Browsing by Author "Amarnath R. Allu"

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Correlation of structure and ionic-conductivity in phosphate glass using MAS-NMR and impedance spectroscopy: Influence of sodium salt
(American Physical Society, 2022) Indrajeet Mandal; Shweta R. Keshri; Lekhan Lodhi; Krishna K. Dey; Manasi Ghosh; Aswini Ghosh; Amarnath R. Allu
In the process of diminishing the safety concerns of sodium-ion batteries, the development of glass-based solid electrolyte materials has received adequate interest. Nevertheless, achieving a high ionic-conductivity at room temperature for glass materials remains a challenging task because of the poor correlation between the conductivity and the glass structure. Here, we attempt to understand the effective influence of NaCl on the structure and ionic-conductivity of the phosphate-based glass network. For this study, xNaCl-(100-x) (31.725Na2O-12.69Al2O3-31.725P2O5-8.46NaF-5.40Na2SO4-10MoO3) glass systems (mol %) were selected, where x=0, 5, 10, 15, and 20 mol %. To investigate structural changes with the addition of different NaCl concentrations, Al27, Na23, P31 magic angle spinning nuclear magnetic resonance (MAS-NMR), P31 two-dimensional (2D) phase-adjusted spinning sideband (PASS), and P31 2D J-resolved NMR techniques and Raman spectroscopic techniques were utilized. Impedance spectroscopy and ac conductivity spectra were used to assess ionic-conductivity and sodium-ion dynamics, respectively. Impedance spectral analysis reveals that the ionic-conductivity of the base glass is increased by 2.4 times (from 1.85 × 10-7 to 4.44 × 10-7 S/cm at 373 K) with the addition of 20 mol % of NaCl. Raman spectra confirm the presence of P-O-Mo and the absence of Mo-O-Mo bonds in these glass systems, and P31 2D J-resolved spectra indicate the absence of P-O-P bonds. Upon increasing the NaCl concentration, significant changes in the shapes of P31 and Al27 MAS-NMR spectra were observed, indicating the effective influence of NaCl on the distribution of alumina and phosphorus structural units. Irrespective of the temperature, sodium-ion dynamic studies show that the mean-square displacement (R2(tp)) decreases with increasing NaCl concentration up to 10 mol % and then increases with a further increase in NaCl concentration. This investigation aids in understanding the sodium-ion dynamics and the structural information of a multicomponent glass system to enhance the room-temperature conductivity. © 2022 American Physical Society.
Role of Sodium-Ion Dynamics and Characteristic Length Scales in Ion Conductivity in Aluminophosphate Glasses Containing Na2SO4
(American Chemical Society, 2022) Indrajeet Mandal; Saswata Chakraborty; K. Jayanthi; Manasi Ghosh; Krishna K. Dey; K. Annapurna; Jayanta Mukhopadhyay; Abhijit Das Sharma; Amarnath R. Allu
Achieving high ion conductivity in glass-based Na-ion conducting materials for their applications as solid electrolytes in batteries is still challenging owing to the vague knowledge on the factors governing Na-ion dynamics. In the present study, an attempt has been made to identify the factors affecting the sodium-ion dynamics through structure and conductivity property correlation for the 37.5Na2O-37.5P2O5-15Al2O3-10NaF (FS-0; mol %) glass system with varied concentrations of Na2SO431P, 27Al, and 23Na MAS NMR (magic-angle spinning nuclear magnetic resonance) and Raman spectroscopy are employed to assess the structural modifications, and impedance spectroscopy is used to measure the variations in ionic conductivity on the addition of Na2SO4 in the FS-0 glass. Raman spectra and MAS NMR analysis indicate that the quantity of P-O-Na bonds and sulfate (SO42-) units surrounded by sodium increase with increasing Na2SO4 concentration. Impedance analysis reveals that the conductivity of FS-0 glass enhances by 1 order with the addition of 6 mol % Na2SO4. We identify from the ac-conductivity spectral analysis that the concentration of charge carriers and the critical hopping length of mobile cations increase with the addition of 6 mol % Na2SO4. Overall, we reveal that the structural modifications, Na-ion concentration, and the shallower potential well that is created for sodium due to its interaction with the nearest neighboring cations affect the Na-ion dynamics. The information obtained from the present study certainly helps to optimize the chemical composition of glasses demonstrating high ionic conductivity. © 2022 American Chemical Society
