Dielectric Loss Values Research Articles

Novel dielectric response in B-site zirconium-doped CaCu3Ti4O12 ceramics: A structural, optical and electrical study

In this study, the CaCu3Ti4-xZrxO12 (with x = 0.0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7 and 0.8) compounds were effectively synthesized through SSR method, and their crystalline structures, microstructures, optical, dielectric and electrical properties were analyzed and discussed in detail. A significant reduction in grain size is observed by Zr4+ doping for CCTZO ceramics. All CCTZO samples have an energy gap of ∼2.08 eV. A relatively high dielectric permittivity (ε'>103) is exhibited by all studied ceramics and impedance spectroscopy shows that they are heterogeneous electrically. The presence of Ti3+ and Cu+ ions as well as the oxygen vacancy in all samples was confirmed by XPS, resulting in structural changes that greatly affect the materials dielectric behaviour. Interestingly, CCTZO with x > 0.5 ceramics showed a dielectric resonance behaviour and were more frequency-stable than pure CCTO. More importantly, the sample x = 0.7 exhibited a higher ε′ at high frequencies which may be due to the enhancement of grains conductivity. The lowest value of dielectric loss while maintaining a relatively high ε′ was possible with the Zr doping content x = 0.1, the reason was discussed. Furthermore, the Zr doping not only enhanced the frequency-stability but also the temperature-stability of pure CCTO ceramic.

Study of the structural, magnetic and dielectric properties of GdMnO3-GdMn2O5 nanocomposites via sol-gel route

Using the sol–gel route, GdMnO3-GdMn2O5 nanocomposite was synthesized at 1000 °C. For the first time, in the above room temperature conditions, Raman, magnetic, and dielectric measurements were taken of the synthesized GdMnO3-GdMn2O5 composite.The diffraction peak position resulting from a XRD pattern confirmed the formation of GdMnO3 and GdMn2O5, as well as an orthorhombic structure. Using the Raman spectra, three Raman peaks (363,475 and 608 cm−1) were detected for the synthesized composite at 350 and 400 K, indicating the formation of a bi-phase of gadolinium manganese oxide. A TEM image of the synthesized product revealed agglomerated spherical particles with a polycrystalline structure. A weak ferromagnetic behavior was found for the synthesized composite using the high-temperature vibrating sample magnetometer. From the dielectric study, it is inferred that the applied frequency and temperature play a vital role affecting the dielectric constant, dielectric loss and AC conductivity values in the synthesized composite.

LiBa2AlO4: A new lithium barium aluminate having an oxygen tetrahedral framework

Single-crystal grains of the new oxide LiBa2AlO4 were obtained from a sample that had been partially melted by heating a compact of a binary oxide powder mixture having a Li:Ba:Al molar ratio of 4:5:1 ​at 1173 ​K. Single-crystal X-ray diffraction analysis demonstrated that this oxide had a trigonal superstructure (hexagonal lattice with a ​= ​5.7879(2) Å and c ​= ​13.2456(6) Å, space group P3121) formed by an ordered Li and Al arrangement. The c-axis period in this structure was found to be approximately twice as long as that in BaZnO2, the space group of which is also P3121, and a three-dimensional framework constructed by sharing all vertices of Li- and Al-centered oxygen tetrahedra. This structure can be derived from the perovskite (ABO3)-type structure via the orderly replacement of BO6 octahedra with LiO4 and AlO4 tetrahedra. Polycrystalline samples of LiBa2AlO4 were synthesized by heating compacts having stoichiometric compositions at 1173 ​K. The relative dielectric constant and dielectric loss values observed for a polycrystalline sample at room temperature were 8.3 and 0.004, respectively. The second harmonic generation intensities for LiBa2AlO4 and BaZnO2 were found to be 4.4 and 19.4 times greater than the value for quartz, respectively.

