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.     

Effects of Ga content on the structure and electrical performances of 0.69BiFe1-xGaxO3-0.31BaTiO3 lead-free ceramics

Lead-free 0.69BiFe_1-xGa_xO₃-0.31BaTiO₃ (x, 0–0.06) piezoceramics were synthesized via traditional sintering techniques. The phase structure, dielectric, piezoelectric and ferroelectric performances of the ceramics were studied systematically. The results revealed that all the samples locate near MPB of rhombohedral (R)-pseudocubic (pC) phase coexistence, and that Ga doping has distinct influences on the R/pC phase content ratio. An appropriate content of Ga doping favors densification and grains growth of the ceramics during sintering. With the increment of Ga content, the Curie temperature of the samples shifts towards lower temperature owing to increased tolerance factor t of the perovskites, and enhanced diffuse phase transition behavior was observed. In addition, both the piezoelectric and ferroelectric property are sensitive to the concentration of Ga doping. Significantly, the excellent piezoelectric coefficient d₃₃ up to 206 pC/N along with strong remanent polarization P_r of 25 μC/cm² are obtained in 0.69BiFe_0.985Ga_0.015O₃-0.31BaTiO₃ materials which would be a promising substitute for the conventional lead zirconate titanate system ceramics.     

Large electrostrictive effect and high energy storage performance of Pr3+-doped PIN-PMN-PT multifunctional ceramics in the ergodic relaxor phase

The photoluminescence, dielectric relaxation, ferroelectric hysteresis, and field-induced strain properties of Pr³⁺-doped 0.24Pb(In_1/2Nb_1/2)O₃-0.42Pb(Mg_1/3Nb_2/3)O₃-0.34PbTiO₃ (PIN-PMN-PT:Pr³⁺) multifunctional ceramics have been investigated. It was found that Pr³⁺ doping enhanced the dielectric diffuseness and relaxation behavior of PIN-PMN-PT ceramics. Slim P-E loops and S-E curves appear in PIN-PMN-PT:Pr³⁺ ceramics when the Pr³⁺ doping concentration reaches 1.4 mol%. Local domain configurations associated with phase transitions were investigated by piezoresponse force microscopy (PFM). Large electrostrictive coefficient Q₃₃ (?0.03 m⁴/C²) and high energy-storage efficiency η (92%) were obtained in 2 mol% Pr³⁺-doped PIN-PMN-PT ceramic in the ergodic relaxor (ER) phase at room temperature. The giant electrostrictive effect and excellent energy-storage performance are related to the field-induced dynamic behavior of polar nanoregions (PNRs). The results show that the PIN-PMN-PT:Pr³⁺ system is an excellent multifunctional material for making electromechanical and energy storage devices.     

Improved piezoelectric properties of Pb(Zr0·70Ti0.30)O3 ceramics doped with non-polar bismuth manganite

This report documents the electrical features of (1-x) Pb(Zr_0·70Ti_0.30)O₃–x BiMn₂O₅ ceramics with x = 0–0.05 (PZT–BM). A structural disorder was introduced by doping with non-polar bismuth manganite (BM) to increase the chemical disorder in PZT ceramics, which is one of the reasons for its marked piezoelectric properties. The chemical disorder was confirmed using scanning electron microscopy. The rhombohedral symmetry of a crystal lattice was determined using the XRD powder test. To assess the influence of BM dopant on the electric properties of PZT, dielectric spectroscopy was performed at a frequency f = 1 kHz–1 MHz and in a temperature range of 290–680 K. Several effects on the dielectric characteristics were induced by the addition of BM, including the shift and diffuseness of the transition from the ferroelectric to the paraelectric phase and the diffuseness of the transition between two ferroelectric phases. The electrical conductivity increased as the BM content increased. Piezoelectric studies have shown that 0.99 PZT–0.01 BM ceramics exhibit better piezoelectric properties and higher permittivity than pure PZT ceramics. The 0.99 PZT–0.01 BM piezoelectric coefficient d₃₃ increased by approximately 30% compared with pure PZT.     

