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.     

Terahertz Time‐Domain Spectroscopy of 0.73Pb(Mg1/3Nb2/3)O3–0.27PbTiO3 Single Crystal

Lead magnesium niobate titanate is an important ferroelectric material. In this study, the terahertz (THz) transmission properties of a 0.73Pb(Mg_1/3Nb_2/3)O₃–0.27PbTiO₃ single crystal were investigated using a time‐domain spectroscopy method. Complex refractive index and dielectric dispersion functions were determined from the amplitude and phase information derived from time‐domain responses. Based on calculations, it was concluded that the room‐temperature dielectric constant of the single crystal equal to ~30 at 1 THz. This result could be a useful reference for development of ferroelectric‐material‐based THz components and devices.     

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‐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.     

BaTiO3–Bi(Mg2/3Nb1/3)O3 Ceramics for High‐Temperature Capacitor Applications

Solid solutions of (1?x)BaTiO₃–xBi(Mg_2/3Nb_1/3)O₃ (0 ≤ x ≤ 0.6) were prepared via a standard mixed‐oxide solid‐state sintering route and investigated for potential use in high‐temperature capacitor applications. Samples with 0.4 ≤ x ≤ 0.6 showed a temperature independent plateau in permittivity (ε_r). Optimum properties were obtained for x = 0.5 which exhibited a broad and stable relative ε_r ~940 ± 15% from ~25°C to 550°C with a loss tangent <0.025 from 74°C to 455°C. The resistivity of samples increased with increasing Bi(Mg_2/3Nb_1/3)O₃ concentration. The activation energies of the bulk were observed to increase from 1.18 to 2.25 eV with an increase in x from 0 to 0.6. These ceramics exhibited excellent temperature stable dielectric properties and are promising candidates for high‐temperature multilayer ceramic capacitors for automotive applications.     

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.     

Fabrication of Transparent Pb(Mg1/3Nb2/3)O3–PbTiO3 Based Ceramics by Conventional Sintering

Transparent 0.9Pb(Mg_1/3Nb_2/3)O₃–0.1PbTiO₃ (PMN‐PT) based ceramics were prepared by a conventional solid‐state synthesis without using a hot‐press method. The ceramics became transparent when they were sintered in an O₂ atmosphere. The optical transmission increased with decreasing diameter of the calcined powder, which was controlled by the size of zirconia ball‐milling media. Substitution of 3 mol% La for Pb in PMN‐PT further increased the optical transmission to 68% at the wavelength of 2000 nm, which was comparable to that of hot‐pressed Pb(Mg_1/3Nb_2/3)O₃‐PbTiO₃ based transparent ceramics.     

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.     

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.     

Anisotropic domain switching in Pb(Mg1/3Nb2/3)O3‐0.30PbTiO3 single crystals with rhombohedral structure

Anisotropic domain switching paths in [001]‐, [011]‐, and [111]‐poled Pb(Mg_1/3Nb_2/3)O₃‐0.30PbTiO₃ single crystals were studied by in situ polarized light microscopic driven by an antiparallel electric field. Orientation‐dependent electric field induced polarization and strain behaviors were investigated systematically. For [001]‐oriented crystals, only one‐step 71° switching occurred during the domain switching process, resulting in the appearance of stripe domain walls whose traces on (001) plane were along 45° or 135° with respect to [100] direction. But for [011]‐oriented samples, a two‐step 71° switching was observed during 109° switching and the projections of formed twin domain walls on the (011) plane are along 35.3° or 144.7° with respect to [01] direction. Moreover, a three‐step 71° switching was found during 180° switching in [111]‐oriented samples. It was demonstrated by the produced domain walls whose projections on the (10) plane are along 35.3°, 90° or 160.6° with respect to [11] direction. The energetically motivated mechanism based on multistep polarization switching process was also proposed to explain the anisotropic domain switching paths. Our results provided a visualized observation on the ferroelectric domain switching process and also laid the solid foundations for controlling polarization order parameter in ferroelectric single crystals.     

