Influence of Cation Order on the Electric Field-Induced Phase Transition in Pb(Mg1/3Nb2/3)O3-Based Relaxor Ferroelectrics

The effect of cation ordering on an electric field-induced relaxor to normal ferroelectric phase transition in Pb(Mg_1/3Nb_2/3)O₃ (PMN)-based ceramics was investigated. Both A-site La doping and B-site Sc doping were found to enhance the chemical ordering in these relaxor ceramics. However, the enhanced chemical orderings showed different impacts on the dielectric and ferroelectric properties in these perovskite materials. The 5% La doping was observed to shift the dielectric maximum temperature ( T _max) to a significantly lower temperature and suppress the electric field-induced transition to a ferroelectric phase. In contrast, the 5% and 10% Sc doping showed little effect on T _max but strengthened the ferroelectric coupling. The difference is discussed on the basis of cation size and charge imbalance. An electric field-temperature phase diagram is also proposed for the 0.90PMN–0.10Pb(Sc_1/2Nb_1/2)O₃ based on its history dependence of the electric field-induced phase transition.     

Electrostrictive Coefficients of 0.9Pb(Mg1/3Nb2/3)O3-0.1PbTiO3 Relaxor Ferroelectric Ceramics in the Ferroelectricity-Dominated Temperature Range

Polarization and strain induced by unipolar electric fields (P_uni, S_uni) as well as those induced by bipolar electric fields (P_bi, S_bi) were measured in 0.9Pb(Mg_l/3Nb_2/3)O₃-0.1PbTiO₃ relaxor ferroelectric ceramics in the temperature range of −50°-90°C to observe the phase transition in this region and calculate the electrostrictive coefficients from the purely electric-field-induced polarization and strain. By considering both the electrostrictive component (F_uni, S_uni) and the piezoelectric component ( P_r , S_r), it is shown quantitatively how the transition occurs from pure electrostrictive to partially piezoelectric properties across the phase transition range. P_uni represents unmixed electric-field-induced polarization.
while F_bi represents the summation of P_uni and P_r . Similarly, S_uni represents unmixed electric-field-induced strain, while S_bi represents the summation of S_uni and S_r . The effective electrostrictive coefficient (Q_eff) is calculated even in the ferroelectric region far below the phase transition temperature using S_uni and P_uni which are purely electric field induced. Q_eff significantly increases as the temperature decreases below the phase transition temperature, which was attributed to the decreased rattling space of B-site atoms.     

Long-Time Relaxation from Relaxor to Normal Ferroelectric States in Pb0.91 La0.06 (Zr0.65 Ti0.35 O3

Pb_0.91 La_0.06 (Zr_0.65 Ti_0.35)O₃ (PLZT 6/65/35) is a relaxor ferroelectric near and above the temperature of the dielectric maximum (∼180°C). The relaxor state can persist to room temperature upon fast cooling. However, this relaxor state gradually changes to a normal ferroelectric over a long time period at 25°C, characterized by an elimination of relaxor-like dielectric dispersion and a significant rhombo-hedral broadening and subsequent splitting of the (220) X-ray diffraction peak. A transmission electron microscopy (TEM) bright-field image of a long-time relaxed sample revealed normal micrometersized ferroelectric domain contrast with relaxor-like "tweed" structure on the submi-crometer scale. The gradually structural evolution is discussed in terms of development of correlations between relaxor polar clusters.     

Relaxor Behavior and Dielectric Properties of MgTiO3-Doped BaZr0.35Ti0.65O3 Composite Ceramics for Tunable Applications

MgTiO₃-doped BaZr_0.35Ti_0.65O₃ (BZT) composite ceramics have been prepared by the conventional solid-state route. The dielectric nonlinear characteristics and relaxor behavior of these composite ceramics have been investigated. The secondary-phase BaMg₆Ti₆O₁₉ is formed among BZT composite ceramics with the increase of MgTiO₃. BZT composite ceramics show typical diffuse phase transition characteristic and ferroelectric relaxor behavior. The dielectric constant of BZT composite ceramics can be tailored from thousands to hundreds by manipulating the addition of MgTiO₃. The dielectric loss still keeps around 0.001 and the tunability is above 20% at a dc-applied electric field of 25 kV/cm. Suitable dielectric constant, low dielectric loss, and high tunability of this kind of composite ceramics can be useful for potential microwave tunable applications.     