Improved ferroelectric properties of BiFeO3-based piezoelectric ceramics through morphotropic phase boundary construction

The ceramic (1-x)BiFe_0.985Sc_0.015O₃-xBaZr_0.2Ti_0.8O₃ + 1mol% MnO₂ (x = 0.20, 0.25, 0.30, 0.35) (BFS-xBZT) was synthesized using the traditional ceramic sintering method. The components of the ceramic were determined by constructing a morphotropic phase boundary (MPB) which consists of rhombohedral (R) and tetragonal (T) phases (0.24≤ x ≤ 0.26). With the accumulation of BZT content, relax behaviors were observed by dielectric properties measurements. At the MPB, the crystal structures of the R phase and T phase change abruptly. The distortion degree of the R phase increases, and the differences between a and c of the T phase decrease. An enhanced ferroelectricity Pr of ~27.8 μC/cm² and apex piezoelectric coefficient d₃₃ of 131 ± 4 pC/N are obtained near the MPB (x = 0.25), due to the R-T phase coexistence near room temperature. The results show that BFS-xBZT ceramics could be a candidate for lead-free piezoelectric ceramics at high operating temperatures.     

Correlation between structural,ferroelectric, piezoelectric and dielectric properties of Ba0.7Ca0.3TiO3-xBaTi0.8Zr0.2O3 (x = 0.45, 0.55) ceramics

We report on the correlation between structural, ferroelectric, piezoelectric and dielectric properties of the (1-x)Ba_0.7Ca_0.3TiO₃-xBaTi_0.8Zr_0.2O₃ (x?=?0.45, 0.55; abbreviated as 55BCT30 and 45BCT30) ceramics close to morphotropic phase boundary (MPB) region. The 55BCT30 and 45BCT30 ceramics were synthesized by the standard, high-temperature solid state ceramic method. X-ray diffraction (XRD) along with Rietveld refinement indicate that the 55BCT30 ceramics exhibit rhombohedral (R, space group R3m), orthorhombic (O, space group Amm2) and tetragonal (T, space group P4mm) phases while 45BCT30 ceramics exhibit only T and O phases. The temperature dependent Raman spectroscopy measurements confirm the structure and phase transformations observed from XRD. All the ceramics are chemically homogeneous and exhibit a dense microstructure with a grain size of 5–7?µm. The presence of polarization-electric field and strain-electric field hysteresis loops confirm the ferroelectric and piezoelectric nature of the ceramics. The polarization current density-electric field curves show the presence of two sharp peaks in opposite directions indicating the presence of two stable states with opposite polarity. Higher values of direct piezoelectric coefficient (d₃₃ ~?360 pC/N) were observed due to the existence of low energy barrier near MPB region and polymorphism. The 55BCT30 ceramics exhibit a higher value of electrostrictive coefficient (Q₃₃ ~?0.1339?m⁴/C²) compared to the well-known lead-based materials. The temperature dependent dielectric measurements indicate the O to T phase transition for 55BCT30 and 45BCT30. These ceramics exhibit a Curie temperature (T_c) of 380?K with a dielectric maximum of ~ 4500.     

Structure,electrical, and thermal expansion properties of PZnTe–PZT ternary system piezoelectric ceramics

xPb(Zn_0.5Te_0.5)O₃–(1?x)Pb(Zr_0.5Ti_0.5)O₃ (PZnTe–PZT) ceramics were prepared by the solid‐state reaction method. The phase structure, microstructure, ferroelectric and dielectric properties and thermal expansion properties were systematically investigated. X‐ray diffraction analysis showed the morphotropic phase boundary (MPB) existed at the composition of x = 0.08, which was the coexistence of the rhombohedral phase and the tetragonal phase. The grain size of ceramics decreased rapidly from 10‐20 μm to 1‐3 μm when the PZnTe was added in. The PZnTe–PZT ceramics at the MPB composition showed the largest high field effective piezoelectric coefficient and the lowest strain hysteresis H. The dielectric permittivity and phase transition temperature exhibited strongly compositional dependence. A good linear relation was shown in T_m temperature vs x content and a DPT behavior was found in xPZnTe–(1?x)PZT (x = 0.02‐0.08). The thermal expansion properties showed a low thermal expansion coefficient in the low temperature while a high thermal expansion coefficient in the high temperature. Besides, the thermal expansion curve also showed the characteristic of DPT in PZnTe–PZT ceramics.     

