Ergodic Relaxor Phase Research Articles

Macroscopic polarization in the nominally ergodic relaxor state of lead magnesium niobate

Macroscopic polarity and its dynamic response to external electric fields and temperature in the nominally ergodic relaxor phase of pristine lead magnesium niobate crystals and ceramics, Pb(Mg1/3Nb2/3)O3 (PMN), were investigated. Dynamic pyroelectric measurements provide evidence for persistent macroscopic polarity of the samples. Annealing experiments below and above Burns temperature of polarized samples relate this polarity to the presence of polar nano-entities and their dynamics. The dc electric field strength required for macroscopic polarization reversal is similar to the amplitude of the ac field where dynamic nonlinear dielectric permittivity reaches its maximum. Consequently, the aforementioned maximum is related to the reorientation of polar nano-entities. The results question the existence of an ergodic state in PMN below Burns temperature.

Strain properties of (1-x)Bi0.5Na0.4K0.1TiO3-xBi(Mg2/3Ta1/3)O3 electroceramics

A ternary solid solution of Bi0.5Na0.5TiO3–Bi0.5K0.5TiO3–Bi(Mg2/3Ta1/3)O3 (BNKT-xBMT) lead-free electroceramics was synthesized by a solid-state reactive sintering technique. The electrostrain, dielectric, and ferroelectric properties as well as the impedance characteristics and the microstructure were systematically assessed. With the increase of BMT, the BNKT-xBMT ceramics gradually transformed from non-ergodic relaxor phase to ergodic relaxor phase, manifested as the ferroelectric-to-relaxor temperature (TF-R) shifts towards below room temperature. Additionally, the ferroelectric hysteresis curves became pinched, and the strain curve changed from butterfly-shaped into sprout-shaped. At the ergodic relaxor composition of x = 0.04, a large electrostrain value (S = 0.4%; under an electric field of 60 kV/cm, d33* = 632 pm/V) was achieved, which is mainly attributed to the electric-field-induced transition from the ergodic relaxor phase to the ferroelectric phase.

Effects of rare-earth dopants on phase structure and electrical properties of lead-free bismuth sodium titanate-based ceramics

In this work, the effects of rare earth (RE) dopants on the phase structure, microstructure, and electrical properties of lead-free bismuth sodium titanate (BNT)-based ceramics were studied. Rare earth elements (i.e., Sm, Gd, Ho, Pr, Y, and Yb) were selected as the dopants to replace the Bi site of Bi0.5(Na0.8K0.2)0.5TiO3 ceramics. It was found that the addition of moderate RE ions reduced the temperature of ferroelectric-relaxor transition (Tf-r) and the dielectric maximum at lower temperature, while the slight influence on the dielectric maximum at higher temperature and microstructure were observed. Hereby, the three-stage evolution of phase structure after introducing RE ions was confirmed. A high piezoelectric coefficient d33 of ∼190 pC/N was achieved due to the improved dielectric constant in the state with stable electric field-induced ferroelectric phase. The high strain property and converse piezoelectric coefficient d33∗ of ∼340 pm/V were obtained in the state with the coexistence of nonergodic and ergodic relaxor phases when Tf-r approached room temperature. The degenerated overall electromechanical properties exhibited in the state with complete ergodic relaxor phase. This study affords a significant guidance for optimizing the piezoelectricity of BNT-based ceramics utilizing rare earth dopants.

Multifunctional bismuth sodium titanate-based ferroelectric ceramics with bright red emission and large strain response

In this paper, we systematically studied the structure and properties of SrPrAlO4-modified (Bi0.5Na0.5)0.935Ba0.065TiO3 (BNT-0.065BT) lead-free piezoelectric ceramics. There is no impurity in the SrPrAlO4-modified BNT-0.065BT, and all samples form pure perovskite structure. The substitution of SrPrAlO4 induces the transformation of ferroelectric to ergodic relaxor phase. As a result, a large electric-field induced strain of 0.35% (@70 kV/cm, corresponds to a large signal piezoelectric d33* (Smax/Emax) of 500 pm/V) is obtained when the SrPrAlO4 dopant concentration is 0.012. In addition, the large strain in this material is very resistant to field cycling, rendering the material attractive for its fatigue-free behavior. Moreover, SrPrAlO4-modified ceramics exhibit orange-red emission under 450 nm photoexcitation. There is a strong red emission peak at 610 nm corresponded to the transition of 1D2 →3H4 and a weak red emission peak at 660 nm ascribed to the 3P0 →3F2 transition. The multifunctional characteristics with good electrical and luminescent properties in BNT-0.065BT-xSrPrAlO4 ceramics render the materials may have broad application prospects in new devices with multiple functions.