The electromagnetic wave absorption properties of woven glass fiber composites filled with Sb2O3 and SnO2 nanoparticles doped mica pigments

AbstractIn this study, the electromagnetic wave absorption properties of woven glass fiber reinforced epoxy composites with Sb2O3 and SnO2 nanoparticles doped mica pigments were investigated. Herein, we synthesized SnO2/mica, Sb2O3/mica, and Sb2O3:SnO2/mica pigments using the sol–gel method. Subsequently, mica pigments filled glass fiber/epoxy composite panels were fabricated with a vacuum assisted resin mold. The phase, crystal, and morphological examinations of particles confirm the deposition of SnO2 and Sb2O3 nanoparticles on the mica surfaces. The electromagnetic wave absorption properties of samples were measured using the S parameters and obtained dielectric data. Sb2O3:SnO2/mica particles display higher complex permittivity and dielectric loss values due to the strong interfacial polarization between conductive nano metal‐oxide shells and mica surfaces. According to the calculated reflection loss values, Sb2O3:SnO2/mica particles exhibit superior electromagnetic wave absorption performance with a minimum reflection loss of −25.62 dB for 2.4 mm thicknesses with effective bandwidth between 9.3 and 12.4 GHz. The S parameters of the prepared structural composites with the size of 30 cm × 30 cm × 3 mm was determined by the free‐space technique using the transmission line technique. According to the S12 parameters, filled glass fiber/epoxy composite containing 25 wt% Sb2O3:SnO2/mica show a minimum reflection loss of −20.426 dB at 8.2 GHz with effective bandwidth between 8.2 and 9.67 GHz. These results indicate that Sb2O3:SnO2/mica‐filled fiber/epoxy composite is an excellent candidate for the practical application of electromagnetic wave absorbers.

Synthesis, characterization, and application of metal-free sulfonamide-vitamin C adduct to improve the optical properties of PVA polymer

Improving optical properties is an important topic in the field of polymer science. In this research, a novel, metal-free, and inexpensive vitamin C sulfonamide adduct has been developed to enhance the optical behaviors of polyvinyl alcohol (PVA). Initially, the vitamin C adduct has been fabricated through atom economic reaction and then characterized using several spectroscopic techniques, including 1 H NMR, 13 C NMR, DEPT-135, Fourier transform infrared spectroscopy (FTIR), and X-ray diffraction (XRD). Accordingly, a dramatic chemical alteration in ascorbic acid structure has been confirmed and led to enhancing chemical interactions with the host polymer. The ascorbic acid adduct has been doped into PVA to prepare a flexible film of polymer composites with potential optical behaviors. The identity of composite film has specified from FTIR, XRD, and UV–vis spectroscopy. The XRD pattern of the hybrid polymer has revealed a remarkable boost in its amorphous structure compared to the PVA host. The FTIR data of both matrix PVA and its composites reveal the potent chemical interactions of functional groups within the hybrid PVA. The main optical information of synthesized hybrid film was obtained from the UV–vis spectra. The refractive index ( n ) and dielectric loss ( ε i ) values are elevated notably, whereas the optical band gap energy (E g ) declined from 6.3 to 3.6 eV. The direct electronic transition between the valence band (VB) and conduction band (CB) was determined by implementing Tauc’s model. These preliminary results suggest that the fabricated flexible composite will have an excellent opportunity to use in the manufacturing optical devices.

AC measurements, impedance spectroscopy analysis, and magnetic properties of Ni0.5Zn0.5Fe2O4/BaTiO3 multiferroic composites

Multiferroics composite materials have been widely used in several applications, such as ceramic supercapacitors and multifunctional and active devices, owing to their high permittivity with ferroelectric and magnetic performance even at room temperature. The chosen preparation technique can be one of the most effective ways for obtaining multiferroic composite with different properties for the same composite. Here, multiferroic composite materials, (x) wt.% Ni0.5Zn0.5Fe2O4 (NZF)-(100-x) wt.% BaTiO3 (BT) (x = 25, 50, 75) were prepared by the co-precipitation synthesis route. The prepared multiferroic samples were characterized with various techniques like X-ray diffraction (XRD), scanning electron microscope (SEM), energy dispersive X-ray spectroscopy (EDXS), and vibrating sample magnetometer (VSM). The magnetic and AC electrical properties like conductivity, dielectric constant, dissipation factor (dielectric loss), and impedance spectroscopy analysis were studied in detail with different frequencies and temperatures. In our case, preparing nanosized NZF on or between microscale BT could enhance the electrical properties by decreasing the porosity (P) percentage, which reaches a low value for the sample x = 50 wt%, and increasing the conductivity. A relatively high dielectric constant (ε‘) at low frequencies and high temperatures was obtained, which is one of the main contributions in modern applications like a ceramic supercapacitor. Also, the studied samples show low dielectric loss (tanδ) values suggesting that it could be a contender for use in high-frequency microwave devices and tunable frequency filters.

