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A detailed comparative study of electron paramagnetic resonance (EPR) in conjunction with d.c. electrical conductivity has been undertaken to know about the charge transport mechanism in polyaniline (PANI) doped with monovalent and multivalent protonic acids. This work is in continuation of our previous work for further understanding the conduction mechanism in conducting polymers. The results reveal that the polarons and bipolarons are the main charge carriers formed during doping process and these cause increase in electrical conductivity not only by increase in their concentration but also because of their enhanced mobility due to increased inter-chain transport in polyaniline at high doping levels. EPR line asymmetry having Dysonian line shape for highly doped samples shows a marked deviation of amplitudes A/B ratio from values close to one to much high values as usually observed in metals, thereby support the idea of high conductivity at higher doping levels. The nature of dopant ions and their doping levels control the charge carriers concentration as well as electrical conductivity of polyaniline. The electrical conductivity has also been studied as a function of temperature to know the thermally assisted transport process of these charge carriers at different doping levels which has been found to follow the Mott's variable range hopping (VRH) conduction model for all the three dopants used. The charge carriers show a change over from 3D VRH to quasi 1D VRH hopping process for multivalent ions at higher doping levels whereas 1D VRH has been followed by monovalent ion for full doping range. These studies collectively give evidence of inter-chain percolation at higher doping levels causing increase in effective mobility of the charge carriers which mainly seems to govern the electrical conduction behaviour in this system.

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Vibrational spectra of insulator emeraldine base (EB) form of polyaniline and electrical conductive sulfuric acid- and phosphoric acid-doped emeraldine salts (ES) were studied in the region of 4000-400 cm(-1) at ambient temperature by Fourier transform infrared spectroscopy. Infrared transmittance spectra of EB and ES were investigated to understand the bonding behavior of different organic and inorganic groups present in the polymeric chains and their structural variations on protonation by sulfate or phosphate ion inclusion in the polymer salt network. These studies revealed the para-coupling of deformed disubstituted benzenoid (B) and quinoid (Q) rings with ends capped predominantly by (B4Q1) units. The deformation of B and Q rings was confirmed by the appearance of many weak bands, very weak bands, and satellite structures in strong transmittance peaks of polymeric chain-constituting groups. Protonation takes place at the nitrogen sites of Q rings and forms semiquinone radical ions in ES. The vibrational bands pertaining to B rings, Q rings, B4Q1 units, semiquinone segment, sulfate ions, and phosphate ions were observed and assigned from these measurements. The shift in peak position of some bands with gain or loss in intensity and appearance of some new bands were observed in sulfuric acid- and phosphoric acid-doped ES spectra. These variations are attributed to the formation of new structural groups in ES on protonation and a change in crystalline field by sulfate and phosphate ion doping for crosslinking the polymeric chains.

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This paper presents a comparative study on gas sensing properties of pure and doped ZnO nano powders. To facilitate doping, Aluminum and nickel precursors were used as dopant/co‐dopants using a simple and reproducible co‐precipitation method. Pure ZnO and samples with compositions Zn0.99M0.01O (M = Al/Ni) and Zn0­.99Al0.005Ni0.005O were prepared to evaluate the effect of Al/Ni doping/co‐doping. The samples were characterized using X‐ray diffraction (XRD), Raman spectroscopy, and field emission scanning electron microscopy (FESEM). The electrical conductivity of these samples was measured. A temperature variation of electrical conductivity was used to calculate activation energy of various samples. The samples were subjected to ethanol tests at concentration ranging between 10 and 50 ppm. The metal ion doping showed a marked increase in relative responsiveness of all doped samples. The variation in gas sensing response has been correlated with electrical conductivity, activation energy, and morphology of these samples. This report clearly demonstrates inter‐connection of multiple factors influencing gas sensing properties of metal oxide semiconductors (MOS). Similar tests performed with methanol exposure show much reduced relative responses for all the samples in comparison to ethanol. These studies can be exploited for tailoring of futuristic sensors with improved responses.

A series of indium doped ZnO (IZO) materials were fabricated, characterised and tested for their gas sensing properties. ZnO was synthesised with indium doping levels of 0.2, 0.5, 1 and 3 mol %. These were fabricated into gas sensors. Production took place using a commercially available screen printer, a 3 × 3 mm alumina substrate containing interdigitated electrodes and a platinum heater track. Materials were characterised using X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX). Electrical conductivity of all samples was also calculated. Sensors were exposed to ethanol, methanol, n-butanol and acetone at concentrations between 5 and 80 ppm. Low levels of indium doping were found to increase the responsiveness of the sensors. However, higher levels of doping were found to inhibit conductivity and responsiveness to gases of IZO sensors. Sensors with low levels of indium doping were found to show minimal response to other gases, demonstrating a lack of cross sensitivity. These sensors show potential for inclusion into an electronic nose for with the aim of selective alcohol detection.

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