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.     

Oxygen‐Vacancy‐Related High Temperature Dielectric Relaxation in (Pb1−xBax)ZrO3 Ceramics

(Pb_1?xBa_x)ZrO₃ (x = 0, 0.025, 0.05, 0.075, 0.1) ceramics were synthesized by a traditional solid‐state reaction method, and the pure phase was obtained of all sintered samples. For all compositions, substitution of Pb²⁺ by Ba²⁺ reduced the phase transition temperature of antiferroelectric to ferroelectric and Curie temperature. Polarization–electric field hysteresis loops were conducted and typical ferroelectric hysteresis loops were observed in higher temperature range. Impedance and dielectric measurements were studied on the high temperature relaxation. Relaxation behavior could be suppressed after annealing treatment in oxygen atmosphere. Value of activation energy calculated from impedance was lower than that calculated from conduction measurements. It was concluded that short‐range hopping of oxygen vacancy contributes to the dielectric relaxation and long‐distance movement of doubly ionized oxygen vacancies contributes to the conduction.     

Dynamic Response in Ba1−xSrxTiO3 and Anomalous Behavior at the Phase Boundary Composition

The dynamic response of Barium Strontium Titanate (Ba_1?xSr_xTiO₃, x = 0.6–0.9) is presented over a temperature range spanning various structural phase transitions and for compositions that extend from the ferroelectric (FE) phase to the FE‐Antiferrodistortive (AFD) phase boundary. We find that while the in‐phase part of the dielectric response is insensitive to applied frequencies over the range 400–500 kHz for all compositions, strong dispersive effects are observed in general for the out of phase part, for almost all compositions. The dielectric peaks corresponding to the lower temperature structural transitions (e.g. tetragonal to orthorhombic T–O etc.) exhibit frequency dependence, while the higher temperature cubic to tetragonal (C–T) transition does not show dispersive effects. The only exception to this is for the Ba_0.1Sr_0.9TiO₃ composition, lying at the boundary of the FE and AFD phases. Detailed frequency dependence studies of this composition (x = 0.9) show that the (C–T) transition exhibits an abrupt change in the dispersive features for high frequencies f > 10 kHz. These features include the constancy of peak temperature, large drop in the magnitude of the losses and a noticeable broadening of the associated loss peak. The anomalous features in the behavior of x = 0.9 composition are attributed to slow relaxation processes in the AFD phase at the boundary separating the FE and AFD phases.     

The influence of phase transition on electrocaloric effect in lead‐free (Ba0.9Ca0.1)(Ti1−xZrx)O3 ceramics

In this paper, the influence of phase evolution on polarization change and electrocaloric response in lead‐free (Ba_0.9Ca_0.1)(Ti_1?xZr_x)O₃ ceramics (BCTZ) was systematically investigated. With increasing Zr/Ti ratio, the phase structure and phase transition behavior were greatly changed, resulting in various temperature and electric field dependence of electrocaloric responses. For x=0.05, a peak electrocaloric temperature change 1.64 K (at 130°C) and corresponding entropy change 1.78 J·kg^?1·K^?1 were obtained for 0‐7 kV·mm^?1 electric field. Negative electrocaloric temperature change in ?0.1 K was obtained below Curie temperature (T_c), which may be induced by the orthorhombic‐tetragonal ferroelectric phase transition. With the increase in x, the peak value of the electrocaloric response decreased but much better temperature stability was observed. Simultaneously the negative electrocaloric response gradually disappeared with the disappearance of the low temperature ferroelectric‐ferroelectric phase transition. For x=0.2, electrocaloric response showed good temperature stability ranging from room temperature to 130°C, attributing to the relaxor ferroelectric feature.     

Dielectric and ferroelectric properties of lanthanum‐modified lead zirconate stannate titanate (42/40/18) ceramics

The effect of lanthanum (La) content on the phase transformation of Pb_1?3x/2La_x(Zr_0.42Sn_0.40Ti_0.18)O₃ (PLZST 100x/42/40/18, 0 ≤ x ≤ 0.06) ceramics was investigated by the dielectric and ferroelectric properties. The base composition PLZST 0/42/40/18 located in the ferroelectric (FE) rhombohedral phase region. As x increased, the compositions showed successively FE and antiferroelectric (AFE) state at room temperature, and their peak temperatures (T_max) decreased gradually in line as T_max = 162.21‐1507x. Evidence was presented that there were two dielectric anomalies in PLZST 2/42/40/18, which were corresponding to the FE‐AFE and AFE‐paraelectric (PE) phase transformations, respectively. With increasing the dc bias fields, the two phases merged into one. PLZST 3/42/40/18 showed AFE characteristics with the first loop outside of the second loop and there was only one dielectric inflection. The critical lanthanum content occurred at x = 0.03 from the dielectric temperature spectra and hysteresis loops. Furthermore increase in La above 0.03, these compositions showed typical antiferroelectric behaviors with double hysteresis loops. The stored energy properties of the three compositions (PLZST 4/42/40/18, 5/42/40/18 and 6/42/40/18) displayed different temperature dependencies from room temperature to 140°C (over their respective T_max). Comparing the above results with previous investigations on PLZSTs, some questions were discussed.     