Enhanced dielectric and electrical properties of polystyrene-2% divinyl benzene (PDB) embedded in SrTiO3-Poly (vinylidene fluoride) three phase composite films

A facile solution casting technique has been employed to fabricate ceramic SrTiO3; STO particle and polystyrene-2% divinyl benzene (PDB) filled three phase composite films using poly(vinylidene fluoride) (PVDF) matrix. The frequency dependence of dielectric and electrical properties of the three phase PVDF-STO-PDB composite films of various weight percentage of PDB (fPDB) were analyzed. With the small change in the AC conductivity and dielectric loss the dielectric constant of the PVDF-STO-PDB composite systems is improved noticeably. The experimental results suggested that, the introduction of 10 wt% of PDB particles in the PVDF-STO composites enhanced the dielectric constant (≈76) and suppressed dielectric loss value (< 0.5) at 100 Hz. This may be attributed to the addition of PDB particles improved the establishment of polarization. The morphological analysis depicts that the PDB particles are uniformly dispersed and well compatibility between filler particles and polymer matrix which may be ascribed to the minimization of dielectric loss of the resultant composites. Further, the strong interaction between PDB particles and PVDF matrix at the interface is the crucial factor in the improvement of the dielectric and electrical properties. The percolation theory was used to elucidate the dielectric and electrical performance of PVDF-STO-PDB composites. It is noticed that the three phase PVDF-STO-PDB composite films exhibited an insulator-conductor transition with percolation threshold of fPDB = 5 wt%. The three phase composites with high dielectric constant (≈76) at percolation threshold might be helpful to understand the influence of PDB particles on the interfaces between the ceramics and polymer matrix. This work will provide an easy and effective solution to fabricate high performance three phase composites to the development of high energy storage applications.

Evaluation of Relative Permittivity and Loss Factor of 3D Printing Materials for Use in RF Electronic Applications

3D printing is more and more often used for the development and manufacturing of electronic devices and components. These applications require knowledge about the dielectric properties of the used materials—in particular minimal and stable values of relative permittivity and dielectric losses. The paper deals with the testing of the relative permittivity and loss factor of materials as follows: PLA (in three dye modifications), PET-G, and ABS and ASA in the frequency range 1–100 MHz. It was found that relative permittivity varied between 2.88–3.48 and the loss factor was in the range 0.03–4.31%. In terms of relative permittivity, all tested materials manifested a slight decline with increasing frequency. Concerning loss factor PLA (colorless) and ABS were proven to be more suitable for electrotechnical application due to the lower values and frequency dependences of the loss factor. Different results were observed in PLA-Silver and PLA-Metallic green. These materials showed a higher frequency dependency of loss factor with increasing frequency. The reasonable influence of added dyes was found. A study of the internal structure of the tested materials has not proven any significant defects (air gaps) that could affect the material’s dielectric properties.

Defect-Induced Self-Poling in a W18O49/PVDF Piezoelectric Energy Harvester.

