This work presents a facile sol-gel method for the deposition of ZnO and ZnO:Mg films. The films are spin coated on silicon and quartz substrates. The impact of magnesium concentrations (0, 0.5, 1, 2 ...and 3 wt%) and post-annealing treatments (300-600 °C) on the film's structural, vibrational and optical properties is investigated. Undoped ZnO films crystallize in the wurtzite phase, with crystallite sizes ranging from 9.1 nm (300 °C) to 29.7 nm (600 °C). Mg doping deteriorates the film crystallization and shifting of 002 peak towards higher diffraction angles is observed, indicating the successful incorporation of Mg into the ZnO matrix. ZnO:Mg films (2 wt%) possess the smallest crystallite size, ranging from 6.2 nm (300 °C) to 25.2 nm (600 °C). The highest Mg concentration (3 wt%) results into a segregation of the MgO phase. Lattice constants, texture coefficients and Zn-O bond lengths are discussed. The diminution of the
lattice parameter is related to the replacement of Zn
by Mg
in the ZnO host lattice. The vibrational properties are studied by Fourier transform infrared (FTIR) spectroscopy. IR lines related to Mg-O bonds are found for ZnO:Mg films with dopant concentrations of 2 and 3 wt%. The optical characterization showed that the transmittance of ZnO:Mg thin films increased from 74.5% (undoped ZnO) to about 89.1% and the optical band gap energy from 3.24 to 3.56 eV. Mg doping leads to a higher refractive index compared to undoped ZnO films. The FESEM (field emission scanning electron microscopy) technique is used for observation of the surface morphology modification of ZnO:Mg films. The doped ZnO films possess a smoother grained surface structure, opposite to the wrinkle-type morphology of undoped sol-gel ZnO films. The smoother surface leads to improved transparency of ZnO:Mg films.
A sol–gel deposition approach was applied for obtaining nanostructured Li-doped ZnO thin films. ZnO:Li films were successfully spin-coated on quartz and silicon substrates. The evolution of their ...structural, vibrational, and optical properties with annealing temperature (300–600 °C) was studied by X-ray diffraction (XRD), Fourier Transform Infrared (FTIR), UV-VIS spectroscopic, and field emission scanning electron microscopic (FESEM) characterization techniques. It was found that lithium doping maintains the wurtzite arrangement of ZnO, with increasing crystallite sizes when increasing the annealing temperature. Analysis of the FTIR spectra revealed a broad main absorption band (around 404 cm−1) for Li-doped films, implying the inclusion of Li into the ZnO lattice. The ZnO:Li films were transparent, with slightly decreased transmittance after the use of higher annealing temperatures. The porous network of undoped ZnO films was transformed to a denser, grained, packed structure, induced by lithium doping.
Here, we report results on the magnetic and microwave properties of polycrystalline Y-type hexaferrite synthesized by sol-gel auto-combustion and acting as a filler in a composite microwave-absorbing ...material. The reflection losses in the 1–20 GHz range of the Y-type hexaferrite powder dispersed homogeneously in a polymer matrix of silicon rubber were investigated in the absence and in the presence of a magnetic field. A permanent magnet was used with a strength of 1.4 T, with the magnetic force lines oriented perpendicularly to the direction of the electromagnetic wave propagation. In the case of using an external magnetic field, an extraordinary result was observed. The microwave reflection losses reached a maximum value of 35.4 dB at 5.6 GHz in the Ku-band without a magnetic field and a maximum value of 21.4 dB at 8.2 GHz with the external magnetic field applied. The sensitivity of the microwave properties of the composite material to the external magnetic field was manifested by the decrease of the reflected wave attenuation. At a fixed thickness, tm, of the composite, the attenuation peak frequency can be adjusted to a certain value either by changing the filling density or by applying an external magnetic field.
The structural, vibrational, optical and morphological properties of ZnO:N:F films, obtained by the sol-gel method, were investigated. The effect of single (fluorine, nitrogen) and F, N co-doping and ...thermal treatments (300–600 °C) on the properties of ZnO films was analyzed. X-ray Diffraction (XRD) revealed that ZnO:N:F films crystallized in a polycrystalline wurtzite structure. F and N incorporation changed lattice parameters, crystallite sizes, texture coefficients (TC) and residual stress. TC (002) of ZnO:N:F films increased with annealing, reaching 1.94 at 600 °C lower than the TC (002) of ZnO and ZnO:N films. The shifting of the characteristic absorption bands and/or the appearance of new IR lines were detected for ZnO:N:F samples. The highest transmittance (90.98%) in the visible spectral region was found for ZnO:F films. ZnO:N:F films possessed optical transparency up to 88.18% and their transmittance decreased at the higher annealings. The optical band gap (Eg) values of ZnO:N:F films were changed with fluorine and nitrogen concentrations. The formation of the wrinkle-like structures on the surface of ZnO and ZnO:N films was depicted in Field Emission Scanning Electron Microscopy (FESEM) images. The F, N dual doping modified ZnO morphology and suppressed wrinkle formation.
