Influence of copper substitution on magnetic and electrical properties of MgCuZn ferrite prepared by microwave sintering method

Polycrystalline MgCuZn ferrites with chemical formula Mg_0.50-xCu_xZn_0.50Fe₂O₄ (x = 0.00, 0.05, 0.10, 0.15, 0.20, 0.25 and 0.30) were prepared by microwave sintering method. These powders were calcined, compacted and sintered at 950 °C for 30 min. Structural, microstructural and elemental analyses were carried out using X-ray diffraction (XRD), scanning electron microscope (SEM) and energy dispersive X-ray spectrometry (EDS), respectively. The lattice parameter is found to increase with increasing copper content. A remarkable densification is observed with the addition of Cu ions in the ferrites. The sintered ferrite was characterized for initial permeability, dielectric constant and dielectric loss tangent and ac conductivity measurements. The temperature variation of the initial permeability of these samples was carried out from 30 °C to 200 °C. The dielectric constant, dielectric loss tangent and ac conductivity have been measured in the frequency range of 100 Hz to 1 MHz. Initial permeability and dielectric constant were found to increase and dielectric loss decreased with Cu substitution for Mg, up to x = 0.20. The ferrite powder prepared is suitable for the application in multilayer chip inductor due to its low-temperature sinterability, good magnetic properties and low loss at high frequency.     

Synthesis,physical, ultrasonic waves,mechanical, FTIR,and dielectric characteristics of B2O3/Li2O/ZnO glasses doped with Y3+ ions

Six specimens of glasses with formula (70???x)B₂O₃/15Li₂O/15ZnO/xY₂O₃: x?=?0.0, 0.5, 1.0, 1.5, 2.0, and 2.5 mol%) have been synthesized via a conventional melt quenching technique. The produced specimens were named as BLZY0.0–BLZY2.5 according to x values. The physical, ultrasonic longitudinal (V_L) and shear (V_S) velocities, FTIR, and dielectric (50 Hz to 5 MHz) characteristics of the prepared glasses have been examined. With increasing content of Y₂O₃ from 0.0 to 2.5 mol%, the density (ρ) of the system increases linearly from 2512?±?11 to 2695?±?14 kg/m³, while the molar volume (V_M) decreases linearly from 2.6?±?0.011 to 2.57?±?0.013?×?10^?5 m³/mol. The oxygen packing density (OPD) as a number of the oxygen per unit composition in the glass sample is describing the packing tightness of the oxide network and thoroughly the compactness of the glass matrix. Values of the average boron–boron separation (d_B–B) decrease from 4.162 to 4.035?×?10^?10 (m) with 0 to 2.5 mol% Y₂O₃. Increasing formation of Y³⁺ ionic bonds with [BO_4/2]^1? may have an effect of lowering bond strength of B–O and thus shifting the absorption IR peak position. By increasing Y₂O₃ content in the investigated samples, the (V_L) and (V_S) increase linearly for the full-studied compositional range. The increasing number of strengthened bonds due to change coordination of B ions from 3 to 4 due to the increasing field strength of inserted accumulated Y³⁺ ions has the incentive impact to higher mechanical properties. The dielectric constant was decreased for Y₂O₃ content up to 1.5 mol% referring to cross-linkage formation with other elements, while the reduction in porosity at high content of Y₂O₃ is the main responsible for gradual enhancement in dielectric constant.

     

Effect of V2O5 additive to 0.4SrTiO3–0.6La(Mg0.5Ti0.5)O3 ceramics on sintering behavior and microwave dielectric properties

The effect of V₂O₅ addition on the microwave dielectric properties and the microstructures of 0.4SrTiO₃–0.6La(Mg_0.5Ti_0.5)O₃ ceramics sintered for 5 h at different sintering temperature were investigated systematically. It was found that the sintering temperature was effectively lowered about 200 °C by increasing V₂O₅ addition content. The grain sizes, bulk density as well as microwave dielectric properties were greatly dependent on sintering temperature and V₂O₅ content. The 4ST–6LMT ceramics with 0.25% V₂O₅ sintered at 1400 °C for 5 h in air exhibited optimum microwave dielectric properties of ɛ_r = 50.7, Q × f = 15049.6 GHz, T_f = −1.7 ppm/°C.     

