Microstructure and electrical properties of the rare-earth doped 0.94Na0.5Bi0.5TiO3-0.06BaTiO3 piezoelectric ceramics

Phase structure, microstructure, piezoelectric and dielectric properties of the 0.4 wt% Ce doped 0.94Bi_0.5Na_0.5TiO₃-0.06BaTiO₃ (Ce-BNT6BT) ceramics sintered at different temperatures have been investigated. The powder X-ray diffraction patterns showed that all of the Ce-BNT6BT ceramics exhibited a single perovskite structure with the co-existence of the rhombohedral and tetragonal phase. The morphologies of inside and outside of the bulk indicated that the different sintering temperatures did not cause the second phase on the inside of bulk. However, the TiO₂ existed on the outside of the bulk due to the Bi₂O₃ and Na₂O volatilizing at higher temperature. The ceramics sintered at 1,200 °C showed a relatively large remnant polarization (P _r) of about 34.2 μC/cm², and a coercive field (E _c) of about 22.6 kV/cm at room temperature. The permittivity ? _r of the ceramics increased with the increasing of sintering temperature in antiferroelectric region, the depolarization temperature (T _d) increased below 1,160 °C then decreased at higher sintering temperature. The resistivity (ρ) of the Ce-BNT6BT ceramics increased linearly as the sintering temperature increased below 1,180 °C, but reduced as the sintering temperature increased further. A maximum value of the ρ was 3.125?×?10¹⁰ ohm m for the Ce-BNT6BT ceramics sintered at 1,180 °C at room temperature.     

Preparation,characterisation, and electrical properties of (K0.5Na0.5)NbO3 lead-free piezoelectric ceramics

Na_0.5?K_0.5NbO₃ (KNN) ceramics were sintered at different temperatures (970 °C, 1000 °C, 1030 °C, 1060 °C, and 1090 °C) for 3 h by a pressureless sintering method. The powders had been synthesised by sol–gel method, using citric acid as a coordination agent and ethylene glycol as an esterifying agent. The effects of temperature on the phase, microstructure, dielectric, ferroelectric, and piezoelectric properties of the as-prepared ceramics were analysed. The results revealed that all of the ceramics had a pure perovskite phase with orthorhombic symmetry. The piezoelectric constant (d ₃₃), the relative dielectric constant (ε _r), the planar electromechanical coupling coefficient (K _p), and the remnant polarization (P _r) initially increased and then decreased with increasing of temperature in such KNN ceramics. The volatilization of sodium and potassium increased with increasing sintering temperature. Over the range of temperatures studied, those ceramics sintered at 1060 °C had the following optimal properties: (ρ?=?3.97 g/cm³, d ₃₃?=?119 pC/N, ε _r?=?362.46, tan δ?=?0.05, K _p?=?0.23, P _r?=?11.97 μC/cm², E _c?=?10.35 kV/cm, and T _c?=?408 °C).     

Phase compositions and microwave dielectric properties of MgTiO<Subscript>3</Subscript>-based ceramics obtained by reaction-sintering method

MgTiO₃-based microwave dielectric ceramics were prepared successfully by reaction sintering method. The X-ray diffraction patterns of the sintered samples revealed a major phase of MgTiO₃-based and CaTiO₃ phases, accompanied with Mg₂TiO₄ or MgTi₂O₅ determined by the sintering temperature and time. The microwave dielectric properties had a strong dependence of sintering condition due to the different phase compositions and the microstructure characteristics. The ceramics sintered at 1360 °C for 4 h exhibited good microwave dielectric properties: a dielectric constant of 20.3, a high quality factor of 48,723 GHz (at 9GHz), and a temperature coefficient of resonant frequency of ?1.8 ppm/^oC. The obtained results demonstrated that the reaction-sintering process is a simple and effective method to prepare the MgTiO₃-based ceramics for microwave applications.     

