Study of influence of Mn dopant on dielectric response of SrTiO3 ceramics

The influence of Mn incorporation into the Sr and Ti sites of SrTiO3 ceramics on the structure, microstructure and dielectric tunability was studied. Manganese doped SrTiO3 ceramics with various manganese dioxide weight percentages (1.5, 3 and 6 wt %) were prepared by a solid-state method in the presence of mechanical activation (10, 30 and 120 minutes). According to Ritveld's analysis it was found that the size of the crystallite in doped activated SrTiO3 ceramics is smaller than the size of the crystallite in undoped ceramics. This lower degree of crystallinity is a consequence of additional distortion of the crystal structure due to ion substitution. SEM analysis showed that with increasing dopant concentration in the sample, at the same time as a time of mechanical activation, the grain size decreases, which is explained by the increasingly dominant incorporation of Mn4+ ions at sites of Ti4+ ions. On the Raman spectra of doped ceramic samples, the appearance of a peak at 750 cm-1 was observed, its change in intensity with the increase of dopant concentration indicates the incorporation of dopant in the SrTiO3 lattice. It was stated that mechanical activation leads to a more pronounced increase in the intensity of the mentioned peak, i.e. that activation leads to effectively higher incorporation of dopant into the strontium-titanate lattice. Higher values of relative dielectric permittivity of doped SrTiO3 ceramics were observed for 1.5 wt %, in relation to inactivated and activated undoped ceramics. Based on all previous analysis, it is estimated that this can be related not only to higher sample densities but also to the contribution of Mn2+ ion incorporation at Sr2+ ion positions in the lattice. Based on all the above, the optimal electrical properties of SrTiO3 ceramics can be achieved by the appropriate choice of mechanical activation time and dopant concentration

Structure, morphology and photocatalytic properties of CoxMg1-xFe2O4 (0<x<1) spinel ferrites obtained by sol-gel synthesis

Nanocrystalline cobalt magnesium ferrites with varying cobalt and magnesium content (CoxMg1-xFe2O4, 0<x<1) were synthesized using the sol-gel self-combustion method with citric acid as fuel, followed by calcination at 700 C for 2 hours. Structural characterization was performed using Xray diffraction (XRD), field emission scanning electron microscopy (FE-SEM) and Raman spectroscopy. It confirmed the formation of agglomerated nanocrystalline ferrites with an inverse cubic spinel structure. The optical band gap energy was determined using UV/Vis spectrophotometry. It reduced with increased Co content. Visible light photocatalytic activity was tested using natural and artificial light sources through a series of experimental degradations of the methylene blue (MB) solution

The influence of mechanical activation on microstructure and dielectric properties of SrTiO3 ceramics

In recent years, a lot of interest has been shown in obtaining materials with predetermined properties. The aim is to establish a functional dependence between the synthesis parameters, structural characteristics, and properties of the material. Ceramic materials based on strontium titanate (SrTiO3) are of special interest due to their unique physical-chemical properties. Having in mind the importance of examining the influence of synthesis parameters on the process of obtaining and properties of functional electroceramic materials, and the importance of SrTiO3 as a perovskite material, the motive was to analyze and consider the influence of mechanical activation. It has been established that the time of mechanical activation (0, 10, 30, 60, 90, and 120 minutes) of SrTiO3 powders indirectly affects on electrical properties of SrTiO3 ceramics. It was noticed that in SrTiO3 ceramics the values of relative dielectric permittivity in the radio frequency range (0,3 MHz - 3 GHz) are stable, which is important for the fabrication of electronic components. Microstructural SEM analysis showed that the increase in mechanical activation time results in less porous samples. It was found that the value of the relative dielectric permittivity of ceramic samples at room temperature changes following the combined effect of changes in sample density, grain size, as well as changes in the grain boundary region. The maximum value of dielectric permittivity was observed in the sample activated for 10 minutes. Also, the sample activated for 10 min exhibits relatively low values of loss tangent, compared to the other mechanically activated samples, providing the best overall dielectric performance compared to other samples

The influence of mechanical activation on microstructure and dielectric properties of SrTiO3 ceramics

In recent years, a lot of interest has been shown in obtaining materials with predetermined properties. The aim is to establish a functional dependence between the synthesis parameters, structural characteristics, and properties of the material. Ceramic materials based on strontium titanate (SrTiO3) are of special interest due to their unique physical-chemical properties. Having in mind the importance of examining the influence of synthesis parameters on the process of obtaining and properties of functional electroceramic materials, and the importance of SrTiO3 as a perovskite material, the motive was to analyze and consider the influence of mechanical activation. It has been established that the time of mechanical activation (0, 10, 30, 60, 90, and 120 minutes) of SrTiO3 powders indirectly affects on electrical properties of SrTiO3 ceramics. It was noticed that in SrTiO3 ceramics the values of relative dielectric permittivity in the radio frequency range (0,3 MHz-3 GHz) are stable, which is important for the fabrication of electronic components. Microstructural SEM analysis showed that the increase in mechanical activation time results in less porous samples. It was found that the value of the relative dielectric permittivity of ceramic samples at room temperature changes following the combined effect of changes in sample density, grain size, as well as changes in the grain boundary region. The maximum value of dielectric permittivity was observed in the sample activated for 10 minutes. Also, the sample activated for 10 min exhibits relatively low values of loss tangent, compared to the other mechanically activated samples, providing the best overall dielectric performance compared to other samples