Growth of Pb(Mg1/3Nb2/3)O3-35 mol% PbTiO3 Single Crystals from (111) Substrates by Seeded Polycrystal Conversion

Fully dense disks, each consisting of a single crystal (111) plate of the relaxor-based ferroelectric Pb(Mg_1/3Nb_2/3)O₃-35 mol% PbTiO₃ (PMN-35PT) embedded in a 0.48 ± 0.05 µm grain size polycrystalline matrix of the same composition, were formed by hot-pressing at 950°C for 30 min under 20 MPa. Specimens were subsequently annealed to promote migration of the single-crystal boundary through the polycrystal (a process termed seeded polycrystal conversion). An anneal of 10 h at 1150°C using PMN-35PT packing powder resulted in minimal single-crystal boundary migration, and was accompanied by matrix grain coarsening to 1.86 ± 0.20 µm. In contrast, an anneal of 10 h at 1150°C using PbZrO₃ (PZ) sacrificial powder resulted in significant migration of the single-crystal boundary through the polycrystal, accompanied by matrix grain coarsening to 13.3 ± 0.3 µm. The shape of the grown crystal relative to the seed plate was consistent with the <111> direction being the fastest growth direction. Based on the grown crystal dimensions, a lower bound <111> growth velocity of 0.14 mm/h was calculated. The increased boundary mobility in the specimen that was annealed using PZ sacrificial powder is attributed to a boundary-wetting liquid PbO-based second phase that formed during the anneal. This phase is believed to have formed via PbO absorption from the surrounding vapor phase due to a higher equilibrium PbO vapor pressure above PZ than above PMN-35PT. The grown single crystal exhibited a promising <100> strain of 0.5% at an applied electric field of 4 MV/m.     

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 Evolution and Polarization Degradation of [101]‐Oriented 0.74Pb(Mg1/3Nb2/3)O3‐0.26PbTiO3 Single Crystal underCyclic Electric Loadings

The polarization degradation of ferroelectrics, reflected in the hysteresis loop as a decrease of remnant polarization, is a serious concern in applications. In situ observation of the polarization and domain structure evolution are carried out for [101]‐Oriented 0.74Pb(Mg_1/3Nb_2/3)O₃‐0.26PbTiO₃ (PMN‐26PT) single crystal under cyclic electric field. Measurements of the polarization hysteresis loops are conducted under a polarized light microscope (PLM), which is effective in detecting the domain structure of the single crystal. Prior to the polarization measurements, the crystal was poled. Upon cyclic electric field, reversal of monoclinic (M_B) takes place, and the phase transition from M_B to orthorhombic (O) phase occurs under positive field, but not under negative field of an electric cycle at a field magnitude up to 840 V/mm. The polarization loop is asymmetrical with the positive coercive field (+E_c) much less than the negative one (?E_c). As the field cycles, micro‐cracking occurs preferably in [101] direction, and a sudden drop appears in the curves of polarization versus number of cycles. Upon electric cycling at a field magnitude of 840 V/mm, the negative polarization increases slightly with the cycle number, indicating the rotation of a M_B phase toward the applied field direction.     

Comparison of direct electrocaloric characterization methods exemplified by 0.92 Pb(Mg1/3Nb2/3)O3‐0.08 PbTiO3 multilayer ceramics

Electrocaloric device structures have been developed as multilayer ceramics (MLCs) based on fundamental research carried out on PMN‐8PT bulk ceramics. Two different MLC structures were prepared with nine layers each and layer thicknesses of 86 μm and 39 μm. The influence of the device design on its properties has been characterized by microstructural, dielectric, ferroelectric, and direct electrocaloric measurement. For direct characterization two different methods, ie temperature reading (thermistor and thermocouple) and heat flow measurement (differential scanning calorimetry), were used. A comparison of results revealed a highly satisfactory agreement between the different methods. This study confirms that MLCs are promising candidates for implementation into energy‐efficient electrocaloric cooling systems providing large refrigerant volume and high electrocaloric effect. Due to their micron‐sized active layers, they allow for the application of high electric fields under low operation voltages. We measured a maximum electrocaloric temperature change of ΔT=2.67 K under application/withdrawal of an electric field of ΔE=16 kV mm^?1, which corresponds to operation voltages below 1.5 kV.     

Pb(Mg1/3Nb2/3)O3–PbTiO3 Textured Ceramics with High Piezoelectric Response by a Novel Templated Grain Growth Approach

Pb(Mg_1/3Nb_2/3)O₃–PbTiO₃ is used as a model system of perovskite solid solutions with very high piezoelectric response at tailored morphotropic phase boundaries to demonstrate the processing of textured ceramics by ceramic‐only technology. A novel homogeneous templated grain growth approach that uses conventional ceramic procedures and a single‐source nanocrystalline powder for the matrix and also for obtaining the templates is described. Two batches of (100) faceted cube‐shaped microcrystals with average sizes of 27 and 10 μm were successfully used as templates, and aligned by tape casting for the processing of <001>‐textured Pb(Mg_1/3Nb_2/3)O₃–PbTiO₃ piezoelectric ceramics. Materials with effective piezoelectric coefficients up to 1000 pC/N and ferroelectric properties approaching those of single crystals are obtained.     