Large strain with low hysteresis in Sn-modified Bi0.5(Na0.75K0.25)0.5TiO3 lead-free piezoceramics

For the sake of excellent strain performance for actuator application, Sn-modified Bi0.5Na0.5TiO3–Bi0.5K0.5TiO3 (BNT–BKT) ceramics were designed and prepared by solid-state reaction method. The crystal structures and microstructures of Bi0.5(Na0.75K0.25)0.5(Ti1−xSnx)O3 (abbreviated as BNKT–xSn, x = 0, 0.02, 0.05, 0.08) were systematically investigated together with their strain performance. It is found that all the compositions possessed a single perovskite structure phase by X-ray diffraction patterns. With increasing Sn content, the ferroelectric phase with mainly tetragonal structure gradually transformed into the ergodic relaxor phase in pseudocubic structure with nanodomains further confirmed by high-resolution transmission electron microscope images. Both the P–E and I–E loops confirmed this structural change and the coexistence of ferroelectric phase and ergodic relaxor phase at x = 0.02, where a large strain of 0.37% was achieved with low hysteresis (21.8%). By analyzing the bipolar and unipolar strain curves and the origin of strain, we believe that the large strain is contributed to the phase transition from ferroelectric phase into ergodic relaxor phase, and the low hysteresis is beneficial from the existence of ergodic relaxor phase, which should pave a way for future developing high-performance actuators.

Electrocaloric effect in BNT-based lead-free ceramics by local-structure and phase-boundary evolution

This work directly tests electrocaloric effect (ECE) of (0.94-x)Bi0.5Na0.5TiO3–0.06BaTiO3–xSrZrO3 (BNBTSZx) with x = 0 (SZ0), x = 0.01 (SZ0.01), x = 0.02 (SZ0.02) and x = 0.03 (SZ0.03) at different temperature points. The Sr2+ and Zr4+ are introduced into 0.94Bi0.5Na0.5TiO3–0.06BaTiO3 to convert nonergodic relaxor phase into ergodic relaxor phase and form new morphotropic phase boundary (MPBⅡ) at room temperature. A temperature change of 0.37 K and electrocaloric strength of 6.17 × 10−3 K cm/kV are obtained at room temperature. According to the temperature dependence of ΔT and the electric-field dependence of electrocaloric strength, this work focus on the mechanism about higher electrocaloric effect at over-MPBⅡ temperature point. Electrical performances, microstructure and piezoelectric properties are investigated in detail to analyze the local-area phase transformation causing the high electrocaloric effect. The electrocaloric strength of ergodic relaxor phase shows stronger dependence on the electric field than that of nonergodic relaxor phase.

Tuning the electrocaloric effect in 0.94Bi0.5Na0.5TiO3-0.06BaTiO3 ceramics by relaxor phase blending

