Browsing by Author "Pankaj Srivastava"

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A comparative study of electrocatalytic performance of metal molybdates for the water oxidation
(Elsevier Ltd, 2018) V.K.V.P. Srirapu; Ajay Kumar; Nirmala Kumari; Pankaj Srivastava; Ravindra Nath Singh
Binary mixed oxides of molybdenum and a metal of the first-row transition metals with compositional formulae, MMoO4 (where M = Cr, Fe, Mn, Co, Ni, Cu or Zn), were prepared by a microwave-assisted co-precipitation method and their electrocatalytic activities have been investigated for oxygen evolution reaction (OER) in 1 M KOH. Materials were characterized for structural and electrocatalytic surface properties using FT-IR, XRD, TEM, BET, XPS, cyclic voltammetry (CV) and anodic Tafel polarization techniques. The crystallite size of oxides ranged between ∼17 and ∼41 nm. For electrochemical studies, oxides obtained in powders form were produced in the thin-film form on the pretreated glassy carbon (GC) support. It has been observed that among electrocatalysts investigated, the CoMoO4/GC electrode was the greatest OER active while that the MnMoO4/GC electrode was the least active. The OER produced low Tafel slopes, ∼36, ∼43 and ∼46 mV respectively on FeMoO4, CoMoO4 and CuMoO4 while it showed the higher Tafel slopes on CrMoO4(∼57 mV), NiMoO4(∼71 mV) and MnMoO4 (∼89 mV). © 2018 Hydrogen Energy Publications LLC
A New Series of Heteroleptic Cd(II) Diimine-Ferrocenyl Dithiocarbamate Complexes which Successfully Co-Sensitizes TiO2 Photoanode with Ru N719 Dye in DSSC
(Wiley-Blackwell, 2017) Krishna K. Manar; Neetu; Anamika; Pankaj Srivastava; Michael G. B. Drew; Nanhai Singh
New heteroleptic complexes of the form [Cd(diimine)(Fcdtc)2] (diimine= 1,10-phenanthroline (phen), Fcdtc=N-ferrocenyl-N-pyridin-3-ylmethyl dithiocarbamate (KL1) Cd1; 2,2’-bipyridyl (bpy), N-ferrocenyl-N-pyridin-4-ylmethyl dithiocarbamate (KL2) Cd2; bpy, (KL1) Cd3 and phen, (KL2) Cd4) have been synthesised and characterized by elemental analyses, spectroscopy (IR, UV-Vis., 1H and 13C {1H} NMR) and their structures have been revealed by X-ray crystallography. These complexes have been explored as co-sensitizers with N719 over TiO2 for application as dye sensitized solar cells (DSSC) photoanodes. The use of these complexes as co-sensitizers resulted in extended UV-Visible spectral response, greater dye loading, enhanced electron life time, reduced charge recombination and thermodynamically more facile charge transfer in the DSSC. Among all the co-sensitized cells (Cd1/N719, Cd2/N719, Cd3/N719 and Cd4/N719), the Cd1-based cell demonstrated not only the highest incident photon to current efficiency (IPCE) 47% but the obtained current conversion efficiency 3.84%, was much higher than that of the N719 based cell (2.70%) under the same illumination condition. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Adaptive soil management
(2013) P.C. Abhilash; Rama Kant Dubey; Vishal Tripathi; Pankaj Srivastava; J.P. Verma; H.B. Singh
[No abstract available]
Application of new natural dyes extracted from Nasturtium flowers (Tropaeolum majus) as photosensitizer in dye-sensitized solar cells
(Elsevier GmbH, 2021) Shalini Singh; Ishwar Chandra Maurya; Shubham Sharma; Shiva Prakash Singh Kushwaha; Pankaj Srivastava; Lal Bahadur
This work reported the natural dyes extracted from yellow and orange Nasturtium (Tropaeolum majus) flower petals and then used them as sensitizer in dye-sensitized solar cells (DSSCs) for the first time. The functional groups present in the dyes were identified by FTIR spectroscopy which revealed the characteristic peaks of pigments anthocyanins and carotenoids. The UV–Visible analysis of dye extracts showed absorption in the visible region and the dye loaded TiO2 exhibited broad absorption. The density functional theory (DFT) calculation was performed on Lutein, Cyanidin-3-sophoroside, Delphinidine-3-dihexoside and Pelargonidin-3-sophoroside