Faculty Publications
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Item Retention of high dielectric constant sodium beta alumina via solution combustion: Role of aluminum ions complexation with fuel(Elsevier Ltd, 2018) Gupta, B.; Pujar, P.; Mal, S.S.; Gupta, D.; Mandal, S.In the present study, solution combustion technique has been explored to synthesize Sodium ?-alumina (SBA; NaAl11O17) powder and thin films. Three fuels namely urea, glycine and citric acid have been used to seek the feasibility of synthesizing crystalline SBA powder at low temperature. Also, the effect of nature of fuels used as well as calcination treatment on phase evolution and morphology of the as-combusted powder was investigated. Thermal analysis and X-ray diffraction studies suggest the formation of crystalline SBA powder at temperature as low as 259 °C, using urea in the combustion reaction whereas other fuels resulted in amorphous SBA phase and this variation in phase was found due to difference in exothermicity of the fuel used. Thermodynamic and spectroscopic analyses showed that the exothermicity of fuel depends on various factors like (i) standard heat of formation of fuel and (ii) the complexation offered by fuel to metal cations. Furthermore, sodium ?-alumina thin film capacitor (metal-insulator-metal) was also fabricated using urea via spray combustion synthesis. The sodium ?-alumina thin film showed a high dielectric value (?r) of ~21. © 2017 Elsevier Ltd and Techna Group S.r.l.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.