Faculty Publications
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Item Fabrication of solution combustion based transparent semiconducting titanium and zinc co-doped indium oxide (Itizo) films(Trans Tech Publications Ltd ttp@transtec.ch, 2019) Vardhan, R.V.; Manjunath, G.; Mandal, S.In this work, solution combustion processed titanium, zinc co-doped indium oxide high transparent semiconducting thin films were demonstrated at annealing temperatures of 300, 350 °C. In the process, low-temperature combustion at 123 °C was verified through thermogravimetric analysis; acetylacetone, 2-methoxyethanol served as fuel and solvent respectively in the redox reaction. Indium titanium zinc oxide (ITiZO) films were developed on glass substrates by spin coating followed by annealing at different temperatures. ITiZO films, powder exhibited high crystallinity exactly matching with indium oxide peaks without forming secondary phases. But, the presence of In, Ti, Zn, and O is clearly visible on film through energy dispersive spectroscopy. Films had transparency more than 85% in the visible range with optical band gap ranging 3.8-3.9 eV. These ITiZO films with smooth and low roughness ranging 0.46-0.5 nm, can have a potential application as an active layer in transparent thin film transistors and optoelectronic devices. © 2019 Trans Tech Publications Ltd, Switzerland.Item Bio-Inspired, Ultra-hydrophobic Natured Durable Thermal-Sprayed Ytterbium-Oxide Coatings: Review and Perspectives(Taylor and Francis Ltd., 2024) Praveen, L.L.; Kailasam, K.; Vardhan, R.V.; Mandal, S.Ever since the discovery of ultra-hydrophobicity in lotus leaf, rigorous experiments have been carried out to replicate and understand its wetting nature using ceramic oxide based coatings on various substrates. Enormous applications dealing with ultra-hydrophobic nature have been explored which led to the discovery of intrinsic hydrophobic nature in rare-earth oxides. Several studies reported intrinsic hydrophobic behavior exhibited by rare earth oxides. Among all rare earth oxides, ytterbium-oxide (Yb2O3) has numerous applications in different fields because of its ability to phase change with pressure, abrasion resistance, high hardness and melting point. This review gives a basic understanding of wettability studies carried out on Yb2O3 coating via the solution precursor plasma spray (SPPS) technique outlined in the literature and aims to understand the mechanism of post-processing treatments, revealing the conditions affecting the reversible wettability. Additionally, the mechanical durability tests performed on thermal-sprayed Yb2O3 coatings are summarized along with the cost-effective approach of SPPS technique over other plasma spray techniques. The ultra-hydrophobicity in Yb2O3 coatings and its existing applications propels the development of novel device-designing strategies in the field of bio-sensing and oil-water separation. © 2024 Indian Ceramic Society.Item A balancing between super transparency and conductivity of solution combustion derived titanium doped indium oxide: Effect of charge carrier density and mobility(Elsevier B.V., 2018) Pujar, P.; Vardhan, R.V.; Gupta, D.; Mandal, S.In this contribution, super transparent (~100%) and conducting In14Ti1O23 (Titanium doped Indium oxide; InTiO) films were reported via solution combustion processing with acetylacetone as fuel. Both bulk-powder and thin film systems were studied and revealed the efficacy of low temperature combustion synthesis which yielded crystalline InTiO powder at 150 °C and its film counterpart had shown pronounced crystalinity with temperature. Also, all films with varying annealing temperature were smooth with rms value ranging from 0.29 nm to 1.9 nm. In addition, the charge carrier density in all films found to be of the order 1019 cm?3, possessing highest transparency nearly equals to uncoated glass at an annealing temperature of 350 °C having maximum of ~67% metal-oxygen-metal framework (or lattice oxygen) confirmed via X-ray photoelectron spectroscopy. Also, the highest conductivity of 20 S/cm at an annealing temperature of 450 °C clearly conveyed the potential of solution combustion processing in the fabrication of ultra-transparent InTiO films with no sophistication in the film fabrication. © 2018Item Effect of annealing-temperature-assisted phase evolution on conductivity of solution combustion processed calcium vanadium oxide films(Springer, 2018) Manjunath, G.; Vardhan, R.V.; Salian, A.; Jagannatha, R.; Kedia, M.; Mandal, S.In thiswork, the effect of annealing temperature on the conductivity of solution-combustion-synthesized calcium vanadium oxide (CVO) films was studied. Conductivity was tailored by the appearance of the phases like CaVO3, CaV2O5 and Ca2V2O7 as a function of annealing temperature; CaVO3 and CaV2O5 are responsible for high conductivity, whereas V5+ presence in Ca2V2O7 contributes towards dielectric nature. Evolution of phases of CVO was identified through X-ray diffraction, Raman spectroscopy, Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. A detailed conductivity measurement as a function of annealing temperature helps us to identify the decreasing trend