The pseudo-first-order phase transition in 0.94Bi0.5Na0.5TiO3-0.06BaTiO3 ceramics leads to a sharp increase in temperature change (ΔT) in the vicinity of the ferroelectric-to-relaxor transition temperature TFR (~100 °C) [Appl. Phys. Lett. 110 (2017) 182904]. In this study, we add the 0.78Bi0.5Na0.5TiO3-0.06BaTiO3-0.16(Sr0.7Bi0.2)TiO3 relaxor phase to the 0.94Bi0.5Na0.5TiO3-0.06BaTiO3 ferroelectric matrix to tune its electrocaloric effect. The results show that the addition of the relaxor phase plays a vital role in phase and local-structure evolution. A transition occurs between the ferroelectric and ergodic relaxor phases when the mass fraction of the latter increases to 30% (x = 0.3), as verified by X-ray diffraction analysis, Raman spectroscopy, and polarization-electric field (P-E) hysteresis loops. Furthermore, addition of the relaxor phase reduces the TFR from 76 °C at x = 0.1–55 °C at x = 0.2; however, this transition disappears at x = 0.3 and 0.4 composite. In-situ piezo-force microscopy (PFM) images illustrate that domains can be written into x = 0.1 and 0.2 ceramics with a valley in the piezoresponse curves. Increasing the temperature agitates the domain arrangement and decreases the contrast for PFM images; this indicates a gradual phase transition in the composite. The temperature corresponding to maximum ΔT exhibits a downward shift (0.58 K at 80 °C for x = 0.1 and 0.5 K at 65 °C for x = 0.2), while the temperature-ΔT curves are flat when x = 0.3 and 0.4. Moreover, the maximum ΔT shows a decrease with an increase in the relaxor phase content; this is believed to be related to a decrease in the latent heat due to a pseudo-first-order to second-order transition. Thus, we suggest that the incorporation of a relaxor phase into ferroelectric matrices is an effective technique to tune their electrocaloric effect and improve the thermal stability of ceramic composites.

Evaluation of high strain response in lead-free BNBTFS-xNb ceramics by structure and ferroelectric characterizations

Lead-free piezoelectric ceramics of the form (Bi0.5Na0.5)0.945Ba0.055 [Ti0.98(Fe0.5Sb0.5)0.02](1-x)NbxO3 (BNBTFS-xNb with x = 0.00–0.03) in the vicinity of the morphotropic phase boundary were synthesized by a conventional mixed oxide route. The crystal structure, microstructure, and electromechanical properties were investigated as a function of different Nb5+ concentrations. Increasing amount of Nb5+ disrupts the long-range ferroelectric order and induces a relaxor phase with pseudocubic symmetry, which results in a large strain (Smax = 0.39%, equivalent to 666 p.m./V) for a critical composition (x = 0.01). Furthermore, ex situ X-ray diffraction of the poled and unpoled ceramics (x = 0.00 and 0.01) was performed, focusing on the origin of the high strain response. The results suggest that such high strain response originates from the compositionally induced phase transition and electric field–induced reversible phase transition from the ergodic relaxor phase to a temporary long-range metastable (non-ergodic) ferroelectric phase.

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(In1/2Nb1/2)O3-0.42Pb(Mg1/3Nb2/3)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.

BaTiO3 nanowires-induced phase transition and thermally stable strain in (Bi0.5Na0.5)TiO3 piezoelectric ceramics

Environment-friendly lead-free piezoceramics with high strain response and extremely excellent stability in a wide operating temperature range are critically important in practical actuator applications. Here, we develop a new strategy to tune the electrostrictive strain behavior in Bi 0.5 Na 0.5 TiO 3 (BNT)-based ceramics via using high aspect ratio BaTiO 3 nanowires (BT NWs) as a modifier. The addition of BT NWs generates a crossover from a typical ferroelectric (BT conventional spherical particles) to a complete ergodic relaxor (ER) phase at ambient temperature, accompanied by a large electrostrictive strain of ∼0.17% with d 33 *( S max / E max ) = 284 pm/V. Such a high electrostrictive strain is extremely thermally stable with only <7% fluctuation from 27 °C to 120 °C. In addition, the BT NWs-modified ceramics also exhibit acceptable fatigue endurance (<30% up to 10 5 cycles) and frequency dependence (<20% at 10Hz–100Hz). These achieved exceptional performances can be ascribed to the BT NWs-driven complete ER phase at room temperature. The findings of this study can inspire enhanced interest in nanowires as a viable modifier to BNT-based materials due to promising potential for practical actuator applications in a wide temperature range.