Finding optimal conditions and investigating the structure & morphology of cobalt/magnesium ferrite based cubic spinels (CoxMg1-xFe2O4) as photocatalysts

Cobalt/magnesium ferrites with various mole percentage ratio of the metals (obtained structures are CoxMg1-xFe2O4 with x being 0, 0.1, 0.3, 0.5, 0.7, 0.9, 1.0) were synthesized by sol-gel combustion synthesis using glycine as fuel, following the rules of propellant chemistry. The powders were then sintered at 700 °C for 3 hours. Obtained powders were characterized by X-Ray diffraction (XRD), scanning electron microscopy (SEM), Raman spectroscopy, UV/vis diffuse reflectance spectroscopy (DRS). Investigation of the magnetic properties was also conducted by vibrating sample magnetometry (VSM). The obtained powders were proved to be phase-pure cubic spinels which formed agglomerated micrograins. Series of photocatalytic experiments of methylene blue degradation were done. The influence of different experimental conditions was investigated including variations of: pH values, concentrations of the pollutant, masses of the photocatalyst, different light sources and therefore different light irradiation. Interesting results, including enhancement of the degradation rate with the introduction of cobalt into MgFe2O4 and decrease of the degradation rate with further increase of cobalt content and formation of hard agglomerates, open new possibilities for further investigation of the utilisation of Co/Mg ferrites as photocatalysts

Influence of Co2+ ions on photocatalytic properties of MgFe2O4 ferrites

In this work, spinel magnesium cobalt ferrites (CoxMg1-xFe2O4, x = 0.0, 0.1, 0.3, 0.5, 0.7, 0.9) were synthesized by a sol-gel combustion method. Magnesium nitrate, cobalt nitrate and iron nitrate were used as oxidizers and citric acid was used as a reducing agent. The effects of cobalt ions on structural and morphological properties were investigated and characterized by X-ray diffraction (XRD), Raman spectroscopy, Field emission scanning electron microscope (FESEM) and Fourier transform infrared (FT-IR) spectroscopy. A cubic spinel structure formed with a varied distribution of cobalt and magnesium ions on tetrahedral and octahedral sites that depended on their content. All ferrite powders consisted of multigrain agglomerates. Optical properties were investigated by UV- vis spectrophotometry. The photocatalytic activity of as prepared samples was evaluated by measuring the rate of photodegradation reaction of methylene blue (MB) under visible light irradiation. After 240 min, compared to other samples, the sample labeled as Co0.1Mg0.9Fe2O4 showed the best rate of photodecomposition of MB resulting in reduction of 90% of its initial concentration

Visible light photocatalytic activity of nanocrystalline CoxMg1-xFe2O4 (x = 0-1)

The sol-gel combustion method was applied for synthesis of spinel magnesium cobalt ferrites CoxMg1-xFe2O4, with varying cobalt and magnesium content, x = 0.0, 0.1, 0.3, 0.5, 0.7, 0.9. Magnesium nitrate, cobalt nitrate and iron nitrate were used as oxidizers and citric acid was used as a reducing agent. Structural and morphological properties of the obtained ferrite powders were investigated and characterized by X-ray diffraction (XRD), Raman spectroscopy, Field emission scanning electron microscope (FESEM) and Fourier transform infrared (FT-IR) spectroscopy. Optical properties were investigated by UV-VIS spectrophotometry. A cubic spinel structure with multigrain agglomerates formed. Visible light photocatalytic activity of the spinel ferrite powder samples was evaluated by measuring the rate of photodegradation reaction of methylene blue (MB). After 240 min Co0.1Mg0.9Fe2O4 showed the best rate of photodecomposition of MB resulting in 90% of its initial concentration in an alkaline environment

Dielectric Properties of Mechanically Activated Strontium Titanate Ceramics

In this study, microstructure evolution and dielectric properties of SrTiO3 ceramic have been investigated, whereby mechanical activation of SrTiO3 powders was used to modify the functional properties of ceramic materials. Microstructural SEM analysis of SrTiO3 ceramics showed that the increase in mechanical activation time results in less porous samples. Raman spectroscopy indicated changes in the broadening and asymmetry of the TO2 mode with a change in the time of mechanical activation. TO2 mode showed a Fano asymmetry due to its interaction with polarization fluctuations in polar micro-regions, which are a consequence of the presence of oxygen vacancies caused by activation. The maximum value of dielectric permittivity was observed in the sample activated for 10 min. Also, the sample activated for 10 min exhibits relatively low values of loss tangent, compared to the other mechanically activated samples, providing the best overall dielectric performance compared to other samples

Dielectric Properties of Mechanically Activated Strontium Titanate Ceramics

In this study, microstructure evolution and dielectric properties of SrTiO3 ceramic have been investigated, whereby mechanical activation of SrTiO3 powders was used to modify the functional properties of ceramic materials. Microstructural SEM analysis of SrTiO3 ceramics showed that the increase in mechanical activation time results in less porous samples. Raman spectroscopy indicated changes in the broadening and asymmetry of the TO2 mode with a change in the time of mechanical activation. TO2 mode showed a Fano asymmetry due to its interaction with polarization fluctuations in polar micro-regions, which are a consequence of the presence of oxygen vacancies caused by activation. The maximum value of dielectric permittivity was observed in the sample activated for 10 min. Also, the sample activated for 10 min exhibits relatively low values of loss tangent, compared to the other mechanically activated samples, providing the best overall dielectric performance compared to other samples