Publications by Madhu Chennabasappa
Chemical Engineering Journal, 2021
One of the biggest challenges currently in the field of energy generation and conservation is to ... more One of the biggest challenges currently in the field of energy generation and conservation is to develop a stable, scalable and cost-effective electrocatalyst with reduced overpotentials for both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). This unprecedented effort presents a robust, non-costly ternary alkali metal-based chalcogenide (NaFeS2) as an effective and highly active electrocatalyst prepared by the hydrothermal method. The monocrystalline nature of the NaFeS2 nanostructures was shown using SAED patterns. The differences in the atomic radii of Na and Fe favors the formation of Fe-S bonds largely contributing to the enhanced electrocatalytic activity of NaFeS2. Further, a decrease in the kinetic energy of the catalytic reaction increases the electrocatalytic property of NaFeS2. We also highlighted the contribution of the high surface area, the Fermi level and the d-orbitals of Fe in enhancing the OER. NaFeS2/NF shows a current density of 200 mA cm⁻² with a small potential of 1.60 V and an overpotential of 370 mV indicating that the material possesses a remarkable electrocatalytic activity outperforming other electrocatalysts in the category. Further, by displaying a potential of -220 mV, NaFeS2/NF attained a current density of -100 mAcm⁻², demonstrating a significantly improved HER performance of the electrocatalyst. Also, at a potential of -220 mV, the material exhibited a high stability at a continuous electrolysis of about 30 hours. The density functional theory (DFT) calculations indicated that out of the possible adsorption sites on the NaFeS2 surface, only (010) and (100) exhibit catalytically preferential adsorption energy (EH) values, which are eventually responsible for the superior electrocatalytic activity. Finally, both the experimental studies and the DFT calculations complement each other and present NaFeS2 as a potentially promising bifunctional electrocatalyst for water splitting applications, which can be scaled-up and deployed for large-scale hydrogen productions.
Journal of Alloys and Compounds, 2021
When heat transport process occurs in a magnetic refrigeration device, magnetocaloric regenerator... more When heat transport process occurs in a magnetic refrigeration device, magnetocaloric regenerator corrosion could be shed in light. Our work mimicks this phenomenon by subjecting the magnetocaloric material Gd6Co1.67Si3 to controlled water flow. The corrosion is first explained based on the elemental electrochemical oxidation thereby allowing a new test by the exposing material in passive fluid (KOH) up to 1 year. The neglected degradation of the material was justified by X-Ray photoelectron spectroscopy (XPS) and depth profile Auger spectroscopy, and thus the control of its corrosion is reported. The effective control of the corrosion when material is exposed to KOH could be a universal procedure in magnetic refrigeration prototype.
Ceramics International, 2019
We report a two steps synthesis of strontium rich cobaltates La1-xSrxCoO3-δ (0.5 ≤ x ≤ 0.9) compo... more We report a two steps synthesis of strontium rich cobaltates La1-xSrxCoO3-δ (0.5 ≤ x ≤ 0.9) compounds. Following the standard solid state procedure, an oxygen intercalation process has been carried out. All the compounds show a perovskite related type structure. Samples have been characterized from chemical and structural point of view. The cubic “a” cell parameter saturates with the oxygen deficiency parameters δ that is controlled by the thermodynamic parameters (pO2; T). The magnetic properties studies were carried out before and after oxygen intercalation process and a continuous transfer from a localized character to an itinerant one's when oxygen is up taken is supported. A complete magnetic phase diagram with respect to temperature is proposed. One further evidence for attaining of Co+3.58 against Co+3.70 in La0.3Sr0.7CoO3-δ with the help of electrochemical oxidation that definitively both metal like behavior and higher than 280 K paramagnetic to ferromagnetic temperature phase transition unambiguously signed an oxygen stoichiometry close to 3 in La1-xSrxCoO3 perovskites serie.
ResearchGate, 2019
"Rietveld Refinement for Beginners Ver x.doc" This is step by step procedure to perform Rietveld ... more "Rietveld Refinement for Beginners Ver x.doc" This is step by step procedure to perform Rietveld Refinement for first time users. The purpose is to help research scholars, scientists, students(UG/PG) to learn how to analyze x-ray diffraction data of their samples. This is the initial trial, so please send your valuable suggestions and comments to improvise this manual. Based on your suggestions, this document will be updated periodically so download the latest available document.
