Ferrites have been widely studied for their use in the biomedical area, mostly due to their magnetic properties, which gives them the potential to be used in diagnostics, drug delivery, and in ...treatment with magnetic hyperthermia, for example. In this work, KFeO
particles were synthesized with a proteic sol-gel method using powdered coconut water as a precursor; this method is based on the principles of green chemistry. To improve its properties, the base powder obtained was subjected to multiple heat treatments at temperatures between 350 and 1300 °C. The samples obtained underwent structural, morphological, biocompatibility, and magnetic characterization. The results show that upon raising the heat treatment temperature, not only is the wanted phase detected, but also the secondary phases. To overcome these secondary phases, several different heat treatments were carried out. Using scanning electron microscopy, grains in the micrometric range were observed. Saturation magnetizations between 15.5 and 24.1 emu/g were observed for the samples containing KFeO
with an applied field of 50 kOe at 300 K. From cellular compatibility (cytotoxicity) assays, for concentrations up to 5 mg/mL, only the samples treated at 350 °C were cytotoxic. However, the samples containing KFeO
, while being biocompatible, had low specific absorption rates (1.55-5.76 W/g).
The hexaferrite Ba1−xSrxFe12O19 compounds with x = 0, 0.5 and 1 were synthesized by the autocombustion method. X-ray diffraction (XRD), Raman spectroscopy and transmission electron microscopy (TEM) ...were used for structural and morphological studies.
Galactomannans are polysaccharides obtained from legume seed extraction. They present a chemical structure consisting of D-mannose chains linked by glycosidic bonds and galactose branches. The main ...focus lies in their use as thickeners in the food industry, aimed at improving the dielectric properties of food during heating processes within the radiofrequency and microwave ranges. In this work, the prepared galactomannan samples were electrically analyzed through impedance spectroscopy, which is a powerful physical technique. From the experimental measurements, the dielectric permittivity and loss tangent of the galactomannan solutions were analyzed and the electrical modulus formalism was used to study the dielectric relaxations. Crude galactomannans exhibited higher values of permittivity, conductivity, and losses compared to purified galactomannans. Increasing ethanol concentration in galactomannan purification causes an increase in the permittivity and conductivity of galactomannan solutions. In a 1% solution, at 1 kHz, the permittivity increased from 378.56 to 538.09, while in the 2% solution, this increase was from 656.22 to 1103.24. Regarding the conductivity, at the same frequency, the increase was from 1.6 × 10−3 to 3.3 × 10−3 Ω−1m−1 and from 2.9 × 10−3 to 5.5 × 10−3 Ω−1m−1, respectively. The rise of the ethanol concentration in galactomannan purification led to a decrease in the relaxation time, from 448.56 to 159.15 μs and from 224.81 to 89.50 μs in the solution with 1 and 2%, respectively. The results suggest that galactomannan from Adenanthera pavonina L. has potential for use in the food industry.
Double perovskite oxide with general formula LaBa
0.5
Ag
0.5
FeMnO
6
(LBAFMO) has been prepared by the sol–gel-based Pechini method. To study and compare its electrical properties, impedance ...spectroscopy was carried out in the temperature ranging from 200 K to 340 K and frequency range from 100 Hz to 1 MHz. At room temperature, x-ray diffraction analysis revealed the compound to be single phase and to crystallize in the cubic system in space group
Pm-3m
. The imaginary part of the impedance (
Z
″) as a function of frequency indicated non-Debye model relaxation. Impedance data in a Nyquist plot (
Z
″ versus
Z
′) was used to determine an equivalent circuit. The complex impedance of LBAFMO revealed the presence of grain and grain-boundary contributions. The alternating-current (AC) conductivity as a function of frequency was interpreted by applying Jonscher’s law to determine the activation energy. Modulus analysis revealed the occurrence of a relaxation process supplemented by a conduction phenomenon.
The double perovskite structure is interesting for many researches in various fields of physics and their technological applications. The LaPbFeTiO
6
compound is a very important for many ...technologies because it has dielectric and electrical properties. It has made an attractive semiconductor material for the electronic field, such as the realization of filters or capacitors. In this work, LaPbFeTiO
6
was prepared by the sol–gel method. The structural, morphological, chemical and electrical properties of this sample were studied using different techniques. X-ray diffraction analysis revealed that the sample crystallized in the rhombohedral system with space group R
3
¯
C. The chemical composition of the synthesized compound and the morphology of grain size were confirmed by energy dispersion spectroscopy analysis and scanning electron microscopy. The electrical conductivity and dielectric characterizations were studied as a function of frequency and temperature (200–380 K) by impedance spectroscopy. Indeed, the dielectric constant increases with increasing temperature. The AC conductivity obeys the Jonscher power law. The activation energy obtained from the complex impedance and the conductivity are close. The frequency dependence of the electrical impedance shows the existence of a relaxation phenomenon.
Abstract
Er
3+
and Er
3+
/Yb
3+
melilite-based SrLaAl
3
O
7
(SLA) phosphors were synthesized by a facile Pechine method. The differences in emission intensities of
4
I
13/2
→
4
I
15/2
transition in ...NIR region when excited with Ar
+
and 980 nm lasers were explained in terms of energy transfer mechanisms. Temperature and power dependence of upconversion bands in the visible region centered at 528, 548 and 660 nm pertaining to
2
H
11/2
,
4
S
3/2
and
4
F
9/2
→
4
I
15/2
transitions were investigated. Fluorescence intensity ratio (FIR) technique was used to explore temperature sensing behaviour of the thermally coupled levels
2
H
11/2
/
4
S
3/2
of Er
3+
ions in the phosphors within the temperature range 14–300 K and the results were extrapolated up to 600 K. Anomalous intensity trend observed in Er
3+
doped SLA phosphor was discussed using energy level structure. Cytotoxicity of phosphors has been evaluated using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay in Bluegill sunfish cells (BF-2). The non-cytotoxic nature and high sensitivity of the present phosphors pay a way for their use
in vitro
studies and provide potential interest as a thermo graphic phosphor at the contact of biological products.
