Faculty Publications
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Item Review of thermal characterization techniques for salt-based phase change materials(Elsevier Ltd, 2022) Agarwala, S.; Prabhu, K.N.Phase change materials (PCM)-based energy storage system is a quite promising technology for the efficient usage of the excess solar energy produced and utilize it at the hour of high demand. The major challenge here is the selection of PCMs for energy storage applications. Inorganic PCMs possess higher thermal conductivity and energy storage capacity when compared to organic PCMs. Thus, inorganic PCMs have a great potential to be used in energy storage systems majorly in medium to high-temperature applications where organic PCMs cannot be used. An accurate and reliable data on the thermophysical properties of the PCMs is essential before its selection and installation of a energy storage system. In this study, various characterization methods based on calorimetry, temperature difference, cooling rate, and cooling curve used to date are described. Methods such as conventionally used differential scanning calorimetry (DSC), T-history method, and computer-aided cooling curve analysis (CACCA) are reviewed and discussed in this study. The two modes of CACCA, Newtonian, and Fourier techniques are explained. The advantages and limitations associated with all these methods are outlined. Inverse heat conduction problem (IHCP)-energy balance method based on CACCA which is devoid of the limitations associated with the conventional characterization methods is discussed. Thermal conductivity is the main characterization parameter of the PCMs and therefore methods to measure thermal conductivity are critically reviewed in this study. Thermal cycling stability is discussed in the context of the review. © 2021 Elsevier LtdItem Design and fabrication of all-inorganic transport materials-based Cs2SnI6 perovskite solar cells(Springer, 2023) Kumari, D.; Jaiswal, N.; Shukla, R.; Punetha, D.; Pandey, S.K.; Pandey, S.K.With lead-based perovskite materials, lead content and long-term stability are the big concerns. Recently, Cesium tin iodide (Cs2SnI6) double perovskite has gained recognition as a stable and environment-friendly photovoltaic material compared to lead-based perovskite materials. In the present study, we have investigated Cs2SnI6 based solar cell with all inorganic transport materials using SCAPS-1D. The optimized device exhibited a maximum efficiency of about 18%. Further we fabricated Cs2SnI6 perovskite films using a solution process approach, utilizing CsI and SnI4 in a 2:1 ratio. For synthesized double perovskite film, the crystallinity, morphologies, and optical characteristics were examined. Additionally, the stability analysis confirmed that the prepared perovskite films were stable for more than two months under ambient exposure. Finally, utilizing the synthesized Cs2SnI6 thin films as an absorber material, we fabricated two solar cells without and with hole transport layer (HTL), having configurations of glass/FTO/ZnO/Cs2SnI6/Ni and glass/FTO/ZnO/Cs2SnI6/ MoS2/Ni, respectively, in the ambient conditions. As a major finding, it has been observed that the inclusion of MoS2 as HTL improved overall performance, with an enhancement in the power conversion efficiency (PCE) of nearly 45% compared to the device without HTL. © 2023, The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.Item Liquid-infused surfaces for mitigation of corrosion and inorganic scaling(Elsevier Ltd, 2024) Yandapalli, A.V.V.R.P.; A, S.; Kuravi, S.; Kota, K.In this study, the effectiveness of a binary surface (BiS), a type of liquid-infused surface, in enhancing corrosion resistance and mitigating inorganic fouling without compromising heat exchange efficiency is demonstrated. An Ultra-Omniphilic Surface (UOS) was initially prepared from a plain aluminum alloy surface (PS) using a bulk micro-manufacturing approach. Subsequently, the sub-surface micro/nanocavities of UOS were infused with a liquid lubricant to create BiS, characterized by two distinct superficial phases — solid islands and liquid puddles. Lab-scale experiments in a simulated brackish water environment revealed that BiS outperformed both PS and UOS in inhibiting scaling and corrosion. The BiS exhibited nearly 50% less mass gain due to mineral deposition than PS and UOS. Moreover, corrosion rates obtained from electrochemical and immersion tests indicated significantly slower metal degradation on BiS compared to PS and UOS. Furthermore, BiS displayed superior heat exchange capabilities, collecting approximately 73% and 44% more condensate than PS and UOS, respectively. This enhancement is attributed to well-distributed liquid puddles on BiS, promoting a smooth, defect-free surface that reduces foulant adhesion and shields the underlying metal from corrosion, while also enhancing two-phase heat transfer activity. © 2024 Elsevier LtdItem Ultralow thermal conductivity and thermally-deactivated electrical transport in a 1D silver array with alternating δ-bonds(Royal Society of Chemistry, 2024) Hassan, N.; Nagaraja, S.; Saha, S.; Tarafder, K.; Ballav, N.We report the synthesis of a (TMA)AgBr2 (TMA = tetramethylammonium) crystal, which comprises inorganic anionic chains of -(AgBr2)∝- stabilized by columnar stacks of organic TMA cations with a periodic arrangement of shorter and longer Ag(i)⋯Ag(i) bonds, even though all the Ag(i) ions are chemically equivalent. The presence of two chemically non-equivalent bridging Br ions is attributed to the primary cause of such an unusual arrangement, as clearly visualized in the charge density plot of (TMA)AgBr2 extracted from the theoretical calculations based on density functional theory. Remarkably, we