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.

Optical and theoretical study of NaCr(P2O7): a look through the Neuhauser model and Racah theory.

A sample of NaCr(P2O7) was synthesized using the solid-state reaction method. X-ray diffraction and Rietveld refinement confirmed the formation of a monoclinic structure with the P21/a space group. Scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) analysis identified the morphology and homogeneity of the chemical composition. The optical absorption spectrum revealed a direct optical band gap of 2.9 eV and an Urbach energy of 0.44 eV. Notably, the absorption spectrum showed an interference dip on the lowest energy band 4T2g(4F), attributed to spin-orbit coupling between states 2Eg(2G) and 4T2g(4F). This phenomenon was analyzed using the Neuhauser model based on coupled potential energy surfaces. From this analysis, the electronic structure of Cr3+ (3d3) ions in the NaCr(P2O7) sample was determined, enabling a reliable calculation of Racah and crystal-field parameters. The results showed good agreement between experimental and theoretical energy levels. The study demonstrates the impact of spin-orbit interactions using the coupled potential energy surface model.

Structural, morphological, magnetic and electrical properties of La0.8Na0.2-x □ x MnO3 (0.00 ≤ x ≤ 0.15) manganites.

La0.8Na0.2-x □ x MnO3 (0.00 ≤ x ≤ 0.15) manganites were successfully synthesized using the solid-state route. X-ray diffraction was performed to check the samples' purity and phase structure. Scanning electron microscopy analysis reveals a decrease in the average grain size with an increase in the deficiency amount. Analysis of the temperature dependence of magnetization proved the presence of ferromagnetic-paramagnetic transition in all the studied samples. The magnetization derivative (d2 M/dT 2) curves demonstrated a decrease in the transition temperature with an increase in the deficiency amount. Such experimental observations can be correlated with bandwidth evolution, which affected double-exchange interactions. It can be equally accounted for by the average grain size decrease. In this regard, the experimental measurements of effective paramagnetic moments revealed the existence of ferromagnetic correlations within the paramagnetic phase. Notably, different electrical findings were addressed. Indeed, the frequency dependence of electrical conductivity displayed the coexistence of two frequency slopes reflecting the presence of Jonscher's double power law for all the studied samples. A significant decrease in conductivity values was observed when the deficiency amount increased. This experimental observation could be assigned to the decrease in the grain size (conductor region). Such assumption was confirmed by the evolution of the grain boundary resistance with deficiency level. Indeed, a significant mounting in the grain boundary resistance values was obtained presenting the increase of the resistive region for x = 0.15. It is worth noting that the Curie temperature for the x = 0.10 sample was found to be close to room temperature (T C = 297 K). These findings make the La0.8Na0.1□0.1MnO3 compound a powerful candidate for many technological applications.

Study of the correlation between the magnetic and electrical properties of the La0.6Sr0.4MnO3 compound.

In this work, we investigated the relationship between the electrical and magnetic properties of the superparamagnetic (SPM) La0.6Sr0.4MnO3 (S1C0) compound prepared by the sol-gel method. The (S1C0) sample displayed a ferromagnetic metallic (FMM) behavior at low temperatures and a paramagnetic semiconductor (PMSC) behavior at high temperatures. The FMM behavior was described by the Zener Double Exchange (ZDE) polynomial law containing the contributions of the electron-electron (e-e) interactions and the electron-magnon (e-m) scattering. The PMSC behavior was described by the Mott Variable Range Hopping (Mott-VRH) transport model. The semiconductor/metallic transition temperature has been approximated at the blocking temperature. The Thermal Coefficient of Resistivity (TCR), which exhibits a linear variation around ambient temperature, can be used as a calibration curve for thermometry. Thus, our sample can be considered as a good candidate for the detection of infrared radiation used in night vision bolometer technologies.

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.

Correction: Correction: Influence of Ni content on structural, magnetocaloric and electrical properties in manganite La0.6Ba0.2Sr0.2Mn1-xNixO3 (0 ≤ x ≤ 0.1) type perovskites.

[This corrects the article DOI: 10.1039/D3RA90093B.][This corrects the article DOI: 10.1039/D1RA07059B.].

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.

Correction: Influence of Ni content on structural, magnetocaloric and electrical properties in manganite La0.6Ba0.2Sr0.2Mn1-xNixO3 (0 ≤ x ≤ 0.1) type perovskites.

[This corrects the article DOI: 10.1039/D1RA07059B.].

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.

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.

Research on the physical properties of LiMn0.5Fe2O4 spinel ferrites by the combination of optical, magnetic, and dielectric behaviors.