Electrical properties of La2-xPrxTi2O7 (x = 0–0.3) ceramics

The electrical properties of La₂Ti₂O₇ (LTO) ceramics have been enhanced through the substitution of La³⁺ ions by Pr³⁺ ions. Almost all doped Pr³⁺ ions will get at A - site without causing a change on monoclinic phase of LTO. The average grain size is 17.8 μm for La_1.9Pr_0.1Ti₂O₇ ceramics. The relaxation activation energy which is contributed by defect dipoles that are formed from TiO₆ oxygen octahedrons’ distortions in grains is 1.6 eV for La_1.8Pr_0.2Ti₂O₇ ceramics. This kind of defects will be activated from 520 °C and completely be activated until 650 °C. The piezoelectric coefficient d₃₃ = 3.0 pC/N of La_2-xPr_xTi₂O₇ ceramics maintains stable when the Pr³⁺ doping content x ranging from 0.1 to 0.3.     

Investigations on electric properties and domain structures of Nd-doped 0.70Pb(Mg1/3Nb2/3)O3–0.30PbTiO3 relaxor ferroelectric ceramics with high piezoelectric properties

Although rare earth neodymium (Nd) doping is common in Pb(Mg1/3Nb2/3)O₃–PbTiO₃ (PMN–PT) single crystals, it is rarely reported in PMN–PT ceramics. To explore the effect of Nd doping on PMN–PT ceramics, PMN–30PT:xNd³⁺ (x = 0%, 1%, 2%, and 3%) relaxor ferroelectric ceramics were fabricated using a solid-state method via two-step sintering. An enhanced piezoelectric charge coefficient (d₃₃) of ∼870 pC/N and a high piezoelectric strain coefficient (d₃₃*) of ∼1025 pm/V were achieved for x = 2%. Through Rayleigh analysis of polarization–electric field (P–E) hysteresis loops under small electric fields, it was found that the dielectric property was mainly influenced by the intrinsic contribution (local lattice distortion). Furthermore, by investigating domain configurations, high piezoelectric properties were found to be associated with the domain size reduction and local structural heterogeneity. The results indicate that the PMN–30PT:xNd³⁺ ceramics is a promising material for electronic devices, and that rare earth Nd doping is an efficient strategy for improving the electronic performance of Pb-based relaxor ferroelectrics.     

Investigation of enhanced performance in BF-xPT-0.05BZ ternary ceramics for high temperature applications

(0.95-x)BiFeO₃-xPbTiO₃-0.05BaZrO₃ (BF-xPT-0.05BZ) ternary ceramics were synthesized by the solid-state reaction method, which present a perovskite structure without detectable second phase. BF-0.32PT-0.05BZ ceramics display the dominant rhombohedral structure with a small amount of tetragonal phase, revealing the characteristics of morphotropic phase boundary (MPB). The well-densified ceramics possess the average grain size of 8–15 μm with different PT contents. The ferroelectric-paraelectric phase transition of BF-xPT-0.05BZ ceramics shows the characteristic of the first-order transition, which occurs at around 550 °C. It is noticeable that BF-0.32PT-0.05BZ ceramics exhibit the giant remnant polarization of 60 μC/cm² under the field of 175 kV/cm. Moreover, BF-0.32PT-0.05BZ ceramics show the highest piezoelectric constant d₃₃ of 105 pC/N and Q_m of 501. The depolarization temperatures of BF-xPT-0.05BZ ceramics are much close to their Curie temperature T_C, proving the extensive prospect for high temperature piezoelectric applications.     

Composition and poling-induced modulation on photoluminescence properties for NBT-xBT: Pr3+ ceramics

In this work, the modulation of photoluminescence (PL) properties, which was realized by the composition and poling-induced structural evolution, for the Pr³⁺ doped (1-x)(Na_1/2Bi_1/2)TiO₃-xBaTiO₃ (NBT-xBT: Pr³⁺) piezoelectric ceramics was systematically investigated. Based on the Rietveld refinement structural analysis, there were two distinct composition ranges characterized by different structural features for NBT-xBT: Pr³⁺ ceramics at room temperature: (i) rhombohedral R3c + monoclinic Cc phases for the compositions of x ≤ 0.03, and (ii) tetragonal P4bm + monoclinic Cc phases for 0.04 ≤ x ≤ 0.07. It was interesting to notice that the PL emission intensity is positively correlated with the phase fraction of Cc, which is closely related to the crystal symmetry of NBT-xBT: Pr³⁺ ceramics. The compositions with x ≤ 0.06 underwent an irreversible phase transformation on the application of electric field. The dielectric and Raman measurement revealed a transition from a relaxor state to a normal ferroelectric for the x ≤ 0.06 compositions under an applied poling electric field, with not only the reduction in the in-phase octahedral tilting disorder but also the establishment of long-range ordering. These electric field-induced structural changes were responsible for poling-induced PL quenching behaviors as a result of the increased local structure symmetry around doped Pr³⁺ ions in the poled ceramics.     