identified from the orbital-projected density of states the existence of alternate δ-like bonding involving dxy orbitals of 4d10 Ag(i), which was attributed to the cause for ultralow thermal conductivity and thermally-deactivated electrical transport in (TMA)AgBr2. Barring the energetics, our observations on the existence of a δ-bond will shed new light in understanding the nature of metal-metal chemical bonding and its unprecedented implications. © 2024 The Royal Society of Chemistry.Item Comprehensive Modeling of High-Performance All-Inorganic Cs2TiBr6-Based Perovskite Solar Cells(John Wiley and Sons Inc, 2024) Kumar, S.; Thiyyakkandy, J.; Yadav, A.K.; Vinturaj, V.; Garg, V.; Prabhu, S.; Pandey, S.K.The perovskites are desirable materials for photovoltaic and other renewable green energy technologies. Lead-based perovskite solar cells (PSC) have recently gained considerable attention due to the abrupt rise in power conversion efficiency, but lead's well-known toxicity prevents its large-scale commercialization. One compelling option is Cs2TiBr6, which offers a nontoxic alternative. Herein, the electronic and optical characteristics of Cs2TiBr6 absorber material using density functional theory employing the WIEN2K tool are investigated. The energy band structure of Cs2TiBr6 shows an indirect bandgap of 2.2 eV. Additionally, optical properties are calculated, and the suitability of this material as an absorber for indoor and outdoor photovoltaic devices is investigated. The Cs2TiBr6 material has a peak absorption coefficient of 39.57 × 104 cm−1 and optical conductivity of 1.98 × 1015s−1, demonstrating its suitability as an absorber material. After that, a PSC is modeled using SCAPS-1D by using the computed parameters. The performance of the modeled perovskite is enhanced by optimization of various parameters, resulting in the achievement of a high-performance Cs2TiBr6-based PSC, boasting a power conversion efficiency of 19.9% for air mass AM1.5 G spectra and power conversion efficiency of 16.76% for light emitting diode and 17.18% for incandescent light for indoor light conditions. © 2024 Wiley-VCH GmbH.Item Synergistic Photoconductivity and Ultralow Thermal Conductivity upon Stabilizing Iron(III)-tris(2,2?-bipyridine) in a Two-Dimensional Haloargentate Network(American Chemical Society, 2025) Jose, T.M.; Hassan, N.; Ananthram, K.S.; Kalyani, M.; Tarafder, K.; Ballav, N.Crystalline organic–inorganic halometallate hybrids have emerged as promising materials for optoelectronic applications due to their structural diversity and tunable properties. We report a three-dimensional (3D) hybrid organic–inorganic crystal?[Fe(bpy)3]2Ag6Br11·NO3(bpy = 2,2? bipyridine)?consisting of two-dimensional (2D) Ag(I)-based (Ag6Br11)n5n–anionic sheets, zero-dimensional (0D) [Fe(bpy)3]3+complexes (acting as the structure-directing agent), and interlayer disordered NO3–anions. Specifically, the thermodynamically unstable cation [Fe(bpy)3]3+is stabilized under ambient conditions by the two-dimensional (2D) inorganic anionic scaffold. The crystal exhibits strong ligand-supported argentophilic interactions (Ag···Ag bond distance of 2.98 Å), forming an extended (Ag6Br11)n5n–network, and displays broad UV–visible absorption with a band gap of 1.90 eV. Remarkably, this organic–inorganic hybrid shows a ?103-fold increase in photocurrent under 532 nm light illumination. Density functional theory calculations provided the mechanistic insights, and such a remarkable photoconductivity is attributed to an efficient charge delocalization and inorganic-to-organic charge transfer. Additionally, the crystal exhibits an ultralow thermal conductivity over a broad temperature range (?0.3 W/m·K; 300–400 K), making it an excellent candidate for heat management applications. © 2025 American Chemical SocietyItem Rotational Flexibility in Dication Drives Ambient Temperature Ferroelectricity in an Organic–Inorganic Hybrid Halide(John Wiley and Sons Inc, 2025) Hassan, N.; Panday, R.; Chandru, P.G.; Ananthram, K.S.; Jose, T.M.; Bhoi, U.; Sieradzki, A.; Zar?ba, J.K.; Boomishankar, R.; Tarafder, K.; Ballav, N.Organic–inorganic hybrid halides (OIHHs) have gained attention as potential ferroelectric materials due to structure-property synergy of the organic and inorganic constituents. This study introduces an unusual Ag(I)-based ternary OIHH, (4,4?-bpy)Ag2Br4, featuring rotational flexibility in the organic dication to induce asymmetry into the structure. The compound crystallizes in a monoclinic crystal system with a non-centrosymmetric polar P21 space group at room-temperature and undergoes a structural phase transition to a centrosymmetric phase (P21/c) at Curie temperature (Tc) of 330 K which was further supported by differential scanning calorimetry (DSC), second harmonic generation (SHG) signals, dielectric anomaly, current-voltage (I–V) profiles, and X-ray photoelectron spectroscopy (XPS) data. Ferroelectricity is confirmed through polarization–electric field (P–E) hysteresis loops and piezoresponse force microscopy (PFM), exhibiting switchable polar domains. Density functional theory (DFT) calculations revealed electronic structures of the ferroelectric and paraelectric phases, identified the (?-AgBr2)nn? inorganic anionic chain contributing to the net polarization, and in general, complemented the experimental results. Comparative studies with structurally analogous Ag(I)-based OIHHs lacking dication rotational freedom endorse the critical role of organic flexibility in driving ferroelectricity. This study provides insights into the role of organic dications in controlling ferroelectric behavior and offers a promising pathway for developing coinage metal-based OIHH ferroelectric materials. © 2025 Wiley-VCH GmbH.