First principles studies on properties of Pb(II), Sn(II) and Ge(II) ferroelectric materials using density functional theory / Mohamad Fariz Mohamad Taib

Quantum calculations via the first-principles study using the density functional theory (DFT) have offered great opportunities to describe the origin and most fundamental properties of new materials. In addition, detailed properties of the materials can be visualized by providing an accurate view at the atomic level. In this study, works are focused on investigating new lead-free ferroelectric materials that have a similar special ns2 lone pair electrons with Pb (II) such as Sn (II) and Ge (II) via first principles calculation. Modification of Pb-based materials (PTO and PZT) by substituting or doping at the A-site are numerically anticipated to enhance the ferroelectric properties as well as to eventually reduce the consumption of Pb (II) in electroactive devices. Properties of lead-based materials PbTiO3 (PTO), PbZrO3 (PZO) and PbZrTiO3 (PZT) as reference materials were compared with new lead-free ferroelectric materials such as SnTiO3 (SnTO), GeTiO3 (GTO) and SnZrO3 (SnZO). All calculations were performed using first principles study based on Density Functional Theory (DFT) that has been implemented in CASTEP computer code. Functional GGA-PBEsol exhibits the most accurate values for lattice parameter with 0.6 % relative to experimental values for both cubic PbTiO3 and PbZrO3 (reference materials). Meanwhile, LDA-CAPZ functional is accurate for tetragonal PTO

First principles studies on properties of Pb(II), Sn(II) and Ge(II) ferroelectric materials using density functional theory / Mohamad Fariz Mohamad Taib

Quantum calculations via the first-principles study using the density functional theory (DFT) have offered great opportunities to describe the origin and most fundamental properties of new materials. In addition, detailed properties of the materials can be visualized by providing an accurate view at the atomic level. In this study, works are focused on investigating new lead-free ferroelectric materials that have a similar special ns2 lone pair electrons with Pb (II) such as Sn (II) and Ge (II) via first principles calculation. Modification of Pb-based materials (PTO and PZT) by substituting or doping at the A-site are numerically anticipated to enhance the ferroelectric properties as well as to eventually reduce the consumption of Pb (II) in electroactive devices. Properties of lead-based materials PbTiO3 (PTO), PbZrO3 (PZO) and PbZrTiO3 (PZT) as reference materials were compared with new lead-free ferroelectric materials such as SnTiO3 (SnTO), GeTiO3 (GTO) and SnZrO3 (SnZO). All calculations were performed using first principles study based on Density Functional Theory (DFT) that has been implemented in CASTEP computer code. Functional GGA-PBEsol exhibits the most accurate values for lattice parameter with 0.6 % relative to experimental values for both cubic PbTiO3 and PbZrO3 (reference materials). Meanwhile, LDA-CAPZ functional is accurate for tetragonal PTO. The elastic properties values confirm that cubic PTO, SnTO, GTO, SnZO and PZO as well as tetroganal PTO, SnTO and GTO are mechanically stable. The electronic band structure, density of states (DOS) and electron density variation indicate the existence of hybridizations between anion O 2p and cation Pb 6s/Sn 5s/Ge 4s (special lone pair) in tetragonal PTO, SnTO, GTO and SnZO phase. Optical results show that anion O 2p, cation Pb 6p, Sn 5p , Ge 4p and Ti 3d, Zr 4d states respectively correspond to the transition electrons from valence states to the bottom of conduction state of the ATiO3 (A=Pb, Sn, Ge) and AZrO3 (A=Pb, Sn). The phonon calculation and cohesive energy revealed that the PTO and SnTO are stable in the tetragonal P4mm phase compared to the non-polar ilmenite structure. However, GeTiO3 apparently shows non-polar ilmenite structure is more stable compared to the ferroelectric perovskite structure. The phonon dispersion analyses for PZO and SnZO proves that both compounds have ground state structure with antiferroelectric orthorhombic (Pbam, no: 55 space group) and in approximation with the polar ferroelectric phase rhombohedral (R3c, no: 161 space group). In this work, calculations on novel compounds consist of Sn (II) and Ge (II) in PTO and Sn (II) in PZT provide new insights on geometrical and electronic structure of materials. Thus, these findings will be able to gear up efforts in reducing lead consumption by substituting or doping Sn and Ge in Pb-based system, and hence will substantially contribute to greener environment

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

First principles study on electronic and optical properties of Graphene/MoS2 for optoelectronic application

Graphene/MoS2 has been widely used in optoelectronic devices due to its unique optical properties. First principles calculation on the properties of graphene/MoS2 have been performed by using density functional theory (DFT) with a plane wave basis set as implemented in the CASTEP computer code. Electronic and optical properties were further discussed comprehensively to explain the electron transfer mechanism in atomic structure of graphene/MoS2. The results reveal the opening in graphene's band gap at the k-point of the Brillouin zone when MoS2 layer is introduced in the structure. The excellent absorption characteristic in the visible to ultraviolet region demonstrates the graphene/MoS2 as a promising candidate material for broadband operation wavelength

Experimental and Theoretical Studies on Extract of Date Palm Seed as a Green Anti-Corrosion Agent in Hydrochloric Acid Solution

