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Undoped and palladium-doped perovskite bismuth ferrite nitrogen dioxide (NO2) gas sensors (BiFeO3 i.e. BFO and Pd-BiFeO3 i.e. Pd-BFO) are successfully synthesized via an easy and low-cost sol–gel process. The Pd-doping in BFO is confirmed through an X-ray diffraction data, field emission scanning electron microscopy images, energy-dispersive X-ray spectroscopy analysis, and its influence on the structure, morphology, surface area, and the NO2 gas sensor performance of the BFO sensor has been examined and explored. Moreover, the plausible gas sensing response mechanism of Pd-BFO film sensor has also been proposed. The nanocubes embedded into a uniformly distributed upright standing nanoplates facilitate better gas adsorption and diffusion behavior on providing an excellent NO2-sensing performance with good sensitivity, excellent selectivity, better response (90 s)/recovery (110 s), and noticeable repeatability under a fixed 100 ppm NO2 gas concentration level at an optimized low operating temperature i.e. 150 °C.

We report the electric and magnetic properties of nanocrystalline Tb3+ substituted Ni0.25Cu0.30Zn0.45TbxFe2−xO4, with x = 0.0–0.125 mol., step: 0.025 mol ferrites, synthesized by glycine assisted autocombustion route. The structural studies confirm the formation of spinel cubic structure for NiCuZn ferrites with the formation of agglomerated polydisperse grains. The presence of two intrinsic IR absorption bands of spinel lattice at ν1 (760–768) cm−1 and ν2 (650–665) cm−1 for NiCuZn ferrite system confirms the existence of tetrahedral-A and octahedral-B sites over which the cations are distributed in spinel lattice. Complex permeability measurements signified the decrease in the initial permeability due to spin canting and spin frustration by paramagnetic Tb3+ ions. The frequency dependent dielectric constant of NiCuZn ferrites revealed dielectric dispersion behavior in accordance with Maxwell–Wagner model. The incorporation of rare earth element (Tb3+) in NiCuZn ferrite at relatively lower sintering temperature (1173 K), significantly alters the structural and electromagnetic properties of the host material. Therefore, the present Tb3+ substituted NiCuZn ferrite system with moderate electrical resistivity and soft magnetic properties are potential candidate for multilayer chip inductor (MLCI) component applications.

This work reports the chemical spray synthesis of bismuth ferrite (BiFeO3, abbreviated as BFO) and tungsten-doped bismuth ferrite (W-BiFeO3, abbreviated as BWFO) nanostructured films and their nitrogen dioxide (NO2) and hydrogen (H2) gas sensor applications. The influence of tungsten-doping on the structure, morphology, surface area, and the characteristics towards NO2 and H2 gas sensing of BFO has been studied and explored and also compared with pristine BFO. The W-doping in BFO, confirmed by X-ray diffraction, energy dispersive X-ray and Fourier-transform infrared spectroscopy measurements, is proposed to explain the relative improvement in gas sensing performance between BFO and BWFO nanostructured films. At dilute concentration (100 ppm) of NO2 and H2, BWFO displays an enhanced sensitivity over BFO, which is attributed to specific changes in the morphology, structure and surface area.

Co2+ is a fast relaxing ion which can enhance microwave properties. This work focuses on the synthesis and analysis of Ni0.25-xCoxCu0.30Zn0.45Fe2O4 (x = 0.00, 0.05, 0.01, 0.15, 0.20 and 0.25) ferrites by auto combustion method using glycine as the chelating agent. From X-ray Diffraction (XRD) spectra, the structural parameters are analysed. The lattice parameter (a) decreases due to smaller ionic radius of Co2+ (0.072 nm) which replaces Ni2+ (0.078 nm). Bulk density and porosity measurements show that there are pores and lattice imperfections. The cation distribution of the ferrites based on Neel’s two sublattice model is proposed. Transmission Electron Micrographs (TEM) indicate narrow size distribution of spherical shaped nanoparticles. DC electrical resistivity (ρD.C.) is very important factor of low temperature sintered ferrites for MLCI applications. Electroplating of the devices is much affected by electrical resistivity. Maximum DC resistivity (2.89 × 106 Ω-cm) is observed for the sample with x=0.2...

