Dielectric and microstructural properties of sintered BaTiO3 ceramics prepared from different TiO2 raw materials

BaTiO₃ ceramics, sintered from powders previously synthesized using TiO₂ of different characteristics, have been studied. The microstructural development depended on the crystalline nature and impurity types and levels, when the same sintering schedules were applied. Anatase leads to BaTiO₃ powders which showed a controlled grain growth after sintering. Rutile with very low impurity levels gave materials in which a non-uniform grain growth was promoted. Dielectric constant and loss tangent were measured and correlated with the density and microstructure. From these correlations, it seems that the raw materials' nature has a greater effect on the dielectric properties that the sintering schedule of a given material.     

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.     

Optical,morphological, electrical properties of ZnO-TiO2-SnO2/CeO2 semiconducting ternary nanocomposite

Low dielectric constant and low dielectric loss with moderate wide bandgap, novel semiconducting metal oxide composites are useful materials for applying optoelectronic, microwave dielectric ceramics. A less dielectric constant is required for wireless communication to reduce the cross pairing between conductors and also for fast signal transmission. In the present study, the structural, optical, and dielectric properties of ternary ZnO - TiO₂ added with SnO₂/CeO₂ semiconducting nanocomposite materials were investigated and synthesized by the solid-state gelation method. The samples were sintered at a temperature of 450 ⁰C. The X-ray diffraction patterns of composites revealed the existence of TiO₂ anatase phase, SnO_2, and CeO₂. The average crystallite size at d₁₀₁ was measured using the Scherer method, ranging from 6.18 nm to 9.13 nm. The overall crystallite size was calculated using the Size-strain plot method, and it is in the range of 14.8 nm to 17.16 nm. The surface morphology of all samples appears uniform in size and spherical shape. The average particle size of grains was 35 nm. The absorbance properties studied by UV–Visible spectroscopy and bandwidth were 2.6 eV calculated using Tauc’s plot method, and it reveals the formation of new energy levels. The dielectric properties of pellet dimensions of 1 mm thickness and 10 mm diameter, measured from the LCR meter, are indicated at 1 kHz frequency. The most significant dielectric constant (ε_r) and lowest loss tangent (Tan δ) are 53.89 and 0.25 for pure ZnO - TiO₂, and the lowest dielectric constant (ε_r) and less loss tangent (Tan δ) are 9.69 and 0.38 for 1 wt% CeO₂ doped to ZnO - TiO₂. The conductivity of the composite is in the range of 10^-7 S/cm. With additive concentration to ZnO - TiO₂, both SnO₂ and CeO₂ are equally potential and modifies the parameters due to the similar bandgaps and more oxygen availability.     

Current–voltage nonlinear and dielectric properties of CaCu3Ti4O12 ceramics prepared by a simple thermal decomposition method

In this work, pure-CaCu₃Ti₄O₁₂ was successfully prepared by a simple thermal decomposition method. This can easily be achieved by direct firing of starting raw materials dissolved in an aqueous citric acid solution at 800 °C for 6 h. The results show that sintering conditions have a remarkable influence on the microstructure of the CaCu₃Ti₄O₁₂ ceramics. Interestingly, dense CaCu₃Ti₄O₁₂ ceramic sintered at 1,050 °C for 2 h exhibits a high dielectric constant of ~5.1 × 10³ with low loss tangent of ~0.048 at 30 °C and 1 kHz. The dielectric properties, electrical response of grain boundaries, and related nonlinear current–voltage behavior are found to be associated with the microstructure of CaCu₃Ti₄O₁₂ ceramics.     

Enhanced microwave dielectric properties of Ba<Subscript>0.40</Subscript>Sr<Subscript>0.60</Subscript>TiO<Subscript>3</Subscript>–Zr<Subscript>0.80</Subscript>Sn<Subscript>0.20</Subscript>TiO<Subscript>4</Subscript> composite ceramics

The (1−x) Ba_0.40Sr_0.60TiO₃ (BST)−xZr_0.80Sn_0.20TiO₄ (ZST) composite ceramics with x = 10, 20, 30, and 40 wt% were fabricated by conventional solid-state reaction method. With increasing of ZST content, the dielectric constant of composite ceramics was decreased and dielectric loss increases. The effect of ZnO addition to 70 wt% BST–30 wt% ZST composition on the microstructure and dielectric properties was investigated. The improvements in dielectric constant, dielectric loss, and microwave dielectric properties of composite ceramics can be achieved by ZnO addition. The sample with 98 wt% (70 wt% BST–30 wt% ZST)–2 wt%ZnO composition exhibits promising dielectric properties, with dielectric constant, loss tangent and tunability at 4 kV/mm, of 125, 0.0016 and 12%, at 10 kHz and room temperature. At ~2 GHz, it possesses a dielectric constant of 101 and a Q factor of 187, which makes it a good candidate for tunable microwave device applications.     

