Materials Science Forum Vol. 819

Abstract: The layered LiNi_1/3Mn_1/3Co_1/3O_{2 ­­} that formed with the α-NaFeO₂ structure were synthesised by conventional solid state method. Rietveld refinement results indicated that the amount of cation disorder (or known as interlayer mixing) affected by temperature. The samples that prepared at 950°C in oxygen possessed slightly lower amount of interlayer mixing and excellent cycling performance compared to samples that prepared at 900°C. The initial charge-discharge capacity delivered was ~204 mAh/g and ~140 mAh/g, respectively. Furthermore, the structural and electrochemical properties were quite comparable to reported in literatures.

Abstract: The suspension of single-walled carbon nanotubes (SWCNTs) was produced by acid functionalization process. After that, the reduced graphene oxide (r-GO) suspension was added into SWCNTs suspension in order to produce a solution of SWCNTs-Graphene mixture. The solution of SWCNTs-Graphene mixture was then deposited onto titanium dioxide (TiO₂) layer as a dye monolayer in dye-sensitized solar cell (DSSC) device using drop – casting methods. Beforehand, the TiO₂ layer was cured with two different temperatures which was 450°C and 550°C. The electrical properties of the device, including the response and efficiency, were studied and compared with different curing temperatures.

Abstract: Thin films of copper oxide were successively deposited on glass substrates by sol-gel like spin coating for 40 s and annealed in air at different temperatures (200-400°C). Precursor solutions were prepared by dissolving cupric chloride in methanol. Various stabilizers and additives were used to enhance the solubility of cupric chloride and to improve the adhesion between the films and the glass substrates. Glucopone was used as a surfactant to reduce the surface energy. The evolution of oxide coatings under thermal treatment was studied by glancing incidence X-ray diffraction and scanning electron microscopy. Annealing the films in air at 300°C converts the films to CuO. The general appearances of the films were uniform and brownish in color.

Abstract: In this paper we reported the electrical conductivity and thermoelectric characterization of silver (Ag) and antimony (Sb) co-doped lead telluride bulk materials, which have been synthesized using solid state microwave technique. The doping level has performed first-principle calculations for the AgPb_mSbTe_m+2 (LAST-m) (m = 0, 2, 4, 6, 8 and 10) to clarify the effect of simultaneous doping of Ag and Sb on PbTe. The Hall effect and thermoelectric measurements have shown n-type conductivity in AgPb_mSbTe_m+2 samples. The samples show large and negative values of the Seebeck coefficient and moderate electrical conductivity. The Seebeck coefficient increased with doping levels increases at m=0 to 10. The value of the Seebeck coefficient is −419.69 μVK⁻¹ for AgPb₈SbTe₁₀ at 338 K. It has been found that AgPb₈SbTe₁₀ sample has a higher thermoelectric power factor 1.87 mW K^-2 m^-1 at 310 K.

Abstract: La-doped barium titanate (BaTiO₃) was prepared using conventional solid state synthesis route. All peaks for sample x=0 are approaching the phase pure of BaTiO₃ structure with tetragonal crystal structure (P4mm). Sintering of pressed powder are performed at 1300oC, 1400oC and 1450oC for overnight for pure BaTiO₃ and 1350oC for 3 days for BaTiO₃ doped lanthanum with intermittent grinding. Phase transition was studied by different x composition. The changes in the crystal structure of the composition x=0.1 and 0.2 were detected by using X-ray diffraction (XRD). The phase changes between tetragonal-cubic and cubic-tetragonal depending on the temperature. Rietveld Refinement analysis is carried out to determine the lattice parameter and unit cell for BaTiO₃.

Abstract: Gallium Arsenide (GaAs) based solar cell which have nearly ideal direct bandgap of 1.43eV hold the highest single junction solar cell efficiency. GaAs solar cell without Anti-Reflective Coating (ARC) layer was studied and shows the efficiency ranges between 8% to 15%, followed by GaAs solar cell with efficiency ranges between 20% to 25% with ARC layer. The substrate thickness for both GaAs solar cell was varied from 0.1μm to 1.0μm. Increased of P-type substrate thickness shows a small variation in efficiency with parabolic shape, while increased of N-type substrate thicknesss increased the efficiency between 21% to 25% for single layer GaAs with ARC thickness. Besides that, increased of P-type doping concentration from 1×10¹⁸cm^-3 to 1×10¹⁹cm^-3 and fixed N-type doping will decreased the efficiency. However increased the N-type doping concentration from 1×10¹⁷cm^-3 to 1×10¹⁸cm^-3 and fixed the P-type doping will increased the efficiency. The thickness of ARC layer on GaAs solar cell was studied and shows that highest efficiency achieved at narrow thickness of ARC.