W18O49 nanostructures, previously used for electrocatalysis, energy storage, electrochromic, and gas sensing applications, are incorporated in poly(vinylidene fluoride) (PVDF) in this work for mechanical energy-harvesting applications. X-ray diffraction spectroscopy (XRD), high-resolution transmission electron microscopy (HR-TEM), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, differential scanning calorimetry (DSC), and the polarization-electric (P-E) field loop test prompts the addition of W18O49 nanorods in PVDF nucleates and stabilizes the piezoelectric polar γ-phase in the nanocomposite. Electrochemical experiments were employed for the first time to relate the event of the evolution of crystalline phases in PVDF to the transfer of electrons to the electrolyte from PVDF using the data from cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). High dielectric constant (ε') and low dielectric loss (ε″) values were obtained proportionately for different weight percentage additions of W18O49 nanorods in PVDF. DSC was employed to study the crystallization kinetics of γ-phase evolution. Piezoresponse force microscopy (PFM) was used to compare the piezoelectric responses from the PVDF nanocomposites. The W18O49/PVDF nanocomposite could generate a peak open circuit voltage of ∼6 V and a peak short circuit current of ∼700 nA. The W18O49/PVDF nanocomposite could light two commercial blue-light-emitting diodes (LEDs) with hand impulse imparting.

Growth, SHG, Z-scan, optical limiting and quantum chemical investigation of hexamethylenetetraminium hydrogen DL-malate – An organic crystal for optoelectronic applications

Single crystals of hexamethylenetetraminium hydrogen dl-malate (HMTM) have been successfully synthesized by slow evaporation method and structurally analyzed by single crystal X-ray diffraction, powder X-ray diffraction, FTIR, FT-Raman, 1H and 13C NMR spectroscopic techniques. These investigations confirm the formation of HMTM crystal which crystallize in the non-centrosymmetric space group Cc with monoclinic crystal system. The N–H⋯O and O–H⋯O intermolecular hydrogen bonding interactions have been investigated by Hirshfeld surface analysis. The optical absorption cut-off wavelength of the grown crystal is observed at 353 nm in the UV–visible spectrum. From the photoluminescence spectrum, two intense emission peaks are identified at 312 nm and 415 nm. Dielectric study reveals low values of dielectric constant and dielectric loss. The positive photoconducting nature of HMTM is identified from the photoconductivity analysis. Second harmonic generation efficiency of the powdered HMTM is found to be 1.25 times greater than that of powdered KDP. The Z-scan and optical limiting results indicate that HMTM exhibits self-defocusing nature and optical limiting response, respectively. In addition, charge transfer interactions, first- and second-order hyperpolarizability values are computed by density functional theory calculations and are discussed in detail.

Effect of Ag2S on electrical conductivity and dielectric relaxation in Ag2O-MoO3-P2O5 ionic glassy systems

The influence of Ag2S incorporation on the electrical and dielectric properties of the host Ag2O-MoO3-P2O5 glassy matrix has been systematically studied in the present communication. By applying the well-known Archimedes principle, the density of the samples has been determined. The ionic property for all the as-prepared glassy systems has been explored methodically. The nearly identical obtained values of the crossover frequency and the activation energy for DC and AC conductivity suggest that the same mechanism is responsible for electrical conduction. For the purpose of inspecting the frequency and temperature dependent AC conductivity, the Almond-West formalism model has been used. The observed values of dielectric constant and dielectric loss are found to increase with the temperature rise and drop with rising frequency. The coinciding scaled complex electric modulus spectra suggest a non-Debye type dynamical relaxation mechanism, which also indicates that the relaxation mechanism is temperature independent but composition dependent.

Ruthenium-doping-induced strong electromagnetic loss in FeCo nanoparticles by orbital hybridization and electron transmission

Ferromagnetic metal/alloy particles are widely used in the field of electromagnetic wave absorption. Doping is an effective means of modulating the electromagnetic properties of magnetic metals and alloys. In this study, (Fe3Co7)1−xRux nanoparticles with different Ru doping contents are prepared using a polyvinylpyrrolidone (PVP)-assisted liquid-phase reduction process. First-principles calculations reveal that strong electron-orbit hybridization occurs between Ru-4d and Fe/Co-3d owing to the strong spin-orbit coupling effect of Ru-4d orbital electrons. This generates a space charge distribution and carries a magnetic moment of 1.80 hbar/2. The use of Ru doping results in a reduction in FeCo alloy particle size from 1.5 µm to 200 nm, slight decrease in the saturation magnetization from 179 to 152 emu/g, and increase in the electrical conductivity from 2.79 × 10-4 to 6.62 × 10-4 S·cm-1. The dielectric and magnetic loss values vary from 0.22 to 0.95 and 0.06–0.37, respectively, in the 2–18 GHz frequency range. Ru doping-induced dipole polarization relaxation, exchange resonance, and increased conductivity loss are the primary reasons for the enhanced electromagnetic loss of the material. When the level of Ru doping x reaches 0.10, the minimum reflection loss (RLmin) increases from − 21.5 to − 41.9 dB. Thus, (Fe3Co7)1−xRux is a promising material for electromagnetic loss due to its tunable composition, size, conductivity, magnetic properties, and excellent electromagnetic loss capability.