Effect of temperature on nonlinear electrical behavior and dielectric properties of (Ca, Ta)-doped TiO2 ceramics

TiO₂ ceramics doped with 0.75 mol% Ca and 2.5 mol% Ta were sintered at different temperatures ranging from 1300 to 1450°C. The effects of sintering temperature on the microstructure, nonlinear electrical behavior, and dielectric properties of the ceramics were studied. The sample sintered at 1300°C exhibits the highest nonlinear coefficient (5.5) and a comparatively lower relative dielectric constant.     

The effect of glass addition on the dielectric properties of barium strontium titanate

Ba_0.7Sr_0.3TiO₃ (BST) ceramics were prepared by the conventional solid state ceramic route. Different weight percentages of twelve different glasses were added to the calcined BST ceramics and sintered. The structure and microstructure of the sintered materials were investigated by X-ray diffraction and Scanning Electron Microscopic techniques. The low frequency dielectric properties of the glass-ceramic composites were measured using LCR meter. Some of the glasses improved the dielectric properties and considerably lowered the sintering temperature. The glasses were prepared and characterized under identical conditions. Among the different glasses, 1.5 wt% addition of 71ZnO–29B₂O₃ lowered the sintering temperature of BST to 975 °C with a dielectric loss of 9 × 10⁻³ and dielectric constant of 875 at 1 MHz. The curie temperature of BST ceramics was found to shift towards lower temperature with glass addition.     

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.     

Structure and microwave dielectric characteristics of lithium-excess Ca0.6Nd0.8/3TiO3/(Li0.5Nd0.5)TiO3 ceramics

Compositions based on (1−x)Ca_0.6Nd_8/3TiO₃−x(Li_1/2Nd_1/2)TiO₃ + yLi (CNLNTx + yLi, x = 0.30–0.60, y = 0–0.05), suitable for microwave applications have been developed by systematically adding excess lithium in order to tune the microwave dielectric properties and lower sintering temperature. Addition of 0.03 excess-Li simultaneously reduced the sintering temperature and improved the relative density of sintered CNLNTx ceramics. The excess Li addition can compensate the evaporation of Li during sintering process and decrease the secondary phase content. The CNLNTx (x = 0.45) ceramics with 0.03 Li excess sintered at 1190 °C have single phase orthorhombic perovskite structure, together with the optimum combination of microwave dielectric properties of ɛ_r = 129, Q × f = 3600 GHz, τ_f = 38 ppm/°C. Obviously, excess-Li addition can efficiently decrease the sintering temperature and improve the microwave dielectric properties. The high permittivity and relatively low sintering temperatures of lithium-excess Ca_0.6Nd_0.8/3TiO₃/(Li_0.5Nd_0.5)TiO₃ ceramics are ideal for the development of low cost ultra-small dielectric loaded antenna.     

Influence of Bi2O3 and CuO addition on low-temperature sintering and dielectric properties of Ba0.6Sr0.4TiO3 ceramics

In this study, we tried to lower the sintering temperature of Ba_0.6Sr_0.4TiO₃ (BST) ceramics by several kinds of adding methods of Bi₂O₃, CuO and CuBi₂O₄ additives. The effects of different adding methods on the microstructures and the dielectric properties of BST ceramics have been studied. In the all additive systems, the single addition of CuBi₂O₄ was the most effective way for lowering the sintering temperature of BST. When CuBi₂O₄ of 0.6 mol% was mixed with starting BST powders and sintered at 1100 °C, the derived ceramics demonstrated dense microstructure with a low dielectric constant (? = 4240), low dielectric loss (tan δ = 0.0058), high tunability (Tun = 38.3%) and high Q value (Q = 251). It was noteworthy that the sintering temperature was significantly lowered by 350 °C compared with no-additive system, and the derived ceramics maintained the excellent microwave dielectric properties corresponding to pure BST.     

Microwave and photoluminesent characterizations of (Ca<Subscript>2</Subscript>Mg<Subscript>3</Subscript>)(X<Subscript>1.75</Subscript>Sb<Subscript>0.25</Subscript>)TiO<Subscript>12</Subscript> [X = Nb and Ta] ceramics

(Ca₂Mg₃)(X_1.75Sb_0.25)TiO₁₂ [X = Nb and Ta] ceramics are prepared through the conventional solid-state route. The samples are calcined at 1,100 and 1,180 °C, and are sintered at 1,250 and 1,375 °C. The substitution of Sb decreases the calcination and sintering temperatures of pure (Ca₂Mg₃)(Nb/Ta)₂TiO₁₂. The structure of the samples is analyzed using X-ray diffraction method. The microstructure of the sintered pellet is studied using scanning electron microscopy. The dielectric properties such as dielectric constant (ε_r), quality factor (Q_uxf) and temperature coefficient of resonant frequency (τ_f) are measured in the microwave frequency region. By Sb substitution, thermal stability is achieved, with the increase in dielectric constant, without much change in the quality factor. The materials have intense emission lines in the wavelength region 500–700 nm. The compositions have good microwave dielectric properties and photoluminescence and hence are suitable for dielectric resonator and ceramic laser applications.     