Abstract: AlN has been widely used as the piezoelectric thin film layer in film bulk acoustic wave resonator (FBAR). The performance of FBAR is influenced by various geometrical parameters and losses from piezoelectric material such as thermoelastic damping and material damping. This research focuses on the estimation of material damping coefficients (α and β) of the AlN by using the Akhieser approximation to estimate more accurate values of the coefficients, thus a more realistic value of the quality (Q) factor is achieved for FBAR operating at Ku-band frequency ranges (12 GHz-18 GHz).

Abstract: Annealing of Zn foils substrates was performed in air for 30 min at 300 oC, 400 oC and 500 oC, respectively. The effects of annealing on the structural and optical properties of Zn foils substrates were investigated using X-ray diffraction (XRD), and photoluminescence (PL) measurements. After annealing, the XRD patterns showed that the annealed ZnO films have c-axis preferential orientation, the crystallinity of the ZnO films was improved, and the grain size decreased by thermal annealing. PL spectra are clearly visible at 376 nm for ZnO film grown on Zn foils substrates. The mean grain size in the annealed ZnO microstructures was estimated using Scherrer’s equation is about 82, 76, 69 nm for 300°C, 400°C, and 500°C, respectively. A PL spectrum is clearly visible at 376 nm for ZnO microstructures grown on Zn foil substrates. The PL analysis indicates that the growth of ZnO thin film with the presence of the defect-related band. Green-yellow band emission is observed at 520 nm.

Abstract: SiC-reinforced aluminum composite was developed by pressureless infiltration technique using polystyrene as external binder. The metal matrix composites obtained were characterized for phase composition, microstructure, density, porosity, hardness and thermal expansion. The SiC particles were uniformly distributed within the Al-Si matrix with the help of polystyrene as external binder. The variation in the density of the composites was found to be linear with volume percent of SiC. The hardness increased with increasing SiC content and highest hardness was 64.52 HV achieved with addition of 20 vol.% SiC. Thermal conductivity of the composites increased with increasing of SiC volume fraction up to 27.34 W/mK.

Abstract: Barium hexaferrite embedded-silica-titania photocatalyst (TiO₂-SiO₂-BaFe₁₂O₁₉) was synthesized through sol-gel, liquid catalytic phase transformation and solid reaction routes. The magnetic photocatalyst was aimed to harvest the photoenergy from the sunlight, minimize the electron-holes recombination rate, improve the long lifetime charge-carriers transfer to maximize the photocatalytic activity and enhances the separation and reusability of it. The as-synthesized photocatalyst was characterized and the photocatalytic activity was evaluated for the reduction of 2, 4-dichlorophenol (2, 4-DCP) under direct sunlight. The presence of SiO₂ interlayer in TiO₂-SiO₂-BaFe₁₂O₁₉ prevents the phase transformation of magnetic core. TiO₂-SiO₂-BaFe₁₂O₁₉ benefits the magnetic separation with appreciable magnitude of coercivity (5035.6 Oe) and saturation magnetization (18.8256E^-3 emu/g), respectively. The ferrite ions from the magnetic core which dispersed into TiO₂ matrix exhibited an evident shift of the absorption in the visible region. This was again confirmed with the reduced band gap energy of 1.90 eV. Furthermore, TiO₂-SiO₂-BaFe₁₂O₁₉ destructed 100% of 2, 4-DCP compound within 150 min under very bright sunlight with an average irradiance of 820.8 W/m² (results not shown). The embedding of BaFe₁₂O₁₉ with a SiO₂ layer onto TiO₂ nanocrystals contributed for an excellent solar-light utilization and ease magnetic separation of the nanosized photocatalyst.