Comprehensive characterization and optoelectronic significance of Ho3+ and Cr3+ Co-doped ZnAl2O4 spinels.

The spinels ZnAl1.99-xHoxCr0.01O4 (with x = 0 and 0.001) were synthesized using a solid-state method, and various techniques were employed for their characterization. X-ray diffraction (XRD) analysis confirmed a cubic spinel structure with the Fd3̄m space group for both spinels. The morphology and homogeneity of the chemical composition were determined using scanning electron microscopy (SEM) and energy dispersive X-ray analysis. Raman and infrared vibrational spectroscopy techniques were also employed for analysis. The optical band gap (Eg) was determined from UV/vis absorption spectra, and the direct transition behavior was confirmed by Tauc's law. The observed large disorder and defect concentration are attributed to the presence of Cr3+ and Ho3+ ions, explaining this behavior. The electron paramagnetic resonance (EPR) measurement presented different types of traps. Room temperature absorption spectra exhibited multiple peaks corresponding to the 3d-3d and 4f-4f transitions of Cr3+ and Ho3+ ions. The results obtained validate the significance of our compounds in optoelectronic device applications.

Optical characterization and defect-induced behavior in ZnAl1.999Ho0.001O4 spinel: Unraveling novel insights into structure, morphology, and spectroscopic features.

The ZnAl1.999Ho0.001O4 phosphor, prepared by the solid-state method, crystallizes in the cubic spinel structure. Morphology and chemical composition homogeneity were determined via Energy Dispersive X-ray and SEM analysis. The (Eg) optical band gap was evaluated from the UV/vis absorption spectrum, confirming direct transition behavior according to Tauc's law. The Urbach energy (Eu) in the ZnAl1.999Ho0.001O4 spinel was higher than that in the ZnAl2O4 spinel, indicating increased disorder and a higher concentration of defects due to Ho3+ ions. The penetration depth (δ(λ)), optical extinction (k(λ)), and refractive index (n(λ)) were assessed across wavelengths (λ). The room temperature absorption spectrum revealed several peaks corresponding to the 4f-4f transitions of Ho3+ ions.

Synthesis, characterization, and sensitivity tests of La0.8Ba0.1Bi0.1FeO3 nanoparticles towards a few parts-per-billion of acetone gas.

In the present paper, the La0.8Ba0.1Bi0.1FeO3 powders were synthesized via the auto-combustion method. The optical, the positron annihilation spectroscopy and the gas sensing properties of our sample were investigated simultaneously. FTIR spectrum revealed the antisymmetric deformation vibrations of the Fe-O and Fe-O-Fe bonds inside the octahedron FeO6. The optical bandgap (Egap) of the La0.8Ba0.1Bi0.1FeO3 compound was found to be equal to 2.23 eV. We confirmed by the positron annihilation studies, the existence of open volume defects and vacancy sized defects, at the grain/interfaces between vacancy clusters and grains at the interfaces intersection (triple-lines). Notably, the La0.8Ba0.1Bi0.1FeO3 perovskite exhibits an excellent response toward acetone gas, with ultra-fast response and recovery times to some parts-per-billion (ppb) of this tested gas.

Study of the effect of the substitution of Fe by Ti on the microstructure and the physical properties of the perovskite system La0.67Ca0.2Ba0.13Fe1-xTixO3 with x = 0 and 0.03 at low temperatures.

La0.67Ca0.2Ba0.13Fe1-xTixO3 samples (x = 0 and 0.03) were synthesized by the auto-combustion method. Analysis of XRD diffractograms revealed that these compounds crystallize in the cubic system with the space group Pm3̄m. The dielectric properties have been studied in the 102-106 frequency range and the 120-280 K temperature range. Analysis of AC conductivity shows that the conduction mechanisms are of polaronic origin and that they are co-dominated by the NSPT and OLPT models. The monotonic increase in conductivity with increasing temperature results from the reduction of defect centers and the increase in charge carrier mobility. Such variation is consistent with impedance variation at different frequencies and temperatures indicating semiconductor behavior. Nyquist diagrams are characterized by the appearance of semi-circular arcs. These spectra are modeled in terms of equivalent electrical circuits confirming the contribution of grains (Rg//CPEg) and grain boundaries (Rgb//CPEgb). The dielectric analysis showed an evolution of the dielectric constant in accordance with Koop's theory and the phenomenological model of Maxwell-Wagner. The low conductivity and the high values of the real permittivity at low frequency make our compounds potential candidates for energy storage and applications for electronic devices and microwaves.