Extracts from plant materials have great potential as alternatives to inorganic corrosion inhibitors, which typically have harmful consequences. Experimental and theoretical methodologies studied the effectiveness of agricultural waste, namely, date palm seed extract as a green anti-corrosive agent in 0.5 M hydrochloric acid. Experimental results showed that immersion time and temperature are closely related to the effectivity of date palm seed as a corrosion inhibitor. The inhibition efficiency reduced from 95% to 91% at 1400 ppm when the immersion time was increased from 72 h to 168 h. The experimental results also indicated that the inhibition efficiency decreased as the temperature increased. The presence of a protective layer of organic matter was corroborated by scanning electron microscopy. The adsorption studies indicated that date palm seed obeyed Langmuir adsorption isotherm on the carbon steel surface, and Gibbs free energy values were in the range of −33.45 to −38.41 kJ·mol−1. These results suggested that the date palm seed molecules interacted with the carbon steel surface through mixture adsorption. Theoretical calculations using density functional theory showed that the capability to donate and accept electrons between the alloy surface and the date palm seed inhibitor molecules is critical for adsorption effectiveness. The HOMO and LUMO result indicated that the carboxyl (COOH) group and C=C bond were the most active sites for the electron donation-acceptance type of interaction and most auxiliary to the adsorption process over the Fe surface

Liquid-phase exfoliated graphene-MoS2 based saturable absorber for Q-switched Erbium Doped fiber laser

Upon exfoliation from the bulk form, two-dimensional materials have shown ubiquitous properties which are suitable for Q-switched pulsed laser generation. In this research, a successful solution process of graphene-MoS2 nanocomposite saturable absorber through liquid phase exfoliation has been carried out. The method offers a low-cost route for simple and scalable production while providing a promising material quality with on-demand properties and integration flexibility. Stable Q-switched laser operation was realized with graphene-MoS2 hybrid saturable absorber. The pulse duration was measured to be 6 µs with repetition rate of 63.92 kHz corresponding to a peak power and pulse energy of 5.05 mW and 30.87 nJ, respectively

First-principles calculation on electronic properties of zinc oxide by zinc 13air system

First-principles calculations are performed to study the electronic properties of zinc oxide (ZnO) formed on an anode after discharging a Zn 13air system. Prior to calculation, the ZnO is characterised by X-ray diffraction using Rietveld refinement. Diffracted patterns proved the formation of single phase ZnO, while Rietveld analysis shows that the ZnO has a hexagonal wurtzite structure with lattice parameters, a= 3.244 and c =5.199 A � . Geometry optimisation of the hexagonal wurtzite structure of the ZnO is performed using various exchange 13correlation energy functionals. The local density approximation functional method is used to explain the structure, electronic band structure and density of state properties of hexagonal ZnO. The calculated energy band gap was 0.75 eV while the density of states reveals that the O 2p (the top valence band) and Zn 4s (the bottom conduction band) states domination

Studies of the absorbance peak on the N719 dye influence by combination between Cadmium Selenide (CdSe)QDs and Zinc Sulfide(ZnS)QDs

The absorption rate of the photoanode can be influenced by the combination between the difference semiconductor quantum dot sensitizer. Six samples were prepared with difference weight percent (wt%) of ZnS from 0% to 50% and constant wt% of CdSe which then will be called as semiconductor QDs were immersed in 0.5mM of N719 dye. The purity of ZnS powder and CdSe powder was determined using x-ray diffraction (XRD).The ultraviolet-visible spectrophotometry (Uv-Vis) use to investigate the absorption spectrum and absorbance peak of this sample. 50 wt% of ZnS is the best composition to increase the absorbance peak of the photoanode. The Cyclic voltammetry (CV) of varying wt% of ZnS, found that the 40 wt% of ZnS is suitable combination for a DSSC’s photoanode and produced the higher current

Quantum dot solar cell studies on the influence of Cadmium Selenide(CdSe)QDs and the Zinc Sulfide(ZnS)QDs in the photoanode

The mixture between the difference semiconductor quantum dot sensitizer which is cadmium selenide(CdSe) and zinc sulfide (ZnS) into the Dye-synthesis solar cell (DSSCs) can affect the value of resistance and capacity photoanode in the system.In this experiment, each sample consists difference weight percent of Zinc sulfide and the constant weight percent of CdSe. Docter blade technique is used to stick and spread evenly the mixture CdSe/ZnS QD on the surface of the thin film. To prove the assembled of CdSe/ZnS on the thin film were observed using Scanning Electron Microscopy (SEM). The resistance and capacity of the photoanode were characterized by using impedance spectroscopy(EIS). The smallest resistance is 37.1kΩ produce by CdSe/ZnS(20 wt%) and the largest resistance 825KΩ produce by CdSe/ZnS(50 wt%) while the highest capacity is 12 µF in the CdSe/ZnS(40 wt%) and the lowest capacity is CdSe/ZnS(20 wt%) which is 538 nF. The most suitable composition to be used as photoanode is CdSe/ZnS(40 wt%) because it has high capacity and low resistance