Effects of Sintering Temperature on Structure and Properties of 0.997(KNN-LS-BF)-0.003V2O5 Lead-Free Piezoelectric Ceramics

0.997(KNN-LS-BF)-0.003V₂O₅ lead-free piezoelectric ceramics were prepared by a traditional sintering method. The effects of sintering temperature on the structure and properties of the 0.997(KNN-LS-BF)-0.003V₂O₅ ceramics were studied. The results show that the sintering temperature exerts a distinct influence on the phase structure and properties. With the increase in sintering temperature from 1040°C to 1060°C, the main crystallographic phase changes from the orthorhombic symmetry to the tetragonal phase, and the optimum dielectric and piezoelectric properties of samples can be obtained when sintering at 1060°C. However, the dielectric and piezoelectric properties of the samples deteriorate when the sintering temperature exceeds 1060°C.     

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.     

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.     

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.     

Dielectric Properties and Defect Chemistry of WO3-Doped K0.5Na0.5NbO3 Ceramics

The dielectric properties and conductivity behavior of WO₃-doped K_0.5Na_0.5 NbO₃ ceramics were investigated as a function of temperature (25°C to 600°C) and frequency (40 Hz to 10⁶ Hz). The dielectric loss and direct-current (DC) conductivity of the ceramics depend strongly on the tungsten content. A high-temperature dielectric relaxation near temperature of 500°C was observed and analyzed using the semiempirical complex Cole–Cole equation. The activation energy of the dielectric relaxation was estimated to be ～2 eV and increased with increasing WO₃. The frequency-dependent conductivity can be well described by the universal dielectric response law. The activation energy obtained from the DC conductivity changes from 0.93 eV to 1.49 eV. A possible mechanism for the high-temperature dielectric relaxation and conductivity is proposed based on the activation energy value and defect compensation.     

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 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.     

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.     

Effects of Annealing Temperature on the Electric Properties of 0.94(Na0.5Bi0.5)TiO3–0.06BaTiO3 Ferroelectric Thin Film

0.94(Na_0.5Bi_0.5)TiO₃–0.06BaTiO₃ (NBT–BT6) ferroelectric thin films have been fabricated on Pt–Ti–SiO₂–Si(100) substrate by metal–organic decomposition. The effects of annealing temperature (650–800°C) on the microstructure, and the piezoelectric, ferroelectric, and dielectric properties of the thin films were studied in detail. The residual stress was evaluated by the orientation average method to clarify its dependence on annealing temperature and grain size, and it was correlated with the electric properties to understand the mechanism of piezoelectric enhancement. Among the thin films, NBT–BT6 thin film annealed at 750°C has the largest effective piezoelectric coefficient, 95.1 pm/V, remnant polarization, 49.7 μC/cm², spontaneous polarization, 105.2 μC/cm², and dielectric constant, 504, and the lowest dielectric loss, 0.05, and tensile residual stress, 24.5 MPa. For the NBT–BT6 thin film annealed at 750°C, a wide temperature range, 183–210°C, around the phase transition temperature (T _m) was observed in the dielectric temperature plots, and the diffusion coefficients (γ) were quantitatively assessed as 1.6, 1.78, and 1.6. Piezoelectric performance is discussed on the basis of the dispersion phase transition and residual stress.     

Effects of Ta2O5/Y2O3 Codoping on the Microstructure and Microwave Dielectric Properties of Ba(Co0.56Zn0.40)1/3Nb2/3O3 Ceramics

The effects of Ta₂O₅/Y₂O₃ codoping on the microstructure and microwave dielectric properties of Ba(Co_0.56Zn_0.40)_1/3Nb_2/3O₃-xA-xB (A = 0.045 wt.% Ta₂O₅; B = 0.113 wt.% Y₂O₃) ceramics (x = 0, 1, 2, 4, 8, 16, 32) prepared according to the conventional solid-state reaction technique were investigated. The x-ray diffraction (XRD) results showed that the main crystal phase in the sintered ceramics was BaZn_0.33Nb_0.67O₃-Ba₃CoNb₂O₉. The additional surface phase of Ba₈CoNb₆O₂₄ and trace amounts of Ba₅Nb₄O₁₅ second phase were present when Ta₂O₅/Y₂O₃ was added to the ceramics. The 1:2 B-site cation ordering was affected by the substitution of Ta⁵⁺ and Y³⁺ in the crystal lattice, especially for x = 4. Scanning electron microscopy (SEM) images of the optimally doped ceramics sintered at 1340°C for 20 h showed a compact microstructure with crystal grains in dense contact. Though the dielectric constant increased with the x value, appropriate addition would result in a tremendous modification of the Q × f and τ _f values. Excellent microwave dielectric properties (ε _r = 35.4, Q × f = 62,993 GHz, and τ _f  = 2.6 ppm/°C) were obtained for the ceramic with x = 0.4 sintered in air at 1340°C for 20 h.     