to find out the HOMO and LUMO levels of each. The DSSCs were constructed using these natural extracts as sensitizer dye and photovoltaic performance such as conversion efficiency (η), short-circuit current density (Jsc), open-circuit voltage (Voc) and fill factor (FF) were investigated. The electrochemical impedance spectroscopy (EIS) studies were performed to analyze the charge transfer characteristics. The light-to-electricity conversion efficiency of 0.28% is achieved with Voc of 0.556 V, Jsc of 0.72 mA/cm2 and FF of 0.70 for natural sensitizer extracted from orange petals of Nasturtium flowers. © 2021 Elsevier GmbH
Broad temperature range low field magnetoresistance in La0.7Ca0.3MnO3:nano-ZnO composites
(2009) P.K. Siwach; Pankaj Srivastava; Jai Singh; H.K. Singh; O.N. Srivastava
We report the enhanced low field magnetoresistance in broad temperature range (∼70 K) in LCMO:(%x) nano-ZnO (%x = 0, 1, 3, 5, 7 and 10) composites. Nano-ZnO has been synthesized by vapor phase transport technique which then admixed with sol-gel synthesized nano-LCMO that leads to LCMO:nano-ZnO composites. Nano-ZnO admixing does not show any significant change in lattice parameter of the composites. All samples exhibits characteristic insulator-metal (TIM) and para-ferromagnetic (TC) transition temperature, which decreases with increase in nano-ZnO content. Higher nano-ZnO (x ≥ 3%) leads to dual I-M as well as PM-FM transitions. The first transition occurs close to TIM or TC of pure LCMO and another at a significant lower temperature. At x > 7%, the double transitions transforms into a single-broad transition and at then finally disappears for x > 10%. The occurrence of dual transition has been explained on the basis of stress induced phase separation due to nanoglobular ZnO structures that result in formation of intragranular and intergranular regions having different transition temperatures. The interesting and important result for the present LCMO:nano-ZnO composites is the observation of improved MR ∼13-18% at a moderate magnetic field of 3 and 5 kG in a broad temperature range of ∼70 K (80-150 K). The improved broad range low field magnetoresistance (LFMR) has been explained on the basis of grain boundary tailoring due to coating of polar nature nano-ZnO on the LCMO grains. © 2009 Elsevier B.V. All rights reserved.
Callindra haematocephata and Peltophorum pterocarpum flowers as natural sensitizers for TiO2 thin film based dye-sensitized solar cells
(Elsevier B.V., 2016) Ishwar Chandra Maurya; Neetu; Arun Kumar Gupta; Pankaj Srivastava; Lal Bahadur
We have studied the performance of dye-sensitized solar cells employing natural dye extracted from the flowers Callindra haematocephata and Peltophorum pterocarpum as sensitizers for TiO2 photoanode. The extracts have shown appreciable absorption in the visible region. FTIR studies indicated the presence of anthocyanins and β-carotene in the flowers of C. haematocephata and P. pterocarpum respectively. The extracts were anchored on TiO2 film deposited on transparent conductive glass (FTO) which were used as photoanode. The dye coated TiO2 film electrode, Pt counter electrode and electrolyte (I−3) assembled into a cell module was illuminated by a light source with intensity 100 mW/cm2 to measure the photoelectric conversion efficiency of the DSSCs. From the J-V characteristic curves of cells, the parameters related to the solar cell performance were determined. The conversion efficiency of the DSSC employing natural dye extract from the flower C. haematocephata and P. pterocarpumwere was found as 0.06% and 0.04%, with open-circuit voltage (VOC) of 370 mV & 400 mV, short-circuit current density (JSC) of 0.25 mA/cm2 & 0.15 mA/cm2, fill factor (FF) of 0.70 & 0.71 and Pmax of 65 & 45 μW cm−2 respectively. The extract of the flower C. haematocephata exhibited better photosensitization action compared to the flower of P. pterocarpum. © 2016 Elsevier B.V.