of conductivity with increasing temperature up to 400°C; beyond this it behaves like an insulator. There was a stable conductivity while aging the films in ambient for a few days. This study revealed safe application temperature domain of CVO, and a clear correlation of electrical conductivity with the in-depth structural-compositional-morphological study. © Indian Academy of Sciences.Item Effect of lanthanum on the phase evolution of perovskite barium stannate synthesized through polymerized complex method(Elsevier Ltd, 2019) Prajapati, M.J.; Vardhan, R.V.; Mandal, S.In this study, electrically conductive perovskite lanthanum-doped barium stannate, LaxBa1-x SnO3-? (x = 0, 0.05, 0.1 and 0.15) ceramics were synthesized through polymerized complex method. The evolution of BaSnO3 phase with temperature and effect of La doping was investigated. Doping of La increased the lattice parameter from 4.1165 to 4.1208 Å, up to solubility limit (x = 0.1); doping further, secondary phase La2Sn2O7 appeared. BaSnO3 phase crystallization initiated at ?528 °C from the reaction of BaCO3 and SnO2 and was retarded by La doping causing an increment in phase formation temperature from 528.4 to 531.1 °C. Fourier transform infrared spectroscopy evidence substantial increment in (SnO3)2- absorption band with temperature strengthening diffraction responses. An incremental response in the electrical conductivity was observed by La doping with a maximum value of ?25 S cm?1, attributed to the generation of charge carriers by substitution of Ba with La ion and oxygen vacancies. In parallel, generated charge carriers also contributed towards the ionic reduction of Sn4+ to Sn2+ aiding the lattice enhancement. La-doped BaSnO3 ceramics can have a potential application in optoelectronic, thermoelectric devices and humidity sensors. © 2019 Elsevier Ltd and Techna Group S.r.l.Item A facile, low temperature spray pyrolysed tungsten oxide (WO3): an approach to antifouling coating by amalgamating scratch resistant and water repellent properties(Springer, 2020) Vardhan, R.V.; Kumar, S.; Mandal, S.In this study, a facile spray pyrolysed hydrophobic robust tungsten oxide (WO3) films were deposited at an annealing temperature of 400°C on inexpensive glass substrates, using clear and homogeneous precursor solution containing tungsten hexachloride and 2-methoxyethanol. The 10 and 15 times sprayed films were polycrystalline with the monoclinic crystal structure, uniform with the submicron-sized grain morphology (size ~320–420 nm), with an average surface roughness ranging from 12 to 17 nm and transparent above 60% in the visible region with a thickness of 380 and 550 nm, respectively. Elemental existence of tungsten and oxygen was recognized on the surface of the films possessing the highest lattice oxygen percentage of 91.1. Increment in the scratch hardness of the films with the number of sprays compared to uncoated glass was identified. The films were hydrophilic in nature (water contact angle <8°), converted to hydrophobic (>120°) by treating chemically with octadecyltrichlorosilane to form a self-assembled monolayer on the top and the hydrophobicity remained same (~120°) even after a year. These films with unique and combined properties of scratch hardness and hydrophobicity can serve in the potential application as antifouling coatings. © 2020, Indian Academy of Sciences.Item Room-temperature detection of ammonia and formaldehyde gases by La xBa1?xSnO3?? (x = 0 and 0.05) screen printed sensors: effect of ceria and ruthenate sensitization(Springer Science and Business Media Deutschland GmbH, 2021) Manjunath, G.; Vardhan, R.V.; Praveen, L.L.; Pothukanuri, P.; Mandal, S.In the present work, gas sensing properties of the screen printed ceria and ruthenate-sensitized BaSnO3 (BSO) with La doping heterostructure sensors towards the detection of ammonia and formaldehyde gases at room temperature were studied. Adhered, porous screen printed films with different morphologies were obtained by depositing the LaxBa1?xSnO3?? (x = 0 and 0.05) powder particles prepared by the polymerized complex method. Ceria and ruthenate sensitization for screen printed LaxBa1?xSnO3?? (x = 0.05) film was processed through dip-coating in the 0.03 M aqueous solution of CeCl3 and RuCl3, respectively. La-doped BaSnO3 (LBSO) sensor with smaller crystallites, needle-like morphology and high concentration of oxygen vacancies exhibited superior gas response of 65 and 29 towards 50 ppm of ammonia and formaldehyde gases, respectively. Superabundant sensitization of ceria and ruthenate reduced the oxygen vacancy and structural open porosity in the LBSO sensor; therefore, the ammonia gas response was decreased from 65 to 14 and 3, respectively, whereas the formaldehyde gas response was reduced to less than 1/6th times the LBSO sensor. Limit of detection of LBSO sensors was estimated to be ~ 1 and ~ 2 ppm against ammonia and formaldehyde, respectively. The presence of fluorite structured phase ceria with high oxygen atoms storage capacity facilitates the rapid oxidization of analyte gases and caused the expeditious response (75 s) and recovery (60 s) in CeOx-sensitized LBSO sensor. This study might give a