Enhancement of the electrical-field-induced strain in sodium bismuth titanate-based lead-free ceramics by co-doping with Mn and Nb

Lead-free (Bi0.5Na0.5)0.935Ba0.065Ti1−x(Mn0.5Nb0.5)xO3 piezoelectric ceramics with excellent strain properties were prepared by conventional solid state reaction route. The effects of Mn/Nb on the structure and electrical properties of the ceramics have been investigated. The replacement of Ti by Mn/Nb induced a ferroelectric–ergodic relaxor phase transition with the degradations of the long-term ferroelectric properties. Near the ferroelectric–ergodic phase boundary, the electric-field-induced strain was significantly enhanced and reached the highest strain value of 0.37% (80 kV/cm, corresponds to a Smax/Emax = 463 pm/V) at 0.005 Mn/Nb addition. Temperature dependent measurements of polarization, permittivity, large signal piezoelectric constant and strain indicate that a reversible field-induced phase transformation from ergodic relaxor phase to ferroelectric is the main reason for the large strain response. Moreover, due to the reversible field-induced phase transition, the material with high-strain showed good fatigue resistance (up to 105 cycles), which can be considered as one of promising candidate used in actuator applications.

Structure-property relationships in the lead-free piezoceramic system K0.5Bi0.5TiO3 - BiMg0.5Ti0.5O3

Distinctive structure-property relationships are revealed in the relaxor ferroelectric ceramic solid solution, (1-x)K0.5Bi0.5TiO3 - xBiMg0.5Ti0.5O3: 0.02 < x < 0.08. The constructed phase diagram and results of in-situ synchrotron X-ray diffraction provide explanations for temperature and electric field dependent anomalies in dielectric, ferroelectric and electromechanical properties. At room temperature a mixed phase tetragonal and pseudocubic phase field occurs for compositions 0 > x ≤ 0.07. As temperature rises to ≥150 °C, the ferroelectric tetragonal relaxor phase changes to a pseudocubic ergodic relaxor phase; this change in length scale of polar order is responsible for an inflection in relative permittivity - temperature plots. The transition is reversed by a sufficient electric field, thereby explaining the constricted form of polarisation-electric field loops measured at >150 °C. It is also responsible for a change in slope of the strain-electric field (S-E) plots which are relatively linear in the ferroelectric regime i.e. at temperatures up to 150 °C, giving unipolar strains of 0.11% at 20 °C and 0.14% at 150 °C (50 kV/cm field). The additional contribution from the effect of the field-induced pseudocubic to tetragonal transition, generates strains of ∼0.2% at 185 °C. Unusual for a piezoelectric solid solution, the maximum strains and charge coefficients (d33 = 150 pC/N, 20 °C) do not coincide with a morphotropic or polymorphic phase boundary.

Phase formation and electrocaloric effect in nonstoichiometric 0.94Bi0.5+xNa0.5TiO3-0.06BaTiO3 ceramics

Excess Bi2O3 was added to 0.94Bi0.5Na0.5TiO3-0.06BaTiO3 ceramic and the evolution of dielectric, electromechanical properties and electrocaloric effect (ECE) were studied. With increasing Bi2O3 addition, the nonergodic relaxor phase transformed to ergodic relaxor phase. The XRD patterns and Raman spectroscopy show the increasing relaxor properties with excess Bi2O3 doping. The Bi0.53Na0.5TiO3-BaTiO3 ceramic exhibited a temperature insensitive ECE with an “Λ” type, the variation of which was less than 26% over 30 ~ 120 °C. The temperature stability of ECE for Bi0.53Na0.5TiO3-BaTiO3 ceramic was related with the characteristics of ergodic relaxor phase, which was clarified by structural and Raman spectroscopy analysis.

Investigations on electrical and energy storage behaviour of PZN-PT, PMN-PT, PZN–PMN-PT piezoelectric solid solutions

Electrical response and energy storage behaviour of PZN-PT, PMN-PT, PZN–PMN-PT (PZN-PbZnl/3Nb2/3O3, PMN-PbMg1/3Nb2/3O3 and PT-PbTiO3) solid solutions were investigated. SEM micrographs of the sample showed grains of unequal sizes distributed throughout the sample. The average grain size observed was about 0.77 μm for PZN-PT, 0.93 for PMN-PT and 1.82 for PZN–PMN-PT solid solutions. All the solid solutions exhibited good dielectric relaxation behaviour up to 500 °C in the frequency range of 1–2 MHz. The solid solutions showed improved ferroelectric properties (Pr ~ 17.4 μC cm−2, Ec ~ 3.65 kV cm−1, Pm ~ 20.1 μC cm−2 for PZN-PT) and crossover from nonergodic to ergodic relaxor phase with respect to temperature. The optimum piezoelectric coefficients, the piezoelectric voltage coefficients of the solid solutions were also studied. P–E loop analysis confirmed high energy storage density (W) of 0.25 J cm−3 at 50 kV cm−1 for PZN–PMN-PT which substantiates its wide use in capacitor applications.

