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June 2010 - present
August 2005 - May 2010
Education
August 1998 - April 2004
Publications
Publications (218)
We report on size induced microstrain-dependent magnetic properties of BiFeO3 nanoparticles. The microstrain is found to be high (ε > 0.3%) for smaller crystallite sizes (d < 30 nm), and shows a sharp decrease as the particle size increases. The presence of pseudo-cubic symmetry is evidenced for these nanoparticles. Raman spectral studies suggest s...
The properties of functional metal oxide nanostructures can be highly susceptible to the presence of defects. The defect concentration in these systems, which have exceedingly large surface to volume ratios, can be very high, potentially leading to qualitatively new phenomena beyond perturbing the existing characteristics. This chapter is focused o...
We demonstrate a tunable bandgap from 2.32 eV to 2.09 eV in phase-pure BiFeO3 by controlling the particle size from 65 nm to 5 nm. Defect states due to oxygen and microstrain show a strong dependence on BiFeO3 particle size and have a significant effect on the shape of absorbance curves. Oxygen-defect induced microstrain and undercoordinated oxygen...
We report on the suppression of FeLi• antisite defects in LiFe(PO 4)1-xF3x with 0 ≤ x ≤ 0.4 prepared by sol-gel and hydrothermal methods. Evidence for a systematic suppression of antisite defects upon fluorine doping in LiFePO4 is inferred from Fourier transform infrared spectra, wherein a noticeable red shift in the symmetric P-O stretching vibrat...
Diamond-shaped, several tens of micrometer-sized flat single crystals of Rb3Sb2I9 grown with (006) facets are studied for their structural and optical properties. These microcrystals are obtained through the facile solution process that yields a large fraction of these micron-sized single crystals. The crystals typically
have areas around 500 μm2 a...
The utilization of single crystals is exponentially growing in optoelectronic devices due to their exceptional benefits, including high phase purity and the absence of grain boundaries. However, achieving single crystals with a porous structure poses significant challenges. In this study, we present a method for fabricating porous single crystals (...
Pristine and alkaline-earth metal-substituted LaFeO3 (La1−xAxFeO3−δ; x = 0 and 0.2; A = Mg²⁺, Ca²⁺, and Sr²⁺) sintered ceramics are prepared from nanoparticles synthesized via a low-temperature citrate sol–gel technique. X-ray diffraction studies confirm the formation of a phase-pure LaFeO3 structure without any secondary phases for all the La1−xAx...
Correction for ‘3D-engineered WO3 microspheres assembled by 2D nanosheets with superior sodium storage capacity’ by Shilpi Sengupta et al., RSC Adv., 2024, 14, 15706–15712, https://doi.org/10.1039/D4RA01800A
Developing transition metal chalcogenides (TMCs) with ferromagnetic and semiconductors properties in two-dimensional (2D) materials is important from both understanding the fundamental functional properties point of view as well as realizing spintronic devices using such 2D materials. The challenge is in the scarcity of such 2D ferromagnets with lo...
BiFeO3 has been the prime choice of multiferroic research, particularly over the past two decades. The rhombohedrally distorted perovskite exhibits weak coupling between the ferroelectric (TC ~ 1120 K) and magnetic (TN ~ 643 K) order parameters above room temperature, observed only in a few other systems. All the research carried out on this materi...
TiO2 microspheres encapsulated with photostable Cs0.5Rb0.5PbBr3 quantum dots (QDs) are shown to exhibit whispering gallery mode (WGM) microcavity lasing. Cs0.5Rb0.5PbBr3-QDs have high photostability and photoluminescence quantum yield (PLQY) compared to CsPbBr3- and CsPbI3-QDs. A strong synergy between the TiO2 optical microcavity and the PL emissi...
With the aid of 3D full‐field finite difference time–domain simulations, model configurations for CsPbI3$\left(\text{CsPbI}\right)_{3}$ thin‐film solar cell devices that include periodically arranged TiO2$\left(\text{TiO}\right)_{2}$ microspheres, exhibiting resonating whispering gallery modes (WGMs), are proposed. The TiO2$\left(\text{TiO}\right)_...
