Structures and Properties of Pb(Zr0.5Ti0.5)O3−Pb(Zn1/3Nb2/3)O3− Pb(Ni1/3Nb2/3)O3 Ceramics for Energy Harvesting Devices

Piezoelectric ceramics with large energy density coefficient d₃₃·g₃₃ value have been found suitable for piezoelectric energy harvesting applications. In this study, the phase structures and piezoelectric properties of xPb(Zr_0.5Ti_0.5)O₃?yPb(Zn_1/3Nb_2/3)O₃?(1?x?y)Pb(Ni_1/3Nb_2/3)O₃ (xPZT?yPZN?(1?x?y)PNN) ceramic were investigated with systematically varying PZN and PNN components. The ternary phase diagram of PZT?PZN?PNN system was illustrated and the composition region of morphotropic phase boundary (MPB) was determined. Piezoelectric and dielectric measurements verify that the materials in MPB region all present large d₃₃ and d₃₃·g₃₃ values. In particular, very high d₃₃·g₃₃ coefficients of 20162.2 × 10^?15 m²/N and 21026.3 × 10^?15 m²/N are observed from samples 0.75PZT?0.15PZN?0.1PNN and 0.8PZT?0.05PZN?0.15PNN with compositions located on the rhombohedral phase side near MPB because the dielectric coefficient ε₃₃^T/ε₀ decreases faster than the d₃₃ coefficient at this side.     

Piezoelectric Ceramics for Use in Multilayer Actuators and Energy Harvesters

Microstructural and piezoelectric properties of 0.72Pb(Zr_1?xTi_x)–0.28Pb(Zn_0.4Ni_0.6)_1/3Nb_2/3O₃ (PZ_1?xT_x‐PZNN) ceramics with 0.50 ≤  x ≤ 0.55 were investigated for evaluating the possibility of their use in multilayer actuators and energy harvesters, which demand a large piezoelectric strain constant (d₃₃) and a small dielectric constant (ε^T₃₃/ε_o). The PZ_0.47T_0.53‐PZNN ceramic with a morphotropic phase boundary (MPB) composition showed large d₃₃ and ε^T₃₃/ε_o values, making it unsuitable for use in multilayer actuators and energy harvesters. However, the PZ_0.48T_0.52‐PZNN ceramic with a rhombohedral structure showed a small ε^T₃₃/ε_o value of 1605, yet maintained a large d₃₃ of 550 pC/N. Thermal stimulation did not have any significant effect on the piezoelectric properties of this specimen, except for a slight increase in the ε^T₃₃/ε_o value upon heating the specimen at 150°C for 4 h. In an effort to reduce the sintering temperature, CuO was used as an additive for the ceramic. As a result, the CuO‐added PZ_0.48T_0.52‐PZNN ceramic was well sintered at 900°C. In particular, the 1.0 mol% CuO‐added PZ_0.48T_0.52‐PZNN ceramic exhibited a large d₃₃ value of 554 pC/N and a small ε^T₃₃/ε_o value of 1620, making it highly suitable for use in multilayer actuators and energy harvesters.     

Phase Diagram and Properties of High TC/TR−T Pb(In1/2Nb1/2) O3–Pb(Zn1/3Nb2/3)O3–PbTiO3 Ferroelectric Ceramics

A ternary ferroelectric ceramic system, (1?x?y)Pb(In_1/2Nb_1/2)O₃–xPb(Zn_1/3Nb_2/3)O₃–yPbTiO₃ (PIN–PZN–PT, x = 0.21, 0.27, 0.36, 0.42), was prepared using a two‐step precursor method. The phase structure, dielectric, piezoelectric, and ferroelectric properties of the ternary ceramics were systematically investigated. A morphotropic phase boundary (MPB) was identified by X‐ray diffraction. The optimum piezoelectric and electromechanical properties were achieved for a composition close to MPB (0.5PIN–0.21PZN–0.29PT), where the piezoelectric coefficient d₃₃, planar electromechanical coupling factor k_p, and remnant polarization P_r are 660 pC/N,72%, and 45 μC/cm², respectively. The Curie temperature T_C and rhombohedral to tetragonal phase transition temperature T_R?T were also derived by temperature dependence of dielectric measurements. The strongly “bended” MPB in the PIN–PT system was found to be “flattened” after addition of PZN in the PIN–PT–PZN system. The results demonstrate a possibility of growing ferroelectric single crystals with high electromechanical properties and expanded range of application temperature.     