Low-temperature sintered (Zn0.65Mg0.35)TiO3 microwave ceramics doped with CuV2O6

The influence of the CuV₂O₆ additives on the densification, microstructural evolution, and dielectric properties of (ZnMg)TiO₃ (ZMT) ceramics was investigated. The sintering agent CuV₂O₆ can significantly enhance the sinterability and lower the firing temperature of ZMT dielectrics to ≤930 °C. SEM shows that liquid phase sintering induced by CuV₂O₆ can promote the grain growth and elevate the bulk density dramatically. XRD indicates that excess CuV₂O₆ beyond the solubility ~1.5 wt% could form the secondary phase and affect the crystalline structure. The microwave results show that the dielectric constant (ε_r) increases gradually, but the quality factor (Q × f) and the temperature coefficients of resonant frequency (τ_f) decrease with increasing CuV₂O₆ content. Moreover, TiO₂ addition can effectively improve the microwave properties of CuV₂O₆-doped ZMT dielectrics and especially compensate the negative τ _f. (Zn_0.65Mg_0.35)TiO₃ ceramics codoped with 1 wt% CuV₂O₆ and 9 wt% TiO₂ sintered at 930 °C exhibited the optimum microwave dielectric properties: ε _r = 26.2, Q × f = 31,930 GHz, τ _f ≈ −0.32 × 10⁻⁶/°C.     

Dielectric properties of Sb2O3-doped Ba0.672Sr0.32Y0.008TiO3

Sb₂O₃-doped Ba_0.672Sr_0.32Y_0.008TiO₃ (BSYT) dielectric ceramics were prepared by conventional solid state method, and their dielectric properties were investigated with variation of Sb₂O₃ doping content and sintering temperature. The X-ray diffraction patterns indicated that all the BSYT specimens possessed the perovskite polycrystalline structure. The experimental results reveal that the introduction of Sb₂O₃ into Ba_0.672Sr_0.32Y_0.008TiO₃ can control the grain growth, reduce the relative dielectric constant and dielectric loss, shift the Curie temperature to lower temperature and significantly improve the thermal stability of the BSYT ceramics. The samples doped with 1.6 wt.% Sb₂O₃ sintered at 1320 °C for 2 h exhibited attractive properties, including high relative dielectric constant (> 1500), low dielectric loss (< 40 × 10^− 4), low temperature coefficient of capacitor(< ± 35%) over a wide temperature range from − 25 °C to + 85 °C.     

Effect of sintering temperature on dielectric properties of Ba0.6Sr0.4TiO3–MgO composite ceramics prepared from fine constituent powders

Composite ceramics of Ba_0.6Sr_0.4TiO₃ + 60 wt.% MgO were prepared from fine constituent powders by sintering at 1200–1280 °C. The composite specimens sintered at the relatively low temperatures showed satisfactory densification due to fine morphology of the constituent powders. The elevation of sintering temperature promoted the incorporation of Mg²⁺ into the lattice of the Ba_0.6Sr_0.4TiO₃ phase and grain growth of the two constituent phases. The dependence of the dielectric properties on sintering temperature was explained in relation to the structural evolution. Controlling the sintering temperature of the composite was found to be important to achieve the desired nonlinear dielectric properties. Sintering at 1230 °C was determined to be preferred for the composite in terms of the nonlinear dielectric properties. The specimen sintered at the temperature attained a tunability of 17.3% and a figure of merit of 127 at 10 kHz and 20 kV/cm.     

Effects of sintering temperature on microstructure and electrical properties of 0.9Pb(Mg1/3Nb2/3)O3–0.1PbTiO3 modified with CuO

The structural, dielectric and ferroelectric properties of Pb(Mg_1/3Nb_2/3)_0.9Ti_0.1O₃ (PMNT) ceramics prepared with CuO as a sintering aid at various sintering temperatures between 950 °C and 1150 °C are investigated. The lattice parameters slightly increase with the sintering temperature >1050 °C. A significant increase in the grain size is observed when the sintering temperature is increased from 1000 °C to 1050 °C. The maximum dielectric constant reaches the highest value of ∼22,000 for the ceramic sintered at 1050 °C. For the ceramics sintered at >1050 °C, the temperature of maximum dielectric constant and the diffuseness parameters tend to increase with the increasing sintering temperature. The optimal sintering temperature for this ceramic is 1050 °C, which displays significant improvements in ferroelectric properties at room temperature, i.e. the increase in the remanent polarization and the ferroelectric loop squareness.     

