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.     

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.     

Transition in temperature scaling behaviors and super temperature stable polarization in BiScO3–PbZrO3–PbTiO3 system

Temperature scaling of dynamic ferroelectric hysteresis for the morphotropic phase boundary (MPB) compositions in xBiScO₃–(1-x-y)PbZrO₃–yPbTiO₃ (xBS–(1-x-y)PZ–yPT, 0.018 ≤ x ≤ 0.264) ternary system was systematically investigated. The power-law relation was obtained for remanent polarization P_r and temperature T, that is, P_r ∝ T^β. It is interesting to find that the power-law exponent β could be modulated by BiScO₃ content x. With the increase of x from 0.018 to 0.264, β varies from −1.09398 to 2.44147. Transition of β from negative to positive produces in the vicinity of 0.054BS–0.476PZ–0.470PT ceramic. At this composition, the magnitude of β is very close to zero with value of only −0.01567, implying an almost temperature-independent polarization characteristic of the ceramic. Comparing with the conventional PZT-based piezoelectric ceramics that usually with negative exponent β, when x > 0.054, the xBS–(1-x-y)PZ–yPT ceramics show positive β value, so that the ferroelectric polarization is enhanced with increasing temperature. Such a positive temperature dependence of ferro-/piezoelectric property makes the ternary system a promising candidate for high-temperature applications.     

Large Piezoelectric Response and Polarization in Relaxor Ferroelectric PbTiO3–Bi(Ni1/2Zr1/2)O3

New binary system (1?x) PbTiO₃?xBi(Ni_1/2Zr_1/2)O₃ (PT–100x BNZ) with x ≤ 0.45 were synthesized via solid‐state reaction route. A morphotropic phase boundary (MPB) was identified around x = 0.40 by X‐ray diffraction (XRD) method. The ceramics with MPB composition exhibit enhanced ferroelectric properties. A large piezoelectric coefficient (d₃₃) up to 400 pC/N was obtained for the PT–40BNZ, which is comparable with the PbTiO₃–BiScO₃ (PT–BS, 450 pC/N).The frequency dependence of dielectric permittivity of PT–40BNZ shows characteristic of a strong relaxor feature and a transition temperature around 290°C (1 MHz). Temperature effect on the unipolar strain was also investigated. The present system with high d₃₃ is a competitive piezoelectric material, as no expensive oxide is used here compared with the PT–BS.     

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.     

Piezoelectric Property and Strain Behavior of Pb(Yb0.5Nb0.5)O3–PbHfO3–PbTiO3 Polycrystalline Ceramics

(1?x)Pb(Hf_1?yTi_y)O₃–xPb(Yb_0.5Nb_0.5)O₃ (x = 0.10–0.44, y = 0.55–0.80) ceramics were fabricated. The morphotropic phase boundary (MPB) of the ternary system was determined by X‐ray powder diffraction. The optimum dielectric and piezoelectric properties were achieved in 0.8Pb(Hf_0.4Ti_0.6)O₃–0.2Pb(Yb_0.5Nb_0.5)O₃ ceramics with MPB composition, where the dielectric permittivity ε_r, piezoelectric coefficient d₃₃, planar electromechanical coupling k_p, and Curie temperature T_c were found to be on the order of 1930,480 pC/N, 62%, and 360°C, respectively. The unipolar strain behavior was evaluated as a function of applied electric field up to 50 kV/cm to investigate the strain nonlinearity and domain wall motion under large drive field, where the high field piezoelectric d₃₃* was found to be 620 pm/V for 0.82Pb(Hf_0.4Ti_0.6)O₃–0.18Pb(Yb_0.5Nb_0.5)O₃. In addition, Rayleigh analysis was carried out to study the extrinsic contribution, where the value was found to be in the range 2%–18%.     

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.     

Temperature‐Dependent Phase Transitions in the Lead‐Free Piezoceramics (1 – x – y)(Bi1/2Na1/2)TiO3–xBaTiO3–y(K0.5Na0.5)NbO3 Observed by in situ Transmission Electron Microscopy and Dielectric Measurements

Lead‐free piezoelectric (1 – x – y)(Bi_1/2Na_1/2)TiO₃–xBaTiO₃–y(K_0.5Na_0.5)NbO₃ (BNT–BT–KNN) ceramics were examined in situ under increasing temperature in the transmission electron microscope. Changing superstructure reflections indicate a transition from rhombohedral to tetragonal to cubic phase with broad coexistence regions. The additional evolution of the microstructure in combination with dielectric measurements leads to a model of two relaxor‐type phase evolutions with temperature.     