Remarkably High‐Temperature Stability of Bi(Fe1−xAlx)O3–BaTiO3 Solid Solution with Near‐Zero Temperature Coefficient of Piezoelectric Properties

The 0.72Bi(Fe_1?xAl_x)O₃–0.28BaTiO₃ (x = 0, 0.01, 0.03, 0.05, and 0.07, abbreviated as BFAx–BT) lead‐free high‐temperature ceramics were prepared by the conventional ceramic processing. Systematic investigation on the microstructures, crystalline structures, dielectric and piezoelectric properties, and high‐temperature stability of piezoelectric properties was carried out. The crystalline structures of BFAx–BT ceramics evolve from rhombohedral structure with x < 0.01 to the coexistence of rhombohedral structure and pseudocubic phases with x ≈ 0.01, finally to pseudocubic phases when x > 0.03. Remarkably high‐temperature stability with near‐zero temperature coefficient of piezoelectric properties (TCk_p), together with improved piezoelectric properties has been achieved for x = 0.01 BFAx–BT ceramics. The BFAx–BT(x = 0.01) ceramics simultaneously show the excellent piezoelectric properties of d₃₃ = 151 pC/N, k_p = 0.31 and super‐high‐temperature stability of T_d = 420°C, TCk_p = 1 × 10^?4. It is considered that the observed strong piezoelectricity and remarkably high‐temperature stability should be ascribed to the phase coexistence of rhombohedral and pseudocubic phases. The rhombohedral phases have a positive TCk_p value and the pseudocubic phases possess a negative TCk_p value. Thus, the TCk_p value of BFAx–BT ceramics can be tuned by composition of x.     

Characterization of the High‐Temperature Ferroelectric (100−x−y)BiScO3–(x)Bi(Zr0.5Zn0.5)O3–(y)PbTiO3 Perovskite Ternary Solid Solution

Ternary compositions based on Bi(B′B″)O₃–PbTiO₃‐type compounds have been investigated for high‐temperature piezoelectric applications. Compositions in the ternary were chosen to be near the binary morphotropic phase boundary (MPB) composition of BiScO₃–PbTiO₃ (BS–PT). Ternary compositions in (100?x?y)BiScO₃–(x)Bi(Zr_0.5Zn_0.5)O₃–(y)PbTiO₃ [(100?x?y)BS–xBZZ–yPT] have been investigated with x ≤ 7.5. For compositions with x > 10, the Curie temperature (T_C) decreased below 400°C. Dielectric, piezoelectric, and electromechanical properties were characterized as a function of temperature, frequency, and electric field. Small additions of BZZ were shown to increase the electromechanical properties with only a small loss in T_C. The electromechanical properties were temperature stable up to the depoling temperature. The most promising composition exhibited a T_C of 430°C, piezoelectric coefficient (d₃₃) of 520 pC/N, and a planar coupling factor (k_p) of 0.45 that remained unchanged up to depoling temperature at 385°C.     

Composition and temperature dependence of structure and piezoelectricity in (1−x)(K1−yNay)NbO3‐x(Bi1/2Na1/2)ZrO3 lead‐free ceramics

Lead‐free piezoceramics with the composition (1?x)(K_1?yNa_y)NbO₃‐x(Bi_1/2Na_1/2)ZrO₃ (KNyN‐xBNZ) were prepared using a conventional solid‐state route. X‐ray diffraction, Raman spectroscopy, and dielectric measurements as a function of temperature indicated the coexistence of rhombohedral (R) and tetragonal (T) phase, typical of a morphotropic phase boundary (MPB) as the BNZ concentration increased and by adjusting the K/Na ratio. High remnant polarization (P_r=24 μC/cm²), piezoelectric coefficient (d₃₃=320 pC/N), effective piezocoefficient ({d_{33}^*}=420 pm/V), coupling coefficient (k_p=48%), and high strain (S=0.168%) were obtained at room temperature, but significant deterioration of P_r, {d_{33}^*}, and k_p were observed by increasing from room temperature to 160°C (17.5 μC/cm², 338 pm/V, and 32%, respectively) associated with a transition to a purely T phase. Despite these compositions showing promise for room‐temperature applications, the deterioration in properties as a function of increasing temperature poses challenges for device design and remains to be resolved.     

