Perovskite oxide BaNi
0.5
Mn
0.25
Fe
0.25
O
3
was successfully synthesized using a sol–gel method. Structural refinement analysis has been performed to investigate the details of the crystalline ...structure which was found to be a rhombohedral system at room temperature with the space group
R
3
¯
C
. Crystallite size, lattice strain, density and porosity parameters were also calculated. The morphology and the elemental composition were analyzed by scanning electron microscopy and energy-dispersive X-ray spectroscopy. Raman scattering spectroscopy has been performed in order to study the vibrational modes and the various bond formations of the synthesized sample. The study of the magnetic properties shows a ferro-paramagnetic transition (FM–PM) at the curie temperature. The electrical behavior of this double perovskite was also studied using complex impedance spectroscopy. Electrical conduction follows Jonscher's power law, and the conduction mechanisms are identified. The variations of the real and imaginary parts of impedance according to the frequency and temperature show the presence of a relaxation phenomenon in the sample, and it is thus a potential candidate for various technological applications in microelectronics and energy storage.
Nanosize La0.8Ca0.2−xPbxFeO3 (x=0.00, 0.05, 0.10, 0.15 and 0.20) compounds were prepared by the sol–gel method using the citric acid route. The Rietveld refinement, from the X-ray diffraction ...patterns, revealed that the sample with x=0.00 presents a single phase that crystallizes in the orthorhombic symmetry with a Pnma space group. However, we found that the substitution of calcium (Ca) ion by lead (Pb) one does not change the principal phase but generates the formation of Fe3O4 and Ca2Fe2O5 secondary phases.
The electrical sensitivity of La0.8Ca0.2−xPbxFeO3 compounds to ethanol gas was investigated using broad band dielectric spectroscopy, at temperature up to 400°C. This study demonstrated that the Pb-doping can lead to the resistivity modification and sensitivity improvement of the of La0.8Ca0.2FeO3 sample. Among the investigated compounds, the La0.8Ca0.1Pb0.1FeO3 (x=0.10) sample showed the highest sensitivity to ethanol. The electrical response was studied in function of the quantity of ethanol presented in the measurement setup.
A great investment has been done in the last decades in the development of numerical and qualitative assessment methods to classify the ecological quality of water bodies. Yet, in spite of all ...attempts to avoid subjectivity, expert judgment is still used at numerous steps of the ecological classification and is considered by some authors as indispensible for management purposes. Thus, the aim of this study is to test the hypothesis that expert judgment, when done by the adequate experts (limnologists/river ecologist) with experience in the study area (i.e., natural conditions and expected communities), could be as good as quantitative indices and measures (i.e., result in the same classification), but quicker and with lower cost. For that we compared the classifications (on 13 aspects of rivers ecosystems) attributed by two experts to 20 sites (10 each) located in their study areas, with the classifications of ecological quality based on biological indices (for invertebrates and diatoms), hydromorphology and water chemistry, calculated by an independent team. Our results show that assessments made by experts and those calculated through indices (biological quality and hydromorphology) are globally very similar (RELATE test; Rho = 0.442; p < 0.001, 999 permutations). Most differences were of one class and experts tended to attribute a better condition than indices to the best quality sites but a worse condition to the worse quality sites. A Principal Components Analysis revealed that sites to which experts attributed a moderate quality had higher nitrate concentration and pH but were well oxygenated. The sites classified as poor and bad where those with stronger modifications in their habitats (given by the higher values of HMS). The difference between experts and indices is small but still represents 15% of sites, and includes both situations: the experts or the indices lead to the need of measures (i.e., classifications below class Good). Experts' evaluations on hydromorphological conditions of the channel and margins are also significantly correlated with the quality assessments made by the field team that has no experience in the study area (Rh0 = 0.518; p = 0.001; 999 permutation), indicating geographic independence in the expert judgment. We concluded that expert judgment could be used in the determination of streams and rivers ecological quality, saving money and time and helping to redirect monitoring funds to actual implementation of restoration measures. Yet, classification’ scoring methods may still be useful for a better targeting of restoration measures.
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•Many quantitative methods were developed for the ecological assessment of streams.•Yet, expert judgment is still widely used in the ecological assessment.•We compared expert judgment with quantitative biological and hydromorphological assessments.•Experts and indices classifications were very similar but there are small differences.•Expert judgment could reduce costs of ecological assessment.