Electronic, electrical and thermoelectric properties of Ba0.95Ca0.05Ti0.95Y0.05O2.975 compound: Experimental study and DFT-mBJ calculation.

This article explores the impact of co-doping BaTiO3 ceramics with Ca2+ and Y3+ using solid-state reactions to improve its dielectric constant and decrease losses. The oxide BCTYO (Ba0.95Ca0.05Ti0.95Y0.05O2.975) exhibits a tetragonal crystal structure, characterized by a space group of P4mm. By examining the behavior of the doped BaTiO3 sample and performing simulations, researchers can better understand the underlying mechanisms and optimize material properties for specific applications. DFT study shows a semiconductor behavior with an indirect gap (Eg = 2.5 eV). The partial DOS proves that the hybridization between the orbitals Ti 3d, Y 3d, and O 2p is responsible for the band gap and the hopping processes. The analysis of conductivity curves provides evidence for the semiconductor characteristics of the material under investigation. By determining the activation energy (Ea) through analyzing Ln(fmax) and conductivity as a function of 1000/T, the interconnection between conduction and relaxation phenomena is demonstrated. The study of the real part of the dielectric permittivity (ε') shows a transition at Tc = 380 K. The obtained results are promising and indicate that the studied material has the potential for various electronic applications (energy storage and diode fabrication …). Moreover, the thermal, electrical, and thermoelectric characteristics were examined utilizing the semi-classical Boltzmann theory. The findings revealed an intriguing result, suggesting that Ba0.95Ca0.05Ti0.95Y0.05O2.975 holds promise as a potential candidate for application in thermoelectric devices.

Study of the structural, electrical, dielectric properties and transport mechanisms of Cu0.5Fe2.5O4 ferrite nanoparticles for energy storage, photocatalytic and microelectronic applications.

Cu0.5Fe2.5O4 nanoparticles were synthesized by the self-combustion method whose XRD and FTIR analyzes confirm the formation of the desired spinel phase. The thermal evolution of conduction shows a semiconductor behaviour explained by a polaronic transport mechanism governed by the Non-overlapping Small Polaron Tunnelling (NSPT) model. DC conductivity and hopping frequency are positively correlated. The scaling of the conductivity leads to a single universal curve where the scaling parameter α has positive values, which testifies to the presence of Coulomb interactions between the mobile particles. Conduction and relaxation processes are positively correlated by similar activation energies. Nyquist diagrams are characterized by semicircular arcs perfectly modeled by an equivalent electrical circuit (R//C//CPE) indicating the contribution of the grains. The dielectric behaviour shows a strong predominance of conduction by the phenomenological theory of Maxwell-Wagner. The low values of electrical conductivity and dielectric loss and the high value of permittivity, make our compound a promising candidate for energy storage, photocatalytic and microelectronic applications.

Effect of frequency on the classical and relaxor ferroelectric behavior of substituted titanate Ba0.7Er0.16Ca0.05Ti0.91Sn0.09O3.

