QIGA) for feature selection, leveraging quantum principles like superposition and rotation gates to enhance exploration and exploitation. D-QIGA introduces adaptive mechanisms and a lengthening chromosome strategy to avoid local optima and improve optimization. Tested on benchmark and real-world problems, it significantly outperforms traditional Genetic Algorithms, achieving over 99.99% classification accuracy compared to GA's 95%.

cs.NE↗
arXiv2019

Structural, Dielectric, Semiconducting and optical properties of High-Energy Ball Milled YFeO3 Nano-particles

In this work, we report the effects of calcination temperature on structural, dielectric, semiconducting and optical properties of YFeO3 nanoparticles prepared by a high energy ball milling process. The structural analysis of the X-ray diffraction data shows that YFeO3 exists in orthorhombic as well as in hexagonal mixed-phase states. The Rietveld analysis confirms that orthorhombic YFeO3 crystallizes into Pnma space group. The optical band gap of YFeO3 reduces from 1.96 eV to 1.68 eV with increasing the calcination temperature of the YFeO3 sample. The bandgap reducing effect might be attributed to the increased crystallite size and decreased lattice strain which is confirmed by the Williamson-Hall plot method. The obtained low bandgap YFeO3 ceramic may provide a new possibility to develop eco-friendly Ferroelectric photovoltaic devices.

cond-mat.mtrl-sci↗
arXiv2019

Synthesis, Structural and Optical Properties of (ALa)(FeMn)O6 (A = Ba and Sr) Double Perovskites

Here, we report structural and optical properties of (ALa)(FeMn)O6 (A = Ba and Sr) double perovskite synthesized via auto-combustion followed by a calcination process. Rietveld refinement of the structure using x-ray diffraction data reveals that (BaLa)(FeMn)O6 crystallizes into cubic crystal structure with space group Pm-3m while (SrLa)(FeMn)O6 crystallizes into rhombohedral crystal structure having space group R-3c. The absorption spectrum measurement using UV-Vis spectroscopy reveals that these samples are perfect insulator having an energy band gap between conduction and valence band of the order of 6 eV.

cond-mat.mtrl-sci↗
arXiv2019

X-ray Diffraction Analysis of Cu2+ Doped Zn1-xCuxFe2O4 Spinel Nanoparticles using Williamson-Hall Plot Method

The nanoparticles (NPs) of Zn1-xCuxFe2O4 (ZCFO) spinels with x = 0, 0.2, 0.4, 0.6 and 0.8 were synthesized by a sol-gel combustion method using acetate precursor. The NPs of ZCFO were prepared by following calcination process at 600C for 8hrs. The synthesized NPs of ZCFO were characterized by X-ray diffraction (XRD) analysis using Rietveld refinement. The Rietveld refinement of the XRD patterns revealed that the ZCFO spinels crystallize into single diamond cubic structure with Fd-3m space group. The lattice constant and unit cell volume for ZCFO NPs shrink with enhancing doping concentration of Cu2+ ion. The crystalline growth in the NPs of ZCFO was examined by peak broadening present in the XRD pattern. The Williamson-Hall (W-H) plot method were used to study the individual involvements of crystallite sizes and lattice strain on the peak broadening of the NPs of ZCFO spinels. Whereas, particle size of the ZCFO sample with x = 0.40 was estimated by high-resolution scanning electron microscopy micrographs

cond-mat.mtrl-sci↗
arXiv2018

Crystallite Size Effect on Lattice Strain and Crystal Structure of Ba1/4Sr3/4MnO3 Layered Perovskite Manganite

The single phase polycrystalline Ba1/4Sr3/4MnO3 layered perovskite manganite has been synthesized by combustion method having various crystallite sizes. The room temperature X-ray diffraction patterns reveal that Ba1/4Sr3/4MnO3 crystallizes into hexagonal crystal structure with space group P63/mmc as confirmed by Rietveld refinement. The scanning electron micrographs of Ba1/4Sr3/4MnO3 reveal uniform crystallite size of the samples. Effect of crystallite size on lattice strain and crystal structure has been studied using Rietveld refinement and Williamson-Hall plot, respectively. The structural lattice parameters decrease with increasing crystallite size. However, lattice strain increases with increasing crystallite-size.

cond-mat.mtrl-sci↗
arXiv2018

Structural, Ferroelectric, Magnetic and Magnetoelectric Response in Multiferroic (1-x)Bi(Ni1/2Ti1/2)O3-PbTiO3/xNi0.6Zn0.4Fe2O4 Particulate Composites

