https://dspace.iiti.ac.in:8080/jspui/handle/123456789/9543 2026-05-12T17:01:12Z 2026-05-12T17:01:12Z Kumar, Dharmendra https://dspace.iiti.ac.in:8080/jspui/handle/123456789/17593 2025-12-30T07:51:50Z 2025-05-29T00:00:00Z

Title: Fluorescent carbon dot aggregates for optoelectronic applications Authors: Kumar, Dharmendra Abstract: The study of Solid-state fluorescent carbon dot (CD) aggregates has been done in two part. In the part one for synthesis solvothermal and precipitation methods has been used with reactants 2,2ʹ-dithiosalicylic acid with adenine or 4-aminobenzenethiol. The initially prepared CDs OD (from adenine) and GD (from 4-aminobenzenethiol) exhibited blue emission, but water treatment triggered a distinct shift to orange (ODA aggregates) and green (GDA aggregates) solid-state fluorescence. This emission switching stems from aggregation-induced emission (AIE) activated by water, with contact angle measurements confirming the hydrophobic surfaces of ODA and GDA. These ODA and GDA have been successfully applied in the fabrication of LEDs. In order to synthesize metal-doped CD aggregates with red fluorescence, synthesized by the same method using Nickel chloride, these hydrophobic aggregates demonstrated practical utility in fabricating fluorescent polymer covers for light-emitting diode (LED) devices, and the contact angle measurement of these CD aggregates is very significant. This type of hydrophobic contact angle may be used in metal corrosion protection applications. Additionally, their high fluorescence contrast enabled effective fingerprint detection, highlighting applications in forensic analysis and security systems.

2025-05-29T00:00:00Z Dharavath Venkatesh https://dspace.iiti.ac.in:8080/jspui/handle/123456789/17567 2025-12-29T04:59:14Z 2025-05-30T00:00:00Z

Title: Structural and electrical properties of Ni- and Mg-doped p-type α-AlCrO3 wide bandgap semiconductor Authors: Dharavath Venkatesh Abstract: In this thesis, we explore α-AlCrO3 as a wide bandgap semiconductor oxide potential candidate for p-type doping through the strategic doping of divalent cations Ni2+ and Mg2+ at the Al3+ site. The host material α-(AlxCr1−x)2O3 (0 ≤ x ≤ 1) exhibits a rhombohedral structure (R-3c) with a tunable bandgap ranging from 3.4-5.3 eV and strong hybridization between Cr 3d and O 2p orbitals that makes it an ideal host for p-type conductivity engineering. Single-phase polycrystalline samples of -Al1-xBxCrO3, where B = Ni2+, Mg2+ and 0≤ x ≤ 0.02 were synthesized via the solid-state reaction method. Structural integrity and doping solubility were confirmed through synchrotron-based X-ray diffraction and Le-Bail refinement. Optical characterization via DRS reveals that with Ni doping no changes in intrinsic band transitions and thus by observed no change in bandgap energy. The electrical charge carriers transport phenomenon was thoroughly investigated using complex impedance spectroscopy (CIS). Both Ni2+ and Mg2+ doping led to significant reductions in energy activation and resistance with superior performance observed at x = 0.01.

2025-05-30T00:00:00Z Kumar, Akash https://dspace.iiti.ac.in:8080/jspui/handle/123456789/17559 2025-12-26T11:29:18Z 2025-05-29T00:00:00Z

Title: Characterization of Fe-based amorphous powder synthesized via mechanical alloying and consecutive consolidation via spark plasma sintering Authors: Kumar, Akash Abstract: This thesis presents a comprehensive study on the synthesis, consolidation, and characterization of Fe-based amorphous alloy powders developed through MA and subsequently consolidated using SPS. Two ternary compositions Fe83.453Al14.560Ti1.987 and Fe69.815Al26.860Ti3.325 were selected based on their potential glass-forming ability and phase stability. The MA process, carried out for up to 80 hours, led to significant structural refinement and partial amorphization, as confirmed by X-ray diffraction (XRD), transmission electron microscopy (TEM), and selected area electron diffraction (SAED). Scanning electron microscopy (SEM) coupled with energy-dispersive X-ray spectroscopy (EDS) showed morphological evolution and compositional homogeneity with increased milling duration. Particle size analysis indicated a trend of particle refinement followed by agglomeration due to cold welding. Differential scanning calorimetry (DSC) highlighted distinct thermal transformation behaviors for both compositions. Subsequent SPS consolidation at temperatures ranging from 300 °C to 1200 °C resulted in improved densification, with Fe83.453Al14.560Ti1.987 exhibiting higher practical density and lower porosity. The XRD patterns of sintered samples revealed the formation of intermetallic phases at elevated temperatures, while SEM analysis demonstrated enhanced inter-particle bonding. Mechanical characterization using the Vickers hardness test showed a substantial increase in hardness with sintering temperature, with a maximum value of 1029 ± 8.7 HV for the Fe83.453Al14.560Ti1.987 sample sintered at 1200 °C. The results establish the effectiveness of combining MA and SPS to fabricate high-density Fe-based amorphous alloys with promising structural and functional properties.

2025-05-29T00:00:00Z Chatterjee, Anik https://dspace.iiti.ac.in:8080/jspui/handle/123456789/17558 2025-12-26T11:23:07Z 2025-05-30T00:00:00Z

Title: Influence of high-temperature rolling and annealing on texture evolution and mechanical properties of Mg -0.4wt%Bi alloy Authors: Chatterjee, Anik Abstract: This work focuses on exploring how sequential thermomechanical processing—specifically hot rolling followed by thermal annealing—affects the microstructural features, crystallographic texture evolution, and deformation response of a Mg-0.4 wt% Bi alloy. The alloy underwent hot deformation at 300°C, after which it was subjected to annealing at three distinct temperatures: 225°C, 325°C, and 425°C. These treatments were systematically analyzed to assess their influence on grain size reduction, texture transformation, and resultant mechanical characteristics.. Scanning Electron Microscopy (SEM) revealed an increase in grain size from 19.88μm at 225°C to 22.79μm at 325°C, indicating full recrystallization. Annealing at 425°C resulted in a significant 61% increase in grain size, reaching 36.77μm, which reflects substantial grain growth at higher temperatures. Electron Backscatter Diffraction (EBSD) assessments performed at varying annealing temperatures revealed that as the temperature rose from 225°C to 325°C, there was a notable decline in peak texture intensity, dropping from 22.01 to 15.10., attributed to texture weakening that leads to random nucleation of grains, However, further increase in temperature to 425°C, maximum texture intensity increased to 20.16μm, pointing to the dominating grain growth orientation.

2025-05-30T00:00:00Z