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Room-temperature ferromagnetism has been observed in undoped GaN and CdS semiconductor nanopartic... more Room-temperature ferromagnetism has been observed in undoped GaN and CdS semiconductor nanoparticles of different sizes with the average diameter in the range 10–25 nm. These nanoparticles were synthesized by simple routes and thoroughly characterized by various techniques. Magnetization measurements at room temperature show that these nanoparticles are ferromagnetic with a saturation magnetization of ∼10−3 emu∕gm, which is comparable to that observed in nanoparticles of nonmagnetic oxides. On the other hand, agglomerated particles of GaN and CdS exhibit diamagnetism or ferromagnetism with small saturation moments. Furthermore, the saturation magnetic moment decreases with the increase in particles size, suggesting that ferromagnetism is due to the defects confined to the surface of the nanoparticles, while the core of the particles remains diamagnetic. The observation of ferromagnetism is consistent with the prediction that Ga vacancies in GaN give rise to a ferromagnetic ground state. *sundaresan@jncasr.ac.in, †cnrrao@jncasr.ac.in
Http Www Theses Fr, Nov 12, 2013
Inorganic Chemistry, 2015
We describe the synthesis and the crystallographic and magnetic properties of a novel NaCoCr2(PO4... more We describe the synthesis and the crystallographic and magnetic properties of a novel NaCoCr2(PO4)3 phosphate. A conventional solid-state reaction was used to obtain single-phase powders. A Rietveld analysis of powder X-ray diffraction data proposes an orthorhombic symmetry similar to α-CrPO4-type structure in space group Imma with the following unit cell parameters: a = 10.413(1) Å; b = 13.027(1) Å; c = 6.372(1) Å. The framework consists of PO4 tetrahedra, M(1)O6 (M(1) = Cr) octahedra, and M(2)2O10 (M(2) = 0.5Cr+0.5Co) binuclear unit of edge-sharing MO6 octahedra. It can be described in terms of two building blocks: sheets consisting of corner-sharing M(2)2O10 units with PO4 tetrahedra found parallel to the (b,c) plane, and chains made by corner-sharing CrO6 octahedra and PO4 tetrahedra running along the b axis. From the interconnection of the sheets and chains, a 3D rigid skeleton is formed, exhibiting two kinds of intersecting tunnel channels containing the Na(+) ions. The proposed structure derives from the α-CrPO4-type structure considering a positive charge balance according to the equation Cr(3+) → Co(2+) + Na(+), resulting in sodium countercation introduction within the unoccupied channels shown in the α-CrPO4 framework. Temperature-dependent DC and AC magnetic susceptibility is indicative of a long-range magnetic ordering occurring at 32 K. Further, spin-flop transition sheds light on a chromium-based phosphate for the first time.
Journal of Materials Engineering
http://nopr.niscair.res.in/bitstream/123456789/8621/1/IJEMS%2017%282%29%20131-139.pdf#!
There is ongoing effort to identify novel materials that have performance better than LiCoO 2 . T... more There is ongoing effort to identify novel materials that have performance better than LiCoO 2 . The objective of this work is to explore materials in the system (1 -x -y) LiNi 0.8 Co 0.2 O 2 • xLi 2 MnO 3 • yLiCoO 2 . A ternary composition diagram was used to identify sample points, and compositions for testing were initially chosen. Detailed characterization of the synthesized materials was done, including Rietveld Refinement of XRD data, XPS analysis for valence state of transition-metals, SEM for microstructure details, and TGA for thermal stability of the materials. Electrochemical performance showed that discharge capacities on the order of 230 mAh/g were obtained. Preliminary results showed that these materials exhibit good cycling capabilities thereby positioning these materials as promising for Li-ion battery applications.
Materials Chemistry and Physics, 2009
Multiferroic BiFeO 3 and Bi 0.98 Y 0.02 FeO 3 samples were prepared by a solution combustion meth... more Multiferroic BiFeO 3 and Bi 0.98 Y 0.02 FeO 3 samples were prepared by a solution combustion method using oxalyldihydrazide (ODH) as a fuel. The as-prepared compounds were annealed at 600 • C for 3 h to obtain single-phase materials. The crystal structure examined by X-ray powder diffraction (XRD) indicates that the samples were of single phase and crystallize in a rhombohedral (space group, R-3c no.161) structure. Magnetic measurements were carried out on the resultant powders from 300 to ∼0 K. A significant increase in magnetization was observed for Y-doped BiFeO 3 .
Journal of Electroceramics, 2010
Perovskite-type Cd-doped LaCoO 3 materials were synthesized by a simple solution-based combustion... more Perovskite-type Cd-doped LaCoO 3 materials were synthesized by a simple solution-based combustion process. The synthesized materials were characterized by powder Xray diffraction (XRD), scanning electron microscopy (SEM), diffuse reflectance (DR) in the UV-VIS, and magnetic property measurements. The parent LaCoO 3 compound showed spin-glass transition at low temperatures, and with progressive Cd doping, showed transition to paramagnetic ordering. The changes in magnetic properties of the materials are correlated to the changes in structural features resulting from the Rietveld structural refinement of the materials.
