Temperature Stability of V2O5-Doped KNN-LS-BF Lead-Free Piezoelectric Ceramics

V₂O₅-doped Na_0.5K_0.5NbO₃-LiSbO₃-BiFeO₃ (KNN-LS-BF) lead-free piezoelectric ceramics were prepared by the traditional sintering method, and their temperature stability was studied. Characterization of the temperature dependences of dielectric and piezoelectric properties of the V₂O₅-doped KNN-LS-BF ceramics showed that V₂O₅ doping could significantly improve the temperature stability in the temperature range of 30°C to 420°C and cause a downward shift in the orthorhombic–tetragonal phase transition to below room temperature. It was also found that the V₂O₅-doped KNN-LS-BF ceramics possess good dielectric and piezoelectric properties (ε _r > 1066, tan δ < 4%, d ₃₃ > 185 pC/N, k _p > 0.25) in the temperature range of 30°C to 300°C.     

Effect of CuO Addition on Microwave Dielectric Properties of 0.80Sm(Mg0.5Ti0.5)O3-0.20Ca0.8Sr0.2TiO3 Ceramics

The effects of CuO addition on phase composition, microstructure, sintering behavior, and microwave dielectric properties of 0.80Sm(Mg_0.5Ti_0.5)O₃-0.20 Ca_0.8Sr_0.2TiO₃(8SMT-2CST) ceramics prepared by a conventional solid-state ceramic route have been studied. CuO addition shows no obvious influence on the phase of the 8SMT-2CST ceramics and all the samples exhibit pure perovskite structure. Appropriate CuO addition can effectively promote sintering and grain growth, and consequently improve the dielectric properties of the ceramics. The sintering temperature of the ceramics decreases by 50°C by adding 1.00 wt.%CuO. Superior microwave dielectric properties with a ε _r of 29.8, Q × f of 85,500 GHz, and τ _f of 2.4 ppm/°C are obtained for 1.00 wt.%CuO doped 8SMT-2CST ceramics sintered at 1500°C, which shows dense and uniform microstructure as well as well-developed grain growth.     

Effect of bismuth addition on sintering behavior and microwave dielectric properties of zinc titanate ceramics

The influences of Bi₂O₃ addition on the sintering behavior and microwave dielectric properties of ZnO-TiO₂ ceramics were investigated. ZnO-TiO₂ ceramics were prepared with conventional solid-state method and sintered at temperatures from 950°C to 1,100°C. The sintering temperature of ZnO-TiO₂ ceramics with Bi₂O₃ addition could be effectively reduced to 1,000°C due to the liquidphase effects resulting from the additives. A proper amount of Bi₂O₃ addition could effectively improve the densification and dielectric properties of ZnO-TiO₂ ceramics. The temperature coefficient of resonant frequency could be controlled by varying the sintering temperature and lead to a zero τ_f value. At 1,000°C, 1ZnO-1TiO₂ ceramics with 1 wt.% addition gave better microwave dielectric properties ɛ_r of 29.3, a Q × f value of 22,000 GHz at 8.36 GHz, and a τ_f value of +17.4 ppm/ °C.     

Piezoelectric and electrical properties of PZT-PSN thin film ceramics for MEMS applications

Piezoelectric and electrical properties of PZT-PSN ceramics have been investigated as a function of WO₃ addition from 0 to 6.0 wt%. The dielectric and piezoelectric characteristics of PZT-PSN ceramics have been investigated at different calcination (800–900°C) and sintering (1100–1300°C) temperatures. The grain size increased in proportion to adding the amount of WO₃ and increasing the sintering temperatures. Anisotropic properties of electromechanical coupling coefficient and piezoelectric coefficient are proven to be dependent on processing temperatures and amount of addition. For the specimen with 0.6 wt% WO₃ addition, using a calcination temperature of 800°C and a sintering temperature of 1100°C, the mechanical quality factor and electromechanical coupling coefficient were 1560 and 0.48, respectively. Thin films were deposited in situ onto Pt/Ti/SiO₂/Si substrates by pulsed laser deposition using a Nd:YAG laser. The microstructure, dielectric, electrical, and piezoelectric properties of thin films with the compound ceramics have been systematically investigated for microtransformer and MEMS applications.     

