Thesis in Physics

Browse

Search Results

Now showing 1 - 6 of 6
  • Thumbnail Image
    Item
    Study of the Structural, Magnetic and Electric Properties of Al Substituted NiCuCd Ferrite Nanoparticles
    (CUET, 11-Sep-2023) Mannan, Md. Abdul
    A series of Ni0.5Cu0.2Cd0.3Fe2-xAlxO4 (where x = 0.0 to 0.075 in step of 0.015) nanoparticles have been synthesized by sol-gel technique which are further annealed at 700oC. X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM) techniques have used to examine the structural and surface morphology of all produced materials. A vibrating sample magnetometer with an applied field of 1.5 T (in μ0H) is used to measure the magnetic (hysteresis) characteristics of these ferrite nanoparticles. Using a Wayne Kerr impedance analyzer and the two probe approach, the electrical and dielectric properties have examined in the frequency range of 20 Hz to 15 MHz. The electric conduction mechanism and the resistances at the grain boundaries in ferrite nanoparticles have studied using complicated impedance and modulus spectroscopy techniques. All samples have showed single-phase cubic spinel structures, according to XRD analysis, which shows peaks with greater sharpness and width. Scherrer's formula and FESEM data have used to calculate the crystallite sizes. On the other hand, the results of the Rietveld analysis have used to determine the cation distribution and other structural factors. Maxwell-Wagner space charge polarization and Koop's phenomena have used to explain the low-frequency dispersion behavior of dielectric properties and their consistency in high-frequency domain. It is worth mentioned that the conductivity phenomena show good agreement with dielectric behavior of the synthesized nanomaterials. Cole-Cole plot has used to separate the contribution of grain resistance and grain boundary resistance with observing the predominance of grain boundary resistance. Theories that already exist have used to discuss potential relationships between structural, magnetic, electrical, and dielectric properties.
  • Thumbnail Image
    Item
    STUDY OF PHYSICAL PROPERTIES OF MAX PHASES M2TlC (M = Ti, Zr, Hf): A DFT CALCULATION
    (CUET, 27-Oct-2023) Sohel, Mohammed
    The projected ternary carbide MAX phases M2TlC (M = Ti, Zr, and Hf) have been investigated for their phonon dispersion and optical properties, including Mulliken population analysis, optical and theoretical Vickers hardness. We reviewed the compound's structural and electrical characteristics to evaluate the accuracy of our calculations. The examined MAX phases are mechanically and dynamically stable, according to the examination of the formation energies, elastic constants, phonon dispersion, and phonon density of states. Ti-3d, Zr-4d, Hf-5p, 5d, and Tl-6p electronic orbitals, which have a substantial impact on the phases' physical characteristics and heavily contribute to electronic conduction, are the main causes of the sub-band crossing the EF. For the phases, the values of total density of states (TDOS) at EF are determined to be 3.0, 2.55, and 2.09 states/eV. In the compounds under investigation, the bond Hf-C has the highest covalency of all the bonds. The hardness of the examined compounds may be compared in such a way that Ti2TlC for both Hmicro (24 GPa) and Hmacro (17 GPa) is harder than that of Hf2TlC (17 and 13 GPa) and Zr2TlC (20 and 16 GPa). The Vickers hardness are discovered to be 2.18, 1.61, and 2.60 GPa, respectively for the phases. The reported hardness values are in the range of 2 to 8 GPa that is comparable with the well-known MAX phase nanolaminates, such as Hf2InC (3.45 GPa) and Ta2InC (4.12 GPa). The values of the longitudinal optical (LO) and transverse optical (TO) components at  are 19.74 and 21.63 THz (Ti2TlC), 16.62 and 17.18 THz (Zr2TlC), and 18.66 and 19.94 THz (Hf2TlC), respectively. The phonon dispersion curves (across the entire BZ) do not exhibit imaginary (negative on the frequency scale) phonon frequency, suggesting the dynamic stability of the phases. The value of reflectivity rises to high as 92%, 82%, and 86% for the compounds Ti2TlC, Zr2TlC, and Hf2TlC, respectively, at energy 8.76 eV, 9.6 eV, and 10.7 eV. It is an intriguing observation that the reflectivity is always greater than 44% for the phases Ti2TlC (11.67 eV), Zr2TlC (12.44 eV), and Hf2TlC (13.8 eV). According to reflectivity's findings, the visible (1.7 eV–3.3 eV) and IR (1.24 eV–1.7 eV) sectors account for more than 44% of the energy up to 12.0 eV. Therefore, the investigated compounds might be a good contender for use as a covering material to reduce solar heating.