Structure and Dielectric Properties of Materials in the Solid Solution System Pb(Mg1/3Nb2/33)O3:Pb(W1/2Mg1/2)O3

Solid solutions between the relaxor ferroelectric Pb₃MgNb₂O₉ (PMN) and the ordered antiferroelectric Pb₂MgWO₆ (PMW) were studied. X-ray diffraction shows that the superstructure reflections characteristic of the doubling of the perovskite subcell evident in pure PMW begin to appear in compositions containing more than 20 mol% PMW. Dielectric measurements, however, show that the diffuse transition behavior characteristic of PMN persists up to compositions Containing 80 mol% PMW. Results are discussed on the basis of present models for ferroelectric relaxor behavior.     

Structure-Property Phase Diagram of BaZrxTi1−xO3 System

In the course of searching environmental friendly lead-free relaxor ferroelectrics a complete phase diagram of barium zirconate titanate, Ba(Zr _x Ti_{1− x} )O₃ system with compositions 0.00≤ x ≤1.00 has been developed based on their dielectric behavior. It has been shown that BaZr _x Ti_{1− x} O₃ system depending on the composition, successively depicts the properties extending from simple dielectric (pure BaZrO₃) to polar cluster dielectric, relaxor ferroelectric, second order like diffuse phase transition, ferroelectric with pinched phase transitions and then to a proper ferroelectric (pure BaTiO₃). A comprehensive structure–property correlation of BaZr _x Ti_{1− x} O₃ ceramics has been studied to understand the various ferroelectric phenomena in the whole phase diagram.     

Diffuse Ferroelectric Phase Transition and Relaxor Behaviors in Ba-Based Bismuth Layer-Structured Compounds and La-Substituted SrBi4Ti4O15

The dielectric characteristics of BaBi₂Nb₂O₉, BaBi₄Ti₄O₁₅, BaBi₈Ti₇O₂₇, and La-substituted SrBi₄Ti₄O₄ were investigated to discuss their ferroelectric phase transition and relaxor behaviors. BaBi₂Nb₂O₉ showed typical relaxor behaviors, and a shift of T _m with increasing frequency was observed in BaBi₄Ti₄O₁₅ and SrBi_{4− x} La _x Ti₄O₁₅ ( x =0.8, 1.0) but they underwent a real paraelectric–ferroelectric phase transition on zero-field cooling, while BaBi₈Ti₇O₂₇ showed a normal ferroelectric nature. The reduced concentration and weakened coupling of the dipoles related to A-site bismuth are believed to be responsible for the appearance of short-range electric ordering and the relaxor behaviors in these bismuth layer-structured compounds.     

Dielectric Behavior of the Relaxor Pb(Mg1/3Nb2/3)O3—PbTiO3 Solid-Solution System in the Microwave Region

Dielectric behavior of the relaxor ferroelectric Pb(Mg_1/3Nb_2/3)O₃—PbTiO₃ solid-solution system was studied from—50° to 200°C in the 100 to 12 × 10⁹ Hz frequency region, and a broad dielectric relaxation was measured for compositions throughout the system. The relative microwave permittivity of the composition 0.9Pb(Mg_1/3Nb_2/3)O₃·0.1 PbTiO₃ decreased by 1 order of magnitude from the 1-MHz value of 11800, and similar decreases were observed for other compositions in the system. Dielectric loss (tan δ) values ranged from 0.5 to 1.0 at microwave frequency. The temperature of the broad dielectric constant maximum shifts toward higher values with increased frequency.     

