From its initial use to describe hydrolysis and condensation processes, the term ‘sol–gel’ is now used for a diverse range of chemistries. In fact, it is perhaps better defined more broadly as covering the synthesis of solid materials such as metal oxides from solution-state precursors. These can include metal alkoxides that crosslink to form metal–oxane gels, but also metal ion–chelate complexes or organic polymer gels containing metal species. What is important across all of these examples is how the choice of precursor can have a significant impact on the structure and composition of the solid product. In this review, we will attempt to classify different types of sol–gel precursor and how these can influence a sol–gel process, from self-assembly and ordering in the initial solution, to phase separation during the gelation process and finally to crystallographic transformations at high temperature.

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The evolution of 'sol-gel' chemistry as a technique for materials synthesis

Spinel ferrite magnetic adsorbents: Alternative future materials for water purification?

Nanosized and nanocrystalline calcium orthophosphates.

Recent developments and applications of protective silicone coatings: A review of PDMS functional materials

Recent developments and trends of sol-gel auto-combustion method for spinel ferrite nanomaterial synthesis are briefly discussed and critically analyzed. The analysis of various parameters of reaction which could be used for better understanding of synthesis process and control of microstructure and property of spinel ferrite nanopowder products was the main objective of this review article. Special attention was paid to variety of particle size and phase purity. For these purposes the correlation between complexant, oxygen balance and combustion process chemical additives, as well as heating mechanism and atmosphere, was established. These results are relevant from standpoints of both application and processing of ferrites.

Sol-gel auto-combustion synthesis of spinel-type ferrite nanomaterials

https://essuir.sumdu.edu.ua/bitstream/123456789/44340/1/Voznyi_Properties_SnS2.pdf

Structural and electrical properties of SnS2 thin films

It is demonstrated for the first time that the gas sensing properties of a spinel ferrite complex metal oxide semiconductor can be improved by controlling iron stoichiometry. Conductivity and sensitivity was analyzed for ZnFe2+zO4± spinel type ferrite with z from −0.01 to 0.15. By increasing iron content from z = −0.01 to z = 0.1, sensitivity increases up to 3 times but for samples with z > 0.1 sensitivity drops. It was observed from impedance spectroscopy measurements that resistance decreases with an increase of the iron content. Complex impedance spectra reveal two phases with different resistance attributed to depletion layer (Rd) and bulk (Rb). With increasing iron content increases Rd/Rb ratio due to decrease of depletion layer width. Outer surface of the grain of the sensing material estimated higher ratio (Rd(air)/Rd(gas)) with gas exposure in comparison with bulk (Rb(air)/Rb(gas)). Overall sensitivity increases due to increase of donor concentration leading down to increase adsorbed oxygen species on grain surface. Sensitivity drops when z > 0.1 due to remarkable decrease of depletion layer width.

Influence of iron non-stoichiometry on spinel zinc ferrite gas sensing properties

The influence of zinc ion to the NiFe2O4 p-type semiconductor gas response characteristics is demonstrated. For characterization of gas sensor material, synthesized by sol–gel auto combustion method, X-ray diffraction (XRD), scanning electron microscopy (SEM), DC resistance and impedance spectroscopy (IS) measurements were employed. The response change of Zn doped nickel ferrite is related to the interruption of hole hopping between nickel ions. This was improved by change of conductivity type with temperature and gas exposure.

Gas sensing properties of Zn-doped p-type nickel ferrite

The results presented in this paper were focused on the easy development of cheap, sensitive and integrable spinel zinc ferrite (ZnFe2O4) thin film gas sensors for the detection of ethanol. ZnFe2O4 layers of about 450 nm thick were deposited by spray pyrolysis technique. The resulting films were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and atomic force microscopy (AFM). Analysis confirmed the formation of monophasic spinel structured thin films with flat surface and dense microstructure consisting of nanosized grains. The sensor detects ethanol concentrations as low as 1 ppm and shows comparably fast behaviour of response and recovery.

Gundars Mezinskis

Papers

Sol-gel auto-combustion synthesis of spinel-type ferrite nanomaterials

Structural and electrical properties of SnS2 thin films

Influence of iron non-stoichiometry on spinel zinc ferrite gas sensing properties

Gas sensing properties of Zn-doped p-type nickel ferrite

Ethanol monitoring by ZnFe2O4 thin film obtained by spray pyrolysis