Because of the inadequate sodium storage capacity of graphite, the exploration of high-performance SIB anodes is a crucial step forward. Herein, we report the hydrothermally synthesized self-assembled interconnected nanosheets of WO3 microspheres possessing admirable sodium storage in terms of cycling stability and acceptable rate capability. Benef...
High energy density Ni‐rich layered oxide cathodes LiNi 0.83 Co 0.12 Mn 0.05− x Al x O 2 ( x = 0 [NMC], 0.025 [NMCA], 0.05 [NCA]) are fabricated in two different microstructural forms: (i) nanoparticles (NP) and (ii) nanofibers (NF), to evaluate the morphology and compositional effect on the electrochemical properties using same precursors, with th...
Temperature-dependent Raman spectral studies of BiFeO3 (BFO) films coated on three different substrates, viz., conducting Si (BFO-Si), sapphire (BFO-SAP), and fluorine-doped tin oxide (BFO-FTO), are reported between 123 and 773 K. The activity of Bi–O and Fe–O modes in these samples as a function of temperature shows different spectral features des...
Li 1.3 Al 0.3 Ti 1.7 (PO 4 ) 3 (LATP) is a promising solid-electrolyte for Li-ion batteries with a favorable open structural framework made up of corner shared LiO 6 and TiO 6 octahedra and PO 4 tetrahedra network. Here we...
High energy density Ni-rich layered oxide cathodes LiNiCoMnAlO (x=0, 0.025, 0.05; NMC, NMCA, and NCA, respectively) are fabricated in two different microstructural forms: (i) nanoparticles (NP) and (ii) nanofibers (NF), to evaluate the morphology and compositional effect on the electrochemical properties using same precursors, with the latter fabri...
Vibrational dynamics in halide double perovskites govern several key aspects including carrier recombination and transport properties. Here, we present comprehensive vibrational studies investigated through micro-Raman spectroscopy to understand how octahedral cation substitution in a wide range of metal halide double perovskites Cs2B′B″Cl6 (B′=Ag1...
Whispering gallery mode (WGM) lasing in CsPbI3 quantum dots (QDs) coated on TiO2 spherical microcavities is demonstrated. The photoluminescence emission from a CsPbI3-QDs gain medium strongly couples with a TiO2 microspherical resonating optical cavity. Spontaneous emission in these microcavities switches to a stimulated emission above a distinct t...
Recently, the cathode materials employed in lithium‐ion batteries are dominated by transition metal oxides, phosphates, and spinels which are known to undergo a rapid capacity fade due to the synergistic effect of transition metal dissolution and lithium plating, especially at higher operating voltages and at elevated temperatures. However, solutio...
Alloy anodes, with twice the capacity of graphite, are promising for next-generation lithium-ion batteries (LIBs). However, poor rate-capability and cycling stability, mainly due to pulverization, have limited their application. By constraining the cutoff voltage to the alloying regime (1 V to 10 mV vs. Li/Li+), we show that Sb1.9Al0.1S3 nanorods p...
This poster explains the synthesis of inorganic lead halide perovskites in an N2 atmosphere. The substitution in A-site cations, leading to changes in optical properties and bandgap is also explored. Coupling of these stable perovskite quantum dots with TiO2 leads to whispering gallery mode resonance, which has vast applications in the field of opt...
Single crystalline (SC) metal halide perovskite absorber film can outperform its polycrystalline counterpart in power conversion efficiency and stability due to the absence of grain boundaries. However, SC perovskite film's direct growth on charge selective contact layer coated substrates for solar cell applications is not widely explored. In this...
A new platform for research and development of inexpensive and efficient solar cells has evolved based on hybrid perovskite absorber material. The power conversion efficiency of polycrystalline perovskite solar cells shot from 3.8% in 2009 to 25.7% in 2022. Even though perovskite solar cells are close to commercialization, their poor operational st...