Niobium oxides are presently very important materials for electronic device applications. In this work, a new approach, using the proteic sol–gel route, was used to prepare niobium pentoxide powders. ...This approach uses powdered coconut water (PCW) for the powders production. The obtained powders, with an amorphous structure, were heat-treated at different temperatures and their structural and morphological properties were studied and related to their dielectric properties. Dielectric measurements as a function of frequency (100 Hz–1 MHz) and temperature (200–400 K) were performed. The heat-treatment promotes the formation of crystalline structures, mainly Nb
2
O
5
with orthorhombic structure, which transforms to monoclinic with treatments at 1000 °C. The formation of CaNb
2
O
6
and NaNbO
3
crystallites, in the samples treated at 800 and 1000 °C is related to the PCW base composition. The samples revealed a quasi-independence of the dielectric constant with temperature and frequency, presenting a
ε
′
≈ 70 and tan ≈ 0.006, at room temperature and 100 kHz.
In this study, hybrid microwave sintering of Ca3Co4O9 thermoelectric materials was implemented for the first time. Thermoelectric properties of samples sintered in different conditions and in ...conventional electrical furnace, using the same temperatures and dwell times, were assessed and compared. Microwave processing was found to promote densification and grain texturing in Ca3Co4O9 bulk ceramics, leading to a significant increase of the electrical conductivity. Seebeck coefficient and thermal conductivity were essentially unaffected by the microstructural changes. Prolonged exposure to microwave radiation at 800°C led to partial phase decomposition and consequent formation of Ca3Co2O6 and Co3O4 impurities, with minor effect on the charge transport. Still, the significant presence of residual porosity suggests the need for further optimization of powder and microwave processing conditions.
In this study, nanocrystalline ZnO–SnO
2
mixed metal oxide powder was prepared by co-precipitation using Zn(CH
3
COO)
2
∙2H
2
O and SnCl
4
∙5H
2
O as precursor materials. The powder was characterized ...by X–ray diffraction, scanning electron microscopy, and Fourier transform infrared spectroscopy. Williamson–Hall method was used to evaluate the micro structural parameters of ZnO–SnO
2
such as crystallite sizes and lattice strain. The photoluminescence property of the sample was studied at different temperatures (10–300 K). Results showed that the emission intensity decreases with temperature increasing. The photocatalytic activity at the gas–solid interface was assessed by monitoring the degradation of nitrogen oxides, a major atmospheric pollutant. The results show that the nanocrystalline ZnO–SnO
2
mixed metal oxide powder exhibits higher and more stable photocatalytic activity against photocorrosion than ZnO alone.
Graphical abstract
The present paper explores of the lanthanum and calcium insertion effect on the physico-chemical properties of the Bi
0.8
(La
0.8
Ca
0.2
)
0.2
FeO
3
(LCBFO-8) Sol–Gel made multiferroic compound. The ...LCBFO-8 compound crystallized in a rhombohedral distorted structure with the
R3c
space group. The Morphological investigation confirmed the nanosize criteria of the examined nanoparticles with an average particle size less than 50 nm. Notably, the studied compound shows a colossal dielectric constant, low loss tangent tg(delta) values, an enhanced magnetization, and a reduction of the Curie transition temperature to 395 K, which confirms well the high utility of such compound for energy storage applications. At low and high temperatures, two dielectric relaxations have been detected in the frequency dependence curves of the dielectric constant and the Modulus imaginary part plots at low and high-temperature ranges. The symmetric and asymmetric dielectric parameters
α
and
β
have been collected from the adjustment of the
M
″ based on the Havriliak–Negami (H–N) formalism. According to their values, it can be concluded that the high-temperature relaxation is a Cole–Cole-type dielectric relaxation, while the Cole–Davidson model fits the high temperature well.
Aiming of self‐sustainable production, the search for biodegradable and biocompatible materials has brought with it the need to know the physicochemical and dielectric characteristics of ...polysaccharide‐based composite structures, which can be used as important and promising raw materials for biotechnology and electronic industries. Galactomannans are polysaccharides, extracted from seeds and microbiological sources, consisting of mannose and galactose. In this context, this work aimed to extract, purify and characterize by XRD, FTIR and impedance spectroscopy galactomannan obtained from seeds of Adenanthera pavonina L. The purification process was made with ethyl alcohol at concentrations of 70, 80 and 90 %. Polymeric films were prepared by solvent slow evaporation at low temperatures. XRD measurements revealed that Galactomannan from Adenanthera pavonina L., after purification, has a semi‐crystalline structure due to the identification of two peaks the first between 5.849° and 6.118° and the second between 20.011° and 20.247°. FTIR spectra showed the functional groups associated with monosaccharides of the galactomannan from Adenanthera pavonina L. seeds, as well as the typical polysaccharide bands and peaks, confirmed by literature data. The impedance results give an increment on the state‐of‐the‐art of this biomaterial by showing the existence of dielectric relaxations, independent of the degree of purification, using the dielectric modulus formalism. The permittivity analysis reveals the presence of water in the structure of the film, whose dipoles contribute to the relatively high value of the dielectric constant. From the results obtained, it can be concluded that purified galactomannan has the potential for possible applications in the electronics industry as a green and eco‐friendly dielectric material.