Ferroelectric Properties of Pb(Zn1/3Nb2/3)O3–PbTiO3–RNbO3(R=Na, K) Ceramics

We investigate the ferroelectric properties of Pb(Zn_1/3Nb_2/3)O₃–PbTiO₃(PZN–PT)-based ceramics, which are stabilized by adding a small amount of NaNbO₃ (NN) and KNbO₃ (KN). As the content of alkali niobate increased, the ferroelectric properties of Pb(Zn_1/3Nb_2/3)O₃–PbTiO₃–RNbO₃ (PZN–PT–RN; R=Na, K) became softer, which was more pronounced in PZN–PT–KN. The difference in the piezoelectric properties between PZN–PT–KN and PZN–PT–NN was explained by the cation size effect. Because the ionic size of Na is smaller than that of K, the Na ion can retain the ferroelectricity of the solid solution more effectively. The field-induced strain of 85PZN–5PT–10NN under 10 kV/cm was as high as 0.1%. Also, the addition of NN increased the tunability of dielectric constant significantly. At a composition of 85PZN–5PT–20NN, the tunability was 90% and no hysteresis was observed. In contrast to RN, the increase in the content of PT caused the transition from relaxor to normal ferroelectrics, which were accompanied by the structural change from the rhombohedral to tetragonal phase.     

In situ TEM Investigations of the High-Temperature Relaxor Ferroelectric BiScO3–Pb(Mg1/3Nb2/3)O3–PbTiO3 Ternary Solid Solution

Compositions near the morphotropic phase boundary (MPB) of the BiScO₃–Pb(Mg_1/3Nb_2/3)O₃–PbTiO₃ ternary system showed high-temperature relaxor properties (1 kHz) of T _max∼250°C and a permittivity maximum of ∼16 000. Transmission electron microscopy (TEM) was used to investigate the nature of the microstructure under ambient conditions and with in situ heating studies for samples with different composition and electric field-temperature histories. A mottled domain structure was observed with diffraction contrast TEM techniques and associated with frozen in polar micro-domains. These observations are consistent with the low field permittivity temperature measurements made under various frequencies (100 Hz–100 kHz) with a freezing temperature, T _f∼160°C. Field-cooled (FC) samples exhibited a macro-domain structure similar to normal ferroelectric behavior. On heating the FC samples to approximately the T _max and above, the domain contrast was no longer apparent. When subsequently cooled to room temperature conditions, a micro-domain structure was observed, similar to the zero FC samples. The results are discussed with respect to permittivity measurements and phenomenological mechanisms contributing to the dispersion in the permittivity below the Curie maximum.     

Domain Growth in Pb(Mg1/3Ta2/3)O3 Perovskite Relaxor Ferroelectric Oxides

Extensive studies that have been conducted on the Pb(Mg^1/3Nb^2/3)O₃ (PMN) family of relaxor ferroelectrics have led to the establishment and acceptance of the"space-charge" model as a basis for explaining their structures and dielectric properties. In this model, the arrangement of the metal cations on the octahedral sites of the perovskite structure is interpreted in terms of the formation of nega-tively charged ordered nanodomains that are dispersed in a positively charged disordered matrix. The primary experi-mental support for this interpretation has come from the apparent absence of any growth of the domains or change in the degree of ordering as the heat treatment is extended. Here, we report on experiments that have been conducted on the tantalate relaxor, Pb(Mg^1/3Ta^2/3)O₃(PMT), and its solid solutions with PbZrO₃, in which the size of the do-mains and the degree of cation ordering have been in-creased by two orders of magnitude through annealing that has been conducted at a temperature of 1325°C. Moreover, fully ordered ceramics that are comprised of large domains retain relaxor behavior. These results cannot be explained by the space-charge model and support a charge-balanced, "random-site" model for the ordering of the metal cations     

Dielectric-State Analysis in Solid-Solution Pb(Yb1/2Ta1/2)O3–Pb(Lu1/2Nb1/2)O3

The structure and temperature dependence of complex lead perovskite dielectrics were investigated for the system (1 − x )Pb(Yb_1/2Ta_1/2)O₃– x Pb(Lu_1/2Nb_1/2)O₃. Superlattice reflections for the compositions 0.8 < x < 1.0 were observed by X-ray diffractometry, and the temperature-composition dielectric-state diagram was determined. In the present study, the disordered middle composition, with 0.2 < x < 0.8, showed a diffuse paraelectric–ferroelectric phase transition, whereas the ordered end compositions, with 0 ≤ x < 0.2 and 0.8 < x ≤ 1.0, revealed successive sharp paraelectric–antiferroelectric and weak antiferroelectric–ferroelectric phase transitions. The dielectric state was confirmed by examining the variation of polarization ( P ) with electric field ( E ).     

