Colossal dielectric permittivity in (Al+Nb) co-doped Ba0.4Sr0.6TiO3 ceramics

Stimulated by the outstanding colossal permittivity behavior achieved in trivalent and pentavalent cations co-doped rutile TiO₂ ceramics, the co-doping effects on the dielectric behavior of Ba_0.4Sr_0.6TiO₃ ceramics were further explored. In this work, (Al + Nb) co-doped Ba_0.4Sr_0.6TiO₃ ceramics were synthesized via a standard solid state ceramic route. The structural evolution was analyzed using X-ray diffraction patterns and Raman spectra. Dense microstructures with no apparent change of grain morphology were observed from the scanning electron microscopy. A huge enhancement of dielectric permittivity was obtained with 1 mol% (Al + Nb) doping and excellent dielectric performances (ε_r ∼ 20,000, tanδ ∼ 0.06 at 1 kHz) were achieved after further heat treatment. The formation of electron pinned defect dipoles localized in grains may account for the optimization of dielectric behaviors and the corresponding chemical valence states were confirmed from the XPS results.     

Effect of SiO2 additive on dielectric response and energy storage performance of Ba0.4Sr0.6TiO3 ceramics

SiO₂-added barium strontium titanate ceramics Ba_0.4Sr_0.6TiO₃-xwt%SiO₂ (x=0, 0.5, 1, 3, BSTSx) were prepared via a traditional solid state reaction method. The effect of SiO₂ additive on the microstructure, dielectric response and energy storage properties was investigated. The results confirmed that with the increase of SiO₂ additive, diffuse phase transition arises and the dielectric constant decreases. An equivalent circuit model and Arrhenius law were used to calculate the activation energy of grain and grain boundary, which indicated that the dielectric relaxation at high temperature was caused by oxygen vacancy. While appropriate SiO₂ additive led to improve the breakdown strength, further increase of SiO₂ deteriorated the energy storage because of the low densification. Finally, optimized energy storage performance was obtained for BSTS0.5 ceramics: dielectric constant of 1002, dielectric loss of 0.45%, energy density of 0.86 J/cm³ and energy storage efficiency of 79% at 134 kV/cm.     

Investigation of structural,physical, spectral,photoluminescence, Raman,and dielectric properties of Ba2Co2GdxFe28-xO46 hexaferrites

Nano-crystalline Gd-substituted X-type hexaferrites with the composition Ba₂Co₂Gd_xFe_28-xO₄₆ (x = 0.00, 0.08, 0.16, 0.24, and 0.32) were synthesized using sol-gel auto-combustion procedure. The establishment of single and pure phases of X-type hexagonal ferrites is verified by X-ray diffraction. The crystallite size ranging from 25 to 31 nm showed the increasing trend with the enhancement of Gd-substitution. The unit cell volume was found in 2502.83–2516.07 Å³. The alteration in lattice parameters and cell volume is due to the difference in ionic radii of the host (Fe) and substituent (Gd) element. FTIR spectra ranging 590-3000 cm⁻¹ revealed the emergence of specific absorption bands verifying the formation of hexagonal ferrites. The behavior of dielectric properties is frequency dependent. The dielectric constant at low frequency for all substitution was high, but over the large frequency values, the dielectric constant was decreased. The dielectric loss factor increases over low frequencies and decreases as frequency rises with a higher concentration level. Higher dielectric parameter values suggest that synthetic material might be good for high-frequency applications and super-capacitors fabrication. The changes in Raman spectra as a function of substitution content are ascribed to the development of strain in the unit cell (x). The XRD investigation well corroborates this conclusion. FESEM images depicted the hexagon shaped particles of the X type hexagonal ferrites. In the PL spectra of synthesized compounds, all emissions invisible (red) zone with PL intensity at 661 nm were observed.     