The Composition and Temperature‐Dependent Structure Evolution and Large Strain Response in (1−x)(Bi0.5Na0.5)TiO3−xBa(Al0.5Ta0.5)O3 Ceramics

The (1?x) (Bi_0.5Na_0.5)TiO₃?xBa(Al_0.5Ta_0.5)O₃((1?x)BNT‐xBAT) lead‐free piezoceramics was fabricated using a conventional solid‐state reaction method. The temperature and composition‐dependent strain behavior, dielectric, ferroelectric (FE), piezoelectric, and pyroelectric properties have been systematically investigated to develop lead‐free piezoelectric materials with large strain response for actuator application. As the BAT content increased, the FE order is disrupted resulting in a degradation of the remanent polarization, coercive field, and the depolarization temperature (T_d). A large strain of 0.36% with normalized strain d₃₃* = 448pm/V was obtained for the optimum composition x = 0.045 at room temperature. The bipolar and unipolar strains for the compositions x = 0.035 and x = 0.04 reach almost identical maximum values when the temperature is in the vicinity of their respective depolarization temperature (T_d). The Raman‐spectra analysis, macroscopic properties, thermal depolarization results, and temperature‐dependent relationships of both polarization and strain demonstrated that the origin of the large strain response for this investigated system is attributed to a field‐induced relaxor to FE phase transformation.     

Thermal Depolarization in the High‐Temperature Ternary Piezoelectric System xPbTiO3–yBiScO3–zBi(Ni1/2Ti1/2)O3

In the high‐temperature ternary perovskite piezoelectric system xPbTiO₃–yBiScO₃–zBi(Ni_1/2,Ti_1/2)O₃ (PT–BS–BNiT), the addition of bismuth to the A site and nickel to the B site leads to compositions that exhibit diffuse relaxor‐like behavior. For these, depolarization temperature, not Curie point, is the critical value of temperature. Depolarization temperature (T_d) is defined as the temperature at which the steepest loss in polarization occurs. This temperature is observed in poled materials through two different methods: loss tangent measurements and in situ d₃₃. Across the ternary system, multiple dielectric anomalies occurred which was observed in dielectric tests where the dielectric peak broadens and becomes frequency dependent as BNiT content increased. For different compositions, the value of T_d ranged between 275°C–375°C. Values for the piezoelectric coefficient increased with temperature up to d₃₃ = 1000 pC/N during in situ d₃₃. High temperature (up to 190°C) and high field (up to 40 kV/cm) were also applied to test ferroelectric properties in these regimes.     

Enhanced Piezoelectric Properties of Praseodymium‐Modified Lead‐Free (Ba0.85Ca0.15)(Ti0.90Zr0.10)O3 Ceramics

The role of Pr₆O₁₁ addition on the structure, microstructure, electrical, and electromechanical properties of lead‐free (Ba_0.85Ca_0.15)(Ti_0.90Zr_0.10)O₃ piezoelectric ceramics has been systemically investigated. Addition of praseodymium (Pr) results in improved ferroelectric and piezoelectric properties. XRD analysis revealed the co‐existence of rhombohedral (R) and tetragonal (T) phases at room temperature. High remanent polarization values (2P_r ~17 μC/cm²) and loop squareness of nearly 0.87 were obtained for the BCZT‐0.04 wt%Pr ceramic, along with high piezoelectric coefficient (d₃₃ = 435 pC/N) and transduction coefficient [(d₃₃·g₃₃) = 11589 × 10^?15 m²/N]. Results are correlated with the crystal structure and microstructure that significantly influence the ferroelectric and piezoelectric properties near the R–T phase transition point. This material seems to be especially suitable for energy harvesting applications, exhibiting outstanding figure of merit.     

