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.     

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 MnO2 Addition on the Electrical Properties of PNZST Ceramics

(Pb_0.99Nb_0.02)[(Zr_0.70Sn_0.30) _x Ti_1?x ]_0.98O₃ (PNZST) piezoelectric ceramics of pure perovskite structure were prepared by a conventional ceramic fabrication method, where x = 0.48–0.56. When x = 0.52, the ceramics exhibit a high piezoelectric coefficient (d ₃₃ ～ 490), but the mechanical quality factor (Q _m) is only 72. To increase the Q _m and not dramatically lower the d ₃₃, MnO₂ was chosen as the additive. The effects of adding MnO₂ on the sinterability, structure, and electrical properties of PNZST ceramics were investigated in detail. With a small addition of MnO₂ (≤0.6 wt.%), the Mn ions are homogeneously dissolved in the PNZST ceramic, leading to full densification when sintered at 1,300 °C. However, further addition of MnO₂ prevents densification, causing a high porosity and small grain size. The doping of MnO₂ transforms the phase structure from tetragonal to rhombohedral. The addition of MnO₂ up to a maximum of 0.6 wt.% remarkably improves the mechanical quality factor (Q _m) of PNZST ceramics, simultaneously as well as maintaining a high d ₃₃ and k _p. PNZST with 0.6 wt.% MnO₂ exhibits excellent electrical properties with piezoelectric coefficient d ₃₃ = 392 pC/N, electromechanical coupling factor k _p = 0.60, mechanical quality factor Q _m = 1,050, dielectric constant ε _r = 1,232, dielectric dissipation tanδ = 0.0058, and Curie temperature T _C = 300 °C.     

Beam-Mode Piezoelectric Properties of Ternary Pb(In1/2Nb1/2)O3-Pb(Mg1/3Nb2/3)O3-PbTiO3 Single Crystals for Medical Linear Array Applications

In this work, the dielectric and beam-mode piezoelectric properties of ternary 0.35Pb(In_1/2Nb_1/2)O₃-0.35Pb(Mg_1/3Nb_2/3)O₃-0.30PbTiO₃ (PIMNT35/35/30) piezoelectric single crystals were investigated. The Curie temperature (T _C) and rhombohedral-to-tetragonal phase-transition temperature (T _rt) are 187°C and 127°C, about 30°C higher than those of PMNT crystals. The beam-mode coupling coefficient k ₃₃ ^w was found to be 90.3%. Furthermore, 3.5-MHz linear arrays based on PIMNT35/35/30 crystals and Pb(Zr_1−x Ti _x )O₃ ceramic (PZT-5H) were simulated using PiezoCAD software. The results indicate that the sensitivity and −6 dB bandwidth of a PIMNT35/35/30 transducer would be approximately 4 dB and 20% higher, respectively, compared with a traditional PZT transducer.     

Thermally Stable BaTiO3-Bi(Mg0.75W0.25)O3 Solid Solutions: Sintering Characteristics,Phase Evolution,Raman Spectra,and Dielectric Properties

(1 ? x)BaTiO₃-xBi(Mg_0.75W_0.25)O₃ [(1 ? x)BT-xBMW, 0.02 ≤ x ≤ 0.24] ceramics were synthesized by a two-step solid-state reaction technique. X-ray diffraction (XRD) patterns show that a systematic structure evolution from tetragonal to pseudocubic phase was observed at x = 0.07. Raman spectra analysis illustrates that a change in average structure was observed with increasing x, and the local crystal symmetry which deviated from the idealized cubic perovskite structure appeared as x ≥ 0.07. Temperature dependence of dielectric properties indicates that the phase transition temperature (T _c) decreased with increasing x. Moreover, (1 ? x)BT-xBMW (0.07 ≤ x ≤ 0.24) ceramics show good dielectric thermal stability over a wide temperature range, which indicates that these ceramics are candidates for thermal stability devices.     

Effect of Sn Content on Structure and Properties Near the Morphotropic Phase Boundary in a PbSnO3-PbZrO3-PbTiO3 Ternary System

Piezoelectric ceramics in the PbSnO₃-PbZrO₃-PbTiO₃ (PZST) ternary system with pure perovskite structure were synthesized by a conventional solid state reaction method with the compositions near the morphotropic phase boundary (MPB). The influences of Sn content on dielectric, piezoelectric, and ferroelectric properties of Pb(Zr _x Sn _y Ti_1?x?y )O₃ ceramics were investigated. The experimental results showed that, with increasing the Sn content along the Ti = 0.48 line, the optimized sintering temperature, tetragonality, and Curie temperature (T _C) decreased monotonically. The polarization–electric field hysteresis loops show a pinning effect in some low Sn compositions. Frequency dependence of the pinning effect was studied accompanied with current–electric field curve analysis. The PZST compositions near MPB show promising advantages for practical 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.     