Structure and Conductivity Correlation in NASICON Based Na3Al2P3O12 Glass: Effect of Na2SO4
(Frontiers Media S.A., 2022) Indrajeet Mandal; Saswata Chakraborty; Manasi Ghosh; Krishna K. Dey; K. Annapurna; Amarnath R. Allu
Identifying the factors influencing the movement of sodium cations (Na+) in glasses accelerates the possible options of glass-based solid electrolyte materials for their applications as a promising electrolyte material in sodium-ion batteries. Nevertheless, due to the poor correlation between the structure and conductivity in glass materials, identifying the factors governing the conductivity still exists as a challenging task. Herein, we have investigated the DC-conductivity variations by correlating the structure and conductivity in sodium superionic conductor (NASICON) based Na3Al2P3O12 (NAP) glass (mol%: 37.5 P2O5—25.0 Al2O3—37.5 Na2O) due to the successive substitution of Na2SO4 for Al2O3. Structural variations have been identified using the Raman and magic-angle spinning nuclear magnetic resonance (MAS-NMR) (for 31P, 23Na, and 27Al nuclei) and conductivity measurements have been done using the impedance spectroscopy. From the ac-conductivity spectra, the correlations between mean square displacement (MSD) and dc-conductivity and between the Na+ concentration and dc-conductivity have also been evaluated. Raman spectra reveal that the increase in the Na2SO4 concentration increases the number of isolated SO42− sulfate groups that are charge compensated by the Na+ cations in the NAP glass. MAS-NMR spectra reveal that the increase in Na2SO4 concentration increases the concentration of non-bridging oxygens and further neither S-O-P nor S-O-Al bonds are formed. Impedance spectroscopy reveals that, at 373 K, the DC conductivity of the NAP glass increases with increasing the Na2SO4 up to 7.5 mol% and then decreases with the further increase. In the present study, we have shown that the mobility of sodium cations played a significant role in enhancing the ionic-conductivity. Further, we have shown that inter-ionic Coulombic interactions and the structural modification with the formation of SO42− units significantly influence the critical hopping length < R2 (tp)> of the sodium cations and consequently the mobility and the ionic conductivity. The present study clearly indicates that, based on the compositions, glass materials can also be treated as strong-electrolyte materials. Copyright © 2022 Mandal, Chakraborty, Ghosh, Dey, Annapurna and Allu.
Thermally stable bioactive borosilicate glasses: Composition–structure–property correlations
(Springer Nature, 2023) Anustup Chakraborty; Sakthi Prasad; Shashi Kant; Rathina Vel; Sucheta Tripathy; P.K. Sinha; Krishna K. Dey; Lekhan Lodhi; Manasi Ghosh; Amarnath R. Allu; Subhadip Bodhak; Kaushik Biswas
Processing of commercial bioactive glasses in the form of scaffolds, fibers and coatings on metal implants is a major challenge due to their high crystallization tendency leading to loss of many desirable functionalities relevant to bone tissue engineering applications. In this context, this work focuses on developing borosilicate bioactive glasses with improved thermal stability from the detailed understanding of composition–structure–property correlations. Structural studies through Raman and magic angle spinning nuclear magnetic resonance (MAS NMR) spectroscopy revealed the formation of a highly crosslinked network rich in B–O–Si bonds facilitating enhanced thermal stability (> 150 °C) for 17.96–35.92 mol% B2O3 containing glasses. These glasses also exhibit substantially improved in vitro biological properties such as biomineralization, cell proliferation, alkaline phosphatase (ALP) expression and antibacterial efficacy owing to predominance of B–O–Si and B–O–B bonds. However, more detailed data with pre-clinical studies are needed to confirm these observations, and for using them for specific applications. Graphical abstract: [Figure not available: see fulltext.]. © 2023, The Author(s), under exclusive licence to The Materials Research Society.
