M. Z. A. Yahya

Ionic conductivity studies of poly(vinyl alcohol) alkaline solid polymer electrolyte and its use in nickel–zinc cells

Abstract X-ray diffraction (XRD) pattern reveals that potassium hydroxide (KOH) disrupts the crystalline nature of poly(vinyl alcohol) (PVA)-based polymer electrolytes and converts them into an amorphous phase. The PVA–KOH alkaline solid polymer electrolyte (ASPE) system with PVA/KOH wt.% ratio of 60:40 exhibits the highest room temperature ionic conductivity of 8.5×10−4 S cm−1. This electrolyte was used in the fabrication of a nickel–zinc (Ni–Zn) cell. The cell was charged at a constant current of 10 mA for 1 h providing it with 1.6 V. The cell was cycled 100 times. At the end of the last cycle, the cell still contained a capacity of 5.5 mA h.

Effect of oleic acid plasticizer on chitosan–lithium acetate solid polymer electrolytes

Abstract Plasticized polymer electrolytes composed of chitosan as the host polymer, oleic acid (OA) as the plasticizer and lithium acetate (LiOAc) as the doping salt were prepared by the solution cast technique. These complexes with different amounts of salts and plasticizers were investigated as possible ionic conducting polymers. The highest ionic conductivity of the plasticized chitosan–LiOAc was ∼10 −5 Sxa0cm −1 for the film containing 40.0 wt.% LiOAc and 10.0 wt.% of OA. Conductivity for the plasticized LiOAc-doped chitosan polymer was also studied as a function of temperature between 300 and 363 K. The plot of ln( σT ) versus 10 3 /T for each sample obeys Arrhenius rule indicating the conductivity to be thermally assisted. XRD and FTIR spectroscopy techniques have been used for the structural studies.

Studies on lithium acetate doped chitosan conducting polymer system

Abstract The structure of chitosan contains the amine group that can act as electron donors. Complexation between chitosan and the salt can be proven by infrared and X-ray photoelectron spectroscopy methods. The NH2, NH3+ and Oue605C-NHR vibrations which can be observed at 1590, 1560 and 1650 cm−1 shift to lower wave numbers when the complexes are formed. The after deconvolution Lixa01s core level spectrum of the chitosan–salt complexes can contain several gaussian components one of which has a binding energy peak at 55.2 eV which signifies Li–N interaction. The component that peaks at ∼403 eV in the Nxa01s core level spectrum complements the proof of N–Li interaction. The highest conductivity achieved for a plasticized chitosan–salt complex is of the order 10−6 S/cm using lithium acetate as the doping salt. Transference number studies prove that this material is ionic conductor and from transient ionic current studies that mobility of the ions is of the order of 10−4 cm2/Vxa0s.

Kinetic and Thermodynamic Study of Cd2+ Adsorption onto Rubber Tree (hevea brasiliensis) Leaf Powder

A batch adsorption system was applied to study the adsorption of Cd 2+ ions from aqueous solution by Hevea Brasiliensis, HB leaf powder. The adsorption capacities and rates of Cd 2+ ions onto HB leaf powder were evaluated. Langmuir and Freundlich models were applied to describe the isotherms and isotherms constants. Equilibrium data agreed well with the Freundlich model. The kinetic experimental data correlated well with the pseudo-second-order kinetic model, indicating that the chemical sorption was the rate-limiting step.

First Principles LDA+U Calculations for ZnO Materials

The electronic, structural, elastic, and optical properties of zinc oxide (ZnO) with wurtzite-type structure were investigated using first-principles calculation based on density functional theory (DFT) with local density approximation (LDA) plus Hubbard U (DFT–LDA+U)method. Hubbard U improved the calculated results, allowing it to exhibit good agreement with experimental data. The DFT–LDA+U method successfully predicted the electronic properties of ZnO with better described the localization of transition metal Zn 3d electron. The calculated optical dielectric function of ZnO and its relation with electronic properties were further discussed.