Dielectric properties of (Ba,Nb) doped TiO2 ceramics: Migration mechanism and roles of (Ba,Nb)

Ultrahigh relative dielectric constants with stable frequency and temperature dependence as well as relatively low loss tangent are found in barium and niobium doped TiO₂ ceramics with a silver electrode. The roles of barium and niobium on the dielectric properties of the ceramics are explained after the migration mechanism and the influence of barium and niobium have been analysed. Both silver electrodes made from silver paste and evaporated aluminium electrodes are employed in the study, their effects are also discussed. The migration mechanism proposed is electron hopping among oxygen vacancies. Dissolving barium into TiO₂ ceramics creates an additional oxygen vacancy which results in an increase in conductivity and relaxation frequency of the loss tangent. In contrast, niobium tends to reduce the concentration of oxygen vacancies and causes the opposite effect. The effects of barium and niobium on the concentration of the oxygen vacancy are supported by results of densification and microstructural investigations.     

A new microwave dielectric ceramic for LTCC applications

A new low-sintering temperature microwave dielectric ceramic was found and investigated in the Li₂O–Nb₂O₅–TiO₂ (Li₂O:Nb₂O₅:TiO₂ = 5.7:1:14.7, by mole, abbreviated as LNT) system. This new microwave dielectric ceramic shows a relatively high permittivity (47), high Q × f values up to 17,800 GHz, and low temperature coefficients (57 ppm/°C), which were obtained via sintering at 1,125 °C. With the low-level doping of B₂O₃–CuO (BCu) (below 2 wt%), the sintering temperature of the LNT ceramic could be effectively reduced to 900 °C. The addition of BCu does not induce apparent degradation in the microwave properties but lowers the τ _f value. Typically, the 2.0 wt% BCu-doped ceramics sintered at 900 °C have better microwave dielectric properties of ε_r = 48.7, Q × f = 16,350 GHz, τ _f  = 32 ppm/°C, which suggest that the ceramics could be applied in multilayer microwave devices requiring low sintering temperatures.     

Low temperature sintering and microwave dielectric properties of zinc silicate ceramics

Effects of ZnO–B₂O₃–SiO₂ glass on the sintering behavior, the microstructure, and the microwave dielectric properties of Zn₂SiO₄ ceramics have been investigated. The ZnO–B₂O₃–SiO₂ glass lowered the sintering temperature of Zn₂SiO₄ ceramics effectively from 1300 to 900 °C. The X-ray diffraction results showed that the secondary phase of SiO₂ in the Zn₂SiO₄ ceramics could be dissolved in the glass. The dielectric constant decreased slightly, and the quality factor decreased with increasing glass content. Especially, when the glass content was chosen as 20 wt%, the ceramics sintered at 900 °C for 2 h exhibited a low dielectric constant of 6.85, a high quality factor of 31,690 and the temperature coefficient of the resonant frequency of −28 ppm/°C, which demonstrated a good potential for use in low temperature co-fired ceramics field.     

Synthesis and dielectric properties of MXTi<Subscript>7</Subscript>O<Subscript>16</Subscript> (M = Ba and Sr; X = Mg and Zn) hollandite ceramics

MXTi₇O₁₆ (M = Ba and Sr; X = Mg and Zn) ceramics have been synthesized by the conventional solid state ceramic route. The dielectric properties such as dielectric constant (ε_r), loss tangent (tan δ) and temperature variation of dielectric constant (τ_εr) of the sintered ceramic compacts are studied using an impedance analyser up to 13 MHz region. The strontium compounds have relatively high dielectric constant and low loss tangent compared to the barium analogue. The phase purity of these materials has been examined using X-ray diffraction studies and microstructure using SEM method.     

Microstructure and electrical properties of K<Subscript>0.5</Subscript>Na<Subscript>0.5</Subscript>NbO<Subscript>3</Subscript> lead-free piezoelectric ceramics sintered in low pO<Subscript>2</Subscript> atmosphere

Pure K_0.5Na_0.5NbO₃ lead-free piezoelectric ceramics without any dopants/additives were sintered at various temperatures (950–1125 °C) in low pO₂ atmosphere (pO₂?~?10^?6 atm). All ceramics exhibit high relative densities (>?94%) and low weight loss (<?0.6%). Compared to the ceramics sintered in air, the ceramics sintered in low pO₂ exhibit improved electrical properties. The piezoelectric constant d₃₃ and converse piezoelectric constant d₃₃* are 112 pC/N and 119 pm/V, respectively. The ceramics show typical ferroelectric behavior with the remnant polarization of 21.6 µC/cm² and coercive field of 15.5 kV/cm under measurement electric field of 70 kV/cm. The good electrical properties of the present samples are related to the suppression of volatility of the alkali cations during the sintering process in low pO₂ atmosphere.