new insight into the development of doped and sensitized BSO-based gas sensors operating at ambient conditions. © 2021, The Author(s), under exclusive licence to Springer-Verlag GmbH, DE part of Springer Nature.Item Ammonia gas detection by solution combustion-processed pristine & Ti-doped ZnO transparent films: a reverse effect of doping on gas response(Springer, 2023) Vardhan, R.V.; Manjunath, G.; Pothukanuri, P.; Mandal, S.In this contribution, pure, polycrystalline wurtzite crystal structured, spin-coated pristine ZnO and Ti-doped (1, 2, and 3 wt%) ZnO transparent films were accomplished at 400 °C through a facile solution combustion synthesis method. Crystallinity, roughness, and porosity in the pristine film were relatively higher than in the doped films. The demonstrated films were transparent, with ~ 70 to 90% in the visible region. The room temperature detection of ammonia (NH3) gas (25–100 ppm) was recognized in all the films. The pristine film revealed a superior gas response at every concentration of NH3 gas in contrast to all the doped films; it is probably due to comparatively high crystallinity, porosity, more oxygen vacancy concentration (1.788), and high fraction of adsorbed oxygen (20.55%). The film exhibited the highest gas response of 34.7 at 100 ppm of NH3 gas and a limit of detection of ~ 10.7 ppm with superior selectivity towards NH3 gas. Although doping enhanced the transparency but diminished the NH3 gas response due to the combined effect of deterioration in the mentioned properties achieved in pristine film. © 2023, The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.Item Evolution of High Dielectric Permittivity in Low-Temperature Solution Combustion-Processed Phase-Pure High Entropy Oxide (CoMnNiFeCr)O for Thin Film Transistors(American Chemical Society, 2023) Salian, A.; Pujar, P.; Vardhan, R.V.; Cho, H.; Kim, S.; Mandal, S.An investigation of dielectric permittivity on the sintered high entropy oxide (HEO) capacitor composed of Co, Cr, Fe, Mn, and Ni (i.e., (CoCrFeMnNi)O) developed using solution combustion synthesis is performed. Stabilization of the phase in HEO is extremely important as it has a direct influence on the properties. In order to explore phase stabilization, in-depth studies of thermal, structural, morphological, and compositional analyses are carried out. The optimized processing parameters are further implemented on depositing (CoCrFeMnNi)O dielectric thin films followed by a thin film transistor. Irrespective of the reaction medium, the precursors undergo combustion at a low temperature below 250 °C, resulting in amorphous HEO. Upon crystallization at 500 °C, no secondary impurity oxides were detected and phase-stabilized to a spinel structure (Fd3m). A homogeneous distribution of all five cations without any segregation and a completely disordered occupancy of the cations were displayed by the bulk and thin films of HEOs. The spinel (CoCrFeMnNi)O exhibited high permittivity, with values approximately 7.3 × 102(in bulk) and 3 × 101(in a thin film), measured at 1 kHz owing to the entropy stabilization effect of HEO. Due to their high permittivity and low leakage current density (∼10-8A/cm2), the (CoMnNiFeCr)O thin film was integrated into thin film transistors (TFTs) with molybdenum disulfide-channel. TFTs showed a field effect mobility of 8.8 cm2V-1s-1, an on-off ratio of approximately 105, a threshold voltage of -1.5 V, and a subthreshold swing of 0.38 V/dec. The low voltage operation (<5 V) of these TFTs makes solution combustion-derived HEO (CoMnNiFeCr)O a potential candidate in microelectronics and optoelectronics applications. © 2023 ACS Applied Electronic Materials. All rights reserved.Item Tracing of Ammonia Gas by Solution-Combustion-Derived Pristine and Nb-Doped TiO2 Films: Beneficial Impact of Crystallinity and Adsorbed Oxygen on the Gas Response(Springer, 2023) Vardhan, R.V.; Manjunath, G.; Pothukanuri, P.; Mandal, S.The current work delivers room-temperature ammonia (NH3) gas-detectable pristine, Nb-doped TiO2 air- and vacuum-annealed films obtained through the solution-combustion process. Polycrystalline anatase crystal structured films without any dopant oxide phases were processed at 400°C on glass substrates. The crystallinity was higher in pristine films than in doped films; the morphological features were similar in all the films. The films were > 50% transparent, and the estimated optical energy band gap was greater in doped films than in pristine films. All the films detected NH3 gas (25 ppm to 100 ppm) at room temperature, and the gas response was highly dependent on the crystallinity and relative area fraction of adsorbed oxygen (% of OA). The vacuum-annealed pristine film exhibited a better gas response than the other films at all NH3 gas concentrations due to high crystallinity and % of OA (10.15%). The film demonstrated maximum gas response of ~16 towards 100 ppm of NH3 gas and displayed good selectivity. Even though the doping reduced the crystallite size from ~17 nm to ~9 nm, it also diminished the crystallinity of the films, which significantly impacted the deterioration of their gas response. © 2023, The Minerals, Metals & Materials Society.