Preparation of non-stoichiometric (Zn,Fe)S chalcogenides and evaluation of their thermal, optical and electrical properties

Non-stoichiometric ternary chalcogenides, Zn1-xFexS, were prepared by co-precipitation of ZnS and FeS by Na2S from aqueous solutions containing FeSO4 and ZnSO4 and sintering of pellets of the co-precipitate repeatedly between 800 and 1000 degreesC. The chemical composition of the resulting solids as analyzed by XRF, EDAX, and EPMA, reflected the composition of the solutions from which precipitation was carried out, with Fe contents up to x = 0.4. X-ray diffraction indicated the presence of solid solutions, Zn1-xFexS (sphalerite). Electrical resistivity studies indicated that the compounds were semiconducting. From the temperature dependence of the resistivity, thermal bandgaps were found to be decreasing with increasing Fe content, in agreement with values on optical bandgaps as estimated from diffuse optical reflectance measurements as a function of wavelength. TEP (Thermo Electric Power) measurements indicated p-type conductivity for most samples. (C) 2003 .

Electrochemical studies of kerosene-pyrolysed carbon films

Polycrystalline thin films of conducting carbon are deposited on alumina substrates by the pyrolysis of kerosene vapour at 1000 degrees C for 2 h in argon atmosphere. Preliminary structural analysis is done by XRD, laser-Raman, FTIR and SEM studies. The electrochemical behaviour of as-grown conducting carbon films was investigated in various electrolytes at different pH and the performance was compared with that of platinum and glassy electrodes. The electrochemical window of the kerosene carbon electrode in 100 mM H2SO4 was found to be 2.91 V which is greater than that of glassy carbon (2.79 V) and platinum (2.02 V). Cyclic voltammetry reveals that Pt electrode has almost an equal tendency towards hydrogen and oxygen evolution, whereas glassy carbon favours hydrogen evolution and kerosene carbon favours oxygen evolution. It is suggested that the kerosene carbon electrode can be used as an oxygen electrode more efficiently. Unlike diamond films or glassy electrodes, kerosene carbon thin films are of low cost and good stability; they are also easy to grow on various ceramic substrates of any size. Moreover, these electrodes are very economical and promising for application in chlor-alkali industry

CVD synthesis of carbon nanotubes using a finely dispersed cobalt catalyst and their use in double layer electrochemical capacitors

Carbon nanotubes (CNT) were obtained by chemical vapour deposition (CVD), decomposing turpentine oil over finely dispersed Co metal as a catalyst at 675 degreesC. Scanning electron microscope (SEM) and transmission electron microscope (TEM) images reveal that the nanotubes are densely packed and of 10-50 nm in diameter. The XRD pattern of purified CNT shows that they are graphitic in nature. Resistivity measurements of these CNT indicate that they are highly conducting. Hall measurements of CNT reveal that electrons are the majority carriers with a carrier concentration of 1.35 X 10(20) cm(-3). Cyclic voltammetry (CV) and constant current charging/discharging was used to characterise the behaviour of electrochemical double layer capacitors of purified CNT with H2SO4. For CNT/2 M H2SO4/CNT, a capacitance of 12 F g(-1) (based on the weight of the active material) was obtained. (C) 200

Electrodeposition of lead sulphide in acidic medium

Polycrystalline thin films of lead sulphide were electrodeposited on titanium, aluminium and stainless steel (SS) substrates at a constant potential of -0.7V vs. Ag\AgCl\(sat)KCl electrode using 1 mM solutions of Pb(NO,), and Na2S2O3 at pH2.7, 2.8 and 2.9. Except at pH 2.9 (which also gave tetragonal PbS2) all other pHs gave single phase PbS (fee). While deposition on Al gave a crystalline phase of PbS with very prominent (200) and (111) planes, that on SS substrate showed growth of the (200) plane only. Although the deposition of PbS on Ti was good, it showed (111) and (200) planes of low intensity compared to that on Al. Film thickness and grain size were found to be of the order of micrometres. The cyclic voltammetry of the film formation was studied in a potential range -1 to OV (Ag\AgCl) followed by XRD, SEM and AFM analyses. The mechanism of growth is discussed. (C) 1997 Elsevier Science S.A