Microwave Attenuation Studies of Polypyrrole-SWCNT Nanocomposite Films for Improved EMI Shielding

In the process of finding stable, lightweight, broadband, cost-effective and improved electromagnetic interference (EMI) shielding material, electromagnetic wave attenuation properties of polypyrrole (PPy)—single-walled carbon nanotube (SWCNT) nanocomposite hybrid films were investigated in X-band region (8.2–12.4 GHz) and reported in the present work. The incorporation of SWCNT as a nanofiller in polymer matrix exhibits enhanced EMI shielding performance as compared to pure polymer films. The substantial values of dielectric loss with good impedance matching contribute to improvement in EMI shielding performance. It is found that with an increase of SWCNT loading in polymer matrix from 0 wt% to 5 wt%, nanocomposite films display a gradual increase in AC conductivity and total shielding effectiveness. The maximum total shielding effectiveness of 32.10 dB and minimum reflection loss of −45.54 dB with a wide bandwidth of 3.1 GHz, were obtained for 5 wt% CNT loading. The present results revealed that the prepared nanocomposite films are appropriate materials for lightweight, broadband EMI shields for radar and stealth applications.

Structural, dielectric, and magnetic properties of Pr–Cr co-doped PrxBa1-xCryFe12-yO19 barium hexaferrites

Praseodymium and chromium co-doped barium hexaferrites PrxBa1-xCryFe12-yO19 (x = 0, 0.1, 0.2, 0.3 and 0.4; y = 0, 0.4, 0.8, 1.2 and 1.6) were synthesized using sol-gel auto-combustion method. The structural, morphological, compositional, magnetic, and dielectric properties were investigated using X-ray diffraction (XRD), Field Emission Scanning Electron Microscopy (FESEM), Energy Dispersive X-ray (EDX) spectroscopy, Vibrating Sample Magnetometer (VSM), and impedance analyzer, respectively. The pure M-type phase formation was confirmed from XRD data with an average crystallite size of 69 nm. FESEM micrographs showed the platelet-like hexagonal structure of the prepared sample. EDX spectra exhibited the presence of all constituent elements (i.e., Pr, Cr, Ba, Fe, and O). VSM results showed an increase in coercivity for sample S2 (i.e., x = 0.1 and y = 0.4). Then, a decreasing trend in coercivity and saturation magnetization was observed for increasing dopant content. The high-frequency dielectric parameters were investigated up to 3 GHz. Results revealed that the dielectric constant and dielectric loss values of Pr/Cr doped samples are greater than the pure sample. The prepared samples exhibited a hard magnetic nature and good dielectric properties, hence, are considered suitable for magneto-optic, magnetic-recording devices, and high-frequency applications.

Structural, electrical and dielectric properties of chitosan/polyaniline/vanadium-pentoxide hybrid nanocomposites