In the present work, we synthesized the perovskite Ba0.70Er0.16Ca0.05Ti0.91Sn0.09O3 compound (BECTSO) by a solid-state reaction and sintering at 1200 °C. The effects of doping on the structural, electrical, dielectric, and ferroelectric characteristics of the material are examined in this work. X-ray powder diffraction analysis shows that BECTSO crystallizes in a tetragonal structure with space group P4mm. A detailed study of the dielectric relaxation of the BECTSO compound has been reported for the first time. Classical low-frequency ferroelectric and high-frequency relaxor ferroelectric behaviors have been studied. The study of the real part of the permittivity (ε') as a function of temperature demonstrated a high dielectric constant and identified a phase transition from the ferroelectric phase to the paraelectric phase at Tc = 360 K. The analysis of conductivity curves shows two behaviors: semiconductor behavior for f < 106 Hz and metallic behavior for f >106 Hz. The relaxation phenomenon is dominated by the short-range motion of the charge carriers. The BECTSO sample could be considered as a potential lead-free material for next-generation non-volatile memory devices and wide-temperature range capacitor applications.

A far-red-emitting ZnAl1.95Cr0.05O4 phosphor for plant growth LED applications.

ZnAl2-xCrxO4 (x = 0 and 0.05) samples were synthesized via a high-temperature solid-state reaction method. The structure, photoluminescence properties, EPR measurements, thermal stability, and chromaticity diagram of the far-red phosphor ZnAl1.95Cr0.05O4 were investigated. These measurements have enabled us to study the Cr3+ transitions and the site symmetry of Cr3+ in the ZnAl2O4 host lattice and examine the suitability of ZnAl1.95Cr0.05O4 for plant growth application. According to optical and EPR measurements, Cr3+ ions substitute Al3+ ions with D3d symmetry in the ZnAl2O4 host. PLE measurement indicates that upon excitation at 390 nm and 530 nm, the far-red phosphor ZnAl1.95Cr0.05O4 exhibited bright far-red emission around 687 nm. Photoluminescence phenomena show a sharp R line origin from the sublevels of the 2Eg(2G) → 4A2(4F) transition in Cr3+ ions. The 2Eg level was split into 2Eg (Eg) and 2Eg (2Ag) levels in the distorted crystal field environment, and the sharp R line in the ZnAl2O4 matrix was split into R1 and R2 lines. In this paper, the temperature-dependent luminescence characteristics of ZnAl1.95Cr0.05O4 have been investigated. As the temperature increased from 300 K to 440 K, a slight decrease in the intensity of the R1 and R2 lines was observed under excitation at 390 nm. The experimental results show that the ZnAl1.95Cr0.05O4 phosphors exhibit a nearly zero-thermal-quenching behavior. The CIE chromaticity coordinates of the ZnAl1.95Cr0.05O4 phosphor were located at the boundary of the chromaticity diagram, signifying that the phosphors possessed high color purity. The emissions of the ZnAl1.95Cr0.05O4 phosphor match well with the PFR absorption of phytochromes in plants. The investigation indicates that ZnAl1.95Cr0.05O4 is a potential far-red phosphor matching ultraviolet (UV) LED chips for plant growth applications.

Study of physical properties of the Li0.5MgFe1.5O3.5 ferrite nanoparticles.

In the present research study, the structural, optical, magnetic, electrical and dielectrical properties of the spinel ferrite Li0.5MgFe1.5O3.5, synthesized using a sol-gel auto-combustion method were studied. X-ray diffraction, Fourier transform infrared spectroscopy (FTIR), and Raman spectroscopy revealed that this sample crystallizes in a cubic spinel structure with space group Fd3̄m. Moreover, the optical investigation by UV-visible spectroscopy has revealed that the band gap for our sample is (E g = 2.87 eV), which shows that our compound is a potential candidate for optoelectronic applications. The values of the remanent magnetization M r = 0.13 emu g-1, of the coercive field H C = 4.65 Oe deduced from the hysteresis loop, are very low, suggesting the superparamagnetic behavior of our sample. Additionally, the temperature coefficient of resistance (TCR) is -19% affirmed that Li0.5MgFe1.5O3.5 ferrite is a good candidate for detecting infrared radiation and infrared bolometric applications. Indeed, the activation energies were calculated from the imaginary part of the impedance, the electrical conductivity, and the imaginary part of the modulus, thus demonstrating that the charge carriers involved in the processes of conduction and relaxation are the same.

Summerfield scaling model and electrical conductivity study for understanding transport mechanisms of a Cr3+ substituted ZnAl2O4 ceramic.

