Browsing by Author "Shail Upadhyay"

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Cation deficiency driven enhancement in electrochemical performance of Sr2-xFeCoO6-δ double perovskite for supercapacitor electrodes
(Elsevier Ltd, 2025) Pramod Rajish Kumar; Arpita Tripathi; Harish Chandra Verma; Aayush Mittal; Bhaskar Bhattacharya; Shail Upadhyay
Properties of perovskite oxides have been tailored to fulfill the requirements of high-capacity and high-power storage devices. This is done by optimizing oxygen vacancy concentration, redox stability, and mixed (ionic and electronic) conductivity. Oxygen intercalation in perovskite oxides is a versatile and robust mechanism for improving the performance of energy storage devices. In this study, a series of non-stoichiometric (Sr-deficient) Sr2-xFeCoO6-δ double perovskite compositions are synthesized using a sol-gel method to increase oxygen vacancy concentration. X-ray diffraction confirmed the formation of a cubic phase with Pm3̅m Space group, stable up to ∼7.5 % Sr deficiency (x = 0.15). Core-level XPS of oxygen revealed that increasing Sr deficiency leads to a higher concentration of adsorbed oxygen species, indicating enhanced oxygen vacancy formation. Sr deficiency leads to a notable increase in specific charge storage capacity, from 15.5 C/g in the stoichiometric sample to 35.3 C/g in the optimized composition. In a symmetric two-electrode configuration, the optimized composition achieved an energy density of 6 Wh/kg, a power density of 780 W/kg, and retained 78 % of its capacity after 5000 cycles. © 2025 Elsevier Ltd
Dielectric and impedance spectroscopy studies of Ba0.90Y0.10SnO3
(American Institute of Physics Inc., 2020) Upendra Kumar; Dharmendra Yadav; Gurudeo Nirala; Shail Upadhyay; Epsita Kar; Manish Kumar Srivastava
The Ba0.90Y0.10SnO3 has prepared by a sol-gel combustion route followed by calcination at 1000°C for 8 h and sintered at 1300°C for 12 h. Rietveld refinement studies of the sintered ceramic sample indicates the cubic crystal structure under space group Pm3m. Further, an increase in the dielectric constant and dissipation factor has been noted with temperature at a particular frequency while they decrease with frequency. The impedance plot of the sample has been generated at various temperatures to separate the contribution of grain, grain boundary, and electrode specimen to the bulk properties. Further, it is noticed that the resistance of grain and grain boundary nicely follows Arrhenius relation with the activation energy of (0.50±0.02) eV and (1.27±0.02) eV, respectively. Based on activation energy, we speculate that there might be either electronic or protonic conduction (OH) within the grain and the migration of doubly ionized oxygen vacancies (Vö) through grain boundary in the available temperature range. The high value of conductivity of grain and grain boundary at 500°C makes it a potential candidate for electrolyte of IT-SOFCs. © 2020 American Institute of Physics Inc.. All rights reserved.
Effect of Niobium Doping on Dielectric, Electrical and Magnetic Properties of Bismuth Copper Titanium Oxide
(Pleiades Publishing, 2025) Biswajit Jena; Anup Kumar; Dinesh Prajapati; Rajni Baranwal; Shail Upadhyay; Narsingh Bahadur R. Singh; Dhanesh Tiwary; Kamdeo Mandal
Abstract: Bi2/3Cu3Ti4 –xNbxO12 (BCTNO) ceramics with compositions x = 0.05, 0.10, and 0.20 were fabricated through a semi-wet route and sintered at 1173 K for 8 h. A detailed study was conducted to investigate the impact of Nb substitution on the structural, dielectric, electrical, and magnetic characteristics of BCTO. The synthesized Bi2/3Cu3Ti4 –xNbxO12 (x = 0.05, 0.10, and 0.20) ceramics were designated as BCTNO-0.05, BCTNO-0.10, and BCTNO-0.20, respectively. X-ray diffraction (XRD) investigation highlights the presence of all characteristic peaks of the pure BCTO compound, confirming the development of a single phase with a well-defined crystal structure upon Nb doping up to a composition of 0.20. Furthermore, the lattice parameter of the synthesized compounds is found to decrease with increasing Nb concentration. Field emission scanning electron microscopy (FE-SEM) was employed to assess the microstructural alterations in the synthesized BCTNO ceramics. High resolution transmission electron microscopy (HR-TEM) images revealed that the BCTNO ceramics’ particle sizes varied from 189 to 191 nm. The valence states of various ions present in the Nb-doped BCTO ceramics were analysed utilizing X-ray photoelectron spectroscopy (XPS). The dielectric permittivity (εʹ) and tangent loss (tan δ) of BCTNO ceramics were found to decrease with rising frequency. Impedance analysis provided confirmation of thermally activated ionic conduction within the ceramics. The magnetization (M) vs. Magnetic field (H) studies revealed antiferromagnetic behaviour at low temperature, with indications of weak ferromagnetism. © Pleiades Publishing, Ltd. 2025.