Phase formation,electrical properties and morphotropic phase boundary of 0.95Pb(ZrxTi1−x)O3–0.05Pb(Mn1/3Nb2/3)O3 ceramics

Ferroelectric ceramics in specific composition of 0.95Pb(Zr_xTi_1?x)O₃–0.05Pb(Mn_1/3Nb_2/3)O₃ or PZT–PMnN (with x=0.46, 0.48, 0.50, 0.52, and 0.54) have been investigated in order to identify the morphotropic phase boundary (MPB) composition. The effects of Zr/Ti ratio on phase formation, dielectric and ferroelectric properties of the specimens have also been investigated and discussed. X-ray diffraction patterns indicate that the MPB of the tetragonal and rhombohedral phase lies in x=0.52. The crystal structure of PZT–PMnN appeared to change gradually from tetragonal to rhombohedral phase with increasing Zr content. The dielectric and ferroelectric properties measurements also show a maximum value (ε_r, tan δ and P_r) at Zr/Ti=52/48, while the transition temperature decreases with increasing Zr content.     

Enhanced dielectric and piezoelectric properties in Na0.5Bi4.5Ti4O15 ceramics with Pr-doping

The bismuth layer-structured Na_0.5Bi_4.5-xPr_xTi₄O₁₅ (x?=?0, 0.1, 0.2, 0.3, 0.4, and 0.5) (NBT-xPr³⁺) ceramics were fabricated using the traditional solid reaction process. The effect of different Pr³⁺ contents on dielectric, ferroelectric and piezoelectric properties of Na_0.5Bi_4.5Ti₄O₁₅ ceramics were investigated. The grain size of Pr³⁺-doping ceramics was found to be smaller than that of pure one, the maximum dielectric constant and Curie temperature T_c gradually decreased with increasing Pr³⁺ contents, and the dielectric loss decreased at high temperature by Pr³⁺-doping. Moreover, the activation energy (E_a), resistivity (Z’), remanent polarization (2P_r) and piezoelectric constant (d₃₃) increased by Pr³⁺-doping. The NBT-xPr³⁺ ceramics with x?=?0.3 achieved the optimal properties with the maximum dielectric constant of 1109.18, minimum loss of 0.00822 (250?kHz), E_a of 1.122?eV, Z’ of 7.9?kΩ?cm (725 ºC), d₃₃ of 18 pC/N, 2P_r of 12.04 μC/cm². The enhancement was due to the addition of Pr³⁺ which suppressed the decreasing of resistivity at high temperature and made it possible for NBT-xPr³⁺ ceramics to be poled in perpendicular direction, implying that it is a great improvement for Na_0.5Bi_4.5Ti₄O₁₅ ceramics in electrical properties.     

Enhanced energy storage properties and large electrostrictive effect of Bi0.35Na0.35Ba0.09Sr0.21Ti(1-x)(Al0.5Nb0.5)xO3 relaxor ceramics