Microstructure and Electrical Properties of K0.5Na0.5NbO3-LiSbO3-BiFeO3-x %molZnO Lead-Free Piezoelectric Ceramics

Lead-free piezoelectric ceramics {0.996[(0.95(K_0.5Na_0.5)NbO₃-0.05LiSbO₃]-0.004BiFeO₃}-xmol%ZnO were prepared through a conventional ceramics sintering technique. The effect of ZnO content on structure, microstructure, and piezoelectric properties of KNN-LS-BF ceramics was investigated. The results reveal that ZnO as a sintering aid is very effective in promoting sinterability and electrical properties of the ceramics sintered at a low temperature of 1,020 °C. The ceramics show a single-perovskite structure with predominant tetragonal phase, and coexistence of orthorhombic and tetragonal phases is observed for x = 2.5–3.0. The addition of ZnO causes abnormal grain growth. A dense microstructure is also obtained at x = 2.0 because the relative density reaches up to 94.6 %. The morphotropic phase boundary and dense microstructure lead to significant enhancement of the piezoelectric properties. The ceramic with x = 1.5 exhibits optimum electrical properties as follows: d ₃₃ = 280 pC/N, k _p = 46 %, Q _m = 40.8, P _r = 25 μC/cm², E _c = 1.2 kV/mm, and T _c = 340 °C.     

Microwave Dielectric Properties of ZnO-2TiO<Subscript>2</Subscript>-Nb<Subscript>2</Subscript>O<Subscript>5</Subscript> Ceramics with BaCu (B<Subscript>2</Subscript>O<Subscript>5</Subscript>) Addition

The influence of BaCu(B₂O₅) (BCB) addition on the sintering temperature and microwave dielectric properties of ZnO-2TiO₂-Nb₂O₅ (ZTN) ceramic has been investigated using dilatometry, x-ray diffraction, scanning electron microscopy, and microwave dielectric measurements. A small amount of BCB addition to ZTN can lower the sintering temperature from 1100°C to 900°C. The reduced sintering temperature was attributed to the formation of the BCB liquid phase. The ZTN ceramics containing 3.0 wt.% BCB sintered at 900°C for 2 h have good microwave dielectric properties of Q × f = 19,002 GHz (at 6.48 GHz), ε _r = 45.8 and τ _f  = 23.2 ppm/°C, which suggests that the ceramics can be applied in multilayer microwave devices, provided that Ag compatibility exists.     

Enhanced Piezoelectric Properties and Tunability of Lead-Free Ceramics Prepared by High-Energy Ball Milling

Zirconium-doped barium titanate Ba(Zr_0.15Ti_0.85)O₃ lead-free ceramics (hereinafter referred to as BZT) were synthesized using the solid-state reaction method by adopting the high-energy ball milling technique. Nanosized BZT powders resulted from high-energy ball milling, which in turn enhanced the dielectric and piezoelectric properties of the ceramics. A single-phase perovskite structure free from secondary phase peaks was observed for sintered BZT samples, and a relative density of ～94% of the theoretical density was achieved. The electric-field-induced polarization-current data indicate the ferroelectric nature of the samples. Unipolar strain as high as 0.12% was realized for the ceramics sintered at 1350°C, indicating their potential for use in actuator applications. Very high tunability of >70% for these ceramics is also reported.     

MnO2-Modified Ba(Ti,Zr)O3 Ceramics with High Q m and Good Thermal Stability

MnO₂-modified Ba(Ti_0.9625Zr_0.0375)O₃ ceramics have been prepared by the conventional solid-state reaction technique at different sintering temperatures. Room-temperature piezoelectric properties, thermal stability, and crystalline structures were investigated. It was found that both the MnO₂ additive and sintering temperature significantly influence the piezoelectric properties of the MnO₂-modified Ba(Ti_0.9625Zr_0.0375)O₃ ceramics. The sample sintered at 1400°C exhibited the best room-temperature piezoelectric properties of Q _m = 1907, d ₃₃ = 205 pC/N, and k _p = 40.5% with tan δ = 0.46%, and its k _p remains larger than 35% in the broad temperature range from ?38°C to 65°C. The results indicate that MnO₂-modified Ba(Ti_0.9625Zr_0.0375)O₃ ceramics are promising lead-free materials for frequency device and power device applications.     