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.     

New Antiferroelectric Solid Solution of Pb(Mg1/2W1/2)O3–Pb(Zn1/2W1/2)O3 as Dielectric Ceramics

A new solid solution of (1?x)Pb(Mg_1/2W_1/2)O₃–xPb(Zn_1/2W_1/2)O₃ has been prepared in the form of ceramics by solid‐state reaction with composition x up to 30%. It is found that with the substitution of Zn²⁺ for Mg²⁺ on the B site of the of complex perovskite structure the antiferroelectric (AFE) Curie temperature T_C of PMW increases from 40°C (x = 0) to 67°C (x = 30%), indicating an enhancement of antiferroelectric order, whereas, at the same time, the phase transition becomes more diffuse due to a higher degree of chemical inhomogeneity. X‐ray diffraction analysis indicates that the crystal structure adopts an orthorhombic space group (Pmcn) with a decrease in lattice parameter a, but an increase in b and c as the Zn²⁺ concentration increases. The low dielectric constant (~ 10²), low dielectric loss (tanδ ≈ 10^?3), linear‐field‐induced polarization, and significantly high breakdown field (~ 125 kV/cm) at room temperature make this family of dielectric materials a promising candidate for ceramic insulators.     

Structural and Electrical Characteristics of (1−x)Pb(Lu1/2Nb1/2)O3–xPbTiO3 Ceramics with Low PbTiO3

A solid solution of (1?x)Pb(Lu_1/2Nb_1/2)O₃–xPbTiO₃ with composition of 0.01 ≤ x ≤ 0.08 have been prepared successfully. XRD analysis indicates the crystal structure adopts an orthorhombic (O) phase in 0.01 ≤ x ≤ 0.06 interval and becomes the coexistence of O and rhombohedral (R) phase at x = 0.07, then turns into R phase mostly at x = 0.08. In addition, two sets of superlattice reflections due to B‐site ordering and antiparallel cation displacement are distinguished by XRD and the superstructures which arise from antiparallel cation displacement disappear gradually with the increasing x. The grain size increases gradually with the increasing x, and then becomes the bimodal microstructure at x ≥ 0.06 due to the coexistence of O and R phase. The dielectric spectra exhibit Curie temperature decreases from 248°C to 147°C with increasing x from 0.01 to 0.08. As 0.01 ≤ x ≤ 0.04, the samples display typical double hysteresis loops, suggesting antiferroelectric nature, then turn into ferroelectric gradually at x = 0.05. Finally, it exhibit typical ferroelectric hysteresis loops in 0.06 ≤ x ≤ 0.08 interval.     

High‐Temperature Dielectric Relaxations in LiF Single Crystals

By means of dielectric permittivity, electric modulus and impedance, the dielectric properties of LiF single crystals were investigated in the temperature range of 30°C–800°C and frequency range of 50 Hz–10 MHz. Two thermally activated relaxations, R1 and R2, were observed. The relaxation R1 showing activation energy around 0.8 eV was found to be related to the Li‐ion diffusion in the crystal. The relaxation R2 contains three Arrhenius segments, the low‐, mid‐, and high‐T segments, separated by boundary temperatures of 325°C and 425°C. These segments in the order of ascending temperature were found to be associated with F₃, F₃⁺ centers, F₂ centers, and F centers, respectively.     

Dielectric behavior of single crystals near the (1-X) Pb(Mg1/3Nb2/3)O3-(x) PbTiO3 morphotropic phase boundary

Single crystals in the lead magnesium niobate-lead titanate-(1-x) Pb(Mg_1/3 Nb_2/3)O₃-(x) PbTiO₃ solid solution system were grown using a flux growth technique. Crystals over the compositional range of 0.3 ≤ ' ≤ 0.4 being near the rhombohedra1 (pseudo-cubic)-tetragonal morphotropic phase boundary were characterized. The dielectric behavior along the pseudo cubic [111] and [100] directions were measured as a function of temperature and frequency. The effect of poling was also examined.