Now showing 1 - 10 of 11
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    Optimizing conditions and improved electrochemical performance of layered LiNi1/3Co1/3Mn1/3O2 cathode material for Li-ion batteries
    (01-01-2022)
    Satyanarayana, Maddukuri
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    Jibin, A. K.
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    Umeshbabu, Ediga
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    James, Joseph
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    Herein, we have explored performance of layered LiNi1/3Co1/3Mn1/3O2 (NCM111) cathode material for Li ion battery applications, prepared by different preparation strategies namely co-precipitated mixed hydroxide and solid state high temperature approach combined with high-temperature calcination. The effect of crystal structure and morphology of the obtained materials were characterized by means of X-ray diffraction and scanning electron microscopy. X-ray analysis reveals that the observed lattice parameter ratio c/a is greater than 4.89 for materials with different approaches, which indicates the formation of hexagonal layered α-NaFeO2 structure. The electrochemical properties of the materials were thoroughly characterized by means of charge–discharge experiments and electrochemical impedance spectroscopy. The direct solid state synthesized NCM111 material exhibits a low retention and discharge capacity of 60 mAh g−1 at the end of 50 cycles with high irreversible capacity during cycling. The present studies have shown that the importance of material synthesis route and its sintering process, prepared at 900 °C for 8 h results low cation mixing between Li and metal ions layer in NCM111 lattice compared to other sintered samples, resulting in superior electrochemical performance. The reversible capacity of 175 mAh g−1 is noticed at C/10 rate within the voltage window of 2.5–4.4 V for 900 °C treated sample. Even at C/3 rate, a stable high reversible capacity of 145 mAh g−1 is obtained with high capacity retention of 95%. The Rietveld and EIS spectroscopic analysis conforms the existence stable layered structure and electrode, interface for NCM11 approached through co-precipitation.
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    Publication
    Eu(III)-doped barium tellurooxyphosphate phosphor with orange-red emission
    (01-12-2020)
    MohanRao, K.
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    Tiwari, Hansnath
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    Naidu, S. Asiri
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    Eu 3 + photoluminescence (PL) is studied in the tellurooxyphosphate, Ba2TeO(PO4)2, host. A series of phosphor compositions with varying concentrations of Eu 3 + dopant in Ba2TeO(PO4)2 are synthesized by high temperature solid-state reaction and the PL spectra are recorded. Under 395 nm wavelength excitation, the emission spectrum shows a single peak corresponding to the non-degenerate transition, 5D → 7F indicating that Eu 3 + preferentially occupies a single crystallographic site. The peak due to the degenerate hypersensitive 5D → 7F 2 electric dipole transition of Eu 3 + in the emission spectrum indicates that the site occupied by Eu 3 + in the tellurooxyphosphate host lattice is non-centrosymmetric. The CIE coordinate values are x= 0.61 and y= 0.34 and are found to be close to the values of the reference phosphor Y 2O 3: Eu 3 +.
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    Publication
    Multi-stimuli responsive and intrinsically luminescent polymer metallogel through ring opening copolymerization coupled with thiol-ene click chemistry
    (23-05-2022)
    Soman, Chindhu
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    Sebastian, Alphy
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    Mahato, Malay Krishna
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    Prasad, Edamana
    Luminescent polymer based metallogels have gained considerable interest due to their wide range of applications in the fields of drug delivery, tissue engineering, sensing, and optical systems. One of the challenges in the area is to tune the properties of metallogels for a given application, which is largely controlled by the choice of the functional groups in the polymer and the binding metal ions. In the present study, efforts are made to utilize ring opening copolymerization followed by functionalization by thiol-ene click chemistry to attach desirable functional groups to the polymer for preparing polymer based metallogels. A norbornene-alt-cyclohexene oxide based polymer is synthesized to develop an intrinsically luminescent metallogel using lanthanide metal-ligand complexation. The optical properties of the polymer metallogel are modulated via a dual channel process where a cluster induced intrinsic emission surpasses resonance energy transfer mechanism, leading to cool white light emission from the metallogel [CIE coordinates (0.33, 0.37);correlated color temperature 5752 K], with reversible vapochromism and irreversible chemochromism. Our studies suggest that the combination of ring opening co-polymerization and thiol-ene click chemistry is a potential design strategy for preparing polymer based metallogels with multi-stimuli responsive properties.
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    Electrochemical lithium and sodium insertion studies in 3D metal oxy-phosphate framework MoWO3(PO4)2 for battery applications
    (01-10-2021)
    Satyanarayana, M.