Chitosan/polyaniline/V2O5 hybrid nanocomposites were synthesized by an oxidative polymerization technique by varying V2O5 content and using (NH4)2S2O8 as an oxidizing agent. The structural and morphological properties were characterized by using Fourier Transform Infrared Spectroscopy (FTIR), X-Ray Diffraction (XRD), and Scanning Electron Microscopy (SEM). The characterization results corroborate the successful formation of the nanocomposites and reveal modifications in morphological features. The AC conductivity, dielectric, impedance, and electric modulus properties were studied in the frequency range of 10 Hz–8 MHz at room temperature. The AC conductivity and dielectric constant values of the chitosan/polyaniline matrix were remarkably improved with the addition of V2O5 nanoparticles. The AC conductivity of the CPAV-0.6 nanocomposite increased significantly at higher frequencies (5.78×10–3 S/m at 8 MHz). The CPAV-0.4 nanocomposite showed a drastic enhancement in dielectric constant values for lower frequencies (2×105 at 10 Hz). The prepared nanocomposites exhibited lower dielectric and tangent loss values at higher frequencies, implying that they are lossless materials at higher frequencies and have applicability in high-frequency devices. The relaxation time decreased with increasing V2O5 concentration (∼7.5×10–5 s for CPA and ∼2.5×10–5 s for CPAV-0.2 and CPAV-0.4), which is in good agreement with electrical results. The electrical results are further supported by the impedance and electric modulus studies. As a result of these improved properties, as-prepared nanocomposites in their optimum form are particularly helpful in energy storage and conversion devices, optoelectronic and biomedical applications, sensors, supercapacitors, and photovoltaic devices such as solar cells.

Structure and sintering behavior of BaO–SrO–B2O3–SiO2 sealing glass for Al2O3 ceramic substrates

BaO–SrO–B2O3–SiO2 sealing glass for Al2O3 ceramic substrates was prepared and the effect of B2O3 on its structure, sintering behavior, and properties was studied. Owing to the fluxing action of B2O3, the glass transition temperature, sintering temperature, and crystallization temperature of the sealing glass were decreased with increasing B2O3. With an increase in the B2O3/SiO2 ratio, the average bridge oxygen number of the glass network first increased and then decreased, and the boron abnormality phenomenon was detected at a B2O3/SiO2 ratio of 0.55, at which the polymerization degree of the glass network was maximized. Furthermore, the precipitation of BaAl2Si2O8 crystals was promoted and the crystallinity of the sealing glass was increased, inhibiting sintering densification and weakening the material. The sealing glass with a B2O3/SiO2 ratio of 0.55 sintered at 800 °C for 10 min showed the best properties: a thermal expansion coefficient of 7.89 × 10−6 K−1, flexural strength of 114.28 MPa, Vickers hardness of 622.98 HV, dielectric constant of 12.14, and a dielectric loss value of 4.11 × 10−3. After the sealing glass was co-sintered with the Al2O3 ceramic substrate, the interface was tightly bonded. This indicates the great potential applicability of BaO–SrO–B2O3–SiO2 sealing glass for Al2O3 ceramic substrate packaging.

Study on relaxation behavior of all-polymer PVDF-based films containing dielectric fluoroelastomer

All-polymer PVDF-based films consisting of fluoroelastomer were prepared through simple hot-pressing method, which were comprehensively explored by dielectric relaxation spectroscopy with the frequency of 20–30 M Hz and the temperature from 25 °C to 205 °C. Compared with single-layered PVDF film, The permittivities of both 30% FKM/PVDF blend film and sandwich-structured FKM/PVDF film were elevated, and the values of dielectric loss and DC conductivity dramatically dropped throughout whole temperature range. The characteristic peaks of Curie transition temperature (Tc) were detected for all samples, while Tc of sandwich-structured FKM/PVDF film shifted to a higher temperature. Moreover, the results of electric modulus spectra and Cole-Cole plots revealed the non-Debye relaxation mechanism of the studied samples. Furthermore, the values of both Eτ and Eσ for FKM/PVDF films were increased compared with single-layered PVDF, with a more profound effect on sandwich-structured FKM/PVDF film. Such higher value is beneficial to restrain the relaxing and conducing behaviors Thus, sandwich-structured FKM/PVDF film will be a potential material for enhancing electric displacement and reducing the energy loss.