We report results on the structural and microwave properties and magnetic phase transitions in polycrystalline Sr3Co2Fe24O41 hexaferrite synthesized by sol-gel auto-combustion and acting as a filler ...in a composite microwave absorbing material. The zero-field-cooled (ZFC) and field-cooled (FC) magnetization curves revealed a change in the magnetization behavior at 293 K. The reflection losses in the 1–20 GHz range of the Sr3Co2Fe24O41 powder dispersed homogeneously in a polymer matrix of silicon rubber were investigated in both the absence and presence of a magnetic field. In the latter case, a dramatic rise in the attenuation was observed. The microwave reflection losses reached the maximum value of 32.63 dB at 17.29 GHz in the Ku-band. The sensitivity of the microwave properties of the composite material to the external magnetic field was manifested by the appearance of new reflection losses maxima. At a fixed thickness tm of the composite, the attenuation peak frequency can be adjusted to a certain value either by changing the filling density or by applying an external magnetic field.
•(Zn,Ni)2Y-type hexaferrites are prepared by modified citric-acid self-combustion.•The temperature is measured of helicoidal-to-ferrimagnetic spin-order transition.•The magnetic properties show ...complex behavior expressed in triple hysteresis loops.•The magnetic field-induced transitions depend on the degree of nickel substitution.
We consider the influence of the magnetic cation (Ni2+) substitution on the structural and magnetic properties of Ba0.5Sr1.5Zn2-xNixFe12O22 (x = 0.8, 1, 1.5) powders. The powders were synthesized by using the citric-acid sol–gel auto-combustion method. Their ac-magnetization was measured in an ac-magnetic field with an amplitude of 10Oe and a frequency of 1000 Hz to detect any magnetic phase transitions. A strong influence of the Ni-substitution on the magnetic properties was thus observed. A magnetic phase transition from a helicoidal to a ferrimagnetic spin order at 284 K was observed for the sample Ba0.5Sr1.5Zn0.5Ni1.5Fe12O22. The magnetic-phase transition from conical spin order to hellicoidal spin order was registered at 149 K and 177 K for x = 0.8 and x = 1, respectively. Triple hysteresis loops were observed for all samples at 4.2 K, which indicates the presence of two kinds of ferromagnetic states with different magnetization values.
•Ba0.5Sr1.5Zn2Fe12O22 powders were formed by auto-combustion and sonochemistry.•The synthesis procedure affected the powders’ structural and magnetic properties.•Metamagnetic phase transitions ...occurred in an ac magnetic field.•Intermediate phases appeared at room temperature in the sonochemistry sample.
We present results from a study on the influence of the preparation technique on the structural and magnetic properties of Ba0.5Sr1.5Zn2Fe12O22 powders synthesized by citric-acid sol-gel auto-combustion and sonochemistry and characterized by X-ray diffraction, scanning electron microscopy and magnetic measurements. Two magnetic intermediate phases were observed at room temperature in magnetic fields of moderate strength. Metamagnetic phase transitions were observed in an ac magnetic field. Their temperature increased with the magnetic field amplitude.
We report a complete procedure to achieve multilayer YBa2Cu3O7−δ (YBCO) thick films by electrophoretic deposition on silver tubes using a suspension of YBCO powder in butanol. With the aim to ...optimize the magnetic shielding performances of the coatings, we have carried out an extensive investigation of the influence of the deposition parameters, the multilayer deposition sequence and the intermediate final heat treatments on the coating microstructure. Using the optimized conditions, a 24-layer YBCO coating has been successfully prepared on an 80 mm long Ag tube: the melt growth processed multilayered YBCO thick film thus obtained can shield an applied magnetic field of 1.9 mT at 77 K, the highest value per thickness unit reported so far in the literature for these materials.
Multilayered YBa2Cu3O7−δ (YBCO) thick films were coated on silver substrates by electrophoretic deposition (EPD) followed by heat treatment. A butanol-based YBCO suspension is used instead of the ...common acetone–iodine combination. Tests with several dispersing agents reveal that a branched polyethyleneimine (PEI) dispersant develops large positive surface charge on suspended YBCO particles. As a demonstration of the performance of this new suspension formulation, a 12-layer 100µm-thick YBCO coating was deposited on an Ag tube. The superconducting transition is sharp with onset critical temperature at 92K. The sample can shield a magnetic field of ~1.3mT at 77K, i.e., the best value so far for an YBCO coating on a metallic substrate.
•YBa2Cu3O7−δ thick films were prepared by electrophoretic deposition and sintering.•Butanol-based suspension was formulated instead of the usual acetone-based suspension.•Branched polyethyleneimine is a better dispersant than fish oil, Emphos or iodine.•A 100µm-thick YBa2Cu3O7−δ coating on Ag tube is able to shield 1.3mT at 77K.
The data presented has to do with identifying the various phases arising during the synthesis of the Y-type hexaferrite series Ba0.5Sr1.5Zn2-xNixFe12O22 by auto-combustion that we deem important for ...their microstructural and magnetic properties. The data and the related analyses support the research paper “Ni-substitution effect on the properties of Ba0.5Sr1.5Zn2-xNixFe12O22 powders” 1. Thus, the parameters are presented of the phases appearing after auto-combustion and after the initial annealing at 800 °C, namely, crystal cell and crystallite size. Also, additional data are provided obtained by EDS concerning the Ba:Sr:Zn:Ni:Fe ratio in Ba0.5Sr1.5Zn2-xNixFe12O22 (x = 0.8, 1, 1.5) samples synthesized at 1170 °C for 10 h. The data can be used as a reference in establishing how the phases distinguished during the initial process of auto-combustion affect the Ba0.5Sr1.5Zn2-xNixFe12O22 powders, which are candidates for room-temperature multiferroic materials. The data have not been published previously and are made available to permit critical or further analyses.
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