Solid-state and sol-gel procedures were used to prepare ZnAl1.95Cr0.05O4 nanocrystal spinels. From the results obtained by X-ray diffraction (XRD) and transmission electron microscopy (TEM), it can be concluded that the samples prepared by sol-gel synthesis are better crystallized than the ones resulting from the solid-state method. Studies by spectroscopy of impedance were done in function of frequency (40-107 Hz) and temperature (540-680 K) in the sample prepared by sol-gel synthesis. The electrical conductivity spectra obey Jonscher's law and two models were observed studying the variation of the exponent 's' as a function of temperature, Correlated Barrier Hopping (CBH) and Non-overlapping Small Polaron Tunnelling (NSPT). The predominant conduction mechanism is bipolaron hopping. The scaling behavior of conductivity spectra was checked by Summerfield scaling laws. The time-temperature superposition principle (TTSP) points to a common transport mechanism working for the low and middle frequency ranges. The scaling mechanism fails in the high-frequency ranges suggesting that conduction dynamics, and the usual hopping distance of mobile species, have changed. The values obtained for the activation energy from the hopping frequency, conductivity σ dc, bulk resistance R gb, and relaxation (f max), in the temperature range of 540-680 K, are very close. A higher and negative temperature coefficient of resistivity (TCR coefficient) equal to -2.7% K-1 is found at 560 K. This result shows that our compound is suitable for uncooled infrared bolometric applications and infrared detectors.

Investigation of temperature and frequency dependence of the dielectric properties of multiferroic (La0.8Ca0.2)0.4Bi0.6FeO3 nanoparticles for energy storage application.

In this work we synthesized the multifunctional (La0.8Ca0.2)0.4Bi0.6FeO3 material using a sol-gel process. Structural and morphologic investigations reveal a Pnma perovskite structure at room temperature with spherical and polygonal nanoparticles. A detailed study of the temperature dependence of the dielectric and electrical properties of the studied material proves a typical FE-PE transition with a colossal value of real permittivity at 350 K that allows the use of this material in energy storage devices. Thus, the investigation of the frequency dependence of the ac conductivity proves a correlated barrier hopping (CBH) conduction mechanism to be dominant in the temperature ranges of 150-170 K; the two observed Jonscher's power law exponents, s 1 and s 2 between 180 K and 270 K correspond to the observed dispersions in the ac conductivity spectra in this temperature region, unlike in the temperature range of 250-320 K, the small polaron tunnel (NSPT) was considered the appropriate conduction model.

Electrical conductivity and dielectric properties of Sr doped M-type barium hexaferrite BaFe12O19.

The hexaferrite Ba1-x Sr x Fe12O19 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.

Structural, morphological, Raman, dielectric and electrical properties of La1-2x Ba x Bi x FeO3 (0.00 ≤ x ≤ 0.20) compounds.

La1-2x Ba x Bi x FeO3 (0.00 ≤ x ≤ 0.20) nanoparticles were prepared by the auto-combustion method using glycine as a combustion fuel. X-ray diffractometry (XRD) measurements confirmed the orthorhombic structure of the synthesized compounds with the Pnma space group as a principal majority phase and showed the presence of a very minor secondary phase when x > 0.1. The nanosize criterion of the prepared compounds was confirmed from the crystallite size values calculated using the Williamson-Hall formalism. The relaxation process has been studied by the frequency dependence of the imaginary parts of impedance and modulus (Z'' and M'') which satisfied the Arrhenius law. Nyquist plots allowed us to obtain an adequate equivalent circuit involving the grains and grain boundary contributions. The activation energies calculated from Z'', M'' and the resistance of both contributions deduced from the Nyquist plots are found to be very similar. The conduction mechanism has been analyzed using the temperature dependence of the exponent Jonscher's power law parameter which confirms the NSPT conduction mechanism type for all compounds with an enhancement of the binding energy of the charge carrier (W H) with the substitution.

