DSpace Community: Physics

Computational study of structural, elastic, electronic, And optical properties of sulfur substitute perovskites, AtaO3-xSx (A=K, Rb, Cs).

Sun, 11 Aug 2024 00:00:00 GMT

Title: Computational study of structural, elastic, electronic, And optical properties of sulfur substitute perovskites, AtaO3-xSx (A=K, Rb, Cs). Authors: Akter, Hasina Abstract: 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. Description: Thesis in Physics

Radiation induced structural and electric properties of Al-Substituted NiCuCd nanoparticles

Wed, 31 Jan 2024 00:00:00 GMT

Title: Radiation induced structural and electric properties of Al-Substituted NiCuCd nanoparticles Authors: Sharma, Bishakar Abstract: 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. The magnetization has measured by using Vibrating Sample Magnetometer at room temperature with an applied field of 1.5 T (in μ0H) after irradiation (gamma) by different doses. The saturation magnetization initially increase with irradiation. The frequency dependence of conductivity, dielectric constant, and dielectric loss has been studied. The Cole-Cole plots of (Z// vs Z/) give different two over lapping incomplete semicircles depending upon the electrical parameters. Also, the modulus plots of (M// vs M/) insure that the electric stiffness is the dominant property of the investigated samples. Electrical and dielectric properties have carried out with the influence of γ irradiation and interpret using existing theories. Description: Master of Philosophy thesis in Physics

DFT INSIGHTS INTO Nb-BASED 211 MAX PHASE CARBIDES: Nb2AC (A = Ga, Ge, Tl, Zn)

Tue, 26 Sep 2023 00:00:00 GMT

Title: DFT INSIGHTS INTO Nb-BASED 211 MAX PHASE CARBIDES: Nb2AC (A = Ga, Ge, Tl, Zn) Authors: Das, Prima Abstract: 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. Description: An M.Sc. Thesis from the Department of Physics

STUDY OF PHYSICAL PROPERTIES OF MAX PHASES M2TlC (M = Ti, Zr, Hf): A DFT CALCULATION

Fri, 27 Oct 2023 00:00:00 GMT

Title: STUDY OF PHYSICAL PROPERTIES OF MAX PHASES M2TlC (M = Ti, Zr, Hf): A DFT CALCULATION Authors: Sohel, Mohammed Abstract: 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. Description: An M.Sc. Thesis from the Department of Physics