Colossal magnetoresistance study in nanophasic La0.7Ca 0.3MnO3 manganite
(2006) P.K. Siwach; U.K. Goutam; Pankaj Srivastava; H.K. Singh; R.S. Tiwari; O.N. Srivastava
In this study we report the effect of sintering temperature on the low field magnetotransport properties of La0.7Ca0.3MnO 3 manganite synthesized through the polymeric precursor route. The La0.7Ca0.3MnO3 has been sintered at 600 °C (S6), 700 °C (S7), 800 °C (S8), 900 °C (S9) and 1000 °C (S10). X-ray diffraction confirms that phase formation starts at 600 °C. All the samples are single phasic having an orthorhombic unit cell. The lattice parameters decrease on lowering the sintering temperature (TS). The crystallite as well as the grain size also show strong dependence on the sintering temperature. All the samples possess characteristic insulator-metal (TIM) as well as paramagnetic-ferromagnetic (PM-FM) (TC) transitions. The TC varies in a small range [272-256 K] as a function of sintering temperature whereas the TIM goes down from 267 K (S10) to 138 K (S6), a strong decrease of 129 K. This TC-T IM discrepancy is due to the fact that whereas the former is an intrinsic characteristic, the latter depends strongly on the extrinsic factors e.g. synthesis conditions, grain boundaries and associated disorders. For all the samples magnetoresistance (MR) shows strong dependence on TS. The MR increases on lowering the temperature as well as on increasing the field with the occurrence of an intrinsic contribution around TC. These variations of MR for all the samples have been explained in terms of the microstructural variations and spin-polarized tunnelling at low temperatures.
Comparative study of natural dyes extracted from dark red and yellow Frangipani flowers (Plumeria rubra L.) as DSSC sensitizer
(Elsevier GmbH, 2024) Abhilasha Tiwari; Shubham Sharma; Nikhil Srivastav; Pankaj Srivastava
Dye-sensitized solar cells (DSSC) provide credible alternative for the inorganic solid-state photovoltaic devices. In this work, natural sensitizer extracted from Plumeria rubra L. flower (Frangipani) in ethanol has been used as the sensitizer dye. Dark red and yellow species of Frangipani flower petals extracted natural dyes have been studied for their comparative performance as sensitizer dye. FTIR revealed the presence of hydroxyl and carbonyl group in the sensitizer dye, which helped in binding with TiO2. UV-Visible analysis revealed absorption in visible region, which got broadened for dye loaded TiO2. Mass spectrometry confirmed major chemical constituents present in Plumeria rubra L. flower. For the HOMO and LUMO levels of dark red and yellow Frangipani flowers, the density functional theory (DFT) calculation was performed. Light-to-electricity conversion efficiency (ɳ%) of dark red Frangipani flowers was achieved 0.148 % with Voc 0.27 V, Jsc 0.88 mA/cm2 and FF 0.62, which was comparatively higher than yellow Frangipani flowers-based cell having ɳ% 0.128 % with Voc 0.54 V, Jsc 0.37 mA/cm2 and FF 0.64, respectively. For analyzing the charge transfer characteristics, electrochemical impedance spectroscopy (EIS) studies were carried out. The dark red species of Frangipani flower showed better result as sensitizer dye compared to the yellow species. © 2024 Elsevier GmbH
Comparison of physical and electrochemical properties of ZnO prepared via different surfactant-assisted precipitation routes
(Springer Nature, 2015) Arun Gupta; Pankaj Srivastava; Lal Bahadur; D.P. Amalnerkar; Ratna Chauhan
The flakes-, hexagons-, nanoparticle-, and flower-like ZnO nanostructures have been synthesized via different surfactant-assisted precipitation routes. The XRD of all ZnO nanostructures is hexagonal single crystalline in nature and the UV–Vis absorption spectra showed blue shift in wavelength corresponding to bulk. The synthesized zinc-oxide nanopowders were used to fabricate dye solar cells sensitized by N719 dye. The comparative study of cells prepared by above ZnO nanopowders has been done. The highest conversion efficiency (2.48 %) for the cell is shown by flower-like ZnO than the others. The difference in photovoltaic parameters for the ZnO nanopowders is due to the difference in surfactants which directly correlate with surface area and dye loading. © 2014, The Author(s).