  • Thumbnail Image
    Item
    Study of physical properties of Lead-Free metal halide perovskite compounds CsMI3(M=Mg,Ga) for solar cells applications by Ab-Initio simulations.
    (CUET, 9-Jun-2024) Biswas, Mautushi
    The primary objectives are to thoroughly examine the CsMI3 (M = Mg, Ga) lead-free perovskite materials for photovoltaic and optoelectronic applications using first-principle calculations. This study observed the mechanical, electrionic, optical, thermal, and structural aspects while also verifying the stability of the cell. The calculated results are compared with experimentally synthesized similar perovskite compound CsPbI3. The computed formation energies of the compounds as follows: CsMgI3(-1.81 eV/atom)  CsPbI3(-1.624 eV/atom)  CsGaI3(-1.326 eV/atom) and negative results are represented the mechanically stability of the compounds. Since there was no negative frequency, the phonon research demonstrated the compound’s dynamic stability. The computed  values support the CsMI3 (M= Pb, Ga) compounds possess pure ductility, whereas the CsMgI3 compounds lie on the ductile-brittle transition line. The bandgap (Eg) is calculated and found to be in the range of 1.63 to 3.26 eV that makes them potential candidate to be used as absorbance materials in solar cell applications. The Eg is further tuned to achieve more appropriate range for the solar cell applications by doping into the CsMg(I1-xBrx)3 where x = (0, 0.25, 0.50, 0.75, 1). The Eg is found to be 1.12 to 1.87 eV and  increase due to doping that makes them more apposite for the suggested range of absorbance materials in the solar cell. The best combination CsMg(I0.75Br0.25)3 shows Eg  1.4 eV that is well agreement with the optimum band gap suggested the Shockley-Queisser limit in a single layer solar cell absorbance material to be shown highest efficiency.
  • Thumbnail Image
    Item
    Radiation induced structural and electric properties of Al-Substituted NiCuCd nanoparticles
    (CUET, 31-Jan-2024) Sharma, Bishakar
    The effect of gamma (γ) irradiations on the physical, magnetic and electrical properties of nanoferrites samples with a chemical formula of Ni0.5Cu0.2Cd0.3Fe2-xAlxO4 have studied. These samples have prepared by sol-gel auto combustion method. The synthesized samples have irradiated for γ rays from 60Co source at room temperature with a dose of 1 and 3 MRad, at a dose rate of 1.067 MRad/h. X-ray diffraction (XRD) parameters, magnetization, dielectric constant, dielectric loss factor, electric modulus, impedance and ac conductivity have analyzed for the irradiated samples. XRD patterns show that the irradiation has caused a change in the lattice constant due to ions redistribution. The lattice constant of the investigated samples has increased with the increase in irradiation (gamma) due to the conversion of Fe3+ (0.67Å) to Fe2+ (0.76Å). Moreover, the cation redistribution play an important role in increasing the values of ac conductivity with increasing the irradiation (gamma) dose.