Impact of Current Collectors on the Electrochemical Performance of Pseudocapacitive Material: Sr2FeCoO6
(John Wiley and Sons Inc, 2025) Pramod Kumar; Harish Chandra Verma; Aayush Mittal; Bhaskar Bhattacharya; Shail Upadhyay
This work reports the synthesis of Sr2FeCoO6, double perovskite, via a wet chemical method. X-ray diffraction (XRD) analysis and Rietveld refinement confirmed the successful formation of pure, single-phase perovskite structure with the (Formula presented.) space group. The Raman spectrum showed minor peaks, suggesting structural distortions likely caused by defects. Transmission electron microscopy (TEM) revealed irregularly shaped polycrystalline particles, while Brunauer–Emmett–Teller (BET) analysis indicated an average surface area of 3.01 m2/g and a pore diameter of 37.8 nm. Current collectors, namely, carbon Toray paper, carbon cloth, nickel foam, and nickel strip, were selected to evaluate the electrochemical properties of Sr2FeCoO6. The morphology of the current collectors was captured using a scanning electron microscope (SEM). The electrochemical performance of bare and loaded (with Sr2FeCoO6) current collectors was assessed under similar measurement conditions. The high specific capacitance of the sample is observed over the carbon cloth and nickel foam to be 105.7 and 93.3 F/g, respectively, while bare carbon cloth shows very high capacitance. By comparing the performance of different current collectors, we have identified the key factors influencing the material's performance. This study will enhance our understanding of its potential applications in energy storage and other pertinent areas. © 2025 John Wiley & Sons Ltd.
Investigation of La2FeO4-rGO nanocomposite electrode material for symmetric and asymmetric supercapacitor
(Elsevier Ltd, 2025) Harish Chandra Verma; Pramod Kumar; Satyendra Kumar Satyarthi; Bhaskar Bhattacharya; Akhilesh Kumar Singh; Shail Upadhyay
Ruddlesden-Popper (RP) oxides, represented by the general formula of An+1BnO3n+1, are emerging as promising electrode materials for supercapacitors (SCs) electrodes due to their stable crystal structure, rich oxygen vacancies, and good reversible redox behavior. In this study, La2FeO4 and 2D reduced graphene oxide (rGO) were synthesized via a solid-state reaction method and Modified Hummer method, respectively. Nanocomposites of La2FeO4/rGO in a varying weight ratios (0:1, 1:0, 1:1, 1:2, 1:3, 1:4, and 1:5 wt %) were subsequently synthesized through a hydrothermal method. The synthesized La2FeO4 and optimized La2FeO4-rGO (1:4) nanocomposite were characterized by X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), high-resolution SEM (HR-SEM), high-resolution transmission electron spectroscopy (HR-TEM) techniques and Brunauer-Emmett-Teller (BET) techniques. Electrochemical measurement evaluated in a 3 M KOH electrolyte solution revealing the remarkable performance of the composites. Fabricated symmetric supercapacitors (SSCs) based on La2FeO4-rGO (1:4)/La2FeO4-rGO (1:4) have demonstrated the gravimetric capacitance values of 633, 298, 226, 139, and 72 F/g at current densities of 1, 2, 3, 5, and 10 A/g, respectively. Similarly, an asymmetric supercapacitor (ASC) configuration La2FeO4-rGO (1:4)/rGO have shown capacitance 197, 160, 108, 89, and 58 F/g values at the same current densities. SSCs and ASCs assemblies have exhibited outstanding capacitance retention (91.1 % for SSCs, 99.9 % for ASCs) and high coulombic efficiency (99.5 % for SSCs, and 74 % for ASCs). Additionally, these devices displayed a maximum specific power density (7.8 KW/kg for SSCs, and 20 KW/kg for ASCs) and a maximum specific energies (148 Wh/kg for SSCs, and 70 Wh/kg for ASCs). © 2025
Phase Evolution, Dielectric, and Electric Behavior of Sm-Doped BCTO Ceramic Fabricated by Semi-Wet Method
(John Wiley and Sons Inc, 2024) Dinesh Prajapati; Vishnu Shankar Rai; Atendra Kumar; N.B. Singh; Harish Verma; Shail Upadhyay; K.D. Mandal
Bi(2/3)-xSmxCu3Ti4O12 (BSCTO x = 0.05, 0.10, and 0.20) ceramics are synthesized using semi-wet technique and an extensive investigation into their structural, morphological, and elemental properties, alongside dielectric and impedance behaviors, is meticulously carried out. X-ray powder diffraction analysis unequivocally confirmed the formation of a monophasic BCTO cubic phase without any discernible secondary phases. and the crystallite size of the BSCTO ceramic, obtained by X-ray diffraction using Debye Scherrer formula, range from 62 to 81 nm. Rietveld analysis reveals that ceramics have a body centered cubic structure with space group Im-3. The Scanning electron microscope image displays the dense microstructure of the ceramics, while EDX analysis unveils the elemental composition of resulting products. Doping with Sm3+ induced a notable reduction in grain size, as observed through Scanning electron microscope and Atomic Force Microscope analyses, indicating Sm3+ hindered grain growth during sintering, potentially resulting in reduced dielectric constant (ε′). Dielectric constant and dielectric loss of the composition (x = 0.2) are found to be (Formula presented.) 152 and 0.04, respectively at room temperature (1 kHz). Impedance characteristics revealed a substantial increase in grain boundary resistance, leading to improved dielectric loss. The AC conductivity of BSCTO ceramics exhibited a frequency-dependent increase satisfying to Johncher's power law. © 2024 Wiley-VCH GmbH.