Investigation of Structural and Electrical Properties of B-Site Complex Ion (Mg1/3Nb2/3)4+-Modified High-Curie-Temperature BiFeO3-BaTiO3 Ceramics

B-site complex ion (Mg_1/3Nb_2/3)-modified high-temperature ceramics 0.71BiFeO₃-0.29BaTi_1?x (Mg_1/3Nb_2/3) _x O₃ (BF-BTMNx) have been fabricated by the conventional solid-state reaction method. The compositional dependence of the?phase structure, electrical properties, and depolarization temperature of the ceramics was studied. The main phase structure of BF-BTMNx ceramics is perovskite phase with pseudocubic symmetry. The experimental results show that the dielectric and piezoelectric properties, and temperature stability strongly depend on the (Mg_1/3Nb_2/3)⁴⁺ content. The optimum (Mg_1/3Nb_2/3) content enhances the piezoelectric properties, Curie temperature, and depolarization temperature. The ceramic with x = 1% exhibited enhanced electrical properties of d ₃₃ = 158 pC/N and k _p = 0.322, combined with high-temperature stability with Curie temperature of T _c = 453°C and depolarization temperature of T _d = 400°C. These results show that the ceramic with x = 1% is a promising lead-free high-temperature piezoelectric material.     

Dielectric Properties and Microstructure of MgO-TiO<Subscript>2</Subscript>-ZnO-CaO Ceramics

The effects of CaTiO₃ addition on the microstructure, phase formation, and dielectric properties of MgO-TiO₂-ZnO ceramics were investigated. The sintering temperature of CaTiO₃-doped (Mg_0.63Zn_0.37)TiO₃ ceramics can be lowered to 1290°C when the additive is used. The dielectric properties are found to be strongly correlated with the amount of CaTiO₃ addition. At 1290°C, (Mg_0.63Zn_0.37)TiO₃ ceramic with 1.0 mol% CaTiO₃ exhibited a dielectric constant ε _r of 23.3, dielectric loss tan δ of 1 × 10⁻⁵, and temperature coefficient of capacitance (TCC) of 10 ppm/°C.     

Cu<Subscript>3</Subscript>Mo<Subscript>2</Subscript>O<Subscript>9</Subscript>: An Ultralow-Firing Microwave Dielectric Ceramic with Good Temperature Stability and Chemical Compatibility with Aluminum

An ultralow-firing microwave dielectric ceramic Cu₃Mo₂O₉ with orthorhombic structure has been fabricated via a solid-state reaction method. X-ray diffraction analysis, Rietveld refinement, Raman spectroscopy, energy-dispersive spectrometry, and scanning electron microscopy were employed to explore the phase purity, crystal structure, and microstructure. Pure and dense Cu₃Mo₂O₉ ceramics could be obtained in the sintering temperature range from 580°C to 680°C. The sample sintered at 660°C for 4 h exhibited the highest relative density (～ 97.2%) and best microwave dielectric properties with ε _r = 7.2, Q × f = 19,300 GHz, and τ _f = ? 7.8 ppm/°C. Chemical compatibility with aluminum electrodes was also confirmed. All the results suggest that Cu₃Mo₂O₉ ceramic is a promising candidate for use in ultralow-temperature cofired ceramic applications.     

Characteristics of ZnOV2O5MnO2Nb2O5Er2O3 semiconducting varistors with sintering processing

The effects of sintering temperature on the microstructure, electrical properties, and dielectric characteristics of ZnOV₂O₅MnO₂Nb₂O₅Er₂O₃ semiconducting varistors have been studied. With increase in sintering temperature the average grain size increased (4.5–9.5 μm) and the density decreased (5.56–5.45 g/cm³). The breakdown field decreased with an increase in the sintering temperature (6214–982 V/cm). The samples sintered at 900 °C exhibited remarkably high nonlinear coefficient (50). The donor concentration increased with an increase in the sintering temperature (0.60×10¹⁸–1.04×10¹⁸ cm^?3) and the barrier height exhibited the maximum value (1.15 eV) at 900 °C. As the sintering temperature increased, the apparent dielectric constant increased by more than four-fold.     