Study of the influence of 2.5% Mg2+ insertion in the B-site of La0.8Ca0.1Pb0.1FeO3 on its structural, electrical and dielectric properties.

This work involves the synthesis and study of physical properties of the La0.8Ca0.1Pb0.1Fe0.975Mg0.025O3 compound, which has been characterized by various experimental techniques, such as X-ray diffraction, SEM and complex impedance spectroscopy. The structural study showed that the La0.8Ca0.1Pb0.1Fe0.975Mg0.025O3 compound crystallized in the orthorhombic structure with the Pnma space group. The particle size and the surface morphology of this compound have been analysed using SEM. The particle size was found to be around 120 nm and we confirmed that one particle contains more than one crystallite. Importantly, the studied compound presented a giant dielectric permittivity (ε' of around 9 × 104 at high temperature and low frequencies). An equivalent electric circuit has been deduced from the Nyquist plots of the complex impedance parts (Z'' vs. Z') to correctly describe the electrical behavior of the La0.8Ca0.1Pb0.1Fe0.975Mg0.025O3 compound. The chosen circuit consists of two cells mounted in series corresponding to the grain and grain boundary contributions. The electrode contribution has been detected from the frequency dependence of the imaginary part of modulus where the activation energy of each constitution has been calculated. The relaxation process and the electrical conductivity are attributed to the same type of charge carriers characterized by similar values of the activation energy determined from loss factor tangent (tg(δ)), the imaginary part of the permittivity and the modulus spectrum.

Effect of Bi-substitution into the A-site of multiferroic La0.8Ca0.2FeO3 on structural, electrical and dielectric properties.

(La0.8Ca0.2)1-x Bi x FeO3 (x = 0.00, 0.05, 0.10, 0.15 and 0.20) (LCBFO) multiferroic compounds have been prepared by the sol-gel method and calcined at 800 °C. X-ray diffraction results have shown that all samples crystallise in the orthorhombic structure with the Pnma space group. Electrical and dielectric characterizations of the synthesized materials have been performed using complex impedance spectroscopy techniques in the frequency range from 100 Hz to 1 MHz and in a temperature range from 170 to 300 K. The ac-conductivity spectra have been analysed using Jonscher's power law σ(ω) = σ dc + Aω s , where the power law exponent (s) increases with the temperature. The imaginary part of the complex impedance (Z'') was found to be frequency dependent and shows relaxation peaks that move towards higher frequencies with the increase of the temperature. The relaxation activation energy deduced from the Z'' vs. frequency plots was similar to the conduction activation energy obtained from the conductivity. Hence, the relaxation process and the conduction mechanism may be attributed to the same type of charge carriers. The Nyquist plots (Z'' vs. Z') at different temperatures revealed the appearance of two semi-circular arcs corresponding to grain and grain boundary contributions.

Structural study and large magnetocaloric entropy change at room temperature of La1-x □ x MnO3 compounds.

In this study, our central focus is to investigate the magnetocaloric characteristics of a La1-x □ x MnO3 (x = 0.1, 0.2 and 0.3) series prepared by a sol-gel technique published in Prog. Mater. Sci., 93, 2018, 112-232. The crystallographic study revealed that our compounds crystallize in a rhombohedral structure with R3̄c. Ferromagnetic (FM) and paramagnetic (PM) characters were detected from the variation in magnetization as a function of magnetic fields at different temperatures. The second order transition was verified from the Arrott plots (M 2 vs. (µ 0 H/M)), where the slopes have a positive value. In order to verify the second order, we traced the variation of magnetization vs. temperature at different magnetic fields for x = 0.2. This revealed a ferromagnetic (FM)-paramagnetic (PM) transition when temperature increases. Relying on the indirect method while using the Maxwell formula, we determined the variation in the entropy (-ΔS M) as a function of temperature for different magnetic fields for the three samples. We note that all the studied systems stand as good candidates for magnetic refrigeration with relative cooling power (RCP) values of around 131.4, 83.38 and 57.26 J kg-1 with magnetic fields below 2 T, respectively. Subsequently, the magnetocaloric effect was investigated by a phenomenological model for x = 0.2. The extracted data confirm that this phenomenological model is appropriate for the prediction of magnetocaloric properties. The study also demonstrated that this La0.8□0.2MnO3 system exhibits a universal behaviour.