Composition‐ and Temperature‐Dependent Large Strain in (1−x)(0.8Bi0.5Na0.5TiO3–0.2Bi0.5K0.5TiO3)– xNaNbO3 Ceramics

Ternary solid solutions of (1 ? x)(0.8Bi_0.5Na_0.5TiO₃–0.2Bi_0.5K_0.5TiO₃)– xNaNbO₃ (BNKT–xNN) lead‐free piezoceramics were fabricated using a conventional solid‐state reaction method. Pure BNKT composition exhibited an electric‐field‐induced irreversible structural transition from pseudocubic to ferroelectric rhombohedral phase at room temperature. Accompanied with the ferroelectric‐to‐relaxor temperature T_F‐R shifted down below room temperature as the substitution of NN, a compositionally induced nonergodic‐to‐ergodic relaxor transition was presented, which featured the pinched‐shape polarization and sprout‐shape strain hysteresis loops. A strain value of ~0.445% (under a driving field of 55 kV/cm) with large normalized strain of ~810 pm/V was obtained for the composition of BNKT–0.04NN, and the large strain was attributed to the reversible electric‐field‐induced transition between ergodic relaxor and ferroelectric phase.     

Reduced Dielectric Loss and Strain Hysteresis in Fe and Mn Comodified High‐Temperature BiScO3–PbTiO3 Ceramics

There is a growing requirement for high‐temperature piezoelectric materials in the petrochemical, automotive, and aerospace industries. Here, the piezoelectric materials of Fe and Mn comodified 0.36BiScO₃–0.64PbTiO₃ (BS‐PTFMn) ceramics with high Curie temperature (T_c), large mechanical quality factor (Q_m), and reduced strain hysteresis were presented. XRD results revealed that all the BS‐PTFMn ceramics have a pure perovskite structure with tetragonal symmetry, and the ratio of c/a is insensitive to the contents of Fe. With the modifications of Fe, the dielectric loss tanδ and strain hysteresis decrease clearly, while the mechanical quality factor improves significantly. The Curie temperature, piezoelectric constant, planar electromechanical coupling factor, dielectric loss, and mechanical quality factor of the BS‐PTFMn with 3% Fe content are 492°C, 235 pC/N, 0.38, 0.6%, and 280, respectively. BS‐PTFMn ceramics show 50°C higher T_c than BS‐PT morphotropic phase boundary composition. The figure of merit (product of Q_m, and k_ij) of BS‐PTFMn ceramics is about five times than that of pure BS‐PT ceramics. Furthermore, for the BS‐PTFMn ceramics with Fe content of 3 mol%, the high field strain coefficient value calculated from the electric‐field‐induced strain curves (S_max/E_max) is 320 pm/V, while the strain hysteresis (under 40 kV/cm) is reduced to one fifth that of unmodified BS‐PT ceramics. Moreover, the temperature‐dependent electromechanical coupling coefficient and dielectric constant are very stable in the temperature range from room temperature (RT) to 450°C. These results indicated that BS‐PTFMn ceramics are promising for high‐temperature piezoelectric applications.     

Reduced dielectric loss and strain hysteresis in (0.97−x)BiScO3–xPbTiO3–0.03Pb(Mn1/3Nb2/3)O3 piezoelectric ceramics

(0.97−x)BiScO₃–xPbTiO₃–0.03Pb(Mn_1/3Nb_2/3)O₃ (BS–PT–PMnN) ceramics were prepared by solid-state reaction method. X-ray diffraction analysis revealed that the morphotropic phase boundary (MPB) of BS–PT–PMnN ceramics located near x=0.58. The high Curie temperature (437 °C), large piezoelectric constant (300 pC/N), low dielectric loss (0.015) and small strain hysteresis (20%) were obtained for the MPB composition. Its dielectric loss and strain hysteresis were reduced down to one third and half those of pure BiScO₃–PbTiO₃ (BS–PT) ceramics, respectively. In addition, the maximum vibration velocity of the BS–PT–PMnN ceramics was 0.85 ms⁻¹, much superior to those of BS–PT (0.15 ms⁻¹) and modified PZT (0.4 ms⁻¹) ceramics. These results indicated BS–PT–PMnN ceramics were promising candidates for high temperature piezoelectric applications.     