The thermal stability of lead-free double perovskite Cs2AgBiBr6 for stable optoelectronic and photovoltaic devices is essential. There are contradicting reports, with some claiming stability from 300 to 400 °C based on X-ray diffraction and thermogravimetry studies and others up to 250 °C from Raman studies for Cs2AgBiBr6. We perform thermogravimet...
Optical trapping of magnetic Fe-oxide particles is notoriously difficult due to their high refractive indices, not to mention high absorptivity at the trapping infra-red wavelengths. We synthesize Fe co-doped NaYF4:Yb,Er ferromagnetic upconversion particles that not only have refractive indices conducive for optical trapping, but also heat less tha...
Perovskite solar cells (PSCs) are hailed as the game-changer technology in solar photovoltaics owing to their excellent optoelectronic properties, ease of fabrication, reduced material consumption, low cost, and flexibility. The architecture of a PSC consists of a transparent conducting substrate, perovskite absorber material sandwiched between ele...
Most high-performing organic–inorganic hybrid perovskite solar cells (PSCs) are fabricated using expensive organic hole-transporting materials (HTMs). The poor moisture- and thermal-stability of organic HTMs are significant factors contributing to the degradation of PSCs. Inorganic HTMs are promising cost-effective alternatives to achieve high effi...
Irradiation of materials by high energy (∼MeV) ions causes intense electronic excitations through inelastic transfer of energy that significantly modifies physicochemical properties. We report the effect of 100 MeV Ag ion irradiation and resultant localized (∼few nm) thermal spike on vertically oriented TiO2 nanorods (∼100 nm width) towards tailori...
Semiconductor heterostructures such as TiO2/Sb2S3 and ZnO/Sb2S3 are promising for photoelectrochemical applications. In this work, we demonstrate the photoelectrochemical performance with enhanced current densities of Sb2S3 sensitized nanorods of TiO2 (TNR) and ZnO (ZNR) photoanodes. ZNR and TNR are synthesized by the hydrothermal method and anneal...
Enhanced rate capability of interconnected LiNi1/3Mn1/3Co1/3O2 (NMC) nanoparticles fabricated via electrospinning method is presented. Interconnected NMC nanoparticles have a discharge capacity of 175 mAh g⁻¹ at 0.1C and 94 mAh g⁻¹ at 1C. Similar nanoparticular NMC cathode without interconnections, fabricated by co-precipitation method, has a capac...
We investigate the structural and ferromagnetic properties of Mo1-xMnxS2 and Mo1-xCoxS2 (x=0, 0.025, 0.05, 0.075, 0.1 and 0.25) nanosheets synthesized by a wet chemical process. X-ray diffraction (XRD) patterns confirm the 2H polytype of MoS2 for both pristine and doped nanosheets. From X-ray absorption near-edge spectral (XANES) studies, Mn doping...
The recent surge of interest in using all-inorganic materials like CsPbI3 for photovoltaic devices has brought significant interest in exploring the properties of BiFeO3 (BFO) by substituting Cs⁺ and K⁺ at the Bi³⁺ site. The aim of the present work is to study the parameters like controlling the lattice and surface oxygen vacancy (VO) defects which...
Magnetodielectric (MD) properties of as-prepared (AP) and air-annealed Bi1−xCaxFe1−yTiyO3−δ nanoparticle ceramics made by spark plasma sintering process are investigated as a function of temperature. Aliovalent Ca2+ substitution at Bi3+ site creates oxygen vacancies (VO) in the lattice disrupting the intrinsic spin cycloid of BiFeO3, which are supp...
LiVPO4F (LVPF) is a promising high voltage (4.2 V vs. Li/Li⁺) and high energy density (655 WhKg⁻¹) cathode material for lithium ion batteries. The challenge is to prepare phase pure and conducting material suitable for battery application. In this work carbon coated LiVPO4F (LVPF/C) is synthesized by sol-gel method, and the effect of carbon coating...