Preparation and characterization of Pb(Lu1/2Nb1/2)O3–Pb(In1/2Nb1/2)O3–PbTiO3 ternary ferroelectric ceramics with high phase transition temperatures

To explore new relaxor‐PbTiO₃ systems for high‐power and high‐temperature electromechanical applications, a ternary ferroelectric ceramic system of Pb(Lu_1/2Nb_1/2)O₃–Pb(In_1/2Nb_1/2)O₃–PbTiO₃ (PLN–PIN–PT) have been investigated. The phase structure, dielectric, piezoelectric, and ferroelectric properties of the as‐prepared PLN–PIN–PT ceramics near the morphotropic phase boundary (MPB) were characterized. A high rhombohedral‐tetragonal phase transition temperature T_R‐T of 165°C and a high Curie temperature T_C of 345°C, together with a good piezoelectric coefficient d₃₃ of 420 pC/N, were obtained in 0.38PLN–0.20PIN–0.42PT ceramics. Furthermore, for (0.8?x)PLN–0.2PIN–xPT ceramics, the temperature‐dependent piezoelectric coefficients, coercive fields and electric‐field‐induced strains were further studied. At 175°C, their coercive fields were found to be above 9.5 kV/cm, which is higher than that of PMN–PT and soft P5H ceramics at room temperature, indicating PLN–PIN–PT ceramics to be one of the promising candidates in piezoelectric applications under high‐driven fields. The results presented here could benefit the development of relaxor‐PbTiO₃ with enhanced phase transition temperatures and coercive fields.     

Structure Stability and Microwave Dielectric Properties of (1 − x) Ba(Mg1/2W1/2) O3 + xBa(Y2/3W1/3)O3 Ceramics

The structure stabilities of double perovskite ceramics‐ (1 ? x) Ba(Mg_1/2W_1/2)O₃ + xBa(Y_2/3W_1/3)O₃ (0.01 ≤ x ≤ 0.4) have been studied by X‐ray powder diffraction (XRD), scanning electron microscopy (SEM), and Raman spectrometry in this study. The microwave dielectric properties of the ceramics were studied with a network analyzer at the frequency of about 8–11 GHz. The results showed that all the compounds exhibited face‐centered cubic perovskite structure. Part of Y³⁺ and W⁶⁺ cations occupied 4a‐site and the remaining Y³⁺ and Mg²⁺ distributed over 4b‐site, respectively, and kept the B‐site ratio 1:1 ordered. Local ordering of Y³⁺/Mg²⁺ on 4b‐site and Y³⁺/W⁶⁺ cations on 4a‐site within the short‐range scale could be observed with increasing Y‐doping content. The decomposition of the double perovskite compound at high temperature was successfully suppressed by doping with Y on B‐site. However, Ba₂Y_0.667WO₆ impurity phase appeared when x > 0.1. The optimized dielectric permittivity increased with the increase in Y doping. The optimized Q × f value was remarkably improved with small amount of Y doping (x ≤ 0.02) and reached a maximum value of about 160 000 GHz at x = 0.02 composition. Further increasing in Y doping led to the decrease in Q × f value. All compositions exhibited negative τ_f values. The absolute value of τ_f decreased with increasing Y‐doping content. Excellent combined microwave dielectric properties with ε_r = 20, Q × f = 160 000 GHz, and τ_f = ?21 ppm/°C could be obtained for x = 0.02 composition.     

Phase-formation,microstructure, and piezoelectric/dielectric properties of BiYO3-doped Pb(Zr0.53Ti0.47)O3 for piezoelectric energy harvesting devices

This paper proposes a method for the composition and synthesis of lead zirconate titanate (PZT) piezoelectric ceramic for use in energy harvesting systems. The proposed material consists of (1?x)Pb(Zr_0.53Ti_0.47)O₃–xBiYO₃ [PZT–BY(x)] (x=0, 0.01, 0.02, 0.03, 0.04, and 0.05 mol) ceramics near the morphotropic phase boundary (MPB) region, prepared by a solid-state mixed-oxide method. The optimum sintering temperature was found to be 1160 °C, which produced high relative density for all specimens (96% of the theoretical density). Second phases were found to precipitate in the composition containing x≥0.01 mol of BY. It is shown that the addition of BY inhibits grain growth, and exhibits a denser and finer microstructure than those in the un-doped state. Fracture surface observation revealed predominant intergranular fracture for x=0 and x=0.01, while a mixed mode of transgranular and intergranular fracture appeared for x≥0.02. The optimal doping level was found to be x=0.01, for which a dielectric constant (K₃₃^T) of 750, a Curie temperature (T_C) of 373 °C, a remnant polarization (P_r) of 50 µC/cm², a piezoelectric constant (d₃₃) of 350 pC/N, and an electro-mechanical coupling factor (k_p) of 65% were obtained. In addition, the piezoelectric voltage constant (g₃₃), and transduction coefficient (d₃₃×g₃₃) of PZT–BY(x) ceramics have been calculated. The ceramic PZT–BY(0.01) shows a considerably lower K₃₃^T value, but higher d₃₃ and k_p. Therefore, the maximum transduction coefficient (d₃₃×g₃₃) of 18,549×10^?15 m²/N was obtained for PZT–BY(0.01). The large (d₃₃×g₃₃) indicates that the PZT–BY(0.01) ceramic is a good candidate material for energy harvesting devices.     