Structural, Electronic, and Lattice Dynamics of PbTiO3, SnTiO3, and SnZrO3: A Comparative First-Principles Study

The properties of cubic (Pm3m, 221 space group) perovskite prototypes PbTiO3 (PTO), SnTiO3 (STO), and SnZrO3 (SZO) were investigated via first-principles calculation using the density functional theory as implemented in CASTEP computer code. The lattice parameters of PbTiO3 (as the reference compound) were calculated. The accuracy values of the calculation functional (GGA-PBEsol) were acceptable relative to the experimental values with typical error of approximately 0.6% underestimate. The independent elastic constants (C11, C12, and C44) and bulk modulus, B, were obtained and analyzed. The density of state studies indicated hybridizations among anion O 2p, cation Pb 6s/Sn 5s and the Ti 3d/Zr 4d states of PTO, STO, and SZO. An indirect band gap was respectively obtained for both PTO and STO at the X-G point. A direct band gap was attained for SZO at the X-X point along the high-symmetry direction in the Brillouin zone. The born effective charge values of PTO, STO, and SZO were attributed to the responses of the bond charges to the displacement caused by the strong covalency between the cation orbital and O 2p (strong covalency A-O and B-O bonding). Results also reveal that anion O 2p, cation Pb 6s/Sn 5s, and Ti 3d/ Zr 4d states have played an important role in the instability of perovskite oxide. Comparative results from the PTO, STO, and SZO prototypes showed the calculated theoretical and experimental values were in good agreement.

Self-interaction corrected LDA + U investigations of BiFeO3 properties: plane-wave pseudopotential method

The structural, electronic, elastic, and optical properties of BiFeO3 were investigated using the first-principles calculation based on the local density approximation plus U (LDA + U) method in the frame of plane-wave pseudopotential density functional theory. The application of self-interaction corrected LDA + U method improved the accuracy of the calculated properties. Results of structural, electronic, elastic, and optical properties of BiFeO3, calculated using the LDA + U method were in good agreement with other calculation and experimental data; the optimized choice of on-site Coulomb repulsion U was 3 eV for the treatment of strong electronic localized Fe 3d electrons. Based on the calculated band structure and density of states, the on-site Coulomb repulsion U had a significant effect on the hybridized O 2p and Fe 3d states at the valence and the conduction band. Moreover, the elastic stiffness tensor, the longitudinal and shear wave velocities, bulk modulus, Poissons ratio, and the Debye temperature were calculated for U = 0, 3, and 6 eV. The elastic stiffness tensor, bulk modulus, sound velocities, and Debye temperature of BiFeO3 consistently decreased with the increase of the U value.

Conduction mechanism of lithium bis(oxalato)borate-cellulose acetate polymer gel electrolytes

Polymer gel electrolytes (PGE) belonging to salt–solvent–polymer hybrid systems are prepared using a mixture of lithium bis(oxalato)borate (LiBOB), γ-butyrolactone (γ-BL), and cellulose acetate (CA). The increase in ionic conductivity of PGE is due to the dissociation of ion aggregates, as confirmed by Fourier transform infrared analysis. The highest conductivity attained by the PGE is 7.05xa0mSxa0cm−1 at 2.4xa0wt.% CA. The plots of conductivity–temperature show a classical Arrhenius relationship. The electrical properties of the sample with the highest conductivity are analyzed using electrical permittivity and electric modulus formalism studies. Meanwhile, the frequency-dependent conductivity of the polymer gel electrolyte adheres to Jonscher’s power law. Conduction mechanism study also shows that the 2.4xa0wt.% CA PGE is in agreement with the small polaron hopping model.

Optical Characterization of Luminescence Polymer Blends Using Tauc/Davis-Mott Model

The optical and electronic structures of poly (N-carbazole) (PVK) blend with poly(vinylidene fluoride-co-hexafluoropropene) (PVDF-HFP) and polyvinylpyrrolidone (PVP) in the same composition were investigated. Polymer coating was carried out using doctor blade technique on a glass substrate. Uv-vis and photoluminescence spectrum revealed that there are significant different results obtained between PVK, PVK:PVP and PVK:PVDF-HFP. The electronic parameters such as absorption edge (Ee), allowed direct bandgap (Ed), allowed indirect bandgap (Ei) and Urbach edge (Eu) were calculated by using Tauc/Davis-Mott Model. The value of Ee and Ed for PVK and PVK:PVDF-HFP almost same but there was significant different value between Eu and Ei.

Ab initio studies on the structural and electronic properties of bismuth ferrite based on ferroelectric hexagonal phase and paraelectric orthorhombic phase

The structural and electronic properties of bismuth ferrite (BFO) in ferroelectric hexagonal phase and paraelectric orthorhombic phase are investigated using ab initio density functional theory calculation. Calculations based on generalized gradient approximation GGA–PBEsol functional with semi-empirical Hubbard U method show good results for the structural and electronic localization of Fe 3d electrons and are consistent with experimental data. In addition, the calculated electronic band structure of BFO in paraelectric orthorhombic phase shows a smaller energy band gap than BFO in ferroelectric hexagonal phase. Thus, this calculation is consistent with the experimental data. The function of the stereochemically active lone pair of Bi 6s2 and chemical bonding of Fe‒O and Bi‒O on the structural instability of BFO are further elucidated in this study.