Tunable femtosecond nonlinear absorption and optical limiting thresholds of La2O3‒B2O3 glasses by controlling the borate structural units
(Acta Materialia Inc, 2022) G. Jagannath; Anuraag Gaddam; S. Venugopal Rao; D.A. Agarkov; G.M. Korableva; Manasi Ghosh; Krishna Kishor Dey; José M.F. Ferreira; Amarnath R. Allu
Utilization of optical limiting materials to suppress the input intense laser energy is obligatory in a wide variety of applications that deploy the high‒power laser sources. In this letter, we demonstrate that the optimization of borate structural units in lanthanum borate (LB) glasses through the addition of various concentrations of heavy metal oxides (HMOs) (PbO and Bi2O3) resulting in achievement of an optimum optical threshold value. The structural changes of these glasses were analyzed by 11B MAS‒NMR and Raman spectroscopic techniques. Nonlinear optical attributes were assessed by the Z‒scan technique. The enhancement of two‒photon absorption coefficient and decrement in optical limiting threshold factors suggest the LB glasses containing HMOs could be beneficial for power optical limiting devices. The achieved optical limiting threshold values of 0.075 and 0.114 J/cm2 at 700 and 800 nm, respectively, are superior compared to advanced materials such as nanoparticles, carbon nanotubes, and few‒layers of MoS2/Polymethylmethacrylates. © 2022
Tunable, efficient, ultrafast broadband nonlinear optical properties of TiO2–loaded complex phosphate glasses
(Elsevier Ltd, 2023) Jagannath Gangareddy; Hamad Syed; Saswata Chakraborty; Prince Sen; Manasi Ghosh; Krishna Kishor Dey; K. Bhattacharyya; K. Annapurna; Venugopal Rao Soma; Amarnath R. Allu
On account of their excellent optical transparency from ultraviolet to far infrared spectral regions, phosphate glasses have become interesting nonlinear optical (NLO) materials for photonic nonlinear devices. However, small NLO coefficients tend to limit the usage of phosphate–based glasses in nonlinear photonic devices. Herein, we explored the NLO tunability in multicomponent phosphate glasses by increasing the coordination of orthophosphate (PO4)3– structural units with a great number of AlO4 groups through the addition of titanium dioxide (TiO2) in the composition. The NLO absorption and refraction characteristics were ascertained using open and closed–aperture Z–scan configurations respectively in a broadband spectral region ranging from 400 nm to 1200 nm under an ultrafast regime. The Z–scan results illustrate the increase of nonlinear susceptibility of glasses with titanium dioxide content in the composition due to the formation of non–π–conjugated orthophosphate groups which are in connection with AlO4 units. Typically, at 400 nm excitation, the NLO susceptibility improved by 119.91% upon addtion of 5 mol% of TiO2. The outcomes of the study acknowledge a new approach for conceiving highly NLO active phosphate glasses while maintaining deep–ultraviolet transparency through the polymerization of (PO4)3−groups. Consequently, the strategy explored in this work might pave the way for achieving the high NLO features of phosphate–based glasses to excel in their usage in data storage, signal transmission, optical limiting, and harmonic generation functionalities. © 2023 Elsevier Ltd
Water-In-Glass: A Self-Supporting Inorganic Aqueous Electrolyte
(American Chemical Society, 2025) Sinorul Haque; Indrajeet Mandal; K. Jayanthi; Prabir S. Pal; Prince Sen; Bijay Laxmi Pradhan; Krishna Kishor Dey; Manasi Ghosh; Nitya Nand Nand Gosvami; N. M.Anoop Krishnan; Mir Wasim Raja; Amarnath R. Allu
Aqueous rechargeable sodium-ion batteries (ARNIBs) are emerging as cost-effective and safe candidates for large-scale energy storage applications. However, their advancement has been constrained by the narrow electrochemical stability window (ESW) of conventional aqueous electrolytes (1.23 V). Here, we present a transformative approach using an inexpensive and rapidly dissolvable inorganic glass material, water glass (W-glass), to significantly enhance the ESW and enable the development of solid-state, self-supporting aqueous film (SSA film) electrolytes. These SSA film electrolytes exhibit an extended ESW of up to 3.5 V and a conductivity of ∼10–4S/cm at room temperature. Structural analysis using magic-angle spinning nuclear magnetic resonance (NMR) and solution-state NMR reveals that the dissolution of W-glass in water is driven by the interdependent hydrolysis of P–O–P linkages and Na+–H+ion exchange. This work offers a cost-effective and scalable solution for advancing high-performance ARNIB technology, addressing critical barriers to commercial adoption. © 2025 American Chemical Society