High strain (0.4%) Bi(Mg2/3Nb1/3)O3‐BaTiO3‐BiFeO3 lead‐free piezoelectric ceramics and multilayers

The relationship between the piezoelectric properties and the structure/microstructure for 0.05Bi(Mg_2/3Nb_1/3)O₃‐(0.95‐x)BaTiO₃‐xBiFeO₃ (BBFT, x = 0.55, 0.60, 0.63, 0.65, 0.70, and 0.75) ceramics has been investigated. Scanning electron microscopy revealed a homogeneous microstructure for x < 0.75 but there was evidence of a core‐shell cation distribution for x = 0.75 which could be suppressed in part through quenching from the sintering temperature. X‐ray diffraction (XRD) suggested a gradual structural transition from pseudocubic to rhombohedral for 0.63 < x < 0.70, characterized by the coexistence of phases. The temperature dependence of relative permittivity, polarization‐electric field hysteresis loops, bipolar strain‐electric field curves revealed that BBFT transformed from relaxor‐like to ferroelectric behavior with an increase in x, consistent with changes in the phase assemblage and domain structure. The largest strain was 0.41% for x = 0.63 at 10 kV/mm. The largest effective piezoelectric coefficient (d₃₃^*) was 544 pm/V for x = 0.63 at 5 kV/mm but the largest Berlincourt d₃₃ (148 pC/N) was obtained for x = 0.70. We propose that d₃₃^* is optimized at the point of crossover from relaxor to ferroelectric which facilitates a macroscopic field induced transition to a ferroelectric state but that d₃₃ is optimized in the ferroelectric, rhombohedral phase. Unipolar strain was measured as a function of temperature for x = 0.63 with strains of 0.30% achieved at 175°C, accompanied by a significant decrease in hysteresis with respect to room temperature measurements. The potential for BBFT compositions to be used as high strain actuators is demonstrated by the fabrication of a prototype multilayer which achieved 3 μm displacement at 150°C.     

Enhancing high power performances of Pb(Mn1/3Nb2/3)O3–Pb(Zr,Ti)O3 ceramics by Bi(Ni1/2Ti1/2)O3 modification

High power piezoelectric ceramics 0.04Bi(Ni_1/2Ti_1/2)O₃-xPb(Mn_1/3Nb_2/3)O₃-(0.96-x)Pb(Zr_yTi_1-y)O₃ (BNT-xPMnN-PZ_yT) with various contents of PMnN from 0 to 12 mol% (keep y = 0.50) and Zr/Ti ratio gradually increasing from 48/52 to 52/48 (keep x = 0.06) were prepared by solid-state method. X-ray diffraction (XRD) results show a single phase of polycrystalline perovskite and indicate that the phase structure transforms from tetragonal phase to rhombohedral with x and y increasing. The optimal comprehensive properties of BNT-xPMnN-PZ_yT ceramic, d₃₃ (355 pC/N), k_p (0.58), ε_r (1512), tanδ (0.40%), T_c (336 °C) and Q_m (2010), are obtained at x = 0.06 and y = 0.50, which are apparently superior to typical or commercial Pb(Zr,Ti)O₃ (PZT) based power ceramics. Within the range from room temperature to 200 °C, the variation of electric-field induced strains is less than 8.3%, indicating its good temperature stability. The maximum vibration velocity of the ceramic at temperature rise of 20 °C is measured to be 0.92 m/s, which is about 2 times higher than that of commercial hard PZT ceramics, suggesting the BNT-xPMnN-PZ_yT ceramic is a competitive and potential candidate for power piezoelectric transduction and actuation applications.     