Effect of ZnO Nanoparticles on the Sintering Behavior and Physical Properties of Bi<Subscript>0.5</Subscript>(Na<Subscript>0.8</Subscript>K<Subscript>0.2</Subscript>)<Subscript>0.5</Subscript>TiO<Subscript>3</Subscript> Lead-Free Ceramics

Sintered Bi_0.5(Na_0.8K_0.2)_0.5TiO₃ + x wt.% ZnO nanoparticle (BNKT–xZnO_n) ceramics have been fabricated by conventional annealing with the aid of ultrasound waves for preliminary milling. Because of the presence of the liquid Bi₂O₃–ZnO phase at the eutectic point of 738°C, the sintering temperature decreased from 1150°C to 1000°C, and the morphology phase boundary of BNKT–xZnO_n ceramics can be clarified by two separated peaks at (002)_T and (200)_T of 2θ in the x-ray diffraction (XRD) patterns. The improvement of ferroelectric properties has been obtained for BNZT–0.2 wt.% ZnO_n ceramics by the increase of remanent polarization up to 20.4 μC/cm² and a decrease of electric coercive field down to 14.2 kV/cm. The piezoelectric parameters of the ceramic included a piezoelectric charge constant of d ₃₁ = 78 pC/N; electromechanical coupling factors k _p = 0.31 and k _t = 0.34, larger than the values of 42 pC/N, 0.12 and 0.13, respectively, were obtained for the BNKT ceramics.     

Solid-state synthesis of modified (Bi0.5Na0.5)TiO3 piezoelectric nanocrystalline ceramics and evaluating their properties

The piezoelectric nanocrystalline ceramics of (Bi_0.5Na_0.5) TiO₃, 0.94(Bi_0.5Na_0.5) TiO₃–0.06BaTiO₃, 0.82(Bi_0.5Na_0.5) TiO₃–0.18(Bi_0.5K_0.5) TiO₃ and 0.85(Bi_0.5Na_0.5) TiO₃–0.144(Bi_0.5K_0.5)TiO₃–0.006BaTiO₃ (abbreviated as BNT, BNBT6, BNKT18 and BNT–BT–BKT, respectively) have been synthesized by a modified solid state approach using high-energy planetary ball-milling. The crystal structures of ceramics were determined using X-ray diffraction (XRD) method and that the microstructures as well as the morphology of the sintered ceramic specimens were observed using scanning-electron microscopy (SEM). The dielectric coefficient was also calculated based on its relation with a constant capacitance measured by an electrical circuit on the basis of the Wetston–Bridge and the piezoelectric coefficient (d₃₃) measured with a d₃₃-meter. On the calcination of powders the XRD results showed that the perovskite phase was formed perfectly and the crystallite sizes of BNT, BNBT6, BNKT18 and BNT–BT–BKT were estimated at about >100, 55, 36 and 63 nm, respectively. Also, the crystallite sizes of the calcinated BNT powders over the course of 5, 10, 20, 30 and 40 h of ball-milling were estimated at about 86, 82, 72, 53, 81 nm, respectively. Moreover, the results of XRD and SEM analysis of the sintered powders at 750–1150 °C confirmed the positive effect of nanocrystalline formation during ball-milling in decreasing the sintering temperature and increasing the density of the sintered samples. Furthermore, electrical calculations such as dielectric and piezoelectric coefficients showed that the modified BNKT18 nanocrystalline ceramic sintered at 1150 °C was to have the best values of dielectric (ε_r=792 at 1 kHz) and piezoelectric coefficients (d₃₃=85.9 pC/N) in comparison with the other synthesized piezoelectric ceramics.     

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.     