Multiferroic particulate composites have been fabricated by taking the morphotropic phase boundary composition of ferroelectric phase Bi(Ni1/2Ti1/2)O3-PbTiO3 and magnetic phase (Ni,Zn)Fe2O4. The ferroelectric phase has coexisting monoclinic and tetragonal perovskite structures with space group Pm and P4mm, respectively whereas the magnetic phase has spinel cubic structure with space group Fd3m. Rietveld structural analysis for the each components of composite reveals that the tetragonality (c/a) of the ferroelectric phase continuously increases with increasing the concentration of magnetic phase suggesting partial ionic diffusion between ferroelectric and magnetic phases, after composite formation. Composition dependent Mössbauer spectra of (1-x)Bi(Ni1/2Ti1/2)O3-PbTiO3/x(Ni,Zn)Fe2O4 reveals the superparamagnetic like behavior for the ferroelectric rich composition with x=0.2. The magnetic ordering increases for the composition with x=0.4 and 0.6 which completely transform into ferrimagnetic for the composition with x=0.9 for the magnetic phase rich compositions. Unlike the ferroelectric or magnetic components which do not exhibit the magnetoelectric response separately, large value of magnetoelectric coefficient (30 mV/Oe-cm) in (1-x)Bi(Ni1/2Ti1/2)O3-PbTiO3/xNi0.6Zn0.4Fe2O4 composite makes it promise for multifunctional applications.

cond-mat.mtrl-sci↗
arXiv2015

Investigation of Crystal Structure of SrLa(FeTi)O6 and BaLa(FeTi)O6 Perovskites by Rietveld Refinement

The structures of the recently reported ordered perovskites SrLa(FeTi)O6 and BaLa(FeTi)O6 have been revisited using Rietveld analysis of the powder x-ray diffraction data. Our studies clearly show that earlier authors have incorrectly reported the tetragonal structure in the I4/m space group for SrLa(FeTi)O6 and the cubic structure in the Fm3m space group for BaLa(FeTi)O6. The correct structure is found to be orthorhombic in the Pnma space group for SrLa(FeTi)O6 while cubic in the Pm3m space group for BaLa(FeTi)O6. Thus the BaLa(FeTi)O6 is not an ordered double perovskite as the occupancies of Ba/La ions at A-site and Fe/Ti ions at B-site are disordered resulting in the primitive cubic unit cell in the Pm3m space group. Similarly, the occupancies of Sr/La ions at A-site and Fe/Ti ions at B-site are disordered in SrLa(FeTi)O6 also, ruling out the ordered perovskite structure.

cond-mat.mtrl-sci↗
arXiv2014

Electric Field Induced Cubic to Monoclinic Phase Transition in Multiferroic 0.65Bi(Ni1/2Ti1/2)O3-0.35PbTiO3 Solid Solution

The results of x-ray diffraction (XRD) studies on 0.65Bi(Ni1/2Ti1/2)O3-0.35PbTiO3 solid solution poled at various electric field is presented. After poling, significant value of planar electromechanical coupling coefficient (kP) is observed for this composition having cubic structure in unpoled state. The cubic structure of 0.65Bi(Ni1/2Ti1/2)O3-0.35PbTiO3 transforms to monoclinic structure with space group Pm for the poling field greater than equal to 5kV/cm. Large c-axis microscopic lattice strain (1.6 %) is achieved at 30 kV/cm poling field. The variation of the c-axis strain and unit cell volume with poling field show a drastic jump similar to that observed for strain versus electric field curve in (1-x)Pb(Mg1/3Nb2/3)O3-xPbTiO3 and (1-x)Pb(Zn1/3Nb2/3)O3-xPbTiO3.

cond-mat.mtrl-sci↗
arXiv2014

Presence of a monoclinic (Pm) phase in the morphotropic phase boundary region of multiferroic (1-x)Bi(Ni1/2Ti1/2)O3-xPbTiO3 solid solution: A Rietveld study