We report a facile and low-cost solution-based approach to synthesize various binary, ternary and quaternary metal chalcogenide thin films. Homogeneous metal chalcogenides single precursor is prepared by dissolving metal salt (metal chloride/acetate) in ethanolic/methanolic solution of 3-Mercaptopropionic acid (MPA) at room temperature. High-qualit...
Bandgap engineering in lead-free Cs2Ag1-xNaxBiCl6 (x = 0 to 1) double perovskite alloys synthesized through solution-based approach is investigated. The bandgap is shown to vary from 2.64 eV to 3.01 eV as Ag⁺ at B′ site gets replaced with Na⁺ cation. Despite a linear change in the lattice parameter according to Vegard's law, bandgap (Eg) changes in...
Bandgap engineering in lead-free Cs2Ag1-xNaxBiCl6 (x = 0 to 1) double perovskite alloys synthesized through solution-based approach is investigated. The bandgap is shown to vary from 2.64 eV to 3.01 eV as Ag⁺ at B′ site gets replaced with Na⁺ cation. Despite a linear change in the lattice parameter according to Vegard's law, bandgap (Eg) changes in...
Phase pure carbon-coated high voltage cathode material LiVPO4F (LVPF/C) is synthesized by a facile sol-gel method and reacting the precursor powder with PTFE. Secondary phases such as Li3V2(PO4)3, Li9V3(P2O7)3(PO4)2, V2O3 and LiVP2O7 are shown to get mitigated by the addition of lauric acid, which also acts as carbon source. Phase pure LiVPO4F with...
Single crystalline ZnO and TiO2 nanorods are grown on fluorine-doped tin oxide (FTO) substrates by hydrothermal method. The nanorods are annealed under air and reducing conditions to alter the oxygen nonstoichiometry and hence the mid-bandgap defect states. Such an annealing process is shown to impart significant change on the photoelectrochemical...
Li-intercalation and -deintercalation effects on the magnetic properties of defect-rich (DR) and defect-suppressed (DS) MoS2 nanosheets are investigated. Active defect sites take large Li (x ≈ 2 in LixMoS2) for DR-MoS2 compared to that for the DS-MoS2 (x ≈ 1.6). Li intercalation brings phase transition from 2H-MoS2 to 1T-LixMoS2 associated with a c...
Tellurium-rich Bi2Te3 thin films are deposited by electron−beam evaporation technique at 300 K. These as-deposited thin films are further annealed at 100 °C, 200 °C and 300 °C for 1 h at a pressure of 3 × 10⁻⁴ Pa. X-ray diffraction (XRD) patterns of as-deposited films distinctly show Te phase along with Bi2Te3. Peak intensity ratio suggests the pol...
The effect of naphthalimide as auxiliary acceptor in the PTz-based dyes for dye-sensitised solar cell (DSSC) application is reported. In this regard, two new organic dyes with N-alkylated phenothiazine (PTz) core were synthesized by substitution of naphthalimide at C-3 of the PTz via triple bond and incorporation of an electron acceptor at C-7 posi...
Synthesis of phase pure Sb2S3 in open atmosphere has been a long-time challenging task due to the oxidation of metal. Here, we demonstrate a robust, one-step solution approach for synthesis of Sb2S3 thin films in open air atmosphere. One-step thermolysis of Sb-MPA complex obtained by mixing antimony chloride and 3-Mercaptopropionic acid (3-MPA) in...
MAPbI 3 film grown on mesoporous TiO 2 showed better crystallinity, performance and stability compared to its planar counterpart.
Sb2S3 is a promising sensitizer material for solar cell devices. Growth and morphological characteristics of Sb2S3 nanoparticles made by chemical bath deposition on anatase TiO2 with various morphological attributes including mesoporous P25 nanoparticles, microsphere and its composite, anodized nanotubes, and nanorods are shown to widely differ. Sb...