Crystal structure,phonon modes and dielectric properties of B site ordered ABiLiTeO6 (A = Ba,Sr) double perovskites

ABiLiTeO₆ (A = Ba, Sr) double perovskite oxides were synthesised through conventional solid - state ceramic route. X-Ray diffraction patterns indicated pseudocubic symmetry for both compounds. Deconvoluted Raman spectra using Lorentzian function gave 7 first order Raman modes for both BaBiLiTeO₆ and SrBiLiTeO₆ whereas Infrared spectroscopy gave 8 modes for BaBiLiTeO₆ and 9 modes for SrBiLiTeO₆. Observed phonon modes were in good agreement with the corresponding group theoretical predictions for space group I4/m for both compounds. Rietveld refinement of the XRD patterns also confirmed I4/m space group for ABiLiTeO₆ (A = Ba, Sr) with 1:1 B site ordering of Te⁶⁺ and Li⁺ cations. The random occupancy of Ba²⁺ and Bi³⁺ at the A site in BaBiLiTeO₆ whereas Sr²⁺ and Bi³⁺ in SrBiLiTeO₆ were revealed from Rietveld refinement. Microstructure of both the compounds gave average grain size of less than 3?µm. At 1?MHz, BaBiLiTeO₆ and SrBiLiTeO₆ possess porosity corrected dielectric constants of 49.5 and 34.4 and dielectric losses of 0.029 and 0.028 respectively.     

Investigation of structural,optical, magnetic,and dielectric properties of calcium hexaferrite synthesized in presence of Azadirachta indica and Murraya koenigii leaves extract

M-type calcium hexaferrite- CaFe₁₂O₁₉ (CaM) has been prepared in presence of Azadirachta indica, and Murraya koenigii leaves extracts, followed by calcination at 650 °C for 3h. It was observed that the presence of phytochemicals in both leaves extract plays a vital role in deciding the structural, optical, microstructural, magnetic, and dielectric properties of prepared CaM hexaferrites. Prepared samples were characterized using FT-IR, XRD, UV–Vis, SEM, VSM, and dielectric measurements. FTIR, UV– Vis, and antioxidant assay confirmed the presence of phenolic content and antioxidant property of plant extract. This further resulted in the formation of a pure hexagonal phase as revealed by the XRD analysis. The surface morphology of prepared ferrites modified through this greener route was illustrated by the spongy appearance of ferrites in SEM micrographs.The saturation magnetization for the CaM powder prepared using Murraya koenigii leaves extract is 11.78 Am²/kg, while that prepared from Azadirachta indica leaves extract is 3.56 Am²/kg. Both samples show a magnetically soft nature, with a multidomain structure. The energy bandgap was also observed to be 2.01 eV. Moreover, the calcium ferrite synthesized by Murraya koenigii leaves had ε’_max ～ 25 and that synthesized in presence of Azadirachta indica leaves had ε’_max ～ 200 at ～20 Hz.     

Magnetic and microwave properties of BaFe12O19 substituted with magnetic,non-magnetic and dielectric ions

Barium hexaferrite particles were synthesized with conventional solid state reaction route. 1% boron (B₂O₃) was added to the initial mixture of oxides to inhibit crystal growth at lower temperatures. Magnetic (Mn²⁺, Co²⁺, Ni²⁺and Cu²⁺), non-magnetic (Zn²⁺) and dielectric (Ti⁴⁺) ions were replaced by one Fe³⁺ ion of barium hexaferrite to shift the ferromagnetic resonance frequency to low frequencies and to increase the magnetic and dielectric losses. The structural and morphological characterization of samples was done by X-ray powder diffractometer and scanning electron microscopy. Magnetic and microwave properties were determined by vibrating sample magnetometer and vector network analyzer, respectively. The maximum saturation magnetization and the highest reflection losses of −34 dB at 10 GHz, with absoption bandwidth of 1.6 GHz at −20 dB, were observed in Cu²⁺–Ti⁴⁺ and Zn²⁺–Ti⁴⁺ substituted samples. The mechanism of microwave energy dissipation is due to the impedance matching at matching thickness. It was also observed that as the sample thickness increases, the resonance frequency decreases exponentially.     