  • Thumbnail Image
    Item
    DFT INSIGHTS INTO Nb-BASED 211 MAX PHASE CARBIDES: Nb2AC (A = Ga, Ge, Tl, Zn)
    (CUET, 26-Sep-2023) Das, Prima
    In this thesis, to study the 211 MAX phase carbides, the first-principles calculations were performed: Nb2AC (A = Ga, Ge, Tl, Zn) and the obtained properties of these phases are compared with those of Nb2AC (A = P, In, Cd, Al). With those from the prior studies, the structural characteristics are in appropriate agreement. Vickers hardness, stiffness constants and elastic modulus have been calculated to explore mechanical behavior. Besides, the structural stability of the studied compounds was checked using the phonon dispersion curves. Based on the elastic constants, the selected MAX phases are mechanically stable. Among the studied compounds, the value of Poisson’s ratio and Pugh ratio indicate that Nb2GaC (υ = 0.23 and G/B = 0.67) behaves as brittle solids whereas other studied compounds behave ductile nature. According to the values of Vickers hardness for studied materials can be ordered as follows: Nb2GaC > Nb2ZnC > Nb2TlC > Nb2GeC. On the contrary, Nb2PC (10.02 GPa and 9.31 GPa for GGA PBE and GGA PBEsol, respectively) has higher Vickers hardness than selected MAX phases. The anisotropy of the elastic characteristics was exposed through the 2D and 3D plotting of elastic moduli and calculating anisotropy indices. Utilizing the bond overlap and Mulliken atomic population, the mixture of ionic and covalent bonding has been explained among these carbides. To confirm the metallic behavior, the band structure and density of states (DOS) have been calculated. The discussion of the strength and bonding nature of different states also used Partial DOS. To explore the possible relevance in various fields, the optical characteristics of these selected phases have also been computed and analysed. Nb2AC (A = Ga, Ge, Tl, Zn, P, In, Cd, Al) MAX phases can be considered as prospective absorbing materials in this energy range because of the large absorption coefficients in the high energy range (7-10 eV). In order to bring out the potential relevance in high-temperature technology, the Debye temperature (ΘD), minimum thermal conductivity (Kmin), Grünisen parameter (γ) and melting temperature (Tm) were studied. The findings of the present research suggest that the mentioned carbides are suitable for usage as thermal barrier coating (TBC) and solar radiation-protecting coating materials.
  • Thumbnail Image
    Item
    Computational study of structural, elastic, electronic, And optical properties of sulfur substitute perovskites, AtaO3-xSx (A=K, Rb, Cs).
    (CUET, 11-Aug-2024) Akter, Hasina
    In this study, the effects of sulfur substitution on the structural, mechanical, electronic, optical, and thermodynamic properties of ATaO3-xSx have been investigated using the WIEN2k code in the framework of Density Functional Theory (DFT). The cubic phase of ATaO3 (A= K, Rb and Cs) transforms to tetragonal for ATaO2S and ATaOS2, the latter transforms again to a cubic phase with added sulfur for ATaS3. The results indicated a notable reduction in the band gap upon substituting S for O anions in ATaO3. Specifically, KTaO3 exhibited a band gap of 3.57 eV, which subsequently decreased to 1.808 eV, 0.264 eV, and 0.078 eV for KTaO2S, KTaOS2, and KTaS3, respectively. Similarly, RbTaO3 exhabit a reduction in its band gap from 2.717 eV to 1.438 eV, 0.286 eV, and 0.103 eV for RbTaO2S, RbTaOS2, and RbTaS3 compounds. CsTaO3 had an initial band gap of 3.076 eV, which decreased to 0.909 eV, 0.376 eV, and 0.143 eV for CsTaO2S, CsTaOS2, and CsTaS3 compounds, respectively. Furthermore, these compounds have displayed promising optical characteristics characterized by high absorption coefficients (∼106 cm−1), minimal reflectivity (<30%), and robust optical conductivity within the visible spectrum, making them ideal candidates for a range of optoelectronic technologies. Our comprehensive investigation has reinforced the stability of all computed phases, showcasing exceptional electronic, mechanical, and optical properties, including semiconducting behavior, ductility, anisotropy, high absorptivity, and low reflectivity. The altered band gap and optical features observed in KTaO2S and RbTaO2S suggest significant potential for their utilization in solar cells, offering promising prospects for enhancing solar energy conversion efficiency. Additionally, the elevated lattice thermal conductivity observed in KTaO3, RbTaO3, and CsTaO3 indicates their potential as promising candidates for heat sink materials.