Microwave dielectric properties of B2O3-added Li2MgTiO4 ceramics for LTCC applications

Li₂MgTiO₄ (LMT) ceramics which are synthesized using a conventional solid-state reaction route. The LMT ceramic sintered at 1250°C for 4 h had good microwave dielectric properties. However, this sintering temperature is too high to meet the requirement of low-temperature co-fired ceramics (LTCC). In this study, the effects of B₂O₃ additives and sintering temperature on the microstructure and microwave dielectric properties of LMT ceramics were investigated. The B₂O₃ additive forms a liquid phase during sintering, which decreases the sintering temperature from 1250°C to 925°C. The LMT ceramic with 8 wt% B₂O₃ sintered at 925°C for 4 h was found to exhibit optimum microwave dielectric properties: dielectric constant 15.16, quality factor 64,164 GHz, and temperature coefficient of resonant frequency -28.07 ppm/°C. Moreover, co-firing of the LMT ceramic with 8 wt% B₂O₃ and 20 wt% Ag powder demonstrated good chemical compatibility. Therefore, the LMT ceramics with 8 wt% B₂O₃ sintered at 925°C for 4 h is suitable for LTCC applications.     

Effect of microwave sintering on structural, morphological and dielectric properties of Ba(FeNb)0.5O3 ceramics

Polycrystalline Ba(FeNb)_0.5O₃/BFN ceramics were sintered conventionally and in a microwave (MW) furnace, respectively. Conventional and microwave sintering temperatures were same with different soaking times. Microwave sintering of BFN ceramics showed enhanced grain growth with improved dielectric properties. Highest dielectric constant (~29,913 at 1 kHz) at room temperature (RT) was observed in BFN ceramics sintered in MW furnace for 30 min. At RT, a non-Debye type of dielectric relaxation was observed in both conventionally and MW sintered BFN ceramics. The observed giant dielectric constant of conventionally and MW sintered BFN ceramics was attributed to intrinsic (space charge polarization) and extrinsic (Maxwell-Wagner type polarization) effects, respectively.     

Effect of sintering temperature on piezoelectric and dielectric properties of 0.98(Na0.5K0.5)NbO3-0.02Li(Sb0.17Ta0.83)O3+0.01wt%ZnO ceramics

We studied sintering temperature to enhance the piezoelectric and dielectric properties of 0.98(Na_0.5?K_0.5)NbO₃-0.02Li(Sb_0.17Ta_0.83)O₃?+?0.01wt%ZnO (hereafter NKN-LST+ZnO) lead free piezoelectric ceramics. The synthesis and sintering method were the conventional ceramic technique and sintering was executed at 1080?～?1120°C. We found that optimal sintering temperature and NKN-LST+ZnO ceramics showed the highest piezoelectric properties and dielectric properties at the optimal sintering temperature. The NKN-LST+ZnO ceramics sintered at 1090°C show a superior performance with piezoelectric constant d ₃₃?=?185 pC/N, k _p?=?0.36, ε ₃₃ ^T /ε₀?=?491 respectively. These results reveal that NKN-LST+ZnO ceramics are promising candidate materials for lead-free piezoelectric application.     

Synthesis and characterization of novel Ca2Zn4Ti15O36 microwave ceramics derived from sol-gel powder

A novel microwave dielectric ceramics with composition of Ca₂Zn₄Ti₁₅O₃₆ (CZT) have been synthesized at different sintering temperatures, using citrate sol-gel derived powder. The sintering behavior and the phase identification of the powders were evaluated using differential thermal analysis-thermo gravimetric analysis and X-ray powder diffraction analysis techniques. The phase of CZT can be observed in the powder calcined at 900 °C. The single-phase of CZT, however, can only be obtained at sintering temperature of 1,000 °C or above. The single-phase CZT ceramics can be sintered into dense at 1,100 °C, exhibiting excellent microwave dielectric properties of ? _r?=?48.1, Q?×?f?=?27,000 GHz, and τ _f?=?+53.5 ppm/°C. The effects of sintering temperature on the density, microstructure, and dielectric properties of the sintered ceramics were investigated. The mechanism responsible for the change of dielectric properties with sintering temperature was also discussed.     