Solid Solutions in Antiferroelectric Region of the System PbHfO3-PbTiO3-PbSnO3-PbNO2O6

Dielectric, ferroelectric, and piezoelectric properties were investigated for compositions in the high-lead hafnate region of the system PbHfO₃-PbTiO₃-PbSnO₃-PbNO₂O₆. Phase diagrams were prepared that show the existence of a ferroelectric-to-antiferroelectric phase transition with increasing temperature. Five phases were shown to exist in the portion of the system investigated two ferroelectric phases, two antiferroelectric phases, and one paraelectric phase. Ferroelectric-antiferroelectric phase transitions induced by temperature, electric field, and pressure were investigated. The highest spontaneous polarization measured was approximately 25 μcoul per cm².     

Dielectric Properties of (Pb1–xXx) (Zr0.7Ti0.3)O3 (X = Ca, Sr, Ba) Ceramics

The dielectric properties of (Pb_{1– x} X_x) (Zr_0.7Ti_0.3)O₃ (X = Ca, Sr, Ba) ceramics (abbreviated PXZT) were investigated for applications to multilayer ceramic capacitors (MLCs) with dielectric layers thinner than 10 μm. The dissipation factors for MLCs with 5-μm-thick dielectric layers were estimated from those for 100-μm-thick disk specimens measured at an oscillation voltage of 20 V_rms. Those for PCZT and PSZT were less than 1.0% when the oscillation voltage was 20 V_rms, while those for conventional BaTiO₃-based dielectric ceramics were greater than 2.5% at 20 V_rms. According to polarization–electric field hysteresis measurements, PCZT and PSZT revealed linear and double hysteresis loops, respectively, while PBZT and BaTiO₃ indicated typical ferroelectric hysteresis loops. The differences in the dissipation factors for the dielectric compositions are attributed to hysteresis in the polarization–electric field loops. These results suggest that PCZT and PSZT are promising dielectric ceramics for MLCs with dielectric layers thinner than 10 μm.     

Preparation and Characterization of Relaxor Ferroelectric 0.65Pb(Mg1/3Nb2/3)O3–0.35PbTiO3 by a Polymerizable Complex Method

A modified polymerizable complex (PC) method for the preparation of the relaxor ferroelectric 0.65Pb(Mg_1/3Nb_2/3)O₃–0.35PbTiO₃ (PMN–PT) ceramics has been developed using a novel water-soluble Nb precursor. The effects of Pb content and sintering temperature on the structure, morphology, composition, and electrical properties of PMN–PT powders and ceramics were investigated systematically. It was found that the modified PC method could effectively reduce the initial crystallization temperature of the perovskite phase to 500°C. For PMN–PT samples with 15% excess Pb content sintered at 600°C for 2 h, the 87% perovskite phase can be achieved, which is much higher than that in conventional solid-state reactions and other solution-based methods at the same temperature. On further increasing the sintering temperature to 1100°C, the perovskite phase content basically remains constant. This is attributed to the Pb-deficient pyrochlore phase formation. On increasing the sintering temperature to 1250°C, the dielectric constant and remnant polarization of PMN–PT ceramics significantly improved due to the larger grain sizes, enhanced density, and the decreasing pyrochlore phase. PMN–PT ceramics with a 98.5% content of the perovskite phase have been fabricated at 1250°C. It displays typical ferroelectric relaxor characteristics with a remnant polarization of 18 μC/cm², a coercive field of 9.6 kV/cm, a piezoelectric coefficient of d ₃₃=360 pC/N, and room-temperature and maximum dielectric constants of 3600 and 10 500 at 1 kHz, respectively.     