We present here the results of structural studies on multiferroic (1-x)Bi(Ni1/2Ti1/2)O3-xPbTiO3 solid solution using Rietveld analysis on powder x-ray diffraction data in the composition range 0.35 to 0.55. We have determined precisely the stability region of various crystallographic phases at room temperature for (1-x)Bi(Ni1/2Ti1/2)O3-xPbTiO3 . Structural transformation from pseudo-cubic to tetragonal phase is observed via phase coexistence region demarcating the morphotropic phase boundary region. The morphotropic phase boundary region consists of coexisting tetragonal and monoclinic structures with space group P4mm and Pm respectively, stable in composition ranges 0.41 to 0.49 as confirmed by Rietveld analysis. The results of Rietveld analysis completely rules out the coexistence of rhombohedral and tetragonal phases in the morphotropic phase boundary region reported by earlier workers. A comparison between the bond lengths for B-site cations- oxygen anions obtained after Rietveld refinement, with the bond length calculated using Shannon-Prewitt ionic radii, reveals the ionic nature of B-O bonds for the cubic phases and partial covalent character for the other crystallographic phases.

cond-mat.mtrl-sci↗
arXiv2014

Electronic structure and stability of hydrogen defects in diamond and boron doped diamond: A density functional theory study

Isolated hydrogen and hydrogen pairs in bulk diamond matrix have been studied using density functional theory calculations. The electronic structure and stability of isolated and paired hydrogen defects are investigated at different possible lattice sites in pure diamond and boron doped diamond. Calculations revealed that isolated hydrogen defect is stable at bond center sites for pure diamond and bond center puckered site for boron doped diamond. In case of hydrogen pairs, H2 defect (one hydrogen at bond center and second at anti-bonding site) is stable for pure diamond, while for boron doped diamond B-H2BC complex (one H atom at the B-C bond centered puckered position and the other one at the puckered position of one of the C-C bond first neighbor of the B atom) is most stable. Multiple hydrogen trapping sites in boron doped diamond has also been studied. Calculated results are discussed and compared with previously reported theoretical results in detailed.

cond-mat.mtrl-sci↗
arXiv2014

Ground state of (Pb0.94Sr0.06)(Zr0.530Ti0.470)O3 in the morphotropic phase boundary region: Evidence for a monoclinic Cc space group

The antiferrodistortive (AFD) phase transition for a pseudotetragonal composition of Pb(Zr0.530Ti0.470)O3 (PZT) doped with 6% Sr has been investigated using sound velocity (4 to 320K), high resolution synchrotron X-ray powder diffraction (100 to 800K) and high resolution as well as high flux neutron powder diffraction measurements (4K) to settle the existing controversies about the true ground state of PZT in the morphotropic phase boundary (MPB) region. The multiplet character of the neutron diffraction profiles of (3/2 1/2 1/2)pc (pseudocubic or pc indices) and (3/2 3/2 1/2)pc superlattice peaks, appearing below the AFD transition temperature, rules out the rhombohedral R3c space group. The true ground state is confirmed to be monoclinic in the Cc space group in agreement with the predictions of the first principles calculations and earlier findings for pure PZT in the MPB region. 6% Sr2+ substitution and the use of high wavelength (λ=2.44Å) neutrons have played key role in settling the existing controversies about the true ground state of PZT in the MPB region.

cond-mat.mtrl-sci↗
arXiv2014

Structural and Dielectric Characterization on Multiferroic xNi0.9Zn0.1Fe2O4/(1-x)PbZr0.52Ti0.48O3 Particulate Composite

We have carried out the powder x-ray diffraction and dielectric studies on multiferroic particulate composite xNi0.9Zn0.1Fe2O4/(1-x)PbZr0.52Ti0.48O3 with x=0.15, 0.30, 0.45, 0.60, 0.75 and 0.90 to explore the structural and ferroelectric properties. A conventional double sintering method was used to prepare the xNi0.9Zn0.1Fe2O4/(1-x)PbZr0.52Ti0.48O3 composites. The structure of one of the component Ni0.9Zn0.1Fe2O4 is spinel cubic with space group Fd3m, while the other component PbZr0.52Ti0.48O3 is selected around the morphotropic phase boundary region in which the tetragonal and monoclinic phases with space group P4mm and Cm coexist respectively. We have carried out Rietveld refinement of the structure to check the formation of ideal composites with separate ferroelectric and ferrite phases. Even though the structural characterization does not reveal the formation of any new phase due to reaction between the two components of the composite during sintering, the tetragonality of the PbZr0.52Ti0.48O3 continuously decreases with increasing the ferrite fraction while the lattice parameter of ferrite phase increases with increasing fraction of the ferroelectric phase. Similarly, the dielectric study reveals clear shift in the ferroelectric to paraelectric phase transition temperature of PbZr0.52Ti0.48O3 during composite formation suggesting that part of Ni2+, Zn2+/ Fe3+ ions are diffusing at the B-site of PbZr0.52Ti0.48O3 replacing Ti4+, which in turn decreases its transition temperature. Scanning electron micrograph of sintered pellet surface confirms the presence of two types of particle morphology in the particulate composite, corresponding to ferrite and ferroelectric phases.