Liquefied petroleum gas (LPG) sensors of hematite nanostructures viz. nanoparticles, nanoparticle-chains and nanorods, chemically synthesized from iron nitrate, sulfate and chloride precursors, respectively, in presence of urea as pH regulating agent are explored. These nanostructures were examined for their structures and morphologies. The Hematite morphology has an impact on crystal structure, Raman shift and charge transfer resistance value. On the basis of results presented herein, we proposed an importance of hematite nanostructures as a sensing material for the LPG sensors. Superior LPG sensor sensitivity of nanoparticles-chains (77.89%) over nanoparticles (68%) and nanorods (58.80%) at 1000 ppm LPG gas levels are imply that the hematite nanostructure (surface area) plays an important role in mediating charge transfer reaction.

In situ growth of upright-standing SnO2 nanoplates connected to horizontally pointed TiO2 nanoneedles to form a new, high surface area hierarchical nanostructure is proposed for the first time and envisaged in ammonia and liquid petroleum gas sensors. The increased surface area due to a hierarchical nanostructure accounts for enhanced gas sensitivity.

Graphical abstract: Display Omitted Highlights: ► Micro (cubes) structure embedded in nano (plates) of bismuth ferrite was prepared by a chemical method. ► These structures were characterized by XRD and SEM. ► LPG, CO{sub 2} and NH{sub 4} gases were exposed. ► Properties related to gas sensors were measured and reported. -- Abstract: Mixed micro (cubes) and nano (plates) structures of bismuth ferrite (BFO) have been synthesized by a simple and cost-effective wet-chemical method. Structural, morphological and phase confirmation characteristics are measured using X-ray diffraction, field-emission scanning electron microscopy (FE-SEM) and energy dispersive X-ray analysis techniques. The digital FE-SEM photo-images of BFO sample confirmed an incubation of discrete micro-cubes into thin and regularly placed large number of nano-plates. The bismuth ferrite, with mixed structures, films show considerable performance when used in liquefied petroleum (LPG), carbon dioxide (CO{sub 2}) and ammonium (NH{sub 3}) gas sensors application. Different chemical entities in LPG have made it more efficient with higher sensitivity, recovery and response times compared to CO{sub 2} and NH{sub 3} gases. Furthermore, effect of palladium surface treatment on the gas sensitivity and the charge transfer resistances of BFO mixed structures is investigated and reported.

This work reports theoretical infrared and electronic absorption spectra of formaldehyde and its ions in gas phase and H2O ice at different levels of theory. The vibrational frequencies from this work at B3LYP/6-311++G** level are in agreement with the experimental determinations. The gas phase dipole moment of neutral formaldehyde 2.4 D is in excellent agreement with the experimental value of 2.33 D. An influence of ice on vibrational frequencies of neutral formaldehyde molecule was obtained using Self Consistence Isodensity Polarizable Continuum Model (SCI-PCM) with dielectric constant 78.5. Significant shift in vibrational frequencies for neutral formaldehyde molecule when studied in H2O ice and upon ionization is observed. All the vibrational modes in cation and anion of formaldehyde in gas phase are red shifted than the corresponding modes in neutral formaldehyde. Two vibrational modes are blue shifted and all other modes are red shifted for neutral formaldehyde in H2O ice. Time dependent density functional theory (TDDFT) is used to study electronic absorption spectrum of neutral formaldehyde and its charged states. It is found that like neutral formaldehyde, its cation and anion also display strong σ→σ∗ electronic transitions in vacuum and far UV regions. This study should help in detecting formaldehyde molecule and its ions in gas phase and in H2O ice in different astronomical environment.