Large electromechanical strain and electrostrictive effect in (1 − x)(Bi0.5Na0.5TiO3–SrTiO3)–xLiNbO3 ternary lead-free piezoelectric ceramics

Lead-free (1 − x)(0.8Bi0.5Na0.5TiO3–0.2SrTiO3)–xLiNbO3 (BNST–xLN, x = 0–0.08) piezoelectric ceramics were fabricated by a solid-state sintered technology. The effects of LN-doping on the structural and electrical properties of the BNST–xLN system were systematically investigated. The results of Raman spectroscopy revealed that the substitution of LN softens the phonon vibrations in the BNST–xLN system, in accordance with the remarkable reduction in the phase transition temperature (TF−R), remnant polarization (Pr), negative strain (Sneg) and piezoelectric coefficient (d33). However, the degradation of the long-range ferroelectric orders was accompanied by a significant increase in the electric field–induced strain response. At x = 0.04, a maximum unipolar strain of ~ 0.36% with a corresponding normalized strain (Smax/Emax) of ~ 600 pm/V was obtained at room temperature, which should be mainly ascribed to the reversibly electric field-induced phase transition between the ergodic relaxor and ferroelectric phases due to their comparable free energies in the two-phase coexistence region. Moreover, it was also found that the BNST–xLN system processes predominant electrostrictive behaviors with relatively high electrostrictive coefficient (Q33) and excellent temperature stability when the field-induced phase transition cannot be trigged by the applied electric field, as evidenced by a fact that the Q33 value of BNST–0.08LN ceramic keeps almost constant as high as ~ 0.028 m4/C2 in the temperature range from room temperature to 120 °C.

Field-induced large strain and strong green photoluminescence in (Ho,Sb)-modified (Bi0.5Na0.5)0.945Ba0.065TiO3 multifunctional ferroelectric ceramics

(Ho,Sb)-modified (Bi0.5Na0.5)0.945Ba0.065TiO3 (BNBT6.5) multifunctional ferroelectric ceramics were fabricated by a conventional solid-state reaction method. Results showed that (Ho, Sb)-modified BNBT6.5 materials exhibited a bright green photoluminescence while simultaneously obtaining a large electric-field-induced strain of 0.37% (80 kV/cm) in samples with x = 0.50% due to the appearance of an ergodic relaxor phase at zero field. Under the electric field, the ergodic relaxor phase could reversibly transform to ferroelectric phase. As a result, the strain is very resistant to field cycling due to the reversible field-induced phase transition between the ergodic relaxor and ferroelectric phase, giving the materials attractive for its good fatigue resistance. Besides the excellent strain properties, (Ho, Sb)-modified BNBT6.5 host exhibits a bright photoluminescence with a strong green emission located at around 549 nm owing to the 5S2→5I8 transition under the 451 nm light excitation at room temperature. As a multifunctional material, (Ho,Sb)-modified BNBT6.5 ferroelectric materials showed great potential in optical-electro integration and coupling device applications.

Novel barium titanate based ferroelectric relaxor ceramics with superior charge-discharge performance

Lead-free 0.9BaTiO3-0.1(Bi0.9Na0.1)(In0.8Zr0.2)O3 (0.9BT-0.1BNIZ) ferroelectric relaxor ceramic was synthesized by solid-state reaction method. A dense microstructure and fine grain size was obtained with addition of BNIZ content. The dielectric behaviors indicated the dominance of ergodic relaxor phase. The 0.9BT-0.1BNIZ ceramic was found to possess an enhanced recoverable energy density (WR∼1.33 J/cm3) and efficiency (η∼88%) under 18 kV/mm at room temperature. What’s more, WR is maintained ≥0.53 J/cm3 with η ≥ 94% under 10 kV/mm and the variation of WR is less than 15% over 25∼140 °C. The high stability of energy storage properties is mainly ascribed to the characteristics of ergodic relaxor phase. The stored energy was released in sub-microseconds (∼0.19 μs). The superior current density (CD∼796 A/cm2) and the power density (PD∼39.8 MW/cm3) were obtained simultaneously. The enhanced WR and the superior charge-discharge performances strongly demonstrate that the BT-based ceramics are promising candidates of high-power pulse capacitor applications.