Synergistic doping effect of La2O3 on BaO-TiO2-SiO2 glass-ceramics: Evolution of physical, structural, morphological, and dielectric behaviour for electronics applications
(Elsevier Ltd, 2024) Rajat Kumar Mishra; Sarvesh Kumar Avinashi; Savita Kumari; Shweta; Rajbala Nain; Tarun Katheriya; Rakesh Kumar Dwivedi; Shail Upadhyay; Chandkiram Gautam
Herein, numerous investigations such as structural, physical, morphological, optical, and dielectric properties of BaO-TiO2-SiO2 glass-ceramics (GCs) doped with La2O3 were carried out. Various glasses were synthesized within a glass system [(30-x)BaO.30TiO2.40SiO2].x[La2O3], (x=0,2,4, and 6 mol% of La2O3) using a conventional melt-quench method. XRD confirmed the amorphous nature of the glass samples. Differential scanning calorimetry (DSC) was used to identify the glass transition (Tg) and crystallization temperatures (Tc) of the samples. Further, controlled heat treatment of the glasses led to the fabrication of glass-ceramics and their XRD analysis revealed polycrystalline structure, predominantly consisting of a major phase of tetragonal Fresnoite (Ba2TiO8Si2). Furthermore, with the addition of La2O3, the prepared GCs exhibited improved physical properties, including an increase in density (3.783–4.611 g/cm3) and oxygen packing density (81.177–92.303 g-atom/l). Additionally, to study the bonding and structural characteristics, FTIR and Raman spectroscopies were conducted. In order to study the optical properties, UV–visible spectroscopy was executed and showed a reduced indirect energy band gap from 4.290 to 4.220 eV with increasing La2O3. To study the morphological behaviour, SEM and TEM were performed. Eventually, to examine the dielectric characteristics, relative dielectric constant (εr) and dielectric loss (Tan δ) over the glass-ceramics was conducted using a ‘Novocontrol Impedance Analyzer’. The εr and Tan δ values exhibited temperature-dependent behaviour and found to be increased within the frequency range of 1 kHz to 1 MHz. The BTSLC6 glass-ceramic, (24BaO.30TiO2.40SiO2.6La2O3), exhibited a high dielectric constant of ⁓ 9335 and a low dielectric loss of 0.52 at 1 kHz, mainly due to space charge polarization. This makes it a promising candidate for applications in multilayer ceramic capacitors, energy storage, photonics, and electronics. © 2024 Elsevier B.V.
The emergence of Griffiths phase in CaCu3Ti(4−x)Mn xO12 (CCTMO, x = 1, 2 and 3) geometrically frustrated antiferromagnetic complexes perovskite
(Springer, 2024) Vinod Kumar; Anup Kumar; Shruti Singh; Krishna Kumar; Manish Kumar Verma; Vishnu Shankar Rai; Gurudeo Nirala; Shail Upadhyay; Navneet Yadav; N.B. Singh; Dhanesh Tiwary; K.D. Mandal
In this work, we have reported the rare coexistence of a Griffiths phase (GP) in a complex perovskite oxide with geometrically frustrated antiferromagnetism. We have achieved this by substituting Manganese (Mn) in the titanium site of CaCu3Ti(4−x)MnxO12 (CCTMO, x = 1, 2 and 3). The occurrence of a Griffiths phase is observed when a strong contest between antiferromagnetic transition (TN) and paramagnetic (PM) occurs in the magnetic domain. As we increased the molar concentration of Manganese while substituting at titanium site in CaCu3Ti4O12, we observed the appearance of a step-like Griffiths phase. Manganese (Mn)-substituted materials exhibit paramagnetic (PM) to ferromagnetic (FM) phase transitions below CaCu3Ti3Mn1O12 (CCTM1O), CaCu3Ti2Mn2O12 (CCTM2O), and CaCu3Ti1Mn3O12 (CCTM3O), marked by a rapid step-like change in the magnetic moment due to spin ordering. The deviation of inverse magnetic susceptibility (χ−1) from Curie–Weiss behavior occurs in the temperature ranges of 75 to 190 K, 80 to 200 K, and 150 to 280 K, respectively. The emergence of the Griffiths phase before the actual PM–FM transition indicates that the inhomogeneous phase above the Curie temperature (T C), which can be defined as a Griffiths phase, is dominated by ferromagnetic interactions rather than antiferromagnetic ones. The presence of a Griffiths-like phase beyond its Curie temperature (T C) is indicated by low-field DC magnetization of the nanostructures, showing abnormal magnetic behavior. The presence of short-range magnetic correlations and ferromagnetic clusters in the system due to the size decrease is linked to this unexpected behaviour. © 2024, The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.