New Preparation Method of Low-Temperature-Sinterable Perovskite 0.9Pb(Mg1/3Nb2/3)O3-0.1PbTiO3 Powder and Its Dielectric Properties

A relaxor ferroelectric material, 0.9Pb(Mg_1/3Nb_2/3)O₃-0.1PbTiO₃ (0.9PMN-0.1PT) with a pyrochlore-free phase, was prepared by using one-step calcination in the present study. The 0.9PMN-0.1PT powder with the pure perovskite phase was prepared successfully from a mixture of the PMN precursor and the crystalline PT by heating for 2 h at temperatures greaterthan equal to750°C. The PMN precursor was synthesized by adding an aqueous Mg(NO₃)₂ solution, rather than MgO, to the alcoholic slurry of PbO and Nb₂O₅. The 0.9PMN-0.1PT powder sintered to >96% relative density via heat treatment for 2 h at temperatures of 900°-1200°C. The highest room-temperature dielectric constant (epsilon_rt) was 24700 at 1 kHz for the samples that were sintered at 1100°C; however, the samples that were sintered at 900°C still had epsilon_rt values of 22600 at 1 kHz.     

Phase Transition and Ferroelectric Characteristics of Pb[(Mg1/3Nb2/3)1-xTix]O3 Ceramics Modified with La(Mg2/3Nb1/3)O3

The effects of 0–5 mol% addition of La(Mg_2/3Nb_1/3)O₃ (LMN) on the phase transition and ferroelectric behaviors of Pb[(Mg_1/3Nb_2/3)_1-xTi_x]O₃ (PMNT) ceramics with compositions near the morphotropic phase boundary (MPB) were studied. An evolution of structure from rhombohedral to tetragonal was found with increasing PbTiO₃ (PT) content across the MPB (at ∼32.5 mol% PT), and a coexistence of both rhombohedral and tetragonal phases was also found at the MPB. The dual-phase field extended toward the lower PT content side of the MPB, and, moreover, the rhombohedrality or tetragonality was reduced, especially for the compositions near the MPB, by the addition of La in PMNT. The ferroelectric transition was found to change from normal to diffuse as the La content increased and the compositions became more rhombohedral. In accordance with the structural evolution, the change of remanent polarization ( P _r) and coercive field ( E _c) also became gradually indistinct, and both P _r and E _c were reduced. For compositions near the MPB, both PMNT and La-modified PMNT had a similar electromechanical factor ( k _p) in a range around 0.55–0.60, but the mechanical quality factor ( Q _m) was significantly reduced for the La-modified PMNT. The piezoelectric coefficient ( d ₃₃), however, was largely improved with increasing La content in PMNT of compositions at MPB. A high value of d ₃₃∼ 815 pC/N was obtained for the 5-mol%-La-modified ceramics, but it was associated with a low value of Q _m.     

Single Crystals of Pb(Mg1/3Nb2/3)O3—35 mol% PbTiO3 from Polycrystalline Precursors

A potentially more cost-efficient method of growing single-crystal relaxor-based ferroelectric materials has been investigated. Seed single crystals of Pb(Mg_1/3Nb_2/3)O₃(PMN)—;35 mol% PbTiO₃(PT) were embedded within polycrystalline powders and annealed at temperatures from 900° to 1200°C. The boundary of the single crystal migrated through the polycrystal matrix under the influence of grain boundary curvature; growth distances of several millimeters were observed, verifying the feasibility of the approach. The grown single crystals exhibited macroscopic cubic growth morphologies with (100) faces. Strain levels as high as 0.68% under an electric field of 30 kV/cm were observed in initial measurements.     

Effects of B2O3 Addition on the Dielectric and Ferroelectric Properties of Ba0.7Sr0.3TiO3 Ceramics

The effects of B₂O₃ addition on the sintering behavior and the dielectric and ferroelectric properties of Ba_0.7Sr_0.3TiO₃ (BST) ceramics were investigated. The dielectric and ferroelectric properties of a BST sample with 0.5 wt% B₂O₃ sintered at <1150°C were as good as those of undoped BST sintered at 1350°C, and the dielectric loss was better. When >1.0 wt% B₂O₃ was added to BST, the overdoped B₂O₃ did not form a liquid phase or volatilize; it remained in the samples and formed a secondary phase that lowered the sintering behavior and the dielectric and ferroelectric properties of the BST.