Ferroelectric ceramics have good piezoelectric and ferroelectric properties and can be used for energy storage equipment and actuators. Nevertheless, current research on dielectric capacitors has only focused on the energy storage density, but ignored efficiency. Moreover, conventional piezoelectric materials have a large strain hysteresis. In this work, (Al_0.5Nb_0.5)⁴⁺ (AN) complex ions doped 0.7Bi_0.5Na_0.5TiO₃-0.3Ba_0.3Sr_0.7TiO₃ (BNBST) ceramics were prepared. Doping AN destroyed the long-range ordered ferroelectric domains and generated polar nano regions, resulting in a gradual thinning and inclination of polarization hysteresis loops and an increase in relaxor degree. For BNBST-3AN ceramics, a W_rec of 1.52 J/cm³ and a η of 92.1% were achieved at 150 kV/cm. Meanwhile, BNBST-3AN ceramics had good energy storage temperature stability and cycling performance. The AN doping reduced the strain hysteresis in BNBST ceramics. BNBST-2AN ceramics exhibited a longitudinal electrostrictive coefficient Q₃₃ ～ 0.0292 m⁴/C² and a field-induced strain of 0.25% with low strain hysteresis (6.67%). Furthermore, BNBST-4AN ceramics had superior dielectric temperature stability from 24 to 270 °C. All results show that BNBST-100xAN ceramics have great promise for energy storage devices and actuators.     

Crystal structure and piezoelectric properties of xPb(Mn1/3Nb2/3)O3–(0.2 − x)Pb(Zn1/3Nb2/3)O3–0.8Pb(Zr0.52Ti0.48)O3 ceramics

Pb(Mn_1/3Nb_2/3)O₃–Pb(Zn_1/3Nb_2/3)O₃–Pb(Zr_0.52Ti_0.48)O₃ (designated as PMnN–PZN–PZT) piezoelectric ceramics were prepared and the effects of PMnN content on the crystal structure and electrical properties were investigated. The results show that the pure perovskite phase forms in these ceramics. The crystal structure changes from tetragonal to rhombohedral and the lattice constant decreases with increase of PMnN content. The morphotropic phase boundary (MPB) of xPMnN–(0.2 ? x)PZN–0.8PZT ceramics occurs where the content of PMnN, x, lies between 0.05 and 0.085 mol. The dielectric constant (?), piezoelectric constant (d₃₃) and Curie temperature (T_c) decrease, while the mechanical quality factor (Q_m) increases with the increase of PMnN content. The ceramic with composition 0.075PMnN–0.125PZN–0.8PZT has the optimal piezoelectric properties, ? is 842, d₃₃ is 215 pC/N, T_c is 320 °C, k_p is 0.57 and Q_m amounts to 1020, which makes it a promising material for high power piezoelectric devices.     

Complex structural contribution of the morphotropic phase boundary in Na0.5Bi0.5TiO3 - CaTiO3 system

The correlation between structure and dielectric properties of lead-free (1-x)Na_0.5Bi_0.5TiO₃ - xCaTiO₃ ((1-x)NBT - xCT) polycrystalline ceramics was investigated systematically by X-ray diffraction, combined with impedance spectroscopy for dielectric characterizations. The system shows high miscibility in the entire composition range. A morphotropic phase boundary (MPB), at 0.09?≤?x?<?0.15 was identified where rhombohedral and orthorhombic symmetries coexist at room temperature. The fraction of orthorhombic phase increases gradually with x in the MPB region. Dielectric measurements reveal that the relative permittivity increase with addition of Ca²⁺. This behavior is unusual with this kind of doping. A thermal hysteresis occurred only in the MPB composition which varies in a non-monotonically manner with x, detected by dielectric properties. This phenomenon is related to the crystalline microstructure by a linear relationship between the fraction of each phase and dielectric properties, and, more precisely, to the strong interaction between rhombohedral and orthorhombic phases.     

Enhanced ferroelectric,magnetic and magnetoelectric properties of multiferroic BiFeO3–BaTiO3–LaFeO3 ceramics

A lead–free multiferroic ceramic 0.7BiFeO₃–0.3BaTiO₃ showed strong ferroelectric and piezoelectric properties, but weak magnetic and magnetoelectric properties. We herein expected that the electrical and magnetic properties of 0.7BiFeO₃–0.3BaTiO₃ ceramics could be enhanced by introducing LaFeO₃. (0.7–x) BiFeO₃–0.3BaTiO₃–xLaFeO₃ (x?=?0–0.2) were synthesized by solid-state reaction. All the ceramics formed a perovskite structure, and a morphotropic phase boundary (MPB) between rhombohedral and orthorhombic phases formed at x?=?0.025. The ceramics with MPB composition had high unipolar strain (S_max = 0.14%), piezoelectricity (d₃₃ = 223 pC/N, d₃₃ * = 350?pm/V), ferroelectricity (P_r = 25.67 mC/cm²) and magnetoelectricity (a_ME = 466.6?mV/cm·Oe), which can be attributed to addition of La ions. The improved phase angle also demonstrated augmentation of ferroelectricity on the microscopic view. The ferromagnetism was evidently improved after LaFeO₃ doping, and the remanent magnetization M_r increased from 0.0207 to 0.0622?emu/g with rising x from 0 to 0.075. In conclusion, with strong magnetoelectric properties, the prepared ceramics may be applicable as promising lead–free multiferroic ceramic materials for novel electronic devices.     

