Structural origin of room temperature poling enhanced piezoelectricity in modified Pb(Mg1/3Nb2/3)O3‐30%PbTiO3 crystals

The piezoelectric properties of [110]‐oriented Mn‐doped Pb(Mg_1/3Nb_2/3)O₃‐30%PbTiO₃ single crystals was found to be enhanced by poling at room temperature, relative to traditional poling on field‐cooling (FC). High‐resolution x‐ray diffraction data revealed a phase transition sequence of cubic→tetragonal→ orthorhombic (O)→monoclinic B‐type (M_B) on field‐cooling with a phase coexistence of single domain O and M_B at 300 K in the FC state; whereas poling at room temperature revealed a M_B single phase. Accordingly, the structural origin of the piezoelectricity enhancement on poling at room temperature is attributed to a pure M_B phase. It is probable, in the FC state, that field‐cooling results in defect dipole migration, which then acts to stabilize regions of the O phase on cooling into the M_B one.     

Electrical performance and ferroelectric phase transition characteristic in different oriented 0.73PMN-0.27PT single crystals

The electrical and optical properties of (001)- and (110)-oriented 0.73 Pb(Mg_1/3Nb_2/3)O₃-0.27PbTiO₃ single crystals are systematically investigated at various temperatures, both of which present a series of ferroelectric phase transition processes. Dielectric performance measurements reveal that the ferroelectric phase transition occurs over a temperature range, rather than at one temperature point. By testing the ferroelectric hysteresis P–E curves as well as bipolar and unipolar electric field-induced strain S–E curves, the values of remnant polarization, coercive field, maximum strain, and converse piezoelectric constant d₃₃^* change considerably near the phase transition temperatures. Simultaneously, the 0.73PMN-0.27PT single crystals with (001)- and (110)-orientations under a low electric field show ultrahigh d₃₃^* values of 3540 and 2817 pm/V, respectively, which can be attributed to the electric field-induced monoclinic and orthorhombic phases, respectively. The series of ferroelectric phase transitions upon heating, that is, from rhombohedral ferroelectric to monoclinic/orthorhombic, followed by from monoclinic/orthorhombic to tetragonal, and finally from tetragonal to cubic paraelectric, are further investigated via polarized light microscopy and Raman spectroscopy.     

Origin of ferroelectric P‐E loop in cubic compositions and structure of poled (1‐x)Bi(Mg1/2Zr1/2)O3‐xPbTiO3 piezoceramics

Structural analysis of electrically poled samples of polycrystalline, (1‐x)Bi(Mg_1/2Zr_1/2)O₃‐xPbTiO₃ piezoceramics across morphotropic phase boundary reveals electric field‐induced cubic to tetragonal phase transition and significant domain reorientation in tetragonal and two‐phase compositions. The c‐axis domain elongation is observed for tetragonal compositions after poling. The morphotropic phase boundary composition, having coexisting cubic and tetragonal phases in the unpoled state, exhibits alteration in relative proportion of the two phases, in addition to domain extension and reorientation along c‐axis. For the morphotropic phase boundary composition, the tetragonality (c/a) is enhanced with significantly large c‐axis strain (~0.92%) in tetragonal phase after poling. Origin of ferroelectric P‐E loop in cubic compositions is linked with the electric field‐induced phase transition.     

Multi-scale domain structure observation and piezoelectric responses for [001]-oriented PMN-33PT single crystal

Multiple phase coexistence contributes to the extraordinary piezoelectric behavior of (1-x)Pb(Mg_1/3Nb_2/3)O₃–xPbTiO₃ (PMN–xPT) near the morphotropic phase boundaries (MPBs). By incorporating an optical path of crossed polarized light (PLM) into the commercialized Piezoelectric Force Microscope (PFM) (named as PLM-PFM system), in situ domain structure observation from micro- to nanoscale, as well as measurement of the piezoelectric behavior for individual domains can be realized. For [001]-oriented single crystal of 67Pb(Mg_1/3Nb_2/3)O₃-33PbTiO₃ (PMN-33PT), fine domain boundary structures of rhombohedral (R), tetragonal (T), and monoclinic (M) phases are revealed. Measurements of the electric field-induced displacement as a function of the applied DC electric field (V_DC) are performed for domains with different polarization vectors. Values for the electric field-induced displacement are in descending order for c-domains of the M, R, and T phases. For an individual phase of T or M, the displacement increases when the angle between the polarization vector and the applied electric field decreases. The multi-scale perspective of the domain structures and the corresponding piezoelectric response helps in understanding the ultra-high piezoelectric performance for PMN-PT single crystals near MPB.     