High energy-storage properties of Bi0.5Na0.5TiO3-BaTiO3-SrTi0.875Nb0.1O3 lead-free relaxor ferroelectrics

New lead-free ferroelectric (0.94-x)Bi0.5Na0.5TiO3-0.06BaTiO3-xSrTi0.875Nb0.1O3 (BNBT-STN, x=0 and 0.2) are synthesized by using a solid state reaction process. In this work, an obvious evolution of dielectric relaxation behavior and slim P–E hysteresis loops with high Pmax and low Pr is observed for BNBT-0.2STN, indicating the dominant of ergodic relaxor phase with dynamic polar nano-regions (PNRs). A relatively large recoverable energy density (Wrec=1.17J/cm3) with high energy efficiency (η=91%) is obtained. Furthermore, it shows small variation (9%) in the temperature range of 30–150°C and fatigue-free behavior, which can be attributed to the absence of ferroelectric domain in the relaxor phase. The achievement of these characteristics provides that tailoring by B-site vacancies is a potential route when designing a new energy-storage system for BNT-based relaxor ferroelectric materials.

Ultrahigh energy density and improved discharged efficiency in bismuth sodium titanate based relaxor ferroelectrics with A-site vacancy

Novel A-site deficient (1-x-y)Bi0.5Na0.5TiO3-xBaTiO3-yBi0.2Sr0.7TiO3 lead-free relaxor ferroelectrics have been explored for energy storage property. Particularly slim polarization hysteresis (P-E) loops are observed in 0.655Bi0.5Na0.5TiO3-0.065BaTiO3-0.28Bi0.2Sr0.7□0.1TiO3 (6.5BNBT-BST) at ambient temperature resulting in a giant recoverable energy density (Wrec = 1.5 J cm−3) and extremely high efficiency (η = 90%) at 100 kV cm−1, which are closed related to the track of P-E loops. As the addition of Bi0.2Sr0.7TiO3 (BST) content, the ergodic relaxor phase becomes dominant with dynamic polar nano-regions attributed to the absence of ferroelectric domain in the relaxor phase. Furthermore, the recoverable energy density exhibits small variation in elevated temperature where the depressed polarization is compensated by almost hysteresis free loops (η up to 97%). The achievement of these characteristics in P-E loops provides that Bi0.2Sr0.7TiO3 tailoring by A-site vacancies is a potential route when designing new relaxor ferroelectrics for energy-storage applications.

Electric field–temperature phase diagram of sodium bismuth titanate-based relaxor ferroelectrics

The electric field–temperature phase diagrams of three bismuth sodium titanate-based relaxor ferroelectrics are reported, namely 0.94(Na1/2Bi1/2TiO3)–0.06(BaTiO3), 0.80(Na1/2Bi1/2TiO3)–0.20(K1/2Bi1/2TiO3) and 0.75(Na1/2Bi1/2TiO3)–0.25(SrTiO3). Relaxor behavior is demonstrated by temperature-dependent dielectric permittivity measurements in the unpoled and poled states, as well as by the field-induced phase transition into a ferroelectric phase from the relaxor phase. From temperature-dependent thermometry measurements, we identified the threshold electric field to induce the ferroelectric phase and obtained the released latent heat of the phase transition. We determined the nonergodic and ergodic relaxor phase temperature range based on the absence or presence of reversibility of the relaxor to ferroelectric transition. For all three compositions, the electric field–temperature phase diagram was constructed and a critical point was identified. The constructed electric field–temperature phase diagrams are useful to find optimum operational ranges of ferroelectrics and relaxors for electromechanical and electrocaloric applications.