Na1.5MnII3MnIII0.5(AsO4)3 and Na1.5MnII3FeIII0.5(AsO4)3 compounds were synthesized via a high-temperature solid-state combustion reaction. The obtained samples were submitted to structural, ...morphological, and electrical characterizations. X-ray diffraction measurements revealed that both compounds crystallize in the monoclinic system with the space group P21/c. The lattice parameters were determined to be a = 6.78344 Å, b = 12.93830 Å, c = 11.22825 Å, and β = 98.5374° for Na1.5MnII3MnIII0.5(AsO4)3, and a = 6.76723 Å, b = 12.9864 Å, c = 11.256 Å, and β = 98.8636° for Na1.5Mn2+3Fe3+0.5(AsO4)3. The structures consist of octahedral MnII and MnIII or FeIII ions connected by sharing edges, forming infinite chains. These chains are further connected by AsO4 tetrahedra, resulting in a three-dimensional anionic framework with tunnels parallel to the a-direction and cavities according to the c-direction. The structural models were validated using bond valence and charge distribution analyses. In addition to the structural characterization, the electric results depended on the crystal structures, indicating the potential of the studied materials for being used in several applications.
Time evolution of SBF by electric characterization Freire, F. C. M.; Weinand, W. R.; Andrade, T. M. ...
Applied physics. A, Materials science & processing,
06/2023, Letnik:
129, Številka:
6
Journal Article
Recenzirano
Simulated Body Fluid (SBF) for biomedical research, containing several types of ions, is dielectrically characterized by the impedance spectroscopy technique. The real and imaginary parts of the ...electrical admittance of the SBF are determined by several concentrations of ions dissolved in it. The time dependence of the volume dielectric parameters of the SBF with the frequency indicates an exponential behavior and it is practically independent of the hydroxyapatite (HAp) immersed in it. On the other hand, the surface dielectric parameters show significant differences when the hydroxyapatite was present. Qualitatively, related to chemical kinetic and using the integrated rate law, it was possible to find the half-life time.
We report an investigation of the structural, morphological, the ac-dc electrical, magnetic, and Mössbauer spectroscopy properties of 20MnFe
2
O
4
-80SiO
2
nanocomposite prepared using a one-step and ...facile auto-combustion approach. XRD pattern shows the formation of MnFe
2
O
4
nanocrystallite without any crystallization of the SiO
2
phase. However, the presence of a secondary phase of the nanosized α-Fe
2
O
3
particles was also detected. The morphological analysis showed aggregation of polygonal magnetic nano-crystallites dispersed non-uniformly in a silica matrix. The dc electrical measurements performed on a wide range of temperatures from 120 to 400 K showed the semiconducting nature of the nanocomposite. The temperature dependence of dc conductivity could be perfectly fitted to the nearest neighborhood hopping model with activation energy,
ΔE
NNH
, of 0.45 eV. The Nyquist plots demonstrated a nonmonotonous thermally activated trend and non-Debye relaxation behavior. An equivalent circuit was successfully fitted to the complex impedance spectra. The variation of both grain and grain boundary conductivities as a function of temperature exhibited three distinct regions, semiconducting-metallic-semiconducting with different activation energies over the measured temperature window. The provided description of such behavior is further advocated by the ac conductivity and dielectric modulus studies. VSM measurements revealed that the nanocomposite magnetic behavior deviates from the ideal non-interacting superparamagnetic picture, due to the presence of α-Fe
2
O
3
nanocrystalline impurities and relatively intensive exchange interactions between ions. Mössbauer spectra showed the presence of Fe
3+
ions with sixfold environment and also confirmed the existence of a sextet related to α-Fe
2
O
3
with a quantity of about 20% out of magnetic components. Fe
3+
superparamagnetic doublets were also found within the fitting procedure.
The effect of 5% magnesium doping on the structural, magnetic and gas sensing properties of La
0.8
Ca
0.1
Pb
0.1
Fe
0.95
Mg
0.05
O
3
(LCPFMO) has been investigated. The nanosize compound was prepared ...by the Sol–Gel method, using the citric acid route. The Structural study confirms that this compound crystallizes in the orthorhombic structure with the
Pbnm
space group. From the magnetic measurements, we were able to show that the effect of the Mg doping is to increase the saturated magnetization and to decrease the Ferromagnetic–Paramagnetic magnetic phase transition temperature (T
C
). A theoretical modulation was derived in order to confirm the domination of the ferromagnetic contribution over the Antiferromagnetic one. The AC-conductivity dependence on both temperature and frequency was studied; the study confirmed the presence of two behaviors; at high-temperature region, it was found to be only temperature dependent, while at low temperatures, it depends on both frequency and temperature parameters. At low temperature, the conduction mechanism is studied according to the NSPT model, where all parameters were discussed. The electrical Sensitivity (
S
) of the prepared sample to different ethanol gas concentration was investigated, using a broadband dielectric spectroscopy. It was found that 5% of magnesium insertion leads to an improvement in the sensitivity of the LCPFMO sample. This sensitivity was found to be ethanol amount dependent.
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