Morphology dependent electrochemical performance of Li-rich layered oxide (LLO) cathode with the composition Li1.23Mn0.538Ni0.117Co0.114O2 in three different microstructural forms namely, randomly shaped particles, platelets and nanofibers are synthesized through solid-state reaction (SSR-LLO), hydrothermal method (HT-LLO) and electrospinning proce...
Candle soot carbon nanoparticles (CSC-np) collected from candle burning can be converted into an effective universal anode for metal-ion (M-ion; M = Li, Na and K) batteries. As-collected CSC-np particles exhibiting fractal-like interconnected porous carbon nanostructure chains are annealed in air (at 350 °C) and Ar (at 750 °C). The effect of anneal...
Designing solid-state perovskite oxide solar cells with large short circuit current (JSC) and open circuit voltage (VOC) has been a challenging problem. Epitaxial BiFeO3 (BFO) films are known to exhibit large VOC (>50 V). However, they exhibit low JSC (≪μA/cm2) under 1 Sun illumination. In this work, taking polycrystalline BiFeO3 thin films, we dem...
Continuous capacity loss or gain in electrodes during extended cycling is very intriguing. We investigate influence of nanosheet thickness and defects on charge storage properties of MoS2 nanosheets in intercalation regime. Strong correlation with irreversible lithium intake during first cycle is observed. Defect-rich nanosheets (MoS2−5L; with an a...
We show it is possible to tune magnetic properties in MoS2 without any intentional magnetic dopants, however, by simply controlling magnetically active defect sites. Layer thickness and defect density controlled MoS2 (2H-phase) nanosheets are obtained by annealing wet-chemical precursor from 500 °C to 900 °C. HRTEM images show presence of planar an...
Spark plasma sintered Bi1−xCaxFe1−yTiyO3−δ (BCFTO) (x = y = 0.05 and 0.1) nanoparticle ceramics are studied for photoconductivity properties. As-prepared (AP) BCFTO hosts a large concentration of grain boundary (GB) oxygen vacancies (OV), whereas air annealed (AA) BCFTO have significantly suppressed GB OV. X-ray absorption near edge spectroscopy st...
Environmental deterioration and depletion in conventional energy resources greatly demand the need for photovoltaic devices, which use solar radiation to meet future energy demands. Efficient light management plays a pivotal role in improving the performance of photovoltaic devices. Various avenues have been explored to address light management in...
BiFeO3 (BFO), a Pb-free perovskite oxide, is being explored for its potential use in a multitude of applications. We report on the oriented growth of BFO thin films using a facile metal-organic chemical solution deposition. Unlike the growth characteristics observed in Si/SiO2 and glass/FTO substrates, the solution growth process on sapphire (0001)...
Rutile TiO2 (TiO2-NR) and ZnO (ZnO-NR) in nanorod microstructural forms are synthesized by hydrothermal route. The oxides are grown directly on fluorine doped SnO2 coated glass, and annealed in air (AA) and hydrogen (HA) atmosphere for 3 h at 450 °C. A detailed structural, optical, and microstructural study confirms the phase formation in the AA an...
Semiconductor quantum dot (QD)-graphene composites are promising materials for photovoltaics and photocatalysis due to efficient charge extraction and transport property of graphene. Analysis of their ultrafast carrier transfer dynamics has been limited to only QD-graphene sheets, such as CdTe-graphene sheets and CdS-graphene sheets. Herein, we inv...
(i) Edge and planar defect-rich and (ii) defect-suppressed MoS 2 nanosheets are fabricated by controlled annealing of wet-chemically processed precursor. Wrinkles, folds, bends and tears lead to severe defects in MoS 2 ...
One step electrodeposition method has been used to realize highly porous ZnO pin hole (ZP) and ZnO rosette sheets (ZS) nanostructure based photo-anodes for efficient photoelectrochemical (PEC) splitting of water. Electrodeposited ZP and ZS based photo-anodes exhibit enhanced photocurrent density of 0.62 mA/cm ² and 0.76 mA/cm ² respectively (at a b...