Normal‐Relaxor‐Diffuse Ferroelectric Phase Transition and Electrical Properties of Bi(Mg1/2Ti1/2)3–PbZrO3–PbTiO3 Solid Solution Ceramics Near the Morphotropic Phase Boundary

Perovskite‐type xBi(Mg_1/2Ti_1/2)O₃–(0.56 ? x)PbZrO₃–0.44PbTiO₃ (xBMT–PZ–PT) ternary solid solution ceramics were synthesized via a conventional solid‐state reaction method. The phase transition behaviors, dielectric, ferroelectric, and piezoelectric properties were investigated as a function of the BMT content. The X‐ray diffraction analysis showed that the tetragonality of xBMT–PZ–PT was enhanced with increasing the BMT content, and a morphotropic phase boundary (MPB) between rhombohedral and tetragonal phases was identified approximately in the composition of x = 0.08. In addition, the dielectric diffuseness and frequency dispersion behavior were induced with the addition of BMT and a normal‐relaxor‐diffuse ferroelectric transformation was observed from the PZ‐rich side to the BMT‐rich side. The electrical properties of xBMT–PZ–PT ceramics exhibit obviously compositional dependence. The x = 0.08 composition not only possessed the optimum properties with ε^T₃₃/ε₀ = 1450, Q_m = 69, d₃₃ = 390 pC/N, k_p = 0.46, P_r = 30 μC/cm², E_c = 1.4 kV/mm, T_c = 325°C, and a strain of 0.174% (d₃₃^* = 436 pm/V) under an electric field of 4 kV/mm as a result of the coexistence of two ferroelectric phases near the MPB, but also owned a good thermal‐depolarization behavior with a d₃₃ value of >315 pC/N up to 290°C and a frequency‐insensitive strain behavior.     

Dielectric and Piezoelectric Properties of (1−x)K0.5Bi0.5TiO3–xBa(Ti0.8Zr0.2)O3 Ceramics

The properties of relaxor ceramics in the compositional series (1?x)K_0.5Bi_0.5TiO₃–xBa(Ti_0.8Zr_0.2)O₃ have been investigated. Values of T_m, the temperature of maximum relative permittivity, decreased from 380°C at x = 0.0 to below room temperature for x > 0.7. Compositions x = 0.1 and 0.2 were piezoelectric and ferroelectric. The maximum value of d₃₃ piezoelectric charge coefficient, 130 pC/N, and strain, 0.14%, occurred at x = 0.1. Piezoelectric properties of x = 0.1 were retained after thermal cycling from room temperature to 220°C, consistent with results from high‐temperature X‐ray diffraction indicating a transition to single‐phase cubic at ~300°C.     

Structural and piezoelectric properties of <001> textured PZT‐PZNN piezoelectric ceramics

Rhombohedral 0.69Pb(Zr_0.47Ti_0.53)‐0.31Pb(Zn_0.6Ni_0.4)NbO₃ (PZT‐PZNN) ceramics were textured using 10.0 vol. % BaTiO₃ (BT) platelets along the <001> direction at 950°C with a high Lotgering factor of 95.3%. BT platelets did not react with the PZT‐PZNN ceramics, and the textured PZT‐PZNN ceramic had a tetragonal structure. The PZT‐PZNN ceramics exhibited a strain of 0.174% with a piezoelectric strain constant (d*₃₃) of 580 pC/N at 3.0 kV/mm. The textured PZT‐PZNN ceramic showed an increased strain of 0.276% and d*₃₃ of 920 pC/N at 3.0 kV/mm, which can be explained by the domain rotation. However, the d₃₃ values of the textured specimens are smaller than those of the untextured specimens because of the small remanent polarization and relative dielectric constant of BT platelets. The textured PZT‐PZNN ceramic synthesized in this work can be used for piezoelectric multilayer actuators because of its large strain and low sintering temperature.     