Investigation of the structural characteristics,dielectric properties,and infrared reflectivity spectra of AlON transparent ceramics

Al_(8+x)/3O_4?xN_x (x = 0.299–0.575) transparent ceramics were fabricated by presintering and subsequent hot isostatic pressing (HIP) technology. The XRD and SEAD analyses verified that a complete solid solution with a cubic spinel structure was achieved in the entire composition range. The SEM characterization confirmed that the x = 0.299?0.510 samples are highly dense with rare residual pores, which was further demonstrated by HRTEM observations. In combination with phonon modes extracted by far-infrared reflectivity spectra, the intrinsic dielectric properties of AlON ceramics were estimated, which were consistent with the experimental results, revealing that the contribution to dielectric properties is dominated by the absorption of structural phonons. Moreover, as the nitrogen content increased, the measured permittivity (ε_r) of the samples was found to gradually increase from 9.41 to 9.68 at 7 GHz, while the quality factor (Q × f) values fluctuated from 43,750 to 76,923 GHz. Accordingly, the reported AlON transparent ceramics with exceptional dielectric performances are promising candidates for high-frequency 5 G applications.     

Investigation of structural,spectroscopic, dielectric,magnetic, and in vitro biocompatibility properties of Sr/Ni co-doped hydroxyapatites

In this study, the changes caused by Ni and Sr additives on the structural, thermal, dielectric, and magnetic properties of hydroxyapatite (HAp) samples were examined and reported for the first time in detail.Some effects of the Sr/Ni site disorder on the crystallographic, dielectric, and magnetic properties in Sr/Ni-HAp have been examined, as well as their cytotoxicity effects. The addition of Ni affected the morphology of nanoparticles with a low agglomeration increase. Our results showed that the dielectric constant (ε′) and dielectric loss (ε′′) have greater values at low frequencies than at higher frequencies for all the samples.It can be concluded that Ni and Sr additions to the HAp structure contribute to the development of thermal, magnetic, and dielectric properties required to mimic natural HAp in the study conducted with the idea of creating a medical application area for bone healing and regeneration. The cytotoxicity test of the produced nanoparticles and the evaluation of the results were also performed using human foreskin fibroblasts (HFF). The viability of cells after treatment for 48 h ranged between 50 and 75%. While 0.37Ni-0.37Sr-HAp and 1.11Ni-0.37Sr-HAp were similar to 0.37Sr-HAp, 0.74Ni-0.37Sr-HAp had the highest cellular viability. At 0.1 mg/mL, 0.74Ni-0.37Sr-HAp had a viability of 79.97% compared to the untreated control cells. Our Sr/Ni-HAp nanoparticles have promising medical applications in bone healing and regeneration.     

Impedance spectroscopy analysis of BaFe12O19 M-type hexaferrite obtained by ceramic method

The impedance spectroscopy analysis for M-type BaFe₁₂O₁₉ (BaM) ceramics prepared by ceramic route is reported. The main aim is to investigate the electric properties in function of the synthesis parameters (milling time and milling power). It was shown that milling parameters strongly influence the electrical properties such as dielectric constant, whose magnitude increases with the milling power. Moreover the relaxation frequency is fully dependent on the milling parameters and it shifts to high frequencies when milling power decreases. Finally, impedance and dielectric loss tangent also change with milling parameters.     

Conductivity and dielectric properties of SrLaxBixYxFe12−3xO19 (0.0≤x≤0.33) hexaferrites

Both Y-La-Bi substituted and non-substituted Sr-hexaferrites (SrM) were synthesized by sol-gel auto combustion technique and the influences of Y, La and Bi ions on ac/dc conductivities, dielectric constant/loss properties as well as complex dielectric modulus were investigated extensively for a variety of substitutions. It was observed that ac conductivity of SrM increases slightly with increasing Y³⁺ La³, and Bi³⁺ substitutions at first, and then decreases with its further increments. Furthermore, ac conductivity increased with increasing frequency which could be regarded as an origin indication of both electronic and polaron hopping mechanism. It is also worthy to note that the activation energy, which is an indication of both mechanisms depicted in the Arrhenius plot, is increased as the enhanced contributions of substitutions in SrM with the illustration of a better stability and tunability of electrical bonds among substituted ions and ferrous and ferric ions. The dielectric constant, dielectric loss and dielectric modulus represent a very interesting tunability and optimised consequences regarding to the variation of frequencies, temperatures and substitutions of SrM.     