Correction to: Synthesis of nanosized TiO2 using different molecular weight polyethylene glycol (PEG) as capping agent and their performance as photoanode in dye-sensitized solar cells (Journal of Solid State Electrochemistry, (2020), 24, 10, (2395-2403), 10.1007/s10008-020-04768-y)
(Springer, 2020) Shalini Singh; Ishwar Chandra Maurya; Pankaj Srivastava; Lal Bahadur
The author would like to add Acknowledgements in the originally published paper. © 2020, Springer-Verlag GmbH Germany, part of Springer Nature.
DC electrical conduction and morphological behavior of counter anion-governed genesis of electrochemically synthesized polypyrrole films
(John Wiley and Sons Inc, 2012) Rajiv K. Singh; Amit Kumar; Khushboo Agarwal; Mahesh Kumar; H.K. Singh; Pankaj Srivastava; Ramadhar Singh
Highly conducting polypyrrole (PPY) films, doped with various anions [pTS-, ClO4-, and NO3- and mixed electrolyte system (pTS- ClO4-)], have been electrochemically synthesized in aqueous solution at ∼275 K in an inert atmosphere. PPY exhibits metallic order dc conductivity at room temperature and shows variation of conductivity with respect to time of polymerization. Effect of dopant anion on growth mechanism of PPY is evident from its surface morphology. X-ray photoelectron spectroscopy (XPS), used to examine the surface composition and doping level of various PPY films, confirms the anionic doping into the polymer backbone. Both XPS and ultraviolet- visible spectroscopy give evidence of formation of polarons and bipolarons. The temperature (4.2-320 K)-dependent dc conductivity data of these PPY films have been explained by Mott's 3D variable-range hopping conduction model. Mott's parameters have been estimated, and structural disorder with doping is correlated for all the samples. Mott's criterion for distant hopping sites prevails in case of moderately doped samples (PPY3, PPY4, and PPY5), whereas the hopping to nearest neighbor sites is found more suitable in case of highly doped samples (PPY1 and PPY2). The origin of these changes is due to the modification in the molecular structure of PPY, which is governed by different growth mechanisms for organic (pTS-) and inorganic (ClO 4- and NO3-) counter anions. © 2011 Wiley Periodicals, Inc.
Dependence of superconductivity and its weakly linked behavior in bulk LaO 1-xF xFeAs on F doping
(2012) Anurag Gupta; Hannu Huhtinen; Chandra Shekhar; Kim Schlesier; Pankaj Srivastava; Amit Srivastava; O.N. Srivastava; Reino Laiho; A.V. Narlikar
Samples of oxypnictide compound LaO1-xFx FeAs, with x = 0.15 and 0.2 corresponding to over- and highly over-doped compositions, respectively, were prepared by solid-state reaction. We present their characterization by XRD and HRTEM, as well as resistivity ρ(T), magnetization M(B) and microwave modulated absorption (MMA) response between 4.2-300 K and applied fields B = 0-8 T. With change in x, both the superconducting and magnetic behavior of the samples shows an interesting pattern. The "magnetic anomaly" at T ∼ 130 K, observed in M(T) for x = 0, instead of getting totally suppressed shows a tendency to reappear in x = 0.2 sample. Both samples typically show ρ(300 K) > 2.8 × 10- 3 Ω;2 cm and critical current density J c(5 K, 1 T) < 2 × 10 7 A/m 2. The superconducting transitions as measured by ρ(T) at B = 0 are found broad for both x = 0.15 and 0.2 samples with transition widths ∼2.5 and 6 K, respectively. The slope |dB c2/dT|(where B c2 is upper critical field) determined by resistive onsets, for the x = 0.15 and 0.2 samples, has values ∼7.5 and 3.5 T/K, respectively. The superconducting state characteristics as reflected by ρ(T, B), M(T), magnetic J c(B) and MMA response are typical of the presence of weakly linked inter-grain regions in both the samples. Our HRTEM images of the x = 0.15 sample show the presence of high angle (∼43°) grain boundaries, which are well known to limit the J c in cuprate-based high T c bulk materials. © 2012 Springer Science+Business Media, LLC.