Orthorhombic‐pseudocubic phase transition and piezoelectric properties of (Na0.5K0.5)(Nb1−xSbx)‐SrZrO3 ceramics

0.96(Na_0.5K_0.5)(Nb_1?xSb_x)‐0.04SrZrO₃ ceramics with 0.0≤x≤0.06 were well sintered at 1060°C for 6 hours without a secondary phase. Orthorhombic‐tetragonal transition temperature (T_O‐T) and Curie temperature (T_C) decreased with the addition of Sb₂O₅. The decrease in T_C was considerable compared to that in T_O‐T, and thus the tetragonal phase zone disappeared when x exceeded 0.03. Therefore, a broad peak for orthorhombic‐pseudocubic transition as opposed to that for orthorhombic‐tetragonal transition appeared at 115°C‐78.2°C for specimens with 0.04≤x≤0.06. An orthorhombic structure was observed for specimens with x≤0.03. However, the polymorphic phase boundary structure containing orthorhombic and pseudocubic structures was formed for the specimens 0.04≤x≤0.06. Furthermore, a specimen with x=0.055 exhibited a large piezoelectric strain constant of 325 pC/N, indicating that the coexistence of orthorhombic and pseudocubic structures could improve the piezoelectric properties of (Na_0.5K_0.5)NbO₃‐based lead‐free piezoelectric ceramics.     

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.     

New Lead‐Free (1 − x)(K0.5Na0.5)NbO3–x(Bi0.5Na0.5)ZrO3 Ceramics with High Piezoelectricity

For enhancing the piezoelectric properties of ceramics (Bi_0.5Na_0.5)ZrO₃ (BNZ) was used to partially substitute (K_0.5Na_0.5)NbO₃ (KNN). The addition of BNZ changes the symmetry of KNN ceramics from orthorhombic to tetragonal, and finally to rhombohedral phase. A new phase boundary with both rhombohedral–orthorhombic and orthorhombic–tetragonal phase transitions near room temperature is identified for KNN–0.050BNZ ceramics, where optimum electrical properties were obtained: d₃₃ = 360 pC/N, k_p = 32.1%, ε_r = 1429, tanδ = 3.5%, and T_C = 329°C. The results indicated a new method for designing high‐performance lead‐free piezoelectric materials.     

Ultralow dielectric loss of BiScO3-PbTiO3 ceramics by Bi(Mn1/2Zr1/2)O3 modification

BiScO₃-PbTiO₃ ceramics are attractive for high-temperature piezoelectric applications while their high dielectric loss has to be substantially reduced. In this paper, a ternary perovskite system of xBi(Mn_1/2Zr_1/2)O₃-(1-x-y)BiScO₃-yPbTiO₃ (abbreviated as xBMZ-BS-yPT) with x = 0.02, 0.04 and y = 0.62–0.67 were fabricated by conventional solid-phase method, and their ceramics were systematically studied with regards to phase structure, microstructure, dielectric and piezoelectric properties. X-ray diffraction results indicate a gradual change from rhombohedral to tetragonal phase with increasing PT composition. Morphotropic phase boundary (MPB) is revealed for the system with x = 0.02, y = 0.64, at which ultralow dielectric loss factor (0.58 %), almost unchanged Curie temperature (449 °C), high electromechanical properties (d₃₃ = 360 pC/N, k_p = 0.53), and stable strain output below 200 °C are observed. With such excellent piezoelectric properties and high-temperature stability, BMZ modified BS-PT ceramics are promising candidates for power electromechanical devices, especially operating in high-temperature environments.     

Dielectric Relaxor Evolution and Frequency‐Insensitive Giant Strains in (Bi0.5Na0.5)TiO3‐Modified Bi(Mg0.5Ti0.5)O3–PbTiO3 Ferroelectric Ceramics

The 0.45Bi(Mg_0.5Ti_0.5)O₃–(0.55 ? x)PbTiO₃–x(Bi_0.5Na_0.5)TiO₃ (BMT–PT–xBNT) ternary solid solution ceramics were prepared via a conventional solid‐state reaction method; the evolution of dielectric relaxor behavior and the electrostrain features were investigated. The XRD and dielectric measurements showed that all studied compositions own a single pseudocubic perovskite structure and undergo a diffuse‐to‐relaxor phase transition owing to the evolution of the domain from a frozen state to a dynamic state. The formation of the above dielectric relaxor behavior was further confirmed by a couple of measurements such as polarization loops, polarization current density curves, as well as bipolar strain loops. A large strain value of ~0.41% at a driving field of 7 kV/mm (normalized strain d₃₃* of ~590 pm/V) was obtained at room temperature for the composition with x = 0.32, which is located near the boundary between ergodic and nonergodic relaxor. Moreover, this electric field‐induced large strain was found to own a frequency‐insensitive characteristic.     