Optimization of structural,electrical, and magnetic properties of ytterbium substituted W-type hexaferrite for multi-layer chip inductors

The rare earth (Yb³⁺) substituted W-type hexagonal ferrites with composition CaPb_2-xYb_xFe₁₆O₂₇ (x = 0.0, 0.5, 1.0, 1.5, 2.0) were synthesized by a facile and cost-effective sol-gel auto combustion method with post heat treatment. The synthesized hexagonal ferrites were characterized by a variety of analytical techniques, and an impedance analyzer was used to investigate the effects of Ytterbium on structural, magnetic, spectral and dielectric properties. The relationship between their impedance, structure and dielectric properties was investigated. The X-ray diffraction patterns verify the presence of single-phase W-type hexagonal ferrites. Physical properties such as D_bulk (bulk density), D_xrd (X-ray density), and P (porosity) of the CaPb_2-xYb_xFe₁₆O₂₇ W-type hexagonal ferrites were calculated. The bulk density of all the samples was decreased, and X-ray intensity was increased with the Ytterbium replacement in the W-type hexaferrite. By adding Yb³⁺ ions, the lattice parameters, cell volume and X-ray density were reduced due to the substitution of ytterbium with smaller ionic radii compared to the lead ion with large ionic radii. The AC-conductivity was increased from (1.523 × 10^?5 to 6.699 × 10^?5) Ωcm^?1. The dielectric constant and tangent loss was found to decrease substantially. The magnetic properties were found to enhance by the substitution of Yb³⁺. The low coercivity value of Yb³⁺ substituted W-type hexagonal ferrites are suitable for magnetic recording media operated at a high-frequency regime. The enhancement of electrical, dielectric and magnetic characteristics suggests these materials as promising for multi-layer chip inductors (MLCIs) circuit applications.     

Electrical and impedance spectroscopy properties of hydrothermally synthesized Ba0.2Sr0.8-yLayFe12O19 (y = 0.2–0.8) nanorods

The Ba_0.2Sr_0.8-yLa_yFe₁₂O₁₉ (y = 0.2, 0.4, 0.6 & 0.8) (BSLFO) nanorods were prepared via low temperature, and inexpensive hydrothermal method. The presence of hexagonal phases was confirmed using the X-ray diffraction (XRD) patterns. The surface morphology revealed the formation of rectangular nanorods for y = 0.2–0.8 contents. Especially, y = 0.8 content showed the complete formation of rectangular nanorods due to high La-content. Furthermore, the dielectric properties, ac-electrical properties, impedance and dielectric modulus parameters were described as a function of composition, frequency and temperature.     

Crystallization,spectroscopic and dielectric properties of CuO-added magnesium aluminosilicate-based glasses

In this work, CuO-doped MgO-Al₂O₃-SiO₂ based glasses have been synthesized successfully through conventional melt quenching method, and the effect of CuO content on the structure and properties of the glasses was investigated. The results revealed that CuO could act as a glass modifier to depolymerize the silicate network and its effect was superior to that of MgO. In addition, the main crystalline phase was α-cordierite (Mg₂Al₄Si₅O₁₈), indicating that copper ions did not participate in the formation of the crystalline phase, and still existed in the interstitial position. The characteristic absorption band around 750 nm owing to the ²B_1g→²B_2g transition of Cu²⁺ ions appeared on the optical transmittance spectra, which confirmed the existence of Cu²⁺ ions in the tetragonally distorted octahedral sites. The luminescence center was caused by Cu⁺ ions, and the luminescence lifetime decreased with the addition of CuO. The dielectric constant and dielectric loss increased with the increase of CuO content, indicating an increase in the insulation performance. Finally, the obtained chromaticity coordinate parameters indicate that the prepared CuO-doped magnesium aluminosilicate-based glasses can be applied in optical and electrical fields.     