Strategies for low-temperature sintering of BST ceramics with attractive dielectric properties

In this study, the powders of the Ba_0.75Sr_0.25TiO₃ (BST) nanoparticles were directly synthesized by milling of Ba(OH)₂·8H₂O, Sr(OH)₂·8H₂O, and Ti(BuO)₄ in ethanol at room temperature. They have homogenous grains of?~?15 nm and high sintering activity. The dense ceramics with the density?>?90% can be obtained at a sintering temperature of?≤?950 °C by adding 3 wt% sintering aids of Bi₂O₃ and Li₂CO₃. Several Bi-related intermediate compounds act as perovskite-structured templates to sintering the ceramics at a different temperature. They enhance the mass transfer and promote the sintering densification. These compounds such as Ba₂BiO₄ and SrBiO₄ appear at 800 °C, LiBa₄Bi₃O₁₁ and Sr_1.2Bi_0.8O₃ appear over 830 °C, and Bi_8.11Ba_0.89O_13.05 appears at 950 °C. The cation Bi in them can have mixture valences of 3+ and 5+. It makes the ceramics as semiconducting state with the dark gray color and decreases the ceramic resistivities. With the sintering temperature increase, especially at 950 °C, the cation Bi tends back to single valence of +3 in the ceramics. The most of alkaline earth cations in Bi-related compounds will release and resorb into the lattice of BST and drive the sintering densification. The BST ceramics can have a peak dielectric constant?>?6500 (at 53 °C) with loss?<?0.025 at 10 kHz, and resistivity?>?10¹² Ω cm when sintered at a temperature of?≥?900 °C with 3 wt% sintering aids. They have a potential application for multiple layer ceramic capacitors (MLCC) with silver inner electrodes.

     

Effect of B2O3 and CuO additions on the sintering temperature and microwave dielectric properties of 3Li2O–Nb2O5–3TiO2 ceramics

The effects of B₂O₃–CuO (BCu, the weight ratio of B₂O₃ to CuO is 1:1) addition on the sintering behavior, microstructure, and the microwave dielectric properties of 3Li₂O–Nb₂O₅–3TiO₂ (LNT) ceramics have been investigated. The low-amount addition of BCu can effectively lower the sintering temperature of LNT ceramics from 1125 to 900 °C and induce no obvious degradation of the microwave dielectric properties. Typically, the 2 wt% BCu-added ceramic sintered at 900 °C has better microwave dielectric properties of ε _r  = 50.1, Q × f = 8300 GHz, τ _f  = 35 ppm/°C. Silver powders were cofired with the dielectric under air atmosphere at 900 °C. The SEM and EDS analysis showed no reaction between the dielectric ceramic and silver powders. This result shows that the LNT dielectric materials are good candidates for LTCC applications with silver electrode.     

Microwave dielectric properties and compatibility with silver of low-fired Ba2Ti3Nb4O18 ceramics with BaCu(B2O5) addition

The effects of BaCu(B₂O₅) (BCB) additions on the sintering temperature and microwave dielectric properties of Ba₂Ti₃Nb₄O₁₈ ceramic have been investigated. The addition of BCB can lower the sintering temperature of Ba₂Ti₃Nb₄O₁₈ ceramic from 1,250 to 900 °C and induce no obvious degradation of the microwave dielectric properties. Typically, the 5 wt% BCB added Ba₂Ti₃Nb₄O₁₈ ceramic sintered at 900 °C for 2 h exhibited good microwave dielectric properties of Q × f = 17,600 GHz, ε _r = 38.2 and τ _f  = 7 ppm/°C. The dielectric ceramic demonstrated stability against the reaction with the Ag electrode, which suggests that the ceramics could be applied in multilayer microwave devices requiring low sintering temperatures.     

Impact of transition metal doping on Mössbauer,electrical and dielectric parameters of structurally modified lithium ferrite nanomaterials

Zr–Mn doped spinel lithium ferrites Li_0.5Fe_2.5−2xZr_xMn_xO₄ (0.0 ≤ x ≤ 0.5) are synthesized using the citrate precursor method. The spinel ferrite is formed at a relatively lower annealing temperature (873 K) compared to those synthesized by other conformist methods. Powder X-ray diffraction (XRD) and scanning electron microscopy (SEM) analysis are carried out to determine the cell parameters, crystallite size and grain growth. Cation distribution and site preferences for the doped ions are determined by Mössbauer spectroscopy at room temperature. The impact of doping of Li_0.5Fe_2.5O₄ with the binary mixtures of transition metals (Mn, Zr) on hyperfine interaction parameters (δ, Δ and H_int), electrical resistivity (ρ), dielectric constant (?) and dielectric loss tangent (tan δ) over the frequency range of 100 Hz to 3 MHz is discussed in details. Zr–Mn doping enhanced the DC electrical resistivity and decreased the loss tangent value which is considered useful for technological application in microwave and telecommunication devices.     