Structural, optical and dielectric properties of Cu1.5Mn1.5O4 spinel nanoparticles.

In this study, a Cu1.5Mn1.5O4 spinel was successfully synthesized by a sol-gel method at 500 °C for 5 h and characterized by different techniques. X-ray diffraction (XRD), Fourier transformation infrared (FTIR) spectroscopy and Raman spectroscopic analyses confirmed the formation of a spinel cubic structure with the Fd3̄m space group. The SEM proves that the grain size of our compound is of the order of 48 nm. Crystallite sizes determined from three estimates are closer to the grain size obtained from the SEM, indicating the single domain nature of the sample. The optical properties of UV-visible spectroscopy for our sample showed that the gap value is equal to 3.82 eV, making our compound a good candidate for optoelectronic applications. For electrical properties, impedance spectroscopy was performed at a frequency range of 40 ≤ frequency ≤ 106 Hz. This suggested hoping conduction due to three theoretical models. The latter can be attributed to the correlated barrier hopping (CBH) model in region I, overlapping large polaron tunneling (OLPT) in region II and non-overlapping small polaron tunneling (NSPT) mechanism in region III. One dielectric relaxation is detected from the dielectric impedance and modulus, attributed to grain contributions. This behavior was confirmed by both Nyquist and Argand's plots of dielectric impedance at different measuring temperatures.

Development and characterization of iron-pectin beads as a novel system for iron delivery to intestinal cells.

Iron deficiency is the most common nutritional deficit worldwide. The goal of this work was to obtain iron-pectin beads by ionic gelation and evaluate their physiological behavior to support their potential application in the food industry. The beads were firstly analyzed by scanning electronic microscopy, and then physical-chemically characterized by performing swelling, thermogravimetric, porosimetry, Mössbauer spectroscopy and X-ray fluorescence analyses, as well as by determining the particle size. Then, physiological assays were carried out by exposing the beads to simulated gastric and intestinal environments, and determining the iron absorption and transepithelial transport into Caco-2/TC7 cells. Iron-pectin beads were spherical (diameter 1-2 mm), with high density (1.29 g/mL) and porosity (93.28%) at low pressure, indicating their high permeability even when exposed to low pressure. Swelling in simulated intestinal medium (pH 8) was higher than in simulated gastric medium. The source of iron [FeSO4 (control) or iron-pectin beads] did not have any significant effect on the mineral absorption. Regarding transport, the iron added to the apical pole of Caco-2/TC7 monolayers was recovered in the basal compartment, and this was proportional with the exposure time. After 4 h of incubation, the transport of iron arising from the beads was significantly higher than that of the iron from the control (FeSO4). For this reason, iron-pectin beads appear as an interesting system to overcome the low efficiency of iron transport, being a potential strategy to enrich food products with iron, without altering the sensory properties.

Ball milling of an equiatomic sigma--feV alloy in vacuum.

A coarse-grained tetragonal sigma phase Fe47.4V52.6 at% alloy was ground in vacuum in a vibratory mill. The sigma phase transforms into a bcc alpha phase. A concomitant partial amorphization of the bcc phase occurs. The near-equiatomic FeV alloys are concluded to behave in the same way as the related FeCr alloys when they are ball-milled in vacuum in similar milling conditions. In the stationary state of milling, about half of the iron atoms are contained in an amorphous phase both for sigma-FeCr and for sigma-FeV.

Debye temperature of disordered bcc-Fe-Cr alloys.

The Debye temperature, Θ(D), of Fe(100-x)Cr(x) disordered alloys with 0 ≤ x ≤ 99.9 was determined from the temperature dependence of the centre shift of (57)Fe Mössbauer spectra recorded in the temperature range of 60-300 K. Its compositional dependence shows an interesting non-monotonous behaviour. For 0