High-temperature stable dielectrics in Mn-modified (1-x) Bi0.5Na0.5TiO3-xCaTiO3 ceramics

In the current work, the bulk (1-x) Bi_0.5Na_0.5TiO₃-xCaTiO₃ [BNCT100x] system was synthesized via solid-state route. CaTiO₃ in solid solution with Bi_0.5Na_0.5TiO₃ was observed to decrease the dielectric constant at higher temperature and raise the dielectric constant at lower temperature. Polarization hysteresis measurements indicated that the ferroelectricity of Bi_0.5Na_0.5TiO₃ was weakened with an increase of CaTiO₃, resulted in the shift of the depolarization temperature (T _d) toward lower temperatures. X-ray diffraction analysis revealed that TiO₂ was produced as a secondary phase due to the losses of Bi and Na during milling and sintering processes. Moreover, the addition of Ca promoted the segregation of Ti out of BNT grains. Dielectric properties of BNCT12 ceramics with different dopant levels of Mn were characterized as a function of temperature for potential use of high-temperature capacitors. Modification of BNCT12 materials with Mn improved the temperature characteristic of capacitance (?55°C to 250°C, △C/C_25°C ≤ ±15%). Finally, by doping 1.5 wt% Mn, the dielectric constant at room temperature could reach over 900, with a low dielectric loss below 1% and a high insulation resistivity about 10¹² Ω?cm. Furthermore, a small amount of Mn influenced the microstructure in the way to inhibit the long grains and grain growth of BNCT solution ceramics. However, excess Mn caused abnormal grain growth, and therefore, rectangle grains appeared again.     

Effect of attrition milling on the piezoelectric properties of Bi0.5Na0.5TiO3-based ceramics

Bismith sodium titanate (BNT)-based powders were prepared by conventionally mixed-oxide method using Bi₂O₃, Na₂CO₃ and TiO₂. The La₂O₃ was added as the modifier to the BNT composition for easily poling and reducing an abnormal dielectric loss at high temperatures. In this study, the investigated compositions were Bi_0.5Na_0.5TiO₃ and Bi_0.5Na_0.485La_0.005TiO₃. The powders were calcined at 900 °C for 2 h by slow heating rate at 100 °C/h. The calcined BNT-based powders were then attrition-milled for 3 h with a high speed at 350 rpm. After drying, the fine powders were uniaxially pressed and then cold-isostatically pressed (CIP) at 240 MPa for 10 min. All pressed pellets were sintered at 1000–1100 °C for 2 h in air atmosphere. The microstructure of sintered pellets was investigated by SEM. Results of dielectric and piezoelectric property measurement were also reported.     

Sintering and dielectric properties of Bi1.5ZnNb1.5O7 cubic pyrochlore ceramics via high-energy milling technology

The dense Bi_1.5ZnNb_1.5O₇ cubic pyrochlore ceramics is synthesized by high-energy milling technology from the coarse Bi_1.5ZnNb_1.5O₇ cubic pyrochlore powders prepared by solid state route. The sintering and dielectric properties of the Bi_1.5ZnNb_1.5O₇ cubic pyrochlore ceramics are investigated, which show that the sintering temperature of the prepared ceramics could be effectively lowered to 800°C and the bulk density reach 6.889 g/cm³ approximately 97% of the theoretical density of Bi_1.5ZnNb_1.5O₇ cubic pyrochlore ceramics. The excellent dielectric properties of the ceramics sintered at 850°C has been obtained with the relative permittivity of 160 and the dielectric loss of 10^?4. This route would be a low-cost and mass production for lowering the sintering temperature of the Bi_1.5ZnNb_1.5O₇ cubic pyrochlore ceramics without sintering aids.     