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.     

Fabrication of 0.24Pb(In1/2Nb1/2)O3-0.42Pb(Mg1/3Nb2/3)O3-0.34PbTiO3 transparent ceramics by conventional sintering technique

0.24Pb(In_1/2Nb_1/2)O₃-0.42Pb(Mg_1/3Nb_2/3)O₃-0.34PbTiO₃ transparent ceramics were fabricated by a conventional sintering technique. Through optimization of sintering conditions of calcination and sintering temperatures and time, the obtained ceramics showed high optical transmittance of 53% and 71% at light wavelengths of 1300 and 2000 nm, respectively. The ceramics showed a rhombohedral to tetragonal phase transition at ~120°C and a tetragonal to cubic phase transition at 222°C. These transition temperatures were higher than those of 0.67Pb(Mg_1/3Nb_2/3)-0.33PbTiO₃ ceramics. In addition, the ceramics had a ferroelectric hysteresis loop, a large piezoelectric constant d₃₃ of 407 pC/N, and a planar electromechanical coupling factor k_p of 52%. These results suggest that the transparent ceramics may be used as a temperature-stable, linear electro-optic material.     

Temperature–field phase diagrams in Pb(Zn1/3Nb2/3)O3–4.5%PbTiO3 II

Temperature and field dependences of the dielectric constants under the DC biasing fields along the [011]- and [111]-directions in the cubic coordinate in Pb(Zn_1/3Nb_2/3)O₃–4.5%PbTiO₃ were investigated. The temperature–field phase diagrams were constructed in the field range below 10 kV/cm. It was confirmed that in Pb(Zn_1/3Nb_2/3)O₃–4.5%PbTiO₃ the intermediate tetragonal phase as a ground state of the system exists even without the DC field, and the tetragonal phase disappears in the external field above 4 and 3 kV/cm along the [011]- and [111]-directions, respectively. The field-induced orthorhombic-phase in the field along the [011]-direction was also found.     

Domain Reengineering of the [011]‐Poled PMN–0.35PT Single Crystals for Dielectric Bolometer Arrays

The domain configuration was reengineered with a modified poling procedure for the [011]‐poled single‐domain PMN–0.35PT crystals located at the morphotropic phase boundary. As a consequence, the dielectric constant ε_r at room temperature was significantly enhanced by more than 10 times to about 18 000, extremely higher than the reported (1 ? x)Pb(Mg_1/3Nb_2/3)O₃‐xPbTiO₃ ferroelectric crystals. Besides, the decreasing rate of the dielectric constant (dε_r/dT) was about 300/K with a temperature coefficient (α) of 1.7%/K, comparable to the BST materials for dielectric bolometer applications. The ferroelectric phase transition behavior was investigated to establish the poling procedure and a thermal hysteresis of about 25°C was indicated across the room temperature for the orthorhombic–tetragonal phase transition, which contributed to the revolution of the domain pattern.     

Anisotropic domain structures of Pb(Mg1/3Nb2/3)O3–PbZrO3–PbTiO3 single crystals with high ferroelectric phase transition temperature

The anisotropic domain structures and local piezoresponse of rhombohedral Pb(Mg_1/3Nb_2/3)O₃–PbZrO₃–PbTiO₃ single crystals with high ferroelectric phase transition temperature (T_FE‐FE≥120°C) were systematically investigated by vector piezoresponse force microscopy. The typical size of labyrinthine domain pattern for [001]_C sample was in the range of 100‐200 nm, revealing its relaxor feature. While the [011]_C sample exhibited ordered ribbon‐shaped domain pattern with preferential alignment along <011> direction since the modulation effect of polar nanoregions. For [111]_C sample, it had messy and featureless domain patterns. For as‐grown crystal, the incorporation of Zr⁴⁺ cation in Pb(Mg_1/3Nb_2/3)O₃–PbTiO₃ system resulted in that the long‐range coulomb interactions of the charged ions in the short range order regions were weakened, leading to an increased relaxor feature. Concurrently, the incorporation of Zr⁴⁺ cation enhanced the Pb‐B repulsion intensity, resulting in an improved T_FE‐FE. Temperature‐dependent properties of as‐grown crystal exhibited good temperature stability from 30 to 120°C, indicating it is a promising material for actuator and ultrasonic transducer applications.     