Low-temperature firing and microwave dielectric properties of MgTiO3 ceramics with Bi2O3–V2O5

The effects of Bi₂O₃–V₂O₅ additive on the microstructures, the phase formation and the microwave dielectric properties of MgTiO₃ Ceramics were investigated. The Bi₂O₃–V₂O₅ addition lowered the sintering temperature of MgTiO₃ ceramics effectively from 1400 to 875 °C due to the liquid-phase effect. The microwave dielectric properties were found to strongly correlate with the amount of Bi₂O₃–V₂O₅ addition. The saturated dielectric constant decreased and the maximum Qf values increased with the increasing V₂O₅ content, which is attributed to the variation of the second phase including Bi₂Ti₂O₇, Bi₄V_1.5Ti_0.5O_10.85 and BiVO₄. At 875 °C, MgTiO₃ ceramics with 5.0 mol% Bi₂O₃–7 mol% V₂O₅ gave excellent microwave dielectric properties: ε_r = 20.6,Qf = 10420 GHz (6.3 GHz).     

Sintering behaviour of lithium ferrites containing Nb2O5 and V2O5

Lithium ferrite toroids with various compositions and with various amounts of Nb₂O₅ or V₂O₅, have been prepared by a powder compacting method, and their sintering behaviours, microstructures and weight-loss characteristics have been investigated. The rate of sintering is higher in an Fe₂O₃-deficient lithium ferrite than in an Fe₂O₃-excess lithium ferrite due to the presence of excess oxygen vacancy in the Fe₂O₃-deficient lithium ferrite during sintering. The presence Of LiNbO₃ or LiVO₃, which is formed by Nb₂O₅ or V₂O₅, on the surface of lithium ferrite grains causes an increase in oxygen activity of the lithium ferrite and a decrease in the rate Of lithium evaporation during sintering, resulting in a strong enhancement in the sintering rate. The enhancing effect of V₂O₅ in the sintering Of lithium ferrite is stronger than that of Nb₂O₅ due to the possible formation of liquid V₂O, before the formation of LiVO₃.     

Preparation and properties of low-temperature co-fired ceramic of CaO–SiO2–B2O3 system

Low temperature co-fired ceramic (LTCC) was prepared by sintering a glass selected from CaO–SiO₂–B₂O₃ system, in which 0.5 wt% P₂O₅ and 0.5 wt% ZnO were added to optimize the preparation conditions. The glass powder and sintered bodies were characterized by different analytical techniques such as TG-DTA analysis, X-ray diffraction and Scanning electron microscopy. It was found that the optimal sintering temperature was 820°C based on the microstructure and the properties of sintering bodies, and then the major phases of the LTCC were CaSiO₃, CaB₂O₄ and SiO₂. The obtained products, with dielectric constant about 6.5, dielectric loss about 2 × 10⁻³ at 30 MHz and coefficient of thermal expansion about 8 × 10⁻⁶ °C⁻¹ between 20 and 400°C, are supposed to be suitable for application in wireless communications.     

Sintering temperature dependence of microwave dielectric properties in Mg4(TaNb1−xVx)O9 compounds

The relationship between the sintering temperature and the microwave dielectric properties of Mg₄(TaNb_1−xV_x)O₉ (MTNV) compounds were investigated in this study in order to reduce the sintering temperature of the compound. A small amount of V₂O₅ doping lowered the sintering temperature of the MTNV compounds. The variations in the dielectric constant and the quality factor of the MTNV compounds depended on the amount of V₂O₅ doping and the sintering temperature; a small amount of V₂O₅ doping was effective in allowing low sintering temperatures without a detrimental effect on these dielectric properties. As a result, a dielectric constant of approximately 12 and a quality factor of approximately 200,000 GHz were obtained when the MTNV compounds with x = 0.2 was sintered at 1200 °C. The temperature coefficient of resonant frequency of the MTNV compound with x = 0.025 slightly changed from −63 to −73 ppm/ °C with an increased sintering temperature because of the presence of a secondary phase.     