Journal of Alloys and Compounds, 2014
Ageing effect phenomenon is artificially stimulated on room temperature magnetocaloric material G... more Ageing effect phenomenon is artificially stimulated on room temperature magnetocaloric material Gd 6 Co 1.67 Si 3 by using constant flux of water up to time interval of 3 months. A core-shell model of oxide layer formation (SiO x -Gd 2 O 3 ) on surface of Gd 6 Co 1.67 Si 3 due to corrosion is justified using spontaneous single metal electrochemical reactions. The model is first proposed by a detailed microstructure study using Electron Probe Micro-Analysis, X-ray diffraction experiments on the aged slab revealing Gd 2 O 3 phase and elemental depth profile analysis against time by Auger spectroscopy. It is further supported by surface chemical bonding study using X-ray Photoelectron Spectroscopy (XPS) concentrated on Si2p and O1s spectra. It is finally demonstrated that the room temperature bulk magnetocaloric performances of the material are not affected even under formation of corroded layer at the micron level scale. The Gd 2 O 3 shell certainly acts as a passivation layer.
Ionics, 2010
Composite cathode materials produced by integrating isostructural (2D-layered) compounds LiNiO2, ... more Composite cathode materials produced by integrating isostructural (2D-layered) compounds LiNiO2, LiCoO2, and Li2MnO3 (Li(Li1/3Mn2/3)O2) have been investigated utilizing a compositional phase diagram. The samples were characterized by multiple techniques to establish structure–property relationships. Specifically, for structural characterization, powder X-ray diffraction, scanning electron microscopy, thermo-gravimetric analysis, and X-ray photoelectron spectroscopy were carried out. For properties, electrochemical characterization was carried out. The
Energies, 2010
There is ongoing effort to identify novel materials that have performance better than LiCoO 2 . T... more There is ongoing effort to identify novel materials that have performance better than LiCoO 2 . The objective of this work is to explore materials in the system (1 -x -y) LiNi 0.8 Co 0.2 O 2 • xLi 2 MnO 3 • yLiCoO 2 . A ternary composition diagram was used to identify sample points, and compositions for testing were initially chosen. Detailed characterization of the synthesized materials was done, including Rietveld Refinement of XRD data, XPS analysis for valence state of transition-metals, SEM for microstructure details, and TGA for thermal stability of the materials. Electrochemical performance showed that discharge capacities on the order of 230 mAh/g were obtained. Preliminary results showed that these materials exhibit good cycling capabilities thereby positioning these materials as promising for Li-ion battery applications.
Dalton Transactions, 2011
A hydrothermal reaction of Mn(OAc) 2 ·4H 2 O, Co(OAc) 2 ·4H 2 O and 1,2,4 benzenetricarboxylic ac... more A hydrothermal reaction of Mn(OAc) 2 ·4H 2 O, Co(OAc) 2 ·4H 2 O and 1,2,4 benzenetricarboxylic acid at 220 • C for 24 h gives rise to a mixed metal MOF compound, [CoMn 2 {C 6 H 3 (COO) 3 } 2 ], I. The structure is formed by the connectivity between octahedral CoO 6 and trigonal prism MnO 6 units connected through their vertices forming a Kagome layer, which are pillared by the trimellitate. Magnetic susceptibility studies on the MOF compound indicate a canted anti-ferromagnetic behavior, due to the large antisymmetric DM interaction between the M 2+ ions (M = Mn, Co). Thermal decomposition studies indicate that the MOF compound forms a tetragonal mixed-metal spinel phase, CoMn 2 O 4 , with particle sizes in the nano regime at 400 • C. The particle size of the CoMn 2 O 4 can be controlled by varying the decomposition temperature of the parent MOF compound. Magnetic studies of the CoMn 2 O 4 compound suggests that the coercivity and the ferrimagnetic ordering temperatures are dependent on the particle size.
Dalton Transactions, 2009
COMMUNICATION Maji et al. A planar Cu 2+ (S = 1/2) kagomé network pillared by 1,2-bis(4-pyridyl) ... more COMMUNICATION Maji et al. A planar Cu 2+ (S = 1/2) kagomé network pillared by 1,2-bis(4-pyridyl) ethane with interesting magnetic properties PERSPECTIVE Kann et al. Synthetic applications of cationic iron and cobalt carbonyl complexes www.rsc.org/dalton Number 26 | The reaction of Cu(ClO 4 ) 2 ·6H 2 O and 1,2-bis(4-pyridyl)ethane (bpe) in basic aqueous solution yields a 3D compound, {[Cu 3 (CO 3 ) 2 (bpe) 3 ]·2ClO 4 } n (1) through the atmospheric fixation of CO 2 composing Cu(CO 3 ) kagomé layers pillared by the bpe linker that exhibit weak antiferromagnetic interaction in the kagomé layer and interlayer ferromagnetic coupling at low temperature.
We have investigated the magnetocaloric effect across a first order structural transition coupled... more We have investigated the magnetocaloric effect across a first order structural transition coupled to the ferromagnetic transition (T C ~ 270 K) in Pr 0⋅1 Ce 0⋅4 Sr 0⋅5 MnO 3 using magnetization and heat capacity measurements. The adiabatic magnetic entropy change |ΔS| obtained from magnetization measurements for a magnetic field change of 2 T is around 1⋅3 J/kg K. A similar value of |ΔS| was obtained from the analysis of heat capacity data.
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Publications by Madhu Chennabasappa
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