Large-strain 0.7Pb(ZrxTi1−x)O3–0.1Pb(Zn1/3Nb2/3)O3–0.2Pb(Ni1/3Nb2/3)O3 piezoelectric ceramics for high-temperature application

0.7Pb(Zr_xTi_1−x)O₃–0.1Pb(Zn_1/3Nb_2/3)O₃–0.2Pb(Ni_1/3Nb_2/3)O₃ (0.7PZT–0.1PZN–0.2PNN, x = 0.44–0.47) piezoelectric powders and ceramics have been prepared through conventional solid-state reaction method. Outstanding piezoelectric and dielectric properties occurred at the morphotropic phase boundary (MPB), which was characterized by the X-ray diffraction spectrum. The MPB composition (x = 0.46) performed high d₃₃ value (641 pC/N), indicating that the system suited large-strain application. The field-induced strain reached 0.25% under a considerably low electric field (0.8 kV/mm) according to the bipolar strain *S–E loops. The effect of the grain size on the aging phenomenon and temperature stability has also been investigated. Due to higher Curie temperature and smaller grain size, the 0.7PZT–0.1PZN–0.2PNN ceramics maintained a high d₃₃ level after depoling treatment, revealing a superior strain capacity for high-temperature application.     

Structural and electrical properties of ZnO-modified (1−x)Pb(Mg1/3Nb2/3)O3−xPbTiO3 ceramics with wide MPB regions

Ferro-/piezoelectric ceramics with high performances are generally found at the morphotropic phase boundary (MPB), where two or more different ferroelectric phases coexist. However, the MPB region is usually very narrow; for example, that of (1−x)Pb(Mg_1/3Nb_2/3)O₃−xPbTiO₃ (PMN-xPT) locates between x = 0.30−0.34. Herein, we report that ZnO-modified PMN-xPT polycrystalline ceramics have dramatically broadened MPB regions from x = 0.28, with rhombohedral and monoclinic coexisting phases, to x = 0.36, with tetragonal and monoclinic coexisting phases, as confirmed by powder X-ray diffraction and piezoresponse force microcopy measurements. The wide MPB region is attributed to lattice distortion caused by the substitution of Zn for Mg cations. As a result, the ceramics show composition insensitive electrical properties over wide composition ranges; for example, the piezoelectric coefficient (d₃₃) and electromechanical coupling factor (k_p) remain at near constant values of 450 pC/N and 0.5, respectively, in the range from x = 0.28−0.34. This work not only provides a robust and feasible method to broaden the MPB region but also offers some novel insights into promoting fundamental research on high-performance piezoelectric ceramics.     

Ferroelectric‒to‒relaxor crossover in KNN‒based lead‒free piezoceramics

This study investigated the phase transition behavior and electrical properties of (K_0.5Na_0.5)(Nb_1-xZr_x)O₃ (KNN?100xZ) and (K_0.5Na_0.5)NbO₃–yBaZrO₃ (KNN–100yBZ) lead–free piezoelectric ceramics. The phase transitions in crystal structures were compared in KNN ceramics between single Zr⁴⁺ doping and Ba²⁺Zr⁴⁺ co?doping. Piezoelectric properties such as the piezoelectric constant (d₃₃) and electromechanical coupling factor (k_p) are optimized for KNN?6BZ ceramics and were clarified via the polymorphic phase transition from the orthorhombic to pseudocubic phase. The fitted degree of diffuseness (γ) for a phase transition from the modified Curie–Weiss law indicated that KNN ceramics as ferroelectrics are gradually transformed through BaZrO₃ modification. Accordingly, the enhanced strain properties at y = 0.08 consist of coexisting ferroelectric domains and polar nanoregions that are supported by ferroelectric–to–relaxor crossover in KNN?100BZ ceramics.