Faculty Publications
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Item Entropy stabilized multicomponent oxides with diverse functionality–a review(Taylor and Francis Ltd., 2022) Salian, A.; Mandal, S.Over the last few years, high-entropy oxides (HEOs) are subjected to considerable scientific scrutiny due to their exceptional characteristics, tunable properties displaying remarkable performance including colossal dielectric constant, low electrical and thermal conductivity, high-temperature phase stability, excellent magnetic, structural optical properties and extraordinary catalytic behavior. The single-phase crystal structure of multicomponent oxides is stabilized via configurational entropy (S config). An incrementation in the number of elements magnifies S config which dominates the free energy landscape, overcomes enthalpy in Gibb’s free energy, and reaches a maximum magnitude while entire elements are in equiatomic fractions. Therefore, accurate control of configurational entropy is the main motive force used to achieve phase pure HEOs by the incorporation of more than four cations in the system in equiatomic proportions with random distributions. HEOs are becoming hotcakes in the field of research as it emphasizes on compositions proximally near the centers of the multicomponent phase diagram, where unexpected behaviors can be anticipated. Thus, presenting a crucial research frontier for the material scientists to explore. As the novel design approach of entropy stabilization is still immature, these new oxide candidates can be engineered for practical applications in batteries, capacitors, nuclear reactors, and thermal barrier coatings. This review addresses the properties like electrochemical, electrical, magnetic, mechanical, catalytic, thermal, etc., of HEOs to date, with additionally focusing on their classification, theoretical predictions, and fundamental understanding of entropy engineering including entropy dominated phase stabilization effect. © 2021 Taylor & Francis Group, LLC.Item Review on the deposition, structure and properties of high entropy oxide films: current and future perspectives(Springer, 2022) Salian, A.; Mandal, S.High entropy oxides (HEOs) have captivated significant concentration due to their unique properties. Manipulation of configurational entropy is the main key for extraordinary behaviours, leading to unprecedented material design and innovations. Substantial research has been conducted on HEO bulk systems, but films are still in the cradle stage. Inspired by the ground-breaking results of HEOs, a novel form of films named high entropy oxides films (HEOFs) are being fabricated. The focus in this review is on the fabrication process, structure and properties of HEOFs with attention to their strengths and liabilities. Iconic investigations from recent articles are highlighted. The first overview is provided on how HEOFs are fabricated and interesting phenomena such as the impact of processing parameters, the role of dopants on the film are discussed. This review also highlights the structural–microstructural appearance and physical properties, concluding with future possibilities and applications. © 2022, Indian Academy of Sciences.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 Role of Mg–O on phase stabilization in solution combustion processed rocksalt structured high entropy oxide (CoCuMgZnNi)O with high dielectric performance(Elsevier Ltd, 2023) Salian, A.; Praveen, L.L.; P, S.K.; Mandal, S.High entropy oxide (CoCuMgZnNi)O with a phase pure rocksalt was synthesized using low-temperature solution combustion. The precursors were found to combust at 270 °C and 400 °C was considered to be the formation temperature. The high entropy rocksalt oxide (HERO) fully stabilized at 1000 °C shows a single-phase, fcc rocksalt structure with an Fm-3m space group. HERO displays one of its parent oxide Mg–O structural properties as both belong to the cubic family and had lattice parameters very close to each other. The lower cation systems exhibited a transition from spinel to rocksalt structure with the addition of Mg–O. Raman of HERO affirmed a completely disordered occupancy of various metal cations, the formation of HERO at 400 °C, and phase stabilization at 1000 °C. Dielectric measurements at room temperature showed high permittivity (κ) with magnitudes ∼1.9 × 103, 4.7× 101, and 0.9 × 101 at 100, 1k, and 100k Hz. © 2023 Elsevier Ltd and Techna Group S.r.l.Item Phase stabilized solution combustion processed (Ce0.2La0.2Pr0.2Sm0.2Y0.2)O1.6-δ: An exploration of the dielectric properties(Elsevier Ltd, 2023) Salian, A.; K, A.P.; Mandal, S.High entropy oxide (HEO) (Ce0.2La0.2Pr0.2Sm0.2Y0.2)O1.6-δ with a phase pure fluorite was synthesized using low-temperature solution combustion. A low-temperature formation of HEO was evidenced at 500 ºC. The HEO formation at 500 ºC was due to the exothermicity of the combustion redox reaction, where the internal temperature might have reached a much higher temperature for a limited amount of time. The presence of Sm2O3 and Y2O3 was visible upto 500 ºC, while La2O3 was detected up to 900 ºC and the HEO fully got stabilized at 1000 ºC with a single-phase, fcc fluorite structure with an Fm-3 m space group. The HEO displays one of its parent oxide Ce-O structural properties as both belong to the fluorite family and had lattice parameters very close to each other. The presence of a secondary phase in the 2 and 3-cation systems and the display of a single phase in the 4 and 5-cation systems indicated the role of configurational entropy in phase stabilization. Raman of HEO also affirmed the formation of HEO at 500 °C, the complete elimination of secondary phases at 1000 °C, and a fully disordered occupancy of various metal cations with severe lattice distortion. A Flake morphology with a nanogranular cluster on the surface was displayed. Dielectric measurements at room temperature showed permittivity (κ) ≈ 29 – 5.7 from 100 Hz to 1 MHz. © 2023 Elsevier B.V.