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.     

Preparation and Electric Properties of Bi0.5Na0.5TiO3–Bi(Mg0.5Ti0.5)O3 Lead‐Free Piezoceramics

Lead‐free BNT‐based piezoceramics, (1?x)Bi_0.5Na_0.5TiO₃–xBi(Mg_0.5Ti_0.5)O₃ [(1?x)BNT–xBMT] (0.00 ≤ x ≤ 0.06) binary system, were synthesized using a conventional ceramic fabrication method. Effect of Bi(Mg_0.5Ti_0.5)O₃ (BMT) substitution on room temperature (RT) crystal structure, and temperature dependence of electric properties were investigated. The XRD indicates that a pure perovskite phase is formed. The introduction of BMT decreases E_C of BNT from 7.3 to 4.0 kV/mm, and increases d₃₃ from 58 pC/N to 110 pC/N for the x = 0.05. The system shows a typical ferroelectric (FE) polarization loop P(E) and butterfly bipolar strain‐electric S(E) curve at RT. For the composition of 0.95BNT–0.05BMT antiferroelectric (AFE) phase appears near 80°C, characterized by a constricted P(E) loop and altered bipolar S(E) butterfly, and gradually prevails with increasing temperature. Temperature dependence of dielectric constant shows that T_C increases from 310°C for pure BNT to 352°C for the x = 0.05. The results indicate that the piezoelectric properties of BNT have been improved by means of Bi(Mg_0.5Ti_0.5)O₃ substitution.     

Crystal Structure and Electrical Properties of Lead‐Free (1 − x)BaTiO3–x(Bi1/2A1/2)TiO3 (A = Ag,Li, Na,K, Rb,Cs) Ceramics

Ceramics of solid solutions (1  ?  x)BaTiO₃–x(Bi_1/2A_1/2)TiO₃ (A = Ag, Li, Na, K, Rb, Cs, x ≤ 0.20) were prepared and their crystal structures, dielectric, ferroelectric, and piezoelectric properties were investigated. It was found that (Bi_1/2A_1/2)TiO₃‐type doping compounds broadened the temperature range of the tetragonal phase in BaTiO₃ and all the compositions examined displayed a tetragonal structure at room temperature. The Curie temperature (T_C) was observed to increase with respect to pure BaTiO₃ to the range 140°C–210°C through solid solution. Remanent polarization (P_r) tended to decrease with increased content of doping compound, whereas the coercive field (E_C) rose and piezoelectric coefficient (d₃₃) fell. The highest d₃₃ value in the solid solutions was observed in 0.97BaTiO₃–0.03(Bi_1/2Ag_1/2)TiO₃ at 90 pC/N.     

Structural and Piezoelectric Properties of (1−x)Pb(Zr1−yTiy)O3–xPb(Zn0.4Ni0.6)1/3Nb2/3O3 Ceramics Near Triple Point

The crystal structure and piezoelectric properties of (1?x)Pb(Zr_1?yTi_y)O₃‐xPb(Zn_0.4Ni_0.6)_1/3Nb_2/3O₃ [(1?x)PZ_1?yT_y‐xPZNN] ceramics were investigated. The 0.665PZ_0.45T_0.55‐0.335PZNN ceramic has the triple point composition, where the rhombohedral, pseudocubic, and tetragonal structures coexist. Maximum d₃₃ and k_p values of 770 pC/N and 0.69, respectively, were observed from this specimen; it also exhibited a large ε^T₃₃/ε_o value of 3250. Although the maximum d₃₃ value was obtained from the triple point composition specimen, its g₃₃ and d₃₃ × g₃₃ values were relatively small because of its large ε^T₃₃/ε_o value. However, the 0.665PZ_0.46T_0.54‐0.335PZNN ceramic, which has a rhombohedral structure, exhibited a large g₃₃ value of 43 × 10^?3 Vm/N and a d₃₃ × g₃₃ value of 27 000 × 10^?15 m²/N. Therefore, this ceramic is a good candidate for multilayer actuators and piezoelectric energy harvesters.