Good Thermal Stability,High Permittivity,Low Dielectric Loss and Chemical Compatibility with Silver Electrodes of Low-Fired BaTiO<Subscript>3</Subscript>–Bi(Cu<Subscript>0.75</Subscript>W<Subscript>0.25</Subscript>)O<Subscript>3</Subscript> Ceramics

(1 ? x)BaTiO₃–xBi(Cu_0.75W_0.25)O₃ [(1 ? x)BT–xBCW, 0 ≤ x ≤ 0.04] perovskite solid solutions ceramics of an X8R-type multilayer ceramic capacitor with a low sintering temperature (900°C) were synthesized by a conventional solid state reaction technique. Raman spectra and x-ray diffraction analysis demonstrated that a systematically structural evolution from a tetragonal phase to a pseudo-cubic phase appeared near 0.03 < x < 0.04. X-ray photoelectron analysis confirmed the existence of Cu⁺/Cu²⁺ mixed-valent structure in 0.96BT–0.04BCW ceramics. 0.96BT–0.04BCW ceramics sintered at 900°C showed excellent temperature stability of permittivity (Δε/ε _25°C ≤ ±15%) and retained good dielectric properties (relative permittivity ～1450 and dielectric loss ≤2%) over a wide temperature range from 25°C to 150°C at 1 MHz. Especially, 0.96BT–0.04BCW dielectrics have good compatibility with silver powders. Dielectric properties and electrode compatibility suggest that the developed materials can be used in low temperature co-fired multilayer capacitor applications.     

Effect of Sintering Temperature on the Properties of Fused Silica Ceramics Prepared by Gelcasting

Fused silica ceramics were fabricated by gelcasting, by use of a low-toxicity N′N-dimethylacrylamide gel system, and had excellent properties compared with those obtained by use of the low-toxicity 2-hydroxyethyl methacrylate and toxic acrylamide systems. The effect of sintering temperature on the microstructure, mechanical and dielectric properties, and thermal shock resistance of the fused silica ceramics was investigated. The results showed that sintering temperature has a critical effect. Use of an appropriate sintering temperature will promote densification and improve the strength, thermal shock resistance, and dielectric properties of fused silica ceramics. However, excessively high sintering temperature will greatly facilitate crystallization of amorphous silica and result in more cristobalite in the sample, which will cause deterioration of these properties. Fused silica ceramics sintered at 1275°C have the maximum flexural strength, as high as 81.32 MPa, but, simultaneously, a high coefficient of linear expansion (2.56 × 10^?6/K at 800°C) and dramatically reduced residual flexural strength after thermal shock (600°C). Fused silica ceramics sintered at 1250°C have excellent properties, relatively high and similar flexural strength before (67.43 MPa) and after thermal shock (65.45 MPa), a dielectric constant of 3.34, and the lowest dielectric loss of 1.20 × 10^?3 (at 1 MHz).     

Effect of the Second Sintering Temperature on the Microstructure and Electrical Properties of PbNb2O6-0.5 wt.%ZrO2 Obtained via a Two-Step Sintering Process

Lead metaniobate PbNb₂O₆ ceramics with addition of 0.5 wt.% ZrO₂ (PNZr) were processed via the conventional solid-state reaction method and a two-step sintering process. A lower second sintering temperature efficiently prevents volatilization of Pb²⁺. X-ray diffraction patterns indicate that the samples are of orthorhombic ferroelectric phase. Scanning electron microscopy shows that abnormal grain growth was restrained. The dielectric anomalies around 300°C caused by oxygen vacancies are effectively reduced.     

Improvements in the Sintering Behavior and Microwave Dielectric Properties of Geikielite-Type MgTiO3 Ceramics

Microwave dielectric ceramics based on geikielite-type MgTiO₃ were prepared by an aqueous sol–gel process. The precursor powders and dielectric ceramics were characterized by x-ray diffraction, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and microwave methods. Highly reactive nanosized magnesium titanate powders with particle sizes of 20 nm to 40 nm were successfully obtained at 500°C as precursors. Sintering characteristics and microwave dielectric properties of MgTiO₃ ceramics were studied as a function of sintering temperature from 1100°C to 1300°C. With increasing sintering temperature, the density, ε _r, and Qf values increased, saturating at 1200°C with excellent microwave properties of ε _r = 17.5, Qf = 156,300 GHz, and τ _f  = ?44 ppm/°C. Correlations between the microstructure and dielectric properties of MgTiO₃ ceramics were also investigated.     