High-Temperature Capacitor Materials Based on Modified BaTiO<Subscript>3</Subscript>

High-temperature capacitor materials sintered at 1120°C were prepared in a BaTiO₃ (BT)-Na_0.5Bi_0.5TiO₃ (NBT)-Nb₂O₅-ZnO-CaZrO₃ system. The Curie temperature of BaTiO₃ was increased by NBT doping, and a secondary phase occurred when adding ≥5 mol% NBT. The effects of Nb₂O₅, ZnO, and CaZrO₃ on the dielectric properties and the microstructure of BT ceramics doped with 1 mol% NBT were analyzed. The overall dielectric constant decreased when the Nb₂O₅ content increased, and increased when the ZnO content increased. The dielectric constant peak at the Curie temperature was effectively depressed, and a broad secondary dielectric constant peak appeared at 60°C when the ZnO concentration was ≥4.5 mol%. Significant grain growth was observed by scanning electron microscope (SEM) analysis as the amount of ZnO increased. The high-temperature capacitor specification (−55°C to +175°C, ΔC/C _25°C less than ±15%) is met when 7 mol% to 8 mol% CaZrO₃ is added.     

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.     

Effect of TiO2 Ratio on the Phase and Microwave Dielectric Properties of Li2ZnTi3+x O8+2x Ceramics

Low-loss materials Li₂ZnTi_3+x O_8+2x (LZT) (x = 0, 0.10, 0.17, 0.25, 1.00) were prepared by the conventional solid-state route. The effect of TiO₂ ratio on phase composition, microstructure, and the microwave dielectric properties of Li₂ZnTi_3+x O_8+2x ceramics were investigated using x-ray diffraction, scanning electron microscopy, energy-dispersive x-ray spectroscopy, and Vector Network Analyzer. The results revealed that a two-phase system Li₂ZnTi₃O₈-TiO₂ was formed. The appropriate content of TiO₂ ratio can effectively adjust the temperature coefficient of the resonant frequency (τ _f) value from ?14.5 to 0 ppm/ °C without obvious degradation of the microwave dielectric properties. The microwave dielectric properties of the Li₂ZnTi_3+x O_8+2x materials were characterized at microwave frequencies. Typically, the Li₂ZnTi_3+x O_8+2x (x = 0.17) ceramic sintered at 1,160 °C for 5 h showed excellent microwave dielectric properties with ε _r = 28.51, Q × f = 58,511 GHz, and τ _f = + 2.3 ppm/ °C.     

Ultra-Low Loss Microwave Dielectric Ceramic Li<Subscript>2</Subscript>Mg<Subscript>2</Subscript>TiO<Subscript>5</Subscript> and Low-Temperature Firing Via B<Subscript>2</Subscript>O<Subscript>3</Subscript> Addition

Li₂Mg₂TiO₅, a rock-salt structured ceramic fabricated by a solid-state sintering technique, was characterized at the microwave frequency band. As a result, a microwave dielectric permittivity (ε_r) of 13.4, a quality factor of 95,000 GHz (at 11.3 GHz), and a temperature coefficient of resonance frequency (τ_f) of ? 32.5 ppm/°C have been obtained at 1320°C. Li₂Mg₂TiO₅ ceramics have low permittivity, a broad processing temperature region, and a low loss, making them potential applications in millimeter-wave devices. Furthermore, B₂O₃ addition efficiently lowered the sintering temperature of Li₂Mg₂TiO₅ to 900°C, which opens up their possible applications in low-temperature co-fired ceramics (LTCC) technology.     

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.     

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.     

Enhancing Piezoelectric Performance of CaBi2Nb2O9 Ceramics Through Microstructure Control

Calcium bismuth niobate (CaBi₂Nb₂O₉, CBN) is a high-Curie-temperature (T _C) piezoelectric material with relatively poor piezoelectric performance. Attempts were made to enhance the piezoelectric and direct-current (DC) resistive properties of CBN ceramics by increasing their density and controlling their microstructural texture, which were achieved by combining the templated grain growth and hot pressing methods. The modified CBN ceramics with 97.5% relative density and 90.5% Lotgering factor had much higher piezoelectric constant (d ₃₃ = 20 pC/N) than those prepared by the normal sintering process (d ₃₃ = 6 pC/N). High-temperature alternating-current (AC) impedance spectroscopy of the CBN ceramics was measured by using an impedance/gain-phase analyzer. Their electrical resistivity was approximately 6.5 × 10⁴ Ω cm at 600°C. Therefore, CBN ceramics can be used for high-temperature piezoelectric applications.