Impact of ionizing radiation on structural,dielectric, and piezoelectric properties of Sr modified PZT

Ion irradiation effects on piezoceramic (Pb_0.94 Sr_0.04) (Zr_0.52 Ti_0.48)O₃ (PSZT) are investigated by using 4 MeV carbon (C), 9 MeV copper (Cu), and 20 MeV gold (Au) ions. The energies of incident ions are selected in order to target the same range of all incident ions in the material, while producing different amounts of vacancies. The ion irradiation is performed with fluences of 1×10¹³, 1×10¹⁴, and 1×10¹⁵ ions/cm² using Tandem Pelletron accelerator (5UDH-2). Post irradiation changes in PSZT are investigated via various structural, dielectric, and piezoelectric measurement techniques. Results divulge that the irradiation process disturbs the crystallinity along with reduction in X-ray diffraction (XRD) peak intensities owing to strain induced structural defects. A small decrease in dielectric constant is observed due to trapped charges, which screen the depolarization after irradiation. However, a significant decrease is detected in piezoelectric charge coefficients (d₃₃) and piezoelectric voltage coefficients (g₃₃) due to switching of micro domains of PSZT as a result of energy observed during irradiation process. These results indicate that ion irradiation has damaging effects on the properties of PSZT. The discussed information may be utilized to assess performance of PSZT based devices under radiation rich environments such as space.     

The role of Pb and annealing temperature on the structural,magnetic, optical and dielectric properties of W-type hexaferrite nanostructures

In this paper, W-type Sr_1-xPb_xCo₂Fe₁₆O₂₇ nanostructures were synthesized by auto-combustion sol-gel method. Then, the effects of annealing temperature and Pb contents on the structural, magnetic, optical, and dielectric properties of Sr_1-xPb_xCo₂Fe₁₆O₂₇ nanostructure were investigated. First, a gel of metal nitrates with a specific molar ratio with x different was prepared and then the gel was annealed at different temperatures for 4?h. To determine the annealing temperature of the samples, the prepared gel was examined by thermogravimetric analysis and differential thermal analysis. The morphology and crystal structure of the prepared samples were characterized by field emission scanning electron microscopy (FESEM) and X-ray diffraction pattern (XRD). The results of XRD patterns indicated that the annealing temperature of synthesized Sr_1-xPb_xCo₂Fe₁₆O₂₇ was reduced by increasing Pb contents. In addition, FESEM images showed that the microstructure of the samples was homogeneous and uniform, but since the samples have a magnetic property, the particles were aggregated. Fourier transform infrared analysis (FT-IR) was used to confirm the phase formation. The FT-IR results of the samples indicated that the tetrahedral and octahedral sites, which are the important attributes of hexaferrites, were formed. The magnetic properties of the samples were measured by vibrating sample magnetometer (VSM). The VSM results of the samples showed that because of increasing Pb content, the amount of saturation magnetization and that of magnetic coercivity decreased from 81.29 to 10.23?emu/g and 2285–477?Oe, respectively. The optical properties of the samples were investigated by ultraviolet–visible spectroscopy, which revealed that the energy gap decreases and the absorption peaks move towards longer wavelengths by increasing Pb content. The dielectric properties of the samples were investigated by the LCR meter. It was found that by increasing frequency, the dielectric constant (ε^′) and the dielectric loss (?) of the samples were decreased.     

Impact of Dy on structural,dielectric and magnetic properties of Li-Tb-nanoferrites synthesized by micro-emulsion method

A series of Dy-doped Li–Ni ferrites of the following composition Li_0.5Ni_0.48Tb_0.02Dy_xFe_2−xO₄ (0.2≤x≥0) was synthesized by the microemulsion method. The X-ray diffraction (XRD) analysis indicated that Li_0.5Ni_0.48Tb_0.02Dy_xFe_2−xO₄nano-crystalline ferrites exhibited the single-phase spinel structure. The lattice parameter was determined by the Nelson-Riley refinement technique and it increased by increasing the Dy contents. The crystallite size was computed from the Debye Scherrer's formula and it was in range from 27 to 40 nm. The thermal decomposition process was studied by the thermogravimetric analysis and the annealing temperature observed was 980 °C. The real and complex parts of dielectric constant decreases very sharply in the lower frequency region, but in the higher frequency region, the real and complex part of dielectric constant show variable values with Dy contents. The dielectric tangent loss (tan δ) decreases exponentially with Dy contents. The magnitude of the ac conductivity decreases in certain frequency region, as the Dy contents are increased. The possible mechanisms contributing to the above behavior are discussed. The results of these nanocrystalline ferrites are very suitable materials for microwave device applications.     