Large Strain Response in 0.99(Bi0.5Na0.4K0.1)TiO3–0.01(KxNa1−x)NbO3 Lead‐Free Ceramics Induced by the Change of K/Na Ratio in (KxNa1−x)NbO3

Influence of K/Na ratio in (K_xNa_1?x)NbO₃ on the ferroelectric stability and consequent changes in the electrical properties of 0.99(Bi_0.5Na_0.4K_0.1)TiO₃–0.01(K_xNa_1?x)NbO₃ (BNKT–K_xNN) ceramics were investigated. Results showed that change of K/Na ratio in KNN induces a phase transition from ferroelectric to ergodic relaxor phase with a significant disruption of the long‐range ferroelectric order, and correspondingly adjusts the ferroelectric–relaxor transition point T_F?R to room temperature. Accordingly, giant strain of ~0.46% (corresponding to a large signal d₃₃* of ~575 pm/V) which is comparable to that of Pb‐based antiferroelectrics is obtained at a K/Na ratio of ~1, and the emergence of large strain response induced by the change of K/Na ratio of KNN can be well explained by the correlation between the position of ferroelectric–ergodic relaxor phase boundary in the BNKT–K_xNN system and the tolerance factor t of the end number (K_xNN). In situ high‐energy X‐ray scattering experiments with external field reveals that the large strain response in the studied system is likely related to the electric field‐induced distortion from the pseudocubic structure.     

The Composition and Temperature‐Dependent Structure Evolution and Large Strain Response in (1−x)(Bi0.5Na0.5)TiO3−xBa(Al0.5Ta0.5)O3 Ceramics

The (1?x) (Bi_0.5Na_0.5)TiO₃?xBa(Al_0.5Ta_0.5)O₃((1?x)BNT‐xBAT) lead‐free piezoceramics was fabricated using a conventional solid‐state reaction method. The temperature and composition‐dependent strain behavior, dielectric, ferroelectric (FE), piezoelectric, and pyroelectric properties have been systematically investigated to develop lead‐free piezoelectric materials with large strain response for actuator application. As the BAT content increased, the FE order is disrupted resulting in a degradation of the remanent polarization, coercive field, and the depolarization temperature (T_d). A large strain of 0.36% with normalized strain d₃₃* = 448pm/V was obtained for the optimum composition x = 0.045 at room temperature. The bipolar and unipolar strains for the compositions x = 0.035 and x = 0.04 reach almost identical maximum values when the temperature is in the vicinity of their respective depolarization temperature (T_d). The Raman‐spectra analysis, macroscopic properties, thermal depolarization results, and temperature‐dependent relationships of both polarization and strain demonstrated that the origin of the large strain response for this investigated system is attributed to a field‐induced relaxor to FE phase transformation.     

Ferroelectric‐quasiferroelectric‐ergodic relaxor transition and multifunctional electrical properties in Bi0.5Na0.5TiO3‐based ceramics

A‐site substituted 0.88(Bi_0.5Na_0.5)_1?x(Li_0.5Nd_0.5)_xTiO₃–0.12BaTiO₃ (BNTLNx–BT12) ceramics were synthesized using a conventional solid‐state reaction route. The structural transformation and miscellaneous electrical properties were systematically investigated. The A‐site modification induced two sequence transitions from ferroelectric tetragonal (T) to quasi‐ferroelectric pseudocubic (PC) phase, followed closely by the second transition from non‐ergodic to ergodic relaxor (NR‐ER), and finally to dynamic polar nanoregions (PNRs). The significant enhancement in piezoelectric activity, strain response, broad plateau‐like maximum dielectric permittivity over a large temperature range and energy‐storage level at different compositions may be attributed to the compositionally‐induced T‐PC to NR‐ER transition and the alignment of dynamically‐fluctuating PNRs, respectively. The evolution of multifunctional electrical properties, associated with the variations in structure/microstructure, might provide a new insight to investigate the underlying mechanism of structure‐electrical properties relationship in ferroelectric solid solutions.     

Orientation‐Dependence of Thermal Depolarization and Phase Development in Bi1/2Na1/2TiO3‐BaTiO3 Single Crystals

The direction‐dependence of pyroelectric properties of (1 ? x)Bi_1/2Na_1/2TiO₃ ? xBaTiO₃ (BNT ? 100xBT) is investigated, using single crystal samples with well‐defined orientations for x = 0.036 and x = 0.063. The results are compared with those of temperature‐dependent measurements of the ferroelectric and dielectric hysteresis. The depolarization temperature T_d of each crystal composition is found to depend on crystal orientation, a fact that is explained by differences in the stability of respective domain configurations. A rationalization is offered for the observation that T_d differs from the ferroelectric‐relaxor transition temperature, depending on orientation. The hysteresis curves of BNT ? 3.6BT are typical for a rhombohedral system with a ferroelectric‐relaxor transition, with polarization reversal close to T_d occurring in a multistep process that includes decay of ferroelectric domains into polar nanoregions and re‐formation of domains. BNT ? 6.3BT, a composition in the region of the morphotropic phase boundary, shows the same feature, but additionally is characterized by a field‐induced transition between rhombohedral and tetragonal symmetry. This combination results in an effective piezoelectric coefficient of pm/V.     

Electric Field‐Induced Phase Transition Behaviors,Thermal Depolarization,and Enhanced Pyroelectric Properties of (Pb0.97La0.02)(ZrxSn0.89−xTi0.11)O3 Ceramics

(Pb_0.97La_0.02)(Zr_xSn_0.89?xTi_0.11)O₃ (x = 0.60, 0.62, 0.64