Bi-rich Bi2Te3 thin films are prepared at 300 K using e-beam evaporation technique. A source power of 45 W for e-beam is used. Post deposition, these as-deposited Bi-rich Bi2Te3 (Bi-BT-AD) films are annealed at 100 °C (Bi-BT-100), 200 °C (Bi-BT-200) and 300 °C (Bi-BT-300) for 1 h under a pressure of 3 × 10⁻⁴ Pa. X-ray diffraction measurements revea...
Composite photoanode comprising of mesoporous microspheres with smooth spherical morphology(SμS) exhibiting high light scattering due to optical whispering gallery modes (WGM) is used to fabricate whisperonic solar cell (WSC) devices. The photoanode is sensitized with CdS-CuInS2 thin films (CdS-CIS-TF) of ~5 nm thickness. CdS-CIS-TF sensitized phot...
In the present work, Ag‐Au/ZnO nanorods based photo‐anodes were synthesized using a simple electrochemical route and were then evaluated for PEC activity. The Au photo‐anodes with Ag‐Au bi‐metallic system exhibit a prominent character in PEC activity. The amalgamation of Ag and Au nanoclusters broadens the UV‐Vis light absorption in the range 400‐6...
Carbon-coated single crystalline nanotubular (NT) and nanoparticular (NP) LiFe1-xMnxPO4 (x = 0, 0.2, and 0.5) cathodes are fabricated to study the effect of compositional and microstructural changes on Li⁺ diffusion and electrochemical properties. Insight in to the compositional effect on Li⁺ diffusion is obtained from DFT facilitated climbing imag...
Based on experimental and density functional studies, we show that tailoring of oxygen vacancies (OV) leads to large scale enhancement of photoconductivity in BiFeO3 (BFO). The OV concentration is increased by substituting an aliovalent cation Ca²⁺ at Bi³⁺ sites in the BFO structure. Furthermore, the OV concentration at the disordered grain boundar...
Nano-porous nano-silicon (npn-Si) anode for Li-ion battery is a great promise to mitigate problems associated with large volume expansion and pulverization during the charging-discharging cycle. Here we report the synthesis of highly porous Si from MCM-41, through a magnesiothermic reduction ((MR) method. Structural studies confirm the complete con...
The magnetic properties of Bi1-xCaxFe1-yTiyO3-δ (BCFO: y = 0 and BCFTO: x = y) nanoparticles are studied across a wide range of temperatures (20 K to 960 K) for different Ca (and Ti) concentrations [x (= y) = 0, 0.025, 0.05, and 0.1]. X-ray diffraction and electron microscopy revealed the gradual emergence of the orthorhombic phase (Pnma) with an i...
A synergetic approach of employing smooth mesoporous TiO2 microsphere (SμS-TiO2)-nanoparticulate TiO2 (np-TiO2) composite photoanode, and size and defect controlled CdSe quantum dots (QD) to achieve high efficiency (η) in a modified Grätzel solar cell, quantum dot sensitized whisperonic solar cells (QDSWSC), is reported. SμS-TiO2 exhibits whisperin...
CuInS2 (CIS) based solar cell devices are fabricated by sensitizing TiO2 photoanodes with CIS quantum dots (CIS-QDs). Morphologically different TiO2, viz. Degussa P25 nanoparticles, smooth and fibrous microspheres (SμS and FμS respectively) are used to fabricate photoanodes. CIS-QDs are synthesized using dodecanethiol (DDT), CuI and In(OAc)3 precur...
Mesoporous TiO2 nanoparticles are excellent photoanodes for sensitized solar cells. However, significant loss in the photoconversion efficiency (PCE) occurs due to the inefficient light absorption. Large Mie scattering from mesoporous micron-sized spheres could be used to enhance the absorption and hence the PCE. Here, we show that a composite comp...