Effect of vanadium doping on sintering and dielectric properties of strontium barium niobate ceramics

Strontium barium niobate, Sr_0.5Ba_0.5Nb₂O₆ (SBN50) ceramics doping up to 3 wt% V₂O₅ were fabricated by solid state reaction route, starting from raw materials (oxides and carbonates) of analytical grade. The phase composition, microstructure and dielectric properties were investigated by X-ray diffraction, scanning electric microscope and impedance analyzer. The results show that the addition of V₂O₅ improves sintering densification of SBN ceramic samples. The relative density of the samples firstly increases and then slightly decreases with increasing amounts of V₂O₅ and sintering temperature. With the help of the additive of 1 wt% V₂O₅, the relative density of the sample sintered at 1,280 °C for 3 h can reached 97.2%. Only single tetragonal tungsten bronze phase SBN exists in all the doped samples. With increase in V₂O₅ content, the dielectric constant of SBN ceramics at both room temperature and in the vicinity of the phase transition temperature increases significantly and the Curie temperatures (Tc) obviously shifts to low temperature as well as the dielectric loss remains below 0.06. The diffuseness in the phase transition is found to increase with increase in vanadium doping level. The addition of V₂O₅ results in an increased grain size associated with rod-like grain growth.     

The effect of V2O5 on the sintability and physical properties of Bi2O3-NiO-Nb2O5 and Bi2O3-ZnO-Nb2O5 temperature-stable dielectrics

The sintering temperature of the bismuth-based temperature-stable dielectrics (BNN-BZN) is reduced down to 850 °C with 1.0 wt % of V₂O₅, which is the lowest to our knowledge. The effect of dopant is studied in detail. The V₂O₅ seems to provide an eutectic melt below the sintering temperature to increase the sinterability. A composite character was observed with 1.0 wt % of V₂O₂ doping, while a new solid-solution phase was found without or fewer amounts of additive. Nevertheless, the obtained physical property of the sample with 1.0 wt % of V₂O₅ is promising. Following combination of physical properties is obtained consistently without any quenching procedure; dielectric constant >95, Q 2000, T.C. = –8.6 ppm (30–100 °C), and specific resistivity = 10¹² cm.     

Microstructures and microwave dielectric properties of low-temperature sintered Ca2Zn4Ti15O36 ceramics

Low-temperature sintered Ca₂Zn₄Ti₁₅O₃₆ microwave dielectric ceramic was prepared by conventional solid state reaction method. The influences from V₂O₅ addition on the sintering behavior, crystalline phases, microstructures and microwave dielectric properties were investigated. The crystalline phases and microstructures of Ca₂Zn₄Ti₁₅O₃₆ ceramic with V₂O₅ addition were investigated by X-ray diffraction, scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). V₂O₅ addition lowered the sintering temperature of Ca₂Zn₄Ti₁₅O₃₆ ceramics from 1140 °C to 930 °C. Ca₂Zn₄Ti₁₅O₃₆ ceramic with 5wt% V₂O₅ addition could be densified well at 930 °C, and showed good microwave dielectric properties of ε_r ~ 46, Q × f ~ 13400 GHz, and temperature coefficient of resonant frequency (τ_f) ~ 164 ppm/°C.

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Low-firing of BiSbO4 microwave dielectric ceramic with V2O5–CuO addition

Effects of 1.0 wt.% V₂O₅–CuO mixture addition on the sintering behavior, phase composition and microwave dielectric properties of BiSbO₄ ceramics have been investigated. BiSbO₄ ceramics can be well densified below temperature about 930 °C with 1.0 wt.% V₂O₅–CuO mixtures addition with different ratios of CuO to V₂O₅. The formation of BiVO₄ phase and substitution of Cu²⁺ can explain the decrease of sintering temperature. Dense BiSbO₄ ceramics sintered at 930 °C for 2 h exhibited good microwave dielectric properties with permittivity between 19 and 20.5, Qf values between 19,000 and 40,000 GHz and temperature coefficient of resonant frequency shifting between ?71.5 ppm °C^?1 and ?77.8 ppm °C^?1. BiSbO₄ ceramics could be a candidate for microwave application and low temperature co-fired ceramics technology.     