Domain Structure Evolutions During the Poling Process for [011]‐Oriented PMN–xPT Crystals Across the MPB Region

The poling effect on the [011]‐oriented (1?x)Pb(Mg_1/3Nb_2/3)O₃‐xPbTiO₃ (PMN–xPT) single crystals across the morphotropic phase boundary (MPB) was studied. The dielectric and piezoelectric properties were investigated as a function of the poling field. Domain structure evolutions during the poling process were recorded. In the unpoled PMN–xPT phase diagram, an apparent rhombohedral (R)‐tetragonal (T) phase boundary exists. With room‐temperature poling, the structure transformation sequence strongly depends on the composition. The crystal experiences a direct transition to the 2R/2T domain state in the rhombohedral or tetragonal phase field beyond the MPB region, whereas within the MPB zone it is hard to achieve the 2R/2T engineered configuration although the initial state is either rhombohedral or tetragonal as well. The piezoelectric responses of the MPB·PMN–xPTs are extraordinary weak (d₃₃ ~ 250 pC/N), in contrast to the [011]‐oriented multidomain PMN–xPTs with ultrahigh‐piezoelectric coefficient (d₃₃ > 1000 pC/N). We demonstrate that a slight composition variation near the MPB will significantly influence the domain evolution route and piezoelectricity for the [011]‐oriented PMN–xPT crystals. We also confirm the feasibility to realize the 2R/2T engineered domain configuration for the [011]‐oriented MPB crystals, which will extend the desired portion of the Bridgeman‐grown boules with optimal piezoelectric properties.     

Structural Evolution and Properties of 0.3Pb(In1/2Nb1/2)O3–0.38Pb(Mg1/3Nb2/3)O3–0.32PbTiO3 Ferroelectric Ceramics with Different Sintering Times

The structural evolution and properties of 0.3Pb(In_1/2Nb_1/2)O₃–0.38Pb(Mg_1/3Nb_2/3)O₃–0.32PbTiO₃ (0.3PIN‐0.38PMN‐0.32PT) ferroelectric ceramics with different sintering times have been investigated. The content of the tetragonal phase is increased in samples sintered for more than 6 h, despite that the composition falls in the rhombohedral region of the previously established phase diagram. The results show that the metastable tetragonal phase at room temperature is induced and stabilized by the tensile residual stresses. Excessively long sintering time generally leads to grain coarsening, loss of lead, and deterioration of properties, while the increasing amount of the tetragonal phase, and the large residual tensile stress appear to improve the dielectric and electromechanical properties. This study offers new insights into the sintering of Pb‐based ferroelectric ceramics with complex compositions.     

Anisotropic field induced phase transitions and negative electrocaloric effect in rhombohedral Mn doped Pb(In1/2Nb1/2)O3-Pb(Mg1/3Nb2/3)O3-PbTiO3 single crystals

The electrocaloric effect (ECE) of Mn doped Pb(In_1/2Nb_1/2)O₃-Pb(Mg_1/3Nb_2/3)O₃-PbTiO₃ (PIN-PMN-PT:Mn) single crystals with particular emphasis on the impact of crystallographic orientations and phase transitions were investigated systematically. Orientation-dependent phase transitions have been demonstrated by the dielectric and strain behaviors. Intriguingly, the negative ECE of –0.02?°C and –0.002?°C were obtained firstly in [001]-oriented PIN-PMN-PT:Mn crystals near the rhombohedral→tetragonal phase transformation and in [011]-oriented crystals near the rhombohedral→orthorhombic phase transformation, respectively. However, only the positive ECE was found in [111]-oriented crystals near the tetragonal→rhombohedral phase transition. Additionally, the maximum ECE temperature changes calculated in [001]-, [011]- and [111]-oriented crystals were 0.33?°C, 0.46?°C and 0.38?°C, respectively. Our results suggest that the negative ECE is attributed to electric field-induced phase transitions, whose critical field decreases with the increase of temperature. The phase transition-mediated coexistence of positive and negative effects in the relaxor-ferroelectric single crystals is beneficial to enhance the efficiency of the solid-state cooling devices.     