Ferrite compounds have recently attracted significant interest because of their multifunctional properties. This work investigates the optical, magnetic, and dielectric properties of a LiMn0.5Fe2O4 ferrite prepared by a solid-state reaction. Raman spectroscopy analysis substantiated the presence of the 5 active modes representing the vibration of the oxygen anion at both tetrahedral and octahedral sites. The direct optical band gap was estimated to be 3.51 eV, which indicates the semiconductor behavior of the compound. A theoretical modulation of the hysteresis loop was done to confirm the dominance of the ferromagnetic contribution over the antiferromagnetic one. Furthermore, the dielectric permittivity result indicated a colossal value of the order of 103. The dielectric losses are characterized by the Giuntini law to extract the relaxation process, which is hidden by the DC-conductivity process. Our results indicate the potential of LiMn0.5Fe2O4 for applications in multifunctional devices.

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.

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 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.

Influence of Ni content on structural, magnetocaloric and electrical properties in manganite La0.6Ba0.2Sr0.2Mn1-x Ni x O3 (0 ≤ x ≤ 0.1) type perovskites.

We present a detailed study on the physical properties of La0.6Ba0.2Sr0.2Mn1-x Ni x O3 samples (x = 0.00, 0.05 and 0.1). The ceramics were fabricated using the sol-gel route. Structural refinement, employing the Rietveld method, disclosed a rhombohedral R3̄c phase. The magnetization vs. temperature plots show a paramagnetic-ferromagnetic (PM-FM) transition phase at the T C (Curie temperature), which decreases from 354 K to 301 K. From the Arrott diagrams M 2 vs. µ 0 H/M, we can conclude the phase transition is of the second order. Based on measurements of the isothermal magnetization around T C, the magnetocaloric effects (MCEs) have been calculated. The entropy maximum change (-ΔS M) values are 7.40 J kg-1 K-1, 5.6 J kg-1 K-1 and 4.48 J kg-1 K-1, whereas the relative cooling power (RCP) values are 232 J kg-1, 230 J kg-1 and 156 J kg-1 for x = 0.00, 0.05 and 0.10, respectively, under an external field (µ 0 H) of 5 T. Through these results, the La0.6Ba0.2Sr0.2Mn1-x Ni x O3 (0 ≤ x ≤ 0.1) samples can be suggested for use in magnetic refrigeration technology above room temperature. The electrical resistivity (ρ) vs. temperature plots exhibit a transition from metallic behavior to semiconductor behavior in the vicinity of T M-SC. The adiabatic small polaron hopping (ASPH) model is applied in the PM-semiconducting part (T > T MS). Throughout the temperature range, ρ is adjusted by the percolation model. This model is based on the phase segregation of FM-metal clusters and PM-insulating regions.

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.

Impact of synthesis route on structural, magnetic, magnetocaloric and critical behavior of Nd0.6Sr0.4MnO3 manganite.

Nd0.6Sr0.4MnO3 polycrystalline manganite was synthesized by two different methods: the auto-combustion reaction (NSMO-AC) and the sol-gel method (NSMO-SG). The structural, magnetic, magnetocaloric and critical behavior of the samples were examined. Rietveld refinements of the XRD patterns revealed that both compounds are pure single phase indexed to the orthorhombic system adopting the Pnma space group. The nanometric size estimated using the Williamson-Hall method was confirmed by TEM micrographs. Magnetic measurements as a function of temperature indicated that both samples underwent a second order ferromagnetic (FM)-paramagnetic (PM) phase transition at Curie temperature (T C). The relative cooling power was observed to be around 95.271 J kg-1 for NSMO-AC and 202.054 J kg-1 for NSMO-SG at µ 0 H = 5 T, indicating that these materials are potential candidates for magnetic refrigeration application close to room temperature. The critical behavior was estimated using diverse techniques based on the isothermal magnetization data recorded around the critical temperature T C. The calculated values are fully satisfactory to the requirements of the scaling theory, implying their reliability. The estimated critical exponents matched well with the values anticipated for the mean-field model and the 3D Ising model for NSMO-AC and NSMO-SG, respectively, showing that the magnetic interactions depended on the process of elaboration.

Influence of neodymium substitution on structural, magnetic and spectroscopic properties of Ni-Zn-Al nano-ferrites.

Ni0.6Zn0.4Al0.5Fe1.5-x Nd x O4 ferrite samples, with x = 0.00, 0.05, 0.075 and 0.1, were synthesized using the sol-gel method. The effects of Nd3+ doping on the structural, magnetic and spectroscopic properties were investigated. XRD Rietveld refinement carried out using the FULLPROF program shows that the Ni-Zn ferrite retains its pure single phase cubic structure with Fd3̄m space group. An increase in lattice constant and porosity happens with increasing Nd3+ concentration. FTIR spectra present the two prominent absorption bands in the range of 400 to 600 cm-1 which are the fingerprint region of all ferrites. The change in Raman modes in the synthesized ferrite system were observed with Nd3+ substitution. The magnetization curves show a typical transition, at the Curie temperature T C, from a low temperature ferrimagnetic state to a high temperature paramagnetic state. The saturation magnetization, coercivity and remanence magnetization are found to be decreasing with increasing the Nd3+ concentration.

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.