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    Umeshbabu, Ediga
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    Jibin, A. K.
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    James, Joseph
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    Justin, P.
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    A new type of three-dimensional (3D) oxy-phosphate materials are explored for the application of Li and Na batteries. The molybdenum tungsten oxy phosphate, MoWO3(PO4)2, was synthesized by solid-state method and evaluated for Li/Na insertion/de-insertion electrode material for the first time. The cell at charged state (vs. Li+/Li) showed a discharge capacity of 786 mAh g−1 within the voltage window of 0.3 V with amorphization of crystalline MoWO3(PO4)2 as observed from ex-situ powder XRD analysis. The structural integrity was revealed in this material, even with nearly more than 5 Li+ ions into the lattice, leading to the discharge capacity of 250 mAh g−1. The reversible charge/discharge behavior with insertion/de-insertion of 2.4 Li+ ions in the voltage range of 1.65 − 3.5 V resulted in 110 and 95 mAh g−1 at C/10 and C/5 rates, respectively. On the other hand, poor cycling performance was noticed for Na ion insertion and desertion, with a discharge capacity of 250 mAh/g within the voltage range of 0.3 − 3.5 V (vs. Na+/Na).
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    Thermoelectric properties of a high entropy half-Heusler alloy processed by a fast powder metallurgy route
    (30-11-2022)
    Karati, Anirudha
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    Mishra, Soumya Ranjan
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    Ghosh, Sanyukta
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    Mallik, Ramesh Chandra
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    Shabadi, Rajashekhara
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    Ramanujan, R. V.
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    Murty, B. S.
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    A half-Heusler (HH) type high entropy alloy (HEA) Ti2NiCoSnSb has been synthesized by a fast powder metallurgy route for the first time. Mechanical alloying (MA) by wet milling produced a powder with a minor fraction of the HH phase. The dry milling route resulted in the desired single-phase HH material. Consolidation of the nanocrystalline mechanically alloyed (MA) powder by spark plasma sintering (SPS) resulted in a majority HH phase. Interestingly, the nanocrystalline alloy exhibited simultaneous enhancement in the Seebeck coefficient and electrical conductivity, with a maximum ZT of 0.13 at 973 K observed for the dry milled alloy. The band structure obtained by density functional theory (DFT) was in good agreement with the ultraviolet-visible-near infrared (UV-Vis-NIR) absorption spectroscopy results. The DFT calculations and microstructural analysis suggest that phase separation strongly influenced the thermoelectric properties. The band structure calculations provided a good rationale for the phase evolution and thermoelectric properties.
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    Effect of Processing Routes on the Microstructure and Thermoelectric Properties of Half-Heusler TiFe0.5Ni0.5Sb1−xSnx (x = 0, 0.05, 0.1, 0.2) Alloys
    (01-01-2022)
    Karati, Anirudha
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    Ghosh, Sanyukta
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    Mallik, Ramesh Chandra
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    Shabadi, Rajashekhara
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    Murty, B. S.
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    Sn-doped TiFe0.5Ni0.5Sb1−xSnx (x = 0, 0.05, 0.1, 0.2) were synthesized by vacuum arc melting (VAM). In addition to the half-Heusler phase, secondary phases of Fe–Sb-rich compound and Ti-rich compounds were obtained after VAM. The alloys were then subjected to ball milling for 1 h and 5 h. Ball milling for 1h led to microcrystalline grains, while that for 5 h led to nanocrystalline grains. Ball milling followed by spark plasma sintering (SPS) at 1173 K led to significant reduction in size of secondary phases in the microstructure. The undoped sample exhibited a ZT of 0.008 at 873 K for both 1h and 5h BM-SPS samples.