Ferroelectric to Relaxor Transition in BaTiO3–Bi(Zn2/3Nb1/3)O3 Ceramics

The (1?x)BaTiO₃–xBi(Zn_2/3Nb_1/3)O₃ (x = 0.01–0.30) ceramics were synthesized by solid‐state reactions. The solubility limit was determined to be x = 0.20. A systematic structural transition from a tetragonal phase (x ≤ 0.034), to a mixture of tetragonal and rhombohedral phases (0.038 ≤ x ≤ 0.20), and finally to a pseudocubic phase (x ≥ 0.22) at room temperature was identified. Dielectric measurement revealed a ferroelectric (x ≤ 0.04) to relaxor (x ≥ 0.06) transition with permittivity peak broadening and flattening, which was further verified by Raman spectroscopy and differential scanning calorimetry (DSC). Activation energies obtained from the Vogel–Fulcher model displayed an increasing trend from ~0.03 eV for x ~ 0.05, to unusually high values (>0.20 eV) for the compositions with x ≥ 0.15. With the increase in Bi(Zn_2/3Nb_1/3)O₃ content, the polarization hysteresis demonstrated a tendency from high nonlinearity to sublinearity coupled with the reduction in remnant polarization and coervice field. The deconvolution of the irreversible/reversible polarization contribution was enabled by first‐order reversal curve distributions, which indicates that the decreasing polarization nonlinearity with the increase in Bi(Zn_2/3Nb_1/3)O₃ concentration could be related with the change from the ferroelectric domain and domain wall contributions to the weakly coupled relaxor behaviors.     

New Lead‐free (1−x)BaTiO3–xBi(Mg1/2Zr1/2)O3 Solid Solution with Morphotropic Phase Boundary and Diffuse Phase Transition

A new lead‐free perovskite solid solution (1?x)BaTiO₃–xBi(Mg_1/2Zr_1/2)O₃ with morphotropic phase boundary (MPB) has been developed, and its structural and dielectric properties have been investigated. Rietveld structural analysis of the X‐ray diffraction data suggest a composition‐dependent tetragonal (P4mm) to cubic () phase transition with an intermediate, phase coexistence region, demarcating the MPB. The compositions with x ≤ 0.05 are tetragonal in the P4mm space group and the compositions with x ≥ 0.25 are cubic in the space group. Coexistence of monoclinic phase (space group Cm) with tetragonal/cubic phase (space group P4mm/) is observed in the MPB region for the compositions with 0.10 ≤ x ≤ 0.22. The temperature dependence of permittivity exhibits a nonrelaxor type diffuse phase transition for all the compositions across the MPB.     

The Charge Release and Its Mechanism for Pb(In1/2Nb1/2)–Pb(Mg1/3Nb2/3)–PbTiO3 Ferroelectric Crystals Under One‐Dimensional Shock Wave Compression

The charge release and related mechanisms for Pb(In_1/2Nb_1/2)–Pb(Mg_1/3Nb_2/3)–PbTiO₃ (PIN–PMN–PT) ferroelectric crystals under one‐dimensional shock wave compression were investigated using discharge current profile measurement, by which the piezoelectric stress coefficient e₃₁ and the phase transition (from tetragonal to orthorhombic phase) pressure were obtained, being ?2.9 C/m² and 2.3 GPa, respectively. Based on experiment results and thermodynamics analysis, it was found that the one‐dimensional shock compression favored ferroelectric phase, being different from the effect of hydrostatic pressure, which favored paraelectric phase. This phenomenon can be attributed to the crystal anisotropy and electromechanical coupling effects as one‐dimensional shock compression is applied to PIN–PMN–PT ferroelectric crystals.     

High‐Temperature Properties and Ferroelastic Phase Transitions in Rare‐Earth Niobates (LnNbO4)

Phase transition and high‐temperature properties of rare‐earth niobates (LnNbO₄, where Ln = La, Dy and Y) were studied in situ at high temperatures using powder X‐ray diffraction and thermal analysis methods. These materials undergo a reversible, pure ferroelastic phase transition from a monoclinic (S.G. I2/a) phase at low temperatures to a tetragonal (S.G. I4₁/a) phase at high temperatures. While the size of the rare‐earth cation is identified as the key parameter, which determines the transition temperature in these materials, it is the niobium cation which defines the mechanism. Based on detailed crystallographic analysis, it was concluded that only distortion of the NbO₄ tetrahedra is associated with the ferroelastic transition in the rare‐earth niobates, and no change in coordination of Nb⁵⁺ cation. The distorted NbO₄ tetrahedron, it is proposed, is energetically more stable than a regular tetrahedron (in tetragonal symmetry) due to decrease in the average Nb–O bond distance. The distortion is affected by the movement of Nb⁵⁺ cation along the monoclinic b‐axis (tetragonal c‐axis before transition), and is in opposite directions in alternate layers parallel to the (010). The net effect on transition is a shear parallel to the monoclinic [100] and a contraction along the monoclinic b‐axis. In addition, anisotropic thermal expansion properties and specific heat capacity changes accompanying the transition in the studied rare‐earth niobate systems are also discussed.     

