Study of Defects by Rietveld Technique and Gas Response of Excess-Iron Zinc Ferrite

It has been shown that by regulating excess iron content in spinel zinc ferrite it is possible to enhance its gas response. In this work relationships between structural properties and gas response of the non-stoichiometric zinc ferrites are studied. Stoichiometric and excess iron spinel zinc ferrite nanomaterials were synthesized by using sol-gel combustion. Rietveld refinement of site occupancies from powder XRD data shows that excess iron zinc ferrites contain vacancies on oxygen positions, Fe2+ on octahedral crystallographic B sites, and Fe3+ on the A site. As revealed by complex impedance spectra, with increasing oxygen vacancy concentration the depletion layer width decreases. At the same time, increasing oxygen vacancy concentration increases oxygen adsorption for reaction with a test gas, thus increasing the gas response of spinel zinc ferrite. Long term stability of the non-stoichiometric excess iron spinel zinc ferrite gas sensors will be discussed in this work

Study of Defects by Rietveld Technique and Gas Sensing Properties of Non-Stoichiometric Zinc Ferrite

Our previous study has shown that by regulating excess iron content in spinel zinc ferrite it is possible to enhance its gas response.1) In this work relationships between structural properties and gas response of the non-stoichiometric zinc ferrites were studied. Stoichiometric and excess iron spinel zinc ferrite nanomaterials were synthesized by using sol-gel combustion. Rietveld refinement of site occupancies from powder XRD data shows that excess iron zinc ferrites contain vacancies on oxygen positions, Fe2+ on octahedral crystallographic sites, and Fe3+ on the tetrahedral site.. As revealed by complex impedance spectra, with increasing oxygen vacancy concentration the depletion layer width decreases. At the same time, with increasing oxygen vacancy concentration increases oxygen adsorption for reaction with a test gas, thus increasing the gas response of spinel zinc ferrite. Long term stability of the non-stoichiometric excess iron spinel zinc ferrite gas sensors also was not studied previously and will be discussed in this work

Reversible photodoping of TiO2 nanoparticles

Observations on strong photochromic effect of crystalline TiO2 quantum dots (mean size ≈ 4 nm) are presented. The synthesized quantum dots consist of irregularly shaped anatase TiO2 nanoparticles (NPs) and are dispersed in butanol (8 % by mass). Obtained NPs exhibit a dramatic photo-response to UV light, enabling effective transmittance modula-tion of in a broad wavelength range extending from visible to near-infrared region, and even the thermal black body radiation regime beyond 10 μm. The exceptional photo-response is attributed to hole-scavenging by butanol, TiO2 self-reduction, injection of electrons to the conduction band, and consequent localized surface plasmon resonances in NPs. Observed optical effect is reversible and the initial high transmittance state can be restored simply by exposing the NPs to air. Applied NP synthesis route is economic and can be easily scaled for applications such as smart window technol-ogies.acceptedVersionPeer reviewe