Detection of Leptomonas sp. parasites in clinical isolates of Kala-azar patients from India
(2010) Pankaj Srivastava; Vijay Kumar Prajapati; Manu Vanaerschot; Gert Van der Auwera; Jean Claude Dujardin; Shyam Sundar
We report here nine unusual cases of Kala-azar, of which parasites were isolated and found by 18S rRNA gene sequencing to be most similar to Leptomonas species. One of these isolates was used to inoculate Balb/c mice; organs were collected and directly submitted to a genus-specific rDNA-ITS1 PCR analysis: this revealed the presence of both Leptomonas sp. and Leishmania donovani. Therefore, we conclude that there was a mixed infection of Leptomonas sp. and L. donovani in this isolate. We consider that mixed infection may be present in the patients themselves, Leptomonas persisting in them because of the immuno-suppression associated with Kala-azar. © 2010 Elsevier B.V.
Diagnosis of indian visceral leishmaniasis by nucleic acid detection using pcr
(2011) Pankaj Srivastava; Sanjana Mehrotra; Puja Tiwary; Jaya Chakravarty; Shyam Sundar
Background: PCR based diagnosis for Visceral Leishmaniasis (VL), despite numerous published primers, remains far from being applied in the field. The present study was planned to design a Leishmania specific diagnostic assay and to evaluate its sensitivity and specificity on a sample size, which to the best of our knowledge is the largest ever screened in one study. Methods: Leishmania specific primers were developed using 18S rRNA gene and their sensitivity was evaluated on 500 parasitologically confirmed patients with VL and 25 Post Kala-azar Dermal Leishmaniasis (PKDL) patients. Specificity was calculated on 250 healthy endemic controls, 250 healthy non endemic controls and 250 non leishmanial diseases like malaria. Results: Our PCR assay had a sensitivity of 87.8% (95%CI: 84.1-89.8) using 200 μL of patient's peripheral-blood. Specificity was absolute in non-endemic healthy controls and in subjects with different diseases while in endemic controls it was 84% (95%CI: 78.9-88.0). Its overall specificity was 94.6% (95%CI-92.8-96.1). Conclusions: The PCR assay developed is sensitive enough to detect the 18S rRNA gene in an amount equivalent to a single parasite or less in a one million human cell environment. The high sensitivity of this PCR diagnostic test with relatively non-invasive peripheral blood sampling method opens up the possibility of its deployment in field for the routine diagnosis of VL. © 2011 Srivastava et al.
Diagnosis of visceral leishmaniasis
(2011) Pankaj Srivastava; Anand Dayama; Sanjana Mehrotra; Shyam Sundar
Leishmaniasis is a vector-borne disease with up to 350 million people at risk of infection worldwide. Among its different clinical manifestations, visceral is the most severe form. Since clinical features of visceral leishmaniasis (VL) mimic several other common diseases, accurate diagnosis is crucial as the treatment is associated with significant toxicity. Invasive and risky techniques involving demonstration of the parasites in stained preparations from splenic and bone marrow aspirate is still the gold standard for VL diagnosis. Serological tests using rK39 in ELISA or rapid immunochromatographic format, Direct Agglutination Test (DAT), immunoblotting have issues related to a significant proportion of asymptomatic individuals being positive with these tests and their inability to diagnose relapses as these remain positive for several months to years after cure. PCR is the most common molecular technique successfully used for diagnosis and differentiation of species. Through this review we focus extensively on the comparative utilities of the various diagnostic tools currently available for VL, describing in depth their advantages and disadvantages, addressing the recent advances attained in the field. A simple, rapid, non invasive, accurate and cost effective marker of active VL, which can be used in field conditions, is necessary to improve diagnosis of VL. © 2010 Royal Society of Tropical Medicine and Hygiene.