Sintering behaviors,microstructures and dielectric properties of CaO-B2O3-SiO2 glass ceramic for LTCC application with various network modifiers content

CaO-B₂O₃-SiO₂ (CBS) glass ceramic with various glass network modifiers were synthesized to develop a kind of material sintered at low temperature for multi-layer ceramic substrates. The influence of double alkali metal oxides (Na₂O and K₂O) on sintering characteristics, microstructures and dielectric properties of CBS glass ceramic were investigated. XRD analysis showed that the major crystalline phase was β-CaSiO₃ and CaB₂O₄, and the strength of the peak increased with the addition of network modifiers. DSC curve revealed that the process of crystallization and softening were obviously affected. SEM photographs exhibited that the microstructures were composed of amorphous phases, pores and crystalline phases. FTIR showed that the additives changed the continuity of CBS glass structure. An appropriate amount of Na₂O and K₂O additives could significantly improve the sintering characteristics and dielectric properties. CBS samples with 1.5 wt% (Na₂O?+?K₂O) sintered at 850 °C for 15 min presented the best performances with the bulk density of 2.53 g/cm³, ε_r?=?5.94 and tanδ?=?1.22?×?10^?3 at 10 GHz.

     

Impedance spectroscopy study of TiO2 addition on the ceramic matrix Na2Nb4O11

In this paper a study of TiO₂ addition (0, 2, 5 and 10 wt%) and its effects in the impedance spectra of Na₂Nb₄O₁₁ ceramic matrix was carried out. The structural, dielectric properties of the addition in the Na₂Nb₄O₁₁ matrix were discussed. In the preliminary structural studies, X-ray diffractograms of the samples were recorded at room temperature with X-ray diffractometer with Cu-kα. The Rietveld refinement method was used and confirmed the monoclinic structure for pure sample. A study based on complex impedance spectroscopy was carried and the dielectric properties were obtained over a frequency range (100 Hz–1 MHz) in room temperature (300 K). In the dielectric analysis at 1 MHz was observed relative permittivity of 99.46 for pure sample and 84.37 to sample added with 5 wt% of TiO₂, those samples showed losses 3.55 × 10^?2 and 9.22 × 10^?2, respectively. In relation to relaxation phenomenon, Cole–Cole function was used for fitting pure and added samples data.     

Preparation and characterization of the bismuth sodium titanate (Na0.5Bi0.5TiO3) ceramic doped with ZnO

This study investigates effects of the zinc oxide (ZnO) addition and the sintering temperature on the microstructure and the electrical properties (such as dielectric constant and loss tangent) of the lead-free piezoelectric ceramic of bismuth sodium titanate (Na_0.5Bi_0.5TiO₃), NBT, which was prepared using the mixed oxide method. Three kinds of starting powders (such as Bi₂O₃, Na₂CO₃ and TiO₂) were mixed and calcined. This calcined NBT powder and a certain weight percentage of ZnO were mixed and compressed into a green compact of NBT–ZnO. Then, this green compact of NBT–ZnO was sintered to be a disk doped with ZnO, and its characteristics were measured. In this study, the calcining temperature was 800 °C, the sintering temperatures ranged from 1000 to 1150 °C, and the weight percentages of ZnO doping included 0.0, 0.5, 1.0, and 2.0 wt%. At a fixed wt% ZnO, the grain size increases with increase in the sintering temperature. The largest relative density of the NBT disk obtained in this study is 98.3% at the calcining temperature of 800 °C, the sintering temperature of 1050 °C, and 0.5 wt% ZnO addition. Its corresponding dielectric constant and loss tangent are 216.55 and 0.133, respectively.     

A.c. conduction through MIM sandwich samples of evaporated thin films of V2O5 and V2O5/B2O3

The a.c. electrical properties of evaporated V₂O₅ and co-evaporated V₂O₅/B₂O₃ films have been investigated. The conductivity in both types of film follows the theory of Elliott for single polaron hopping. The behaviour of capacitance, tangent of loss angle and dielectric loss agrees with the model proposed by Goswami and Goswami. The co-evaporated films of V₂O₅/B₂O₃ show better dielectric properties than simple V₂O₅ with increasing content of B₂O₃. Because of their hygroscopic character, the films with B₂O₃ content larger than 40% are observed to be unstable in the atmosphere.     

Dielectric characteristics of Ba(Mg1/3Ta2/3)O3 ceramics sintered at low temperatures

Dielectric characteristics of Ba(Mg_1/3Ta_2/3)O₃ ceramics (BMT ceramics) sintered at low temperatures with 2–3 wt% NaF additives were determined. A dielectric constant of 25 and extremely low dielectric loss (< 0.0001) were measured at 100 kHz and 1 MHz in BMT ceramics sintered under these conditions, and no frequency dependence of the dielectric constant was observed. This suggested that NaF as sintering additive had no harmful influence on the dielectric properties of the ceramics.