Microwave dielectric properties of Na<Superscript>+</Superscript> and M<Superscript>3+</Superscript>-doped Ba(Mg<Subscript>0.5</Subscript>W<Subscript>0.5</Subscript>)O<Subscript>3</Subscript> ceramics

In this study, phase evolution, microstructure, and microwave dielectric properties of (Ba_0.98Na_0.02)(Mg_0.48M³⁺_0.02W_0.5)O₃ (M³⁺?=?Al, Ga, Sc, In, Yb, Y, Dy, Gd, and Sm) ceramics sintered at 1700 °C for 1 h were investigated. All the compounds exhibited an ordered cubic perovskite structure. Regardless of the ionic radius of the doped M³⁺ ions, BaWO₄ was detected as the secondary phase in all the compounds. The field emission scanning electron microscopy (FE-SEM) images revealed a dense microstructure in all the compounds, except in the Al-doped compound, which exhibited an insufficient grain growth. The large and irregularly shaped grains indicated that the liquid phase sintering occurred. Splitting of the A_1g(O) mode was observed in the Raman spectra of large M³⁺ ion-doped compounds. Splitting of the F_2g modes did not occur and the bands were sharp, indicating that the cubic symmetry was retained. As the ionic radius of the doped M³⁺ ions increased, the dielectric constant (ε_r) increased slightly. The compounds doped with M³⁺?=?Sc, In, Yb, and Y exhibited a very high quality factor (Q?×?f₀) in the range of 250,000 ~ 280,000 GHz. In the case of the compounds doped with M³⁺?=?Al, Ga, Sc, In, Yb, Y, and Dy, the value of the temperature coefficient of resonant frequency (τ_f) was in the range of ?24 ~ ?19 ppm/°C, while the Gd and Sm-doped compounds exhibited positive values of 2.8 and 31.2 ppm/°C, respectively. The dielectric constant, quality factor, and temperature coefficient of resonant frequency of the In-doped compound, i.e., (Ba_0.98Na_0.02)(Mg_0.48In_0.02W_0.5)O₃, were 18.7, 286,557 GHz, and???24.4 ppm/°C, respectively.     

Synthesis, characterization and giant dielectric properties of CaCu3Ti4O12 ceramics prepared by a polyvinyl pyrrolidone-dimethylformamide solution route

CaCu₃Ti₄O₁₂ powders were successfully prepared by a polyvinyl pyrrolidone-dimethylformamide solution route. Pure phase of CaCu₃Ti₄O₁₂ was achieved at a low calcination temperature and short reaction time at 800 °C for 3 h. High porosity and neck-grain growth network were observed in CaCu₃Ti₄O₁₂ powders. The sintered CaCu₃Ti₄O₁₂ ceramic with fine-grained microstructure exhibited a very high dielectric constant of 1.26?×?10⁴ and low loss tangent of about 0.07 at 1 kHz and 20 °C. Nonlinear current-voltage behavior and dielectric properties were found to be closely related to the microstructure.     

Liquid phase effect of La2O3 and V2O5 on microwave dielectric properties of Mg2TiO4 ceramics

Dielectric ceramics of Mg₂TiO₄ (MTO) were prepared by solid-state reaction method with 0.5–1.5 wt.% of La₂O₃ or V₂O₅ as sintering aid. The influences of La₂O₃ and V₂O₅ additives on the densification, microstructure and microwave dielectric properties of MTO ceramics were investigated. It is found that La₂O₃ and V₂O₅ additives lowered the sintering temperature of MTO ceramics to 1300 °C and 1250 °C respectively, whereas the pure MTO exhibits highest density at 1400 °C. The reduction in sintering temperature with these additives was attributed to the liquid phase effect. The average grain sizes of the MTO ceramics added with La₂O₃, and V₂O₅ found to decrease with an increase in wt%. The dielectric constant (ε_r) was not significantly changed, while unloaded Q values were affected with these additives, and the values were in the range of 92,000–157,550 GHz and 98,000–168,000 GHz with the addition of La₂O₃ and V₂O₅, respectively. The dielectric properties are strongly dependent on the densification and the microstructure of the MTO ceramics. The decrease in Q×f _o value at higher concentration of La₂O₃ and V₂O₅ addition was owing to inhomogeneous grain growth and the liquid phase which is segregated at the grain boundary. In comparison with pure MTO ceramics, La₂O₃ and V₂O₅ additives effectively improved the densification and dielectric properties with lowering of sintering temperature. The proposed loss mechanisms suggest that the oxygen vacancies and the average grain sizes are the influencing factors in the dielectric loss of MTO ceramics.     