Dye-sensitized solar cell based on nanocrystalline ZnO thin film electrodes combined with a novel light absorbing dye Coomassie Brilliant Blue in acetonitrile solution
(2012) Pankaj Srivastava; Lal Bahadur
In this work, characterization of dye-sensitized solar cells (DSSC) using nanocrystalline ZnO thin film electrodes combined with a novel light absorbing dye Coomassie Brilliant Blue (CBB), in acetonitrile solution is reported. The absorption spectrum of this dye in acetonitrile solution indicates appreciable absorption in the range of 500-700 nm with a sharp peak at 597 nm indicating its possible use as a photosensitizer for ZnO. The current-voltage and efficiency characteristics of a DSSC based on this dye and ZnO acceptor are measured for two methods of depositing the ZnO. Better response is achieved for nanocrystalline ZnO thin films than for sprayed films in terms of cell output. © 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.
Dye-sensitized solar cell using extract from petals of male flowers Luffa cylindrica L. as a natural sensitizer
(Elsevier B.V., 2016) Ishwar Chandra Maurya; Pankaj Srivastava; Lal Bahadur
The study reports use of natural dye extracted from petals of male flowers Luffa cylindrica L. as sensitizer for TiO2 based dye-sensitized solar cells. Optical characteristics of the dye extract and photoelectrochemical performance of the cells were studied. The extracts showed the UV-Vis absorptions in the 400-450 nm range with broad maxima at ∼430 nm. FTIR spectra of extract revealed the presence of anchoring groups and coloring constituents. DSSC was fabricated using natural dye loaded TiO2 photoelectrode, electrolyte containing I-/I3- redox mediator and Pt counter electrode by assembling them into a cell module. Conversion of solar light into electricity was successfully accomplished and DSSC based on petals of male flowers Luffa cylindrica L. extract exhibited an open-circuit voltage (Voc) of 0.52 V, short-circuit current density (Jsc) of 0.44 mA cm-2, Pmax 130 μW, fill factor (FF) of 0.60, conversion efficiency of 0.13% and IPCE ∼30% (at λ = 430 nm). © 2015 Elsevier B.V.
Dye-Sensitized Solar Cells Employing Extracts from Four Cassia Flowers as Natural Sensitizers: Studies on Dye Ingredient Effect on Photovoltaic Performance
(Springer New York LLC, 2018) Ishwar Chandra Maurya; Shalini Singh; Neetu; Arun Kumar Gupta; Pankaj Srivastava; Lal Bahadur
Natural dyes extracted from four different flowers, namely, Cassia surattensis, Cassia tora, Cassia alata and Cassia occidentalis were used as sensitizers for TiO2-based dye-sensitized solar cells (DSSC). The dye extracts from flowers were obtained by a simple extraction technique and used without any further purification. Optical characteristics of dye extracts were studied. Fourier-transform infrared (FTIR) spectra were used to identify the constituents of extracted dyes. The photovoltaic performance of DSSC employing dye-capped TiO2 photoanodes was measured. The sensitization performance related to anchoring groups present and interaction between dyes with TiO2 surface is demonstrated. An attempt has been made to rationalize the observations by light absorption of the dye extracts and their adsorption on TiO2. The short-circuit current density (ISC) values ranged from 0.06 mA/cm2 to 0.20 mA/cm2; open circuit voltage (VOC) from 0.292 V to 0.833 V; fill factor (FF) from 0.7 to 0.9; efficiencies (η) from 0.013% to 0.15% and incident photon-to-current conversion efficiency from 13% to 20%, were obtained for DSSC using these natural dye extracts. Cassia occidentalis showed the highest current density of 0.20 mA/cm2 and power conversion efficiency of 0.15%, which was due to better interaction between the carbonyl and hydroxyl group of the anthocyanin molecule of C. occidentalis and surface of TiO2 film. The red and blue shift of absorption wavelength of C. surattensis and the blue shift of absorption wavelength of the C. tora, C. alata and C. occidentalis extract in ethanol solution compared to that on TiO2 film has been used for the interpretation of obtained results. © 2017, The Minerals, Metals & Materials Society.