Microwave absorption of M-type hexaferrite Ba1-xCaxFe12O19 (x ≤ 0.4) ceramics in 2.6–18 GHz

Ba_1-xCa_xFe₁₂O₁₉ (x?=?0.0, 0.1, 0.2, 0.3 and 0.4, BCFO) ceramics were prepared using high-temperature solid-state method and the effect of Ca²⁺ substitution was investigated. The grain size of BCFO ceramics sintered at 1250?°C for 2?h increases from 1?µm to 5?µm as Ca²⁺ added. The BCFO ceramics show a typical hard magnetic behavior with a maximum saturation magnetization (M_S) of 51.8?emu?g^?1 at x?=?0.2. The bandwidth of microwave reflection loss (RL) below ??10?dB (> 90.0% microwave absorption) is obtained in 7.60???9.8?GHz with the minimum RL ??30.8?dB at 8.5?GHz for x?=?0.2 (thickness 2.0?mm), which makes Ba_0.8Ca_0.2Fe₁₂O₁₉ ceramic a potential microwave absorption candidate.     

Raman spectra,bond characteristics,and microwave dielectric properties of Gd2Mo3O12 ceramics

Gd₂Mo₃O₁₂ ceramics were prepared using the traditional solid-phase reaction method. All samples were found to possess an orthorhombic crystal structure with a space group of Pba2, as revealed by refined XRD results. The ceramic sintered at 1000 °C exhibited a high relative density of 96.95 % and superior microwave dielectric properties, including ε_r of 9.42 ± 0.05,  × f of 49258 ± 1200 GHz, and τ_f of −71.8 ± 0.7 ppm/°C. The results suggest a correlation between an increase in ε_r and higher relative density, and a more compact and uniform microstructure can lead to higher  × f value. Chemical bonding theories and Raman spectroscopy analysis reveal that Mo-O bonds, rather than Gd-O bonds, dominate the microwave dielectric properties. Furthermore, the ε_r of Gd₂Mo₃O₁₂ ceramic was closely related to bond ionicity, while  × f and τ_f were mainly determined by lattice energy and bond energy, respectively.     

Hybrid 1-D dielectric microcavity: Fabrication and spectroscopic assessment of glass-based sub-wavelength structures

Two different 1-D multilayer dielectric microcavities are presented, one activated by Er³⁺ ions fabricated by rf-sputtering and other one containing CdSe@Cd_0.5Zn_0.5S quantum dots obtained by a hybrid radio frequency-sputtering/solution deposition process. The rare-earth activated cavity is constituted by an Er³⁺ -doped SiO₂ active layer inserted between two Bragg reflectors consisting of 10 pairs of SiO₂/TiO₂ layers. Starting from the deposition procedure used for this cavity a fabrication protocol was defined with the aim to combine the high reproducibility allowed by the sputtering deposition for the fabrication of multilayers structures with the ability of fabricate films activated with highly luminescent quantum dots dispersed in polymeric matrix. In this case the cavity was constituted by poly-laurylmethacrylate host matrix containing CdSe@Cd_0.5Zn_0.5S quantum dots inserted between two Bragg reflectors consisting of 10 pairs of SiO₂/TiO₂ layers fabricated by rf-sputtering on SiO₂ substrate. The thicknesses of the films of the Bragg reflectors were tailored in order to reflect the visible radiation at around 650 nm. Transmittance spectra were employed to assess the optical features of the single Bragg gratings and whole samples. Luminescence measurements put in evidence that emissions strongly influenced by the presence of the cavities for both the samples.