Optical, dielectric and electrical properties of Gd3+ ions doped barium hexaferrite ceramic compounds for microwave device applications

The present work reports synthesis, optical, dielectric and electrical properties of M-type BaFe12−xGdxO19 (x = 0, 1, 1.25, 1.5, 1.75 and 2 mol%) ceramics. Auto combustion synthesis technique was applied for the preparation of the ceramics. Structural analysis was done using PXRD patterns which confirms the hexagonal structure of prepared ceramics. The average particle size of the prepared samples was found to be 25.29 nm and the lattices parameters 'a' and 'c' values ranges from 5.8864 Å to 5.9282 Å and 23.2135–23.3981 Å respectively. UV-Visible spectroscopy and Photoluminescence (PL) analysis were used to investigate the optical characteristics of the prepared samples. The PL emission spectra show that the emission peaks were observed at 689 nm due to the optical transition 6GJ to 6PJ emission. The direct band gap (Eg) of BaFe12O19 is 4.07 eV and Eg value decreases from 4.07 eV to 3.92 eV with substitution of Gd3+ ions. The indirect band gap value also decreases with Gd3+ substitution. The electrical properties were investigated through CIS (complex impedance spectroscopy), EMS (electrical modulus spectroscopy), ac-conductivity and dielectric studies. The dielectric behavior of the samples is explained by Maxwell- Wagner’s two-layer model. NTCR behavior of the prepared powder samples are confirmed from CIS studies. The ac-conductivity studies follow the universal power law. By the substitution of Gd3+ ions, the dielectric constant value increases up to four times and value of dielectric loss decreases by four times, so the BaFe12−xGdxO19 samples can be used in various microwave devices.

Spinel M0.5Zn0.5Fe2O4 (M = Ni, Co, and Cu) ferrites for energy storage applications: Dielectric, magnetic and electrochemical properties

Spinel structured M0.5Zn0.5Fe2O4 (M = Ni, Co, Cu) were synthesized through a solid state route. Phase analysis of the samples showed the formation of a single phase spinel structure. Fourier transform infrared spectroscopy also confirm the presence of tetrahedral and octahedral sites belonging to spinel structure. The microstructural analysis of the samples revealed a grain size ranging from 0.5 to 3.7 μm. The photoluminescence spectroscopy indicated the generation of oxygen vacancies and structural defects in the lattice of the samples. The obtained dielectric constant and loss values (at 1 MHz) varied between 11 and 35, and 0.006 to 1.2, respectively. The variation in dielectric properties was dependent on polarization species, crystallite size, defects and oxidation states. The samples showed a ferromagnetic behavior at room temperature. The electrochemical performance of Cu0.5Zn0.5Fe2O4 showed the most favorable results such as the lowest overpotential of 490 mV, the highest specific capacitance of 462 F/g, and the lowest charge-transfer resistance of 876 Ω, suggesting its potential for energy storage applications.

Cation distribution, composition effect on magnetic and electrical properties of nano ZnMn2-xCrxO4 (x= 0, 1, 2)

The nanocrystalline ZnMn2-xCrxO4 (x = 0, 1, 2) were successfully synthesized by combustion method. The products were characterized by XRD, FTIR, SEM, and TEM. XRD results revealed the formation of cubic phase spinel structure for ZnCr2O4 and ZnMnCrO4 as well as tetragonal spinel crystal structure for ZnMn2O4. The FT-IR data displayed two absorption bands in a range of 400–600 cm−1 arising from tetrahedral (A) and octahedral (B) stretching vibrations. The magnetic character investigated by vibrating sample magnetometer (VSM) spectra showed that all prepared samples exhibited super-paramagnetic behavior. The electrical properties of the ZnMn2-xCrxO4 (x = 0, 1, 2) system were studied at a frequency range of 102–106 Hz and temperatures ranging between 303 and 573 K. The electrical conductivity increased with increasing temperature referring to the semiconducting behavior of all the investigated samples. The conduction phenomenon could be explained based on the correlated barrier-hopping mechanism (CBH). Both dielectric constant (ε′) and dielectric loss (ε'`) values increased at all frequencies and temperatures which is attributed to the orientation polarization of the dipoles in the sample. The impedance spectroscopy (EIS) was examined to review the impact of grain and grain boundary on the electrical properties of all the investigated samples. The cation distribution and the composition effect on physical properties were discussed.