Dielectric properties of Bi2O3–ZnO–Ta2O5 ceramics sintered by microwave

Here we report dielectric studies carried out on a Bi₂Zn_2/3Ta_4/3O₇ (abbreviated as β-BZT) composition. The material was synthesized by conventional ceramic method and microwave sintering processing. The dielectric properties were studied as a function of frequency and temperature. Dielectric constant of Bi₂Zn_2/3Ta_4/3O₇ ceramics prepared from microwave is slightly smaller than that of the conventional sintered ones. The dissipation factor and temperature coefficient of dielectric constant are low for microwave-sintered samples. Microwave sintering of Bi₂Zn_2/3Ta_4/3O₇ ceramics led to higher densification and the fine microstructure in much shorter time duration compared to conventional procedures, improved microstructure and dielectric properties. To achieve the same densification, it requires 4 h of soaking at the same temperature in conventional sintering process. Microwave sintering method may lead to energy savings because of rapid kinetics of synthesis.     

Low-temperature sintering and microwave dielectric properties of ZnTiO3-based LTCC materials

The low-temperature sintered microwave dielectric ceramics with composition of ZnTiO₃-0.25TiO₂ were prepared by adding a small amount of low-melting compounds CuO-V₂O₅-Bi₂O₃ (CVB). The phase relationship and dielectric properties as a function of sintering temperature and the additional amount were studied. It is demonstrated that the addition of low-melting CVB can suppress the formation of Zn₂TiO₄ at low temperature, but decrease the decomposition temperature of ZnTiO₃. The sintering temperature has a significant effect on the stability of ZnTiO₃ and dielectric properties of sintered ceramics. CVB addition can promote the densification of ceramics through liquid-phase sintering. The dense 2wt% CVB-doped ZnTiO₃-0.25TiO₂ ceramics prepared at 850 °C have excellent dielectric properties of ??=?30, Q×f?=?32,000 GHz, and τ _f ?=?+12 ppm/ °C.     

Enhanced piezoelectric properties of 0.55Pb(Ni1/3Nb2/3)O3-0.135PbZrO3- 0.315PbTiO3 ternary ceramics by optimizing sintering temperature

0.55Pb(Ni_1/3Nb_2/3)O₃-0.135PbZrO₃-0.315PbTiO₃ (PNN-PZ-PT) ternary piezoelectric ceramics with excess 1.0 wt.% PbO were synthesized by the conventional solid-state reaction method at 1175–1300 °C for 2 h, respectively. The influence of sintering temperature (T _s) on microstructure, piezoelectric, dielectric, and ferroelectric properties were systematically investigated. The results of XRD and Raman scattering spectra demonstrated that a typical perovskite structure with mainly rhombohedral symmetry near the MPB region were obtained for all the samples. The tetragonal phase content was increased slightly with the increase of sintering temperature. In addition, with increasing T _s the average grain size increases while the density decreases were also found. The results of electrical measurements confirmed that piezoelectric constant, dielectric constant, remnant polarization were firstly increased and then decreased with the increase of sintering temperature. The optimum and remarkable enhanced electrical properties of d ₃₃?=?1070 pC/N, k _p?=?0.69, ε _r?=?8710, tanδ?=?0.026, P _r?=?24.08 μC/cm², and E _c?=?3.2 kV/cm were obtained for the sample sintered at 1250 °C for 2 h. Meanwhile, the sample exhibits a typical relaxor ferroelectric behavior with the maximum dielectric constant ε _m =24541 at Curie temperature T _c?=?113.3 °C at 1 kHz.     

