Nanostructured yttria powders were prepared by a gel combustion technique. The technique involves exothermic decomposition of an aqueous citrate-nitrate gel. The decomposition is based on a thermally induced anionic redox reaction. A variety of yttria powders with different agglomerate structures can be made by altering the citrate-nitrate ratio γ. The gel with γ = 0.098 in situ yields nanostructured yttria powder at 258 °C that is porous and agglomerated with an average of 25 nm primary particles. Its specific surface area is 55 m2/g. The decomposition of the gels was investigated by simultaneous thermogravimetry analysis (TGA) and differential thermal analysis (DTA) experiments. The produced ashes and calcined powders are characterized by x-ray diffraction (XRD), ir spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and Brunauer, Emmett, and Teller (BET) analysis.

Thin protein films of gelatin molecules grown on flexible substrates have been utilized to fabricate moisture-induced energy-harvesting devices, which work as self-biased sensors. Adsorbed water molecules from ambient moisture generate protons inside the film. A proton transfer path is formed through the hydrogen-bonded water molecules with protein around 55% relative humidity condition, and the protons are transferred due to the gradient of absorbed water molecules within the protein films. The devices are capable of harvesting electric power up to 5.5 μW/ cm 2 with an induced voltage of 0.71 V. Our findings not only provide a futuristic clean power generation concept from protein film as flexible power generator but also demonstrate the use of the energy-harvesting devices as self-biased electronic sensors for various flexible and wearable applications. The devices showed exceptional performance as humidity sensors and have been used for flexible healthcare applications, such as continuous monitoring of breathing pattern and lateral mapping of moisture levels at the finger tip for monitoring the wound healing process. Nevertheless, the diode-like response of the devices with humidity has been found to be suitable as a self-biased humidity-controlled electronic switch.

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Lead zirconate titanate powders are derived from a novel aqueous-based citrate-nitrate/oxynitrate sol-gel combustion process. Aqueous solutions of metal nitrates or oxynitrates are transformed into gels with citric acid under heating. The received gels undergo a self-propagating combustion reaction on heating to 180 °C and subsequently yield voluminous ashes. These ashes form single phase perovskite Pb(Zr0.53Ti0.47)O3 powder with a specific surface area of 8 m2/g upon calcination at 550 °C. The ashes show a homogeneous distribution of lead, zirconium, and titanium ions which guarantees short diffusion paths in solid state formation of PZT perovskite. The redox behavior of the gels was studied with the help of DTA experiments. Powders are characterized in terms of XRD, SEM, and EDX analysis.