cond-mat.mtrl-sci↗
arXiv2013

Phase Coexistence and the Structure of the Morphotropic Phase Boundary Region in (1-x)Bi(Mg1/2Zr1/2)O3-xPbTiO3 Piezoceramics

Structure of the morphotropic phase and the phase coexistence region has been investigated in (1-x)Bi(Mg1/2Zr1/2)O3-xPbTiO3 ceramics. The structure is cubic with space group Pm3m for the compositions with x<0.57 and tetragonal with space group P4mm for the compositions with x>0.59. For the compositions with 0.56<x<0.60, both the tetragonal and cubic phases coexist, which suggest very narrow morphotropic phase boundary region of compositional width Δx~0.03. Rietveld refinement of the structure using x-ray diffraction data confirms coexistence of the tetragonal and cubic phases in the MPB region and rules out the coexistence of tetragonal and rhombohedral structure reported by earlier workers. After poling appearance of significant value of electromechanical coupling coefficient in the cubic compositions (x=0.55, 0.56) suggests the presence of electric field induced transition from centrosymmetric cubic phase to noncentrosymmetric phase. Polarization- Electric field hysteresis loop measurement on the cubic composition with x=0.56 gives well saturated loop similar to that observed in Pb(Mg1/3Nb2/3)O3 relaxor below the freezing temperature.

cond-mat.mtrl-sci↗
arXiv2013

Absence of Tetragonal Distortion in (1-x)SrTiO3-xBi(Zn1/2Ti1/2)O3 Solid Solution

We have carried out powder x-ray diffraction and dielectric studies on the lead free solid solution (1-x)SrTiO3-xBi(Zn1/2Ti1/2)O3 ((1-x)ST-xBZT) with x=0.05, 0.10, 0.15, 0.20, 0.30 and 0.50 to explore the ferroelectric and piezoelectric properties. Analysis of the powder x-ray diffraction data reveals the cubic structure (space group Pm3m) of (1-x)ST-xBZT for the composition with x < 0.20, at room temperature as well as at low temperature. Highly tetragonal BZT fails to introduce any tetragonality when alloyed with ST. The solid solubility is limited to x< 0.20 and for higher BZT concentrations impurity phases start appearing. The ferroelectric and dielectric characterization of (1- x)ST-xBZT solid solution shows that all the compositions are paraelectric. The implications of the absence of tetragonal distortion in (1-x)ST-xBZT solid solution is discussed in connection with recently investigated other solid solutions based on BZT.

cond-mat.mtrl-sci↗
arXiv2013

Investigation of New Lead- free (1-x)BaTiO3-xBi(Mg1/2Zr1/2)O3 Solid Solution with Morphotropic Phase Boundary

We report here the structure and dielectric studies on a new lead free (1-x)BaTiO3-xBi(Mg1/2Zr1/2)O3 solid solution to explore the morphotropic phase boundary. The powder x-ray diffraction studies on (1-x)BaTiO3-xBi(Mg1/2Zr1/2)O3 solid solution suggests that structure is tetragonal (P4mm) for the composition with x=0.05 and cubic for the composition with x=0.30 and 0.40. Morphotropic phase boundary is observed in the composition range 0.10<x<0.30, where phase coexistence is observed and composition dependence of room temperature permittivity shows a peak. High temperature dielectric measurement for the composition with x=0.20 exhibits diffuse phase transition having peak temperature around ~ 396 K at 10 kHz. The diffuseness parameter (γ) was obtained to be 1.68 for composition with x=0.20.

cond-mat.mtrl-sci↗
arXiv2008

Origin of high piezoelectric response of Pb(Zr_xTi_1-x)O_3 at the morphotropic phase boundary: Role of elastic instability

Temperature dependent structural changes in a nearly pure monoclinic phase composition (x=0.525) of Pb(Zr_xTi_1-x)O_3 (PZT) have been investigated using Rietveld analysis of high-resolution synchrotron powder x-ray diffraction data and correlated with changes in the dielectric constant and planar electromechanical coupling coefficient. Our results show that the intrinsic piezoelectric response of the tetragonal phase of PZT is higher than that of the monoclinic phase. It is also shown that the high piezoelectric response of PZT may be linked with an anomalous softening of the elastic modulus (1/S_11) of the tetragonal compositions closest to the morphotropic phase boundary.

cond-mat.mtrl-sci↗