Gundars Mezinskis

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

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.

An alternative method to modify the sensitivity of p-type NiFe2O4 gas sensor

Our objective was to determine the role of cooling rate on gas-sensing properties of annealed nano-grained nickel ferrite (NiFe2O4). The sol–gel auto combustion method was used for the preparation of NiFe2O4. To estimate structural and microstructural features, X-ray diffraction, and scanning electron microscopy techniques were used. For gas-sensing measurements different volatile organic compounds (VOCs) were used as testing gases. To identify the contribution of the different sensing layer elements to the conduction, ac impedance spectroscopy (IS) measurements were performed. It was found that the sensors cooled with lower rate exhibited better sensing performance, due to increase of resistance. Overall, this article covers an alternative method for modifying nickel ferrite gas sensor sensitivity.

The effect of heating conditions on the properties of nano- and microstructured Ni–Zn ferrite

The structural, microstructural and morphological, as well as electric and dielectric, properties of nickel–zinc ferrite (Ni0.3Zn0.7Fe2O4) derived from sol–gel auto-combustion have been studied after sintering from 900 to 1300 °C. The effect of heating rate has not been previously investigated and is reported here. X-ray diffraction showed a pure cubic spinel after calcination. Atomic force microscopy revealed nanosized particles after calcination, but scanning electron microscopy showed nanosized grains after sintering at 900 °C. The heating rate has a marked effect on oxidation of Fe3+ to Fe2+, showing an additional approach to control charge carrier concentration in Ni–Zn ferrites (powder and monoliths). The heating rate also influences the average particle size and distribution. Grain size and resistivity of sintered pellets do not show significant change with heating rate, proving that resistivity is mainly dictated by the number of grain boundaries. The dielectric loss tangent curves at room temperature exhibit dielectric relaxation peaks attributed to the similarity in frequency of charge hopping between the localized charge states and external fields. The relaxation peak shifts to higher frequencies for ferrites with nanosized grains.

Electric and dielectric properties of nanostructured stoichiometric and excess-iron Ni?Zn ferrites

In this paper, we report a study of the effect of excess iron on structural, microstructural, electric and dielectric properties of the nanostructured Ni–Zn ferrites Ni1−xZnxFe2+zO4−δ of different compositions with x = 0, 0.3, 0.5, 0.7, 1 and z = 0, 0.1. The structural and microstructural properties are estimated from x-ray diffraction and atomic force microscopy (AFM) data. The average grain size, evaluated from AFM topographical analysis, is found to be below 70 nm. The samples exhibit low values of dielectric constant and dielectric loss and a high resistivity. Contrary to earlier conclusions regarding microstructured Ni–Zn ferrites, in nanostructured Ni–Zn ferrites sintered at relatively low temperature and duration, the excess of iron in the composition increases the electrical resistivity and reduces the dielectric constant and loss tangent.

A comparative study of Ni0.7Zn0.3Fe2O4 obtained by sol-gel auto-combustion and flash combustion methods

In this study, the nickel–zinc ferrites were prepared via two different methods: the sol-gel auto combustion method and the flash combustion method. Obtained reaction products were sintered at different temperatures 900, 1100 and 1300 °C. The structural and microstructural, as well as electric and dielectric properties of different samples were discussed. The synthesis method has a marked effect on crystalline order, grain size and its distribution, electrical resistivity and dielectric properties.

CO2 laser-induced structure changes in lead zirconate titanate Pb(Zr0.58Ti0.42)O3 sol–gel films

Based on absorption spectra of lanthanum modified lead zirconate titanate Pb0.9La0.1(Zr0.65Ti0.35)O3 (PLZT10/65/35) ferroelectric ceramics an idea of local and selective treatment of lead zirconite titanate Pb(ZrXTi1−X)O3 (PZT) sol–gel film in the multi-layer structure by CO2 laser radiation was formulated. The possibility to obtain PZT perovskite film on the SiO2/Si substrate by irradiation with CO2 laser was shown experimentally. X-ray studies revealed the PZT perovskite structure ratio growth at the expenses of pirochlore structure with an increased power density of laser radiation.

Preparation and characterization of nanostructured Fe-TiO2 thin films produced by electrophoretic deposition

Fe-TiO2 thin films have been produced by a sol-electrophoretic deposition method on metallic Ti foil substrates. X-ray diffractograms and Raman spectra confirms the anatase structure of deposited and annealed Fe-TiO2 films. Obtained Fe-TiO2 thin films demonstrate photoactivity under visible light radiation due to the doping with Fe3+ ions. Open circuit potential results shows that increase of the film thickness and surface area improves the photoactivity of Fe-TiO2.

Effect of Cooling Conditions on Nano-Sized NiFe2O4 Electrical Properties

Nickel ferrite NiFe2O4 nanoparticles have been prepared by sol-gel auto combustion. Two groups of samples were obtained from as-burnt and calcined powders by using various cooling conditions. The X-Ray diffraction (XRD) analyses confirm the single phase spinel structure for all samples. The grain sizes investigated by scanning electron microscopy (SEM) were found within the range of 70-100 nm. DC resistivities for different group of samples are strongly affected by cooling rate, showing the way how to control NiF2O4 electrical properties.

CO 2 -Laser Induced Structure Changes in PZT Sol-Gel Films

Previously thermally annealed at low temperature as 450C PbZr 0.58 Ti 0.42 O 3 (PZT) sol-gel films on Pt(111)/Ti/SiO 2 /Si substrates were treated by CO 2 laser radiation and their structure have been studied by X-ray diffraction. Basing on experimental data on absorption spectra of PLZT ceramics an idea of local and selective treatment of PZT sol-gel film in the multilayer structure by CO 2 pulsed laser radiation was formulated. The possibility to obtain perovskite structure PZT film on Si substrate by irradiation with CO 2 laser was shown experimentally. Growth of perovskite structure ratio at the expenses of pyrochlore structure in PZT with an increased dose of laser radiation has been demonstrated.

Structure and Hydrophobicity of Fe2O3-TiO2 Coatings

Fe2O3–TiO2 coatings were successfully prepared on glass slide substrates using sol–gel method for wettability applications. The microstructure and surface properties of the coatings were extensively characterized by using X-ray diffractometry (XRD), scanning electron microscopy (SEM) and atomic force microscopy (AFM). Different solutions were prepared by adding distilled water to sol solution. Glass substrates were coated by solutions of Ti-alkoxide, Fe-chloride hexahydrate, ethylene glycol, acetic acid, isopropanol and glycerol. The obtained gel films were dried at room temperature for 15 min in air. The oxide thin films were annealed at 500 ºC for 1h. The influence of distilled water concentration and withdraw speed on contact angle of the films was established. In addition, XRD results revealed that Fe2O3–TiO2 films composed of anatase, rutile, brookite and hematite phases. The purpose of this contribution was the investigation of different preparation parameters during the synthesis of iron oxide rich Fe2O3–TiO2 thin hydrophobic films on glass substrate. SEM and AFM observations revealed leaf-like structure formation on a coating surface.