Yen Ping Tan

Preparation and characterization of polypyrrole/graphene nanocomposite films and their electrochemical performance

A one-step electrochemical process had been employed to synthesize nanocomposite films of polypyrrole/graphene (PPy/GR) by electrochemical polymerisation on indium tin oxide (ITO) from an aqueous solution containing pyrrole monomer, graphene oxide (GO) nanosheets and sodium p-toluenesulfonate (NapTS). The X-ray diffraction (XRD) patterns showed that the typical peak of GO at 9.9o was missing from the nanocomposite’s diffraction pattern, suggesting that the GO had been stripped off of its oxygenous groups after the reaction. We postulated that a nanocomposite film was produced through a layer-by-layer deposition based on field emission scanning electron microscope (FESEM) images. The Raman spectroscopy profiles exhibited that the D/G intensity ratio (ID/IG) of PPy was not altered by the inclusion of GO due to the low concentration of the material used. However, the concentration was sufficient to increase the specific capacitance of the nanocomposite by 20 times compared to that of pure PPy, reflecting a synergistic effect between PPy and GR, as analysed by a three-electrode electrochemical cell. The electrochemical performance of the nanocomposites was affected by varying the deposition parameters such as concentrations of pyrrole and GO, scan rate, deposition time and deposition potential.

Doping mechanisms and electrical properties of bismuth tantalate fluorites

Phase-pure bismuth tantalate fluorites were successfully prepared via conventional solid-state method at 900xa0°C in 24–48xa0h. The subsolidus solution was proposed with the general formula of Bi3+xTa1−xO7−x (0xa0≤xa0xxa0≤xa00.184), wherein the formation mechanism involved a one-to-one replacement of Ta5+ cation by Bi3+ cation within ~4.6xa0mol% difference. These samples crystallised in a cubic symmetry, space group Fm-3xa0m with lattice constants, axa0=xa0bxa0=xa0c in the range 5.4477(±xa00.0037)–5.4580(±xa00.0039) Å. A slight increment in the unit cell was discernible with increasing Bi2O3 content, and this may attribute to the incorporation of relatively larger Bi3+ cation in the host structure. The linear correlation between lattice parameter and composition variable showed that the Vegard’s law was obeyed. Both TGA and DTA analyses showed Bi3+xTa1−xO7−x samples to be thermally stable as neither phase transition nor weight loss was observed within ~28–1000xa0°C. The AC impedance study of Bi3TaO7 samples was performed over the frequency range 5–13xa0MHz. At intermediate temperatures, ~350–850xa0°C, Bi3+xTa1−xO7−x solid solution was a modest oxide ion conductor with conductivity, ~10−6–10−3 S cm−1; the activation energy was in the range 0.98–1.08xa0eV.

Synthesis and Characterization of Electrical Properties of Bismuth Titanate

Bismuth titanate solid solutions, Bi12+xTiO10+δ (0 ≤ x ≤ 0.6), were synthesized by conventional solid state method at sintering temperature of 700°C for 48 h. Structural studies were performed by powder X-ray diffraction (XRD) analysis and revealed that single-phase materials were obtained with a general formula of Bi12+xTiO10+δ (0 ≤ x ≤ 0.6). The electrical properties of all the single-phase samples were studied using the impedance spectroscopy technique. Further characterization of the materials was carried out using differential thermal analysis (DTA) and indicated that no phase transition was observed. The TGA analysis was observed and found that all the materials were thermally stable.