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.     

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.     

PIN-PMN-PT Single-Crystal-Based 1–3 Piezoelectric Composites for Ultrasonic Transducer Applications

In this work, Pb(In_1/2Nb_1/2)O₃-Pb(Mg_1/3Nb_2/3)O₃-PbTiO₃ (PIN-PMN-PT) single crystal/epoxy 1–3 composites with different thicknesses (400 μm to 825 μm) were fabricated using the conventional dice-and-fill method. Their properties were compared with the corresponding lead zirconate titanate (PZT) ceramic 1–3 composites. Excellent properties for ultrasonic transducer applications have been achieved, such as high electromechanical coupling coefficient (k _t ≈ 78% to 83%), high piezoelectric strain coefficient (d ₃₃ ≈ 1000 pm/V), and lower acoustic impedance (Z ≈ 20 Mrayl). The strain levels of PIN-PMN-PT composites were almost constant (1000 pm/V) with decreasing thickness, being much higher than those of PZT composites (650 pm/V). However, an increase in strain hysteresis was observed with decreasing thickness, reaching 25.3% for the 400-μm single-crystal 1–3 composite, which is lower than the corresponding PZT composites (44.1% for 350-μm PZT ceramic 1–3 composite). These results show that PIN-PMN-PT single-crystal 1–3 composites have great potential for use in advanced ultrasound transducer applications.     

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.     

Preparation, Characterization, and Microwave Dielectric Properties of Sr2La3Nb1−x Ta x Ti4O17 (0 ≤ x ≤ 1) Ceramics

Sr₂La₃Nb_1?x Ta _x Ti₄O₁₇ (0 ≤ x ≤ 1) ceramics were processed via a solid-state mixed oxide route. Sr₂La₃Nb_1?x Ta _x Ti₄O₁₇ (0 ≤ x ≤ 1) solid solutions were single phase in the whole range of x values within the x-ray diffraction (XRD) detection limit. The microstructure comprised elongated and needle-shaped grains. The ceramics exhibit relative permittivity (ε _r) of 73 to 68.6, product of unloaded quality factor and resonant frequency (Q _u f ₀) of 7100 GHz to 9500 GHz, and temperature coefficient of resonant frequency (τ _f) of 78.6 ppm/°C to 56.6 ppm/°C.     

Effect of Mn and Nb Doped BaTiO3 in the Dielectric Properties in the Ba(Mn1/2Nb1/2)xTi1−xO3

Polycrystalline samples of BaTi_1?x (Mn_0.5Nb_0.5) _x O₃ with x = 0.025, 0.05, 0.075, 0.1, 0.125, 0.15, and 0.175 have been synthesized by the high-temperature solid-state reaction technique. The effects of cationic substitution of manganese and niobium for titanium at B sites of the BaTiO₃ perovskite lattice on symmetry and dielectric properties were investigated. X-ray diffraction at room temperature and dielectric permittivity in the temperature range from 85 K to 500 K and frequency range from 100 Hz to 2 × 10⁵ Hz were studied. The evolution from a normal ferroelectric to a relaxor ferroelectric is emphasized. T _C or T _m decreases when both manganese and niobium are introduced into the lattice of BaTiO₃. High dielectric constant of around 9000 at T _C = 280 K was found for Ba Ti_0.925(Mn_0.5Nb_0.5)_0.075O₃ ceramic. A relaxor ferroelectric with ΔT _m = 60 K and $ \varepsilon_{\rm{r}}^{\prime } $ of about 3500 at 10 kHz with T _m = 150 K was found for the BaTi_0.85(Mn_0.5Nb_0.5)_0.15O₃ sample.     

The Effects of Ta Substitution and K/Na Ratio Variation on the Microstructure and Properties of (K,Na)NbO3-Based Lead Free Piezoelectric Ceramics

[(Na_0.5+y K_0.5?y )_0.94Li_0.06][(Nb_0.94Sb_0.06)_1?x Ta _x ]O₃ + 0.08 mol% MnO₂ lead-free piezoelectric ceramics were fabricated successfully by a conventional solid-state reaction method. The effects of Ta⁵⁺ substitution and K/Na ratio variation on the microstructure and properties of the ceramics have been systematically investigated. With the increasing of Ta⁵⁺ substitution content, the orthorhombic–tetragonal transition temperature T _o–t presents obvious “V” type variation while the Curie temperature T _c decreases monotonically. The ceramics properties were further enhanced by adjusting the Na/K ratio of the A-site. Under systematical optimization of the A-site and B-site elements, good overall electrical properties of d ₃₃ = 276 pC/N, k _p = 44.5%, ε ₃₃ ^T /ε ₀ = 1,175, tanδ = 0.027, T _c = 309 °C, P _r = 21.0 μC/cm², and E _c = 1.14 kV/mm were obtained for ceramics with Ta⁵⁺ content x of 0.05 and Na/K ratio of 57/43 (y = 0.07).     