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    Surfactant-Mediated and Morphology-Controlled Nanostructured LiFePO4/Carbon Composite as a Promising Cathode Material for Li-Ion Batteries
    (01-01-2020)
    Khan, Sourav
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    Raj, ṆRayappan Pavul
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    George, Laurel
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    Kannangara, G. S.Kamali
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    Milev, Adriyan
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    The synthesis of morphology-controlled carbon-coated nanostructured LiFePO4 (LFP/Carbon) cathode materials by surfactant-assisted hydrothermal method using block copolymers is reported. The resulting nanocrystalline high surface area materials were coated with carbon and designated as LFP/C123 and LFP/C311. All the materials were systematically characterized by various analytical, spectroscopic and imaging techniques. The reverse structure of the surfactant Pluronic® 31R1 (PPO-PEO-PPO) in comparison to Pluronic® P123 (PEO-PPO-PEO) played a vital role in controlling the particle size and morphology which in turn ameliorate the electrochemical performance in terms of reversible specific capacity (163 mAh g−1 and 140 mAh g−1 at 0.1 C for LFP/C311 and LFP/C123, respectively). In addition, LFP/C311 demonstrated excellent electrochemical performance including lower charge transfer resistance (146.3 Ω) and excellent cycling stability (95 % capacity retention at 1 C after 100 cycles) and high rate capability (163.2 mAh g−1 at 0.1 C; 147.1 mAh g−1 at 1 C). The better performance of the former is attributed to LFP nanoparticles (<50 nm) with a specific spindle-shaped morphology. Further, we have also evaluated the electrode performance with the use of both PVDF and CMC binders employed for the electrode fabrication.
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    A novel approach to synthesize porous graphene sheets by exploring KOH as pore inducing agent as well as a catalyst for supercapacitors with ultra-fast rate capability
    (01-07-2021)
    Nanaji, Katchala
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    Sarada, B. V.
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    N Rao, Tata
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    Anandan, Srinivasan
    In the present study, an earth-abundant bio-waste is effectively transformed into porous graphene sheets at a low temperature of 900 °C by utilizing Potassium hydroxide (KOH) as an activation agent to create porosity as well as a catalyst to induce graphitization by a simple synthetic approach. The resulted carbon material possesses good textural properties such as high specific surface area (2308 m2/g), high pore volume (1.3 cm3/g), graphene sheet-like morphology with an interlayer d-spacing of 0.345 nm and a highly ordered sp2 carbon as evidenced from detailed textural analysis. A detailed mechanism for the formation of graphene sheets is further explored. Owing to the multiple synergistic properties, the material has been tested as an efficient electrode material for supercapacitor application and it delivered a high specific capacitance of 240 F g−1 at 1 A/g. Furthermore, the assembled symmetric supercapacitor exhibits ultra-fast rate capability of 87% capacitance retention at high current rates (50 A/g), exceptional cyclic stability (93% retention after 25,000 cycles) and displays outstanding energy density of 21.37 W h kg−1 at a high power density of 13,420 W kg−1. The strategy developed here reveals a facile, low-cost, eco-friendly design of graphene sheets at large scale production, where the synthetic approach can be applied as a versatile method to prepare graphene sheets from any carbon sources using KOH activation.
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    Publication
    Thermoelectric properties of half-Heusler high-entropy Ti2NiCoSn1-xSb1+x (x = 0.5, 1) alloys with VEC>18
    (01-09-2020)
    Karati, Anirudha
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    Hariharan, V. S.
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    Ghosh, Sanyukta
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    Prasad, Anil
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    Nagini, M.
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    Guruvidyathri, K.
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    Mallik, Ramesh Chandra
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    Shabadi, Rajashekhara
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    Bichler, Lukas
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    Murty, B. S.
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    A new set of half-Heusler high-entropy alloys Ti2NiCoSn1-xSb1+x (x = 0.5, 1), with a valence electron count higher than 18, were investigated for thermoelectric applications. Vacuum arc melting was employed for synthesis. Atom probe analysis confirmed single-phase at atomic level. The alloys were subsequently ball milled for 1 h followed by spark plasma sintering for consolidation. In 1 h BM cases, the alloy with x = 0.5 exhibited a low lattice thermal conductivity of 2.48 Wm−1K−1, and a ZT of 0.29 at 873 K.
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    Thermoelectric properties of nanocrystalline half-Heusler high-entropy Ti2NiCoSn1−xSb1+x (x = 0.3, 0.5, 0.7, 1) alloys with VEC > 18
    (15-12-2022)
    Karati, Anirudha
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    Ghosh, Sanyukta
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    Nagini, M.
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    Mallik, Ramesh Chandra
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    Shabadi, Rajashekhara
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    Murty, B. S.
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    Powder metallurgy route has been employed to synthesize nanocrystalline Ti2NiCoSn1−xSb1+x (x = 0.3, 0.5, 0.7, 1) alloys for thermoelectric applications. Atom probe analysis confirmed the homogeneous distribution of elements in the half-Heusler phase at a scale of few nanometers. A combination of nanostructuring, lattice distortion and interfacial scattering brings about a reduction in lower thermal conductivity which brings forth an improvement in ZT. Ti2NiCoSb2 exhibited the highest ZT of 0.26 due to the increments effected by higher power factor and lower thermal conductivity.