First-principles studies on structural, electronic and optical properties of Fe-doped NiS2 counter electrode for Dye- sensitised solar cells using DFT+U / Nur Aisyah Ab Malik Marwan …[et al.]

The structural, electronic, and optical properties of nickel disulfide (NiS2) and iron (Fe)-doped NiS2 were computed by using first-principles calculations through the density functional theory (DFT) method. The Fe was used as a dopant element to understand the behaviour and the key mechanism of Fe-doped NiS2 as a counter electrode in dye-sensitised solar cells (DSSC). The results indicated that the structural properties of the NiS2 as the cubic crystal structure with the space group Pa3 (205) (pyrite structure type) agree with experimental data. The density of states (DOS) of NiS2 and Fe-doped NiS2 shows a gapless bandgap due to Mott-Hubbard insulator behavior. As for optical properties, the optical absorption of NiS2 is shifted towards the infrared (IR) region when doping with Fe while the conductivity of Fe-doped NiS2 is slightly higher in conductivity. These optical properties show that Fe-doped NiS2 is suitable for the photocatalytic activity and may provide an excellent electron charge transfer for a counter electrode in DSSC

A Review of PRESAGE Radiochromic Polymer and the Compositions for Application in Radiotherapy Dosimetry

Recent advances in radiotherapy technology and techniques have allowed a highly conformal radiation to be delivered to the tumour target inside the body for cancer treatment. A three-dimensional (3D) dosimetry system is required to verify the accuracy of the complex treatment delivery. A 3D dosimeter based on the radiochromic response of a polymer towards ionising radiation has been introduced as the PRESAGE dosimeter. The polyurethane dosimeter matrix is combined with a leuco-dye and a free radical initiator, whose colour changes in proportion to the radiation dose. In the previous decade, PRESAGE gained improvement and enhancement as a 3D dosimeter. Notably, PRESAGE overcomes the limitations of its predecessors, the Fricke gel and the polymer gel dosimeters, which are challenging to fabricate and read out, sensitive to oxygen, and sensitive to diffusion. This article aims to review the characteristics of the radiochromic dosimeter and its clinical applications. The formulation of PRESAGE shows a delicate balance between the number of radical initiators, metal compounds, and catalysts to achieve stability, optimal sensitivity, and water equivalency. The applications of PRESAGE in advanced radiotherapy treatment verifications are also discussed

Structural and electronic properties of orthorhombic phase Bi₂Se₃ based on first-principles study / Muhammad Zamir Mohyedin ... [et al.]

Bi₂Se₃ is one of the promising materials in thermoelectric devices and is environmentally friendly due to its efficiency to perform in room temperature. Structural and electronic properties of Bi2Se3 were investigated based on the first-principles calculation of density functional theory (DFT) using CASTEP computer code. The calculation is conducted within the exchange-correlation of local density approximation (LDA) and generalised gradient approximation within the revision of Perdew-Burke-Ernzerhof (GGA-PBE) functional. A comparative study is carried out between the electronic properties of LDA and GGA-PBE. Lattice parameter and band gap are consistent with the other reports. Calculation from LDA is more accurate and has a better agreement than GGA-PBE in describing the lattice parameter of Bi2Se3. Band gap and density of states of LDA show higher electrical conductivity than GGA-PBE. Both LDA and GGA-PBE have same degree of thermal conductivity due to the occurrence of indirect band gap at same range of wave vector

First-principles study of structural, electronic and thermoelectric properties of nidoped Bi2 Se3

Direct conversion of waste heat to electrical energy could address present energy challenges. Bi2 Se3 is one of few thermoelectric materials known to operate at room temperature. Comprehensive analysis using density functional theory was conducted to explore the effect of nickel doping on structural, electronic, and thermoelectric properties of Bi2 Se3 . Local density approximation (LDA) was used with an addition of spin-orbit coupling (SOC) and van der Waals interaction scheme consideration. Analysis of the effect of SOC was elaborated. It was found that nickel has changed the crystal structure of Bi2 Se3 . Nickel has also changed band structure and density of state that alter the thermoelectric performance. The decreased band gap has decreased the thermopower. However, it gives advantages to the improvement of electrical conductivity. Higher electrical conductivity has risen thermal conductivity. Despite the decreased thermopower and increased thermal conductivity, the higher electrical conductivity has improved the overall thermoelectric performance of Bi2 Se3 when nickel is introduced

Enhanced mechanism of thermoelectric performance of Bi2Se3 using density functional theory

Good thermoelectric performance is being sought to face major problems related to energy, especially in the concern of the usage of energy on environmental impact. In this work, we investigate the underlying mechanism to enhance the thermoelectric performance of bismuth selenide (Bi2Se3) by employing density functional theory (DFT) followed by the Boltzmann transport equation under relaxation time approximation. The structural, electronic, and thermoelectric properties were calculated and analyzed. From the analysis of combined results of thermoelectric properties and electronic properties as the function of the Fermi level, we found that the power factor of Bi2Se3 is improved by increasing electrical conductivity that contributed by the large density of states and light effective mass of charge carriers. The figure of merit, on the other hand, is enhanced by increasing Seebeck coefficient that contributed by heavy effective mass and decreasing thermal conductivity that contributed by low density of states. We also found that both power factor and figure of merit can be improved through n-type doping at 300 K and p-type doping at higher temperature (400 K and 500 K)

First-Principles Study on Structural and Electronic Properties of Cubic (Pm3m) And Tetragonal (P4mm) ATiO₃ (A=Pb, Sn) / Nurakma Natasya Md Jahangir Alam …[et al.]

This work focuses on exploring lead-free ferroelectric materials that have a comparable unique ns2 solitary pair electrons with Pb (II), for example, Sn (II) using the first-principles study. All counts were performed dependent on ultrasoft pseudopotential of Density Functional Theory (DFT) that has been executed in the Cambridge Serial Total Energy Package (CASTEP). The convergence test for cut-off energy and k-point was performed to measure the accuracy of the calculations. It is shown that the structures have threshold energy of 350 eV and k-point of 4x4x4 with Monkhorst Pack. The structural properties for both cubic and tetragonal structures ATiO3 (Pb, Sn) have shown the comparable value of the lattice parameter that was in agreement with previous work. Generalised gradient approximation (GGA) PBE displays the most exact qualities for cross-section parameters concerning exploratory qualities for both cubic PbTiO₃ while GGA-PBEsol functional is the best functional approximation for tetragonal PTO. The electronic band structure and density of states show the presence of hybridizations between anion O 2p and cation Pb 6s/Sn 5s unique solitary pair in tetragonal PTO and SnTO stage. The calculations have shown that both cubic and tetragonal structure of ATiO3 (A=Pb, Sn) has an indirect bandgap of 1.169 eV, 1.164 eV, 1.703 eV, and 1.016 eV respectively. It is shown that tetragonal structures have a higher value of bandgap compared to cubic structures