Lead‐free (K,Na)NbO3‐based ceramics with high optical transparency and large energy storage ability

Highly transparent lead‐free (1‐x)K_0.5Na_0.5NbO₃–xSr(Zn_1/3Nb_2/3)O₃ (KNN–xSZN) ferroelectric ceramics have been synthesized via a conventional pressureless sintering method. All samples are optically clear, showing high transmittance in the visible and near‐infrared regions (~70% and ~80% at 0.5 mm of thickness, respectively). This exceptionally good transmittance is due to the pseudo‐cubic phase structure as well as the dense and fine‐grained microstructure. In addition, a high energy storage density of 3.0 J/cm³ has been achieved for the 0.94K_0.5Na_0.5NbO₃–0.06Sr(Zn_1/3Nb_2/3)O₃ ceramics with submicron‐sized grains (~136 nm). The main reason is likely to be the typical relaxor‐like behavior characterized by diffuse phase transition, in addition to the dense and fine‐grained microstructure. This study demonstrates that the 0.94K_0.5Na_0.5NbO₃–0.06Sr(Zn_1/3Nb_2/3)O₃ ceramic is a promising candidate of lead‐free transparent ferroelectric ceramics for new areas beyond transparent electronic device applications.     

High‐Performance Ferroelectric Solid Solution Crystals: Pb(In1/2Nb1/2)O3–Pb(Zn1/3Nb2/3)O3–PbTiO3

A series of regular shaped Pb(Zn_1/3Nb_2/3)O₃‐based ternary ferroelectric single crystals (1 ? x)Pb(In_1/2Nb_1/2)O₃–0.33Pb(Zn_1/3Nb_2/3)O₃–xPbTiO₃ (PIN–PZN–PT) have been grown by means of the top‐seeded solution growth method that prevented pyrochlore phase and promoted [001] or [111] growth. The nucleation and crystallization behavior of the Pb(Zn_1/3Nb_2/3)O₃‐based ferroelectric single crystals differed from other relaxor‐based ferroelectric single crystals was discovered. Di‐/piezo‐/ferro‐/pyroelectric properties were characterized systematically. The PIN–PZN–PT single crystals showed large coercive fields E_c, high Curie temperature T_C and high pyroelectric coefficient P, presenting similar performance but better thermal stability compared with the PZN–PT single crystals, and making it a promising material for transducers and IR detectors in a wider temperature range.     

High temperature‐insensitive ferro‐/piezoelectric properties and nanodomain structures of Pb(In1/2Nb1/2)O3–PbZrO3–Pb(Mg1/3Nb2/3)O3–PbTiO3 relaxor single crystals

For rhombohedral (R) Pb(In_1/2Nb_1/2)O₃–PbZrO₃–Pb(Mg_1/3Nb_2/3)O₃–PbTiO₃ (PIN–PZ–PMN–PT) relaxor single crystal, high temperature‐insensitive behaviors under different external stimuli were observed (remnant polarization P_r from 30°C to 180°C and piezoelectric strain d₃₃* from 30°C to 116°C). When electric field E ≥ 50 kV/cm in the case of an activation field E_a = 40‐50 kV/cm was applied, it was found that the domain switching was accompanied by a phase transition. The high relaxor nature of the R phase PIN–PZ–PMN–PT was speculated to account for the large E_a and high piezoelectric response. The short‐range correlation lengths extracted from the out‐of‐plane (OP) and in‐plane (IP) nanodomain images, were 64 nm and 89 nm, respectively, which proved the high relaxor nature due to In³⁺ and Zr⁴⁺ ions entering the B‐site in the ABO₃‐lattice and enhancing the disorder of B‐site cations in the R phase PIN–PZ–PMN–PT. The switching process of R nanodomain variants under the step‐increased tip DC voltage was visually revealed. Moreover, the time‐dependent domain evolution confirmed the high relaxor nature of the R phase PIN–PZ–PMN–PT single crystal.