High quality factor microwave dielectric ceramics in the (Mg1/3Nb2/3)O2–ZrO2–TiO2 ternary system

Novel high quality factor microwave dielectric ceramics (1?x)ZrTiO₄?x(Mg_1/3Nb_2/3)TiO₄ (0.325≤x≤0.4) and (ZrTi)_1?y(Mg_1/3Nb_2/3)_yO₄ (0.2≤y≤0.5) with the addition of 0.5 wt% MnCO₃ in the (Mg_1/3Nb_2/3)O₂–ZrO₂–TiO₂ ternary system were prepared, using solid‐state reaction method. The relationship between the structure and microwave dielectric properties of the ceramics was studied. The XRD patterns of the sintered samples reveal the main phase belonged to α‐PbO₂‐type structure. Raman spectroscopy and infrared reflectivity (IR) spectra were employed to evaluate phonon modes of ceramics. The 0.65ZrTiO₄?0.35(Mg_1/3Nb_2/3)TiO₄?0.5 wt% MnCO₃ ceramic can be well densified at 1240°C for 2 hours and exhibits good microwave dielectric properties with a relative permittivity (ε_r) of 42.5, a quality factor (Q×f) value of 43 520 GHz (at 5.9 Ghz) and temperature coefficient of resonant frequency (τ_f) value of ?5ppm/°C. Furthermore, the (ZrTi)_0.7(Mg_1/3Nb_2/3)_0.3O₄?0.5 wt% MnCO₃ ceramic sintered at 1260°C for 2 hours possesses a ε_r of 31.8, a Q×f value of 35 640 GHz (at 6.3 GHz) and a near zero τ_f value of ?5.9 ppm/°C. The results demonstrated that the (Mg_1/3Nb_2/3)O₂–ZrO₂–TiO₂ ternary system with excellent properties was a promising material for microwave electronic device applications.     

Piezoelectric Properties of a Pioneering 3‐1 Type PZT/Epoxy Composites Based on Freeze‐Casting Processing

Lead zirconate titanate (PbZr_1 ? xTi_xO₃, PZT)/epoxy composites with one‐ dimensional epoxy in PZT matrix (called 3‐1 type piezocomposites) have been fabricated by tert‐butyl alcohol (TBA)‐based directional freeze casting of PZT matrix and afterward infiltration of epoxy. The composites with PZT volume fraction ranging from 0.36 to 0.69 were obtained by adjusting initial solid loading in freeze‐casting slurry. The effect of poling voltage on piezoelectric properties of the composites was studied for various volume fraction of PZT phase. With the increasing of PZT volume fraction, relative permittivity (ε_r) increased linearly and piezoelectric coefficient (d₃₃ and d₃₁) increased step by step. The resultant composites with 0.57 PZT volume fraction possessed the highest hydrostatic piezoelectric strain coefficient (d_h) value (184 pC/N), voltage coefficient (g_h) value (13.6 × 10^?3 V/m Pa), and hydrostatic figure of merit (HFOM) value (2168 × 10^?15 Pa^?1).     

Structure and microwave dielectric properties of the Li2/3(1−x)Sn1/3(1−x)MgxO systems (x = 0‐4/7)

In this paper, the Li_2/3(1?x)Sn_1/3(1?x)Mg_xO (LSMxO) ceramic systems were prepared by solid‐state reaction using novel atmosphere‐controlled sintering (x = 0‐4/7). Pure Li₂SnO₃ was observed for x = 0, the Li₂Mg₃SnO₆ and Li₂SnO₃ coexisted for x = 1/7, and the coexistence of three kinds of phases was detected for x = 1/5 and 1/4, including Li₄MgSn₂O₇ impurity phase. Pure Li₂Mg₃SnO₆‐like phase with cubic rock salt structure in Fm‐3m space group was obtained in the range of 1/3‐4/7. All samples showed well‐dense and smooth microstructures. The microwave dielectric properties highly depended on the phase composition, bond valence, FWHM of Raman spectrum, Raman shift, average grain sizes, and octahedral distortion. The LSMxO ceramics sintered at 1250°C for 5 hours possessed excellent comprehensive properties of ε_r = 15.43, Q×f = 80 902 GHz and τ_f = +5.61 ppm/°C for x = 1/7. Typically, the LSMxO ceramics sintered at 1350°C for 5 hours showed a maximum Q × f of 168 330 GHz for x = 1/2.