Giant Piezoelectricity of Ternary Perovskite Ceramics at High Temperatures

Here, novel ferroelectric ceramics of (0.95 ? x)BiScO₃‐xPbTiO₃‐0.05Pb(Sn_1/3Nb_2/3)O₃ (BS‐xPT‐PSN) of complex perovskite structure are reported with compositions near the morphotropic phase boundary (MPB), and which exhibit a piezoelectric coefficient d₃₃ = 555 pC N^?1, a large‐signal coefficient $d_{33}^{?}$ ≈ 1200 pm V^?1 at room temperature, and a high Curie temperature T_C of 408 °C. More interestingly, this ternary system exhibits a giant and stable piezoelectric response at 200 °C with a large‐signal $d_{33}^{?}$ ≈ 2500 pm V^?1, matching that of the costly relaxor‐based piezoelectric single crystals at room temperature. The mechanisms of such giant piezoelectricity and its characteristic temperature dependence are attributed to the spontaneous polarization rotation and extension under an electric field and the MPB‐related phase transition. The findings reveal that the BS‐xPT‐PSN ceramics constitute a new family of high‐performance piezoelectric materials suitable for electromechanical transducers that can be operated at high temperatures (at 200 °C, or higher).     

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.     

Giant Piezoelectric Coefficients in Relaxor Piezoelectric Ceramic PNN‐PZT for Vibration Energy Harvesting

It is well known that the piezoelectric performance of ferroelectric Pb(Zr,Ti)O₃ (PZT) based ceramics is far inferior to that of ferroelectric single crystals due to ceramics' polycrystalline nature. Herein, it is reported that piezoelectric stress coefficient e₃₃ = 39.24 C m^?2 (induced electric displacement under applied strain) in the relaxor piezoelectric ceramic 0.55Pb(Ni_1/3Nb_2/3)O₃–0.135PbZrO₃–0.315PbTiO₃ (PNN‐PZT) prepared by the solid state reaction method exhibits the highest value among various reported ferroelectric ceramic and single crystal materials. In addition, its piezoelectric coefficient d₃₃* = 1753 pm V^?1 is also comparable with that of the commercial Pb(Mg_1/3Nb_2/3)O₃‐PbTiO₃ (PMN‐PT) piezoelectric single crystal. The PNN‐PZT ceramic is then assembled into a cymbal energy harvester. Notably, its maximum output current at the acceleration of 3.5 g is 2.5 mA_pp, which is four times of the PMN‐PT single crystal due to the large piezoelectric e₃₃ constants; while the maximum output power is 14.0 mW, which is almost the same as the PMN‐PT single crystal harvester. The theoretical analysis on force‐induced power output is also presented, which indicates PNN‐PZT ceramic has great potential for energy device application.     

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 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.     

Phase, Microstructure, and Microwave Dielectric Properties of NaCa4−x Sr x Nb5O17 (x = 0 to 4) Ceramics

A series of A₅B₅O₁₇-type NaCa_4?x Sr _x Nb₅O₁₇ (x = 0 to 4) compounds were processed through a solid-state mixed-oxide route. All the compositions formed dense single-phase ceramics within the detection limit of an in-house x-ray diffraction facility when sintered at 1300°C. The substitution of Sr for Ca changed the crystal symmetry from monoclinic (x = 0) to orthorhombic (x = 1 to 4) along with a slight increase in molar cell volume due to the relatively larger ionic radius of Sr. The relative permittivity (ε _r) and temperature coefficient of resonance frequency (TCF) increased from 46 to 84 and from ?117 ppm/°C to +377 ppm/°C, respectively, while the quality factor (Q × f) decreased from 11,063 GHz to 559 GHz with an increase in x from 0 to 4. Optimum properties were achieved for NaCa₃SrNb₅O₁₇, which exhibited ε _r = 57, Q × f = 4628 GHz, and TCF = ?41 ppm/°C. Compounds in the NaCa_4?x Sr _x Nb₅O₁₇ series exhibited high ε _r and Q × f with adjustable TCF; however, further work is required for simultaneous optimization of all three properties.