Effect of the Addition of B2O3 on the Density, Microstructure, Dielectric, Piezoelectric and Ferroelectric Properties of K0.5Na0.5NbO3 Ceramics

Boron oxide (B₂O₃) addition to pre-reacted K_0.5Na_0.5NbO₃ (KNN) powders facilitated swift densification at relatively low sintering temperatures which was believed to be a key to minimize potassium and sodium loss. The base KNN powder was synthesized via solid-state reaction route. The different amounts (0.1–1 wt%) of B₂O₃ were-added, and ceramics were sintered at different temperatures and durations to optimize the amount of B₂O₃ needed to obtain KNN pellets with highest possible density and grain size. The 0.1 wt% B₂O₃-added KNN ceramics sintered at 1,100 °C for 1 h exhibited higher density (97 %). Scanning electron microscopy studies confirmed an increase in average grain size with increasing B₂O₃ content at appropriate temperature of sintering and duration. The B₂O₃-added KNN ceramics exhibited improved dielectric and piezoelectric properties at room temperature. For instance, 0.1 wt% B₂O₃-added KNN ceramic exhibited d ₃₃ value of 116 pC/N which is much higher than that of pure KNN ceramics. Interestingly, all the B₂O₃-added (0.1–1 wt%) KNN ceramics exhibited polarization–electric field (P vs. E) hysteresis loops at room temperature. The remnant polarization (P _r) and coercive field (E _c) values are dependent on the B₂O₃ content and crystallite size.     

Dielectric Properties in the Microwave Range of K<Subscript>0.5</Subscript>Na<Subscript>0.5</Subscript>NbO<Subscript>3</Subscript> Ceramics

Dielectric properties of a potassium sodium niobate (KNN) system in the microwave range up to GHz have rarely been studied. Since K_0.5Na_0.5NbO₃ is the most common and typical type of KNN materials, non-doped K_0.5Na_0.5 NbO₃ ceramics were synthesized at different temperatures (1080°C, 1090°C, 1100°C, and 1110°C) by a traditional solid reaction method for further characterization and analysis. The ceramics were in perovskite phase with orthorhombic symmetry. A small quantity of second phase was found in the 1110°C sintered specimen, which resulted from the volatilization of alkali oxides as the temperature increased. The complex permittivity was measured for the first time in the microwave range (8.2–12.4 GHz) and in the temperature range from 100°C to 220°C, and the effects of annealing on the dielectric properties were studied. The results indicate that the complex permittivity of KNN ceramics over the microwave range increases mainly due to high bulk density and the additional dielectric contributions of oxygen vacancies at high temperature.     

Effects of Carbon Coating on Microstructure and Dielectric Properties of CaCu3Ti4O12

CaCu₃Ti₄O₁₂ (CCTO) powders coated with carbon were synthesized by using a high-energy ball milling method. The obtained samples were characterized by x-ray diffraction, transmission electron microscopy and scanning electron microscopy. The carbon-coated CCTO particles had a rough surface, which resulted from the growth of the carbon coating on the CCTO particles. It was found that the CCTO phase was observed as the major phase and no reaction occurred between the carbon and CCTO during the sintering process. The grain size of the CCTO ceramics decreased with the increase in carbon content, which indicated that carbon inhibits grain growth of CCTO ceramics. Specially, the dielectric constant decreased with the increase in carbon content. And CCTO1 ceramic (mass ratio of CCTO: carbon = 10:1) showed a lower dielectric constant (3.74 × 10⁴), with the dielectric loss value (0.04) much lower than that of CCTO at 20°C (10 k Hz).     

Preparation and characterization of Si-doped barium titanate nanopowders and ceramics

Si-doped barium titanate nanopowders and ceramics were prepared through the sol-gel process. The powders and ceramics were characterized by methods of XRD, SEM and TEM. The dielectric properties of the ceramics were also determined. The results indicated that the powders were nanopowders and they were all cubic BaTiO₃ phase with the concentration of Si ?5.0 mol%. When the concentration of Si increased to 10.0 mol%, another phase of Ba₂TiSi₂O₈ appeared. After sintering, the cubic BaTiO₃ phase was transformed into tetrahedron BaTiO₃ phase. Si doping with low concentration resulted in improving grain growth and reduced dielectric loss. As the sintering temperature increased, the dielectric properties of the ceramics decreased. BaTiO₃ ceramics doped with Si all had a small peak at room temperature in ε−T cures. Specially, the ceramic doped with 0.3 mol% Si had evident double peaks, the maximum room temperature permittivity (4081) and the minimum dielectric loss (0.004).