High dielectric constant in (1 − x)SrTiO3/xCuO composite ceramics

Semiconductive secondary phase CuO was introduced into SrTiO₃ ceramic matrix to yield dielectric composite ceramics with high dielectric constant. The dense composite ceramics could be obtained by sintering at 1050°C in air for 3 h, in which the co-presence of SrTiO₃ and CuO/Cu₂O was confirmed. The dielectric constant of the present composite ceramics increased firstly and then decreased with increasing the content of CuO, and the highest dielectric constant was obtained at x?=?0.4. There were steps and peaks on the curves of dielectric constant vs temperature and dielectric loss vs temperature, respectively, and the peak temperatures of dielectric loss indicated the Debye-type relaxation.     

Dielectric,ferroelectric and bipolar electric field induced strain properties of MPB composition of NBT-xKNN system

(1-x) (Na_0.5Bi_0.5TiO₃)-xK_0.5Na_0.5NbO₃/NBT-xKNN [x?=?0.07, 0.06, 0.05] ferroelectric ceramics were prepared by solid state synthesis route (SSSR). The effects of KNN contents on the microstructure, dielectric, piezoelectric and ferroelectric properties of the NBT-xKNN system were investigated in detail. For single perovskite phase formation, the calcination temperature was optimized at 800 °C for 6 h. From the XRD study, the morphotropic phase boundary (MPB) was confirmed for x?=?0.07 composition. For better densification, the sintering temperature was optimized for 1150 °C for 4 h. SEM micrographs illustrate the closely packed and non-uniform distribution of grains. Diffusive type of behaviour was observed in all the ceramics. Polarization (P) vs. electric field (E) study confirmed the ferroelectric nature of the NBT-xKNN ceramics. The bipolar field-induced strain measurement for all the ceramic samples showed butterfly-shaped loops indicating their piezoelectric nature. Among all the different compositions in MPB region, high dielectric constant (ε_r) of?~?3011, high remnant polarization (P _r ) of 17.88μC/cm² and high strain % of 0.41, were obtained in NBT-xKNN system with x?=?0.07 confirming the existence of MPB at this composition.     

Dielectric and sintering properties of NaNbO3 ceramic prepared by Pechini method

NaNbO₃ powders and ceramics were prepared by Pechini method. The pure phase NaNbO₃ was obtained at temperature as low as 350 °C, and then they obtained fine powders were used to prepared ceramics through conventional sintering process. The effect of sintering temperature on microstructure evolution and dielectric properties of NaNbO₃ ceramics has been determined. Results shown that the microstructure of NaNbO₃ ceramics consisted of stacked plates, which was related the liquid phase. It was important to note that the stacked plate configuration forming the grain has not been emphasized before, and these grains support adequate wetting characteristics for the liquid phase in order to achieve fully dense microstructure. Above 1195 °C, a number of angular grains with flat interfaces started to appear, and joined to each other with the sintering temperature increase. The effect of grains morphology on dielectric properties of the NaNbO₃ ceramics was also detected.     

Low temperature sintering of high performance KNN-based lead-free piezoelectric ceramic using BCBM frit as sintering aid

High performance lead-free (K_0.49Na_0.51)_0.98Li_0.02(Nb_0.77Ta_0.18Sb_0.05)O₃?+?0.5 mol%BaZrO₃ piezoelectric ceramic was selected as base material, while BaO-CuO-B₂O₃-MnO₂ frit was used as sintering aid to lower the sintering temperature. The effect of BaO-CuO-B₂O₃-MnO₂ frit doping amount on the sintering behavior, structure and electrical properties of the ceramics was investigated. The optimal sintering temperature of the ceramics decreased with the increase of frit doping amount. The ceramic with frit doping amount of 1.0 wt.%, sintered at a reduced temperature of 1100°C, exhibited optimal electrical properties as follows: piezoelectric constant d ₃₃?=?345 pC/N, planar electromechanical coupling coefficient k _p?=?44.5 %, mechanical quality factor Q _m?=?135, dielectric constant ε ₃₃ ^T ?=?1210, and dielectric loss tanδ?=?0.018. Together with its relatively high T _c?=?195°C, this ceramic was an excellent candidate for replacing the lead-based piezoceramics in practical applications.