Effect of ag doping and admixing on the magnetotransport properties of nanophasic La0.7Ca0.3MnO3
(2011) Pankaj Srivastava; Amit Srivastava; O.N. Srivastava; D.P. Singh; P.K. Siwach
We report the comparative study on the effect of Ag doping and admixing on the structure and magnetotransport properties of nanophasic La 0.7Ca0.3MnO3 (LCMO) manganite to resolve the ambiguous issue of Ag substitution at La-site in LCMO manganite. In this context two sets of samples were synthesized, (a) Ag doped La0.7Ca 0.3-xAgxMnO3 (x = 0, 0.1, 0.15, 0.2, 0.3) and (b) chemically synthesized Ag nanoparticles admixed La0.7Ca 0.3MnO3 (LCMO + x wt.% Ag-NP, x = 0, 10, 15, 20, 30) and were annealed at 700°C in oxygen ambience. XRD study reveals that for Ag doped nanophasic LCMO samples, orthorhombic LCMO transforms to rhombohedral for x < 0.10 while for Ag admixed LCMO no such transformation occurs, rather Ag is present as a secondary phase. Resistivity decreases for both types of samples, In the case of Ag admixed LCMO it is due to the metallic nature of silver while for Ag doped LCMO, increase in the number of holes as silver being mono valent may be the reason for decrease in resistivity. Both the insulatormetal (TIM) and ferromagneticparamagnetic (TC) transition temperatures increases with Ag. The corresponding increment in these parameters is ∼100 K and ∼50 K for 30% Ag doped and for Ag admixed (30%) it is ∼60 K and ∼15 K respectively than that of pure LCMO. Room temperature magnetoresistance (MR) values are higher (6.8% for x = 0.30) for Ag doped LCMO than that of undoped LCMO (∼0.5%). © 2011 World Scientific Publishing Company.
Effect of Dye Extraction Solvent on the Photovoltaic Performance of Tecoma stans-Sensitized Solar Cells
(Springer, 2020) Shalini Singh; Ishwar Chandra Maurya; Shubham Sharma; Pankaj Srivastava; Lal Bahadur
Abstract: The use of natural dyes as photosensitizers has several advantages including their easy extraction and their biodegradable, nontoxic, and environmentally friendly nature, which makes them vital for application in dye-sensitized solar cells (DSSC). In the present work, we study the effects of extraction solvent on the photovoltaic performance of a natural dye sensitizer for TiO2-based DSSC. Extracts of Tecoma stans flowers in two different solvents, ethanol and ethanol–water mixture, were used as the dye sensitizer for extending the spectral sensitivity of TiO2. The optical properties of the dye extracts were studied by their UV–visible absorption spectra. Fourier transform infrared spectra revealed the presence of anchoring groups and coloring pigments, and nuclear magnetic resonance spectroscopy and mass spectrometry were used to characterize the main constituents of the dye extract. The photovoltaic characteristics of these dye extracts coated on TiO2 were investigated by employing them as DSSC photoanodes. With the dye extracted in ethanol and coated on TiO2, an open-circuit voltage (Voc) of 0.293 V, short-circuit photocurrent density (Jsc) of 0.790 mA/cm2, fill factor (FF) of 0.46, and conversion efficiency (η) of 0.13% were obtained, whereas dye extracted in the ethanol–water mixture revealed Voc of 0.285 V, Jsc of 0.735 mA/cm2, FF of 0.37, and η of 0.09%. The photovoltaic performance of the dye extracts in the two cases underlines the greater effectiveness of ethanol as dye extraction solvent. Graphical Abstract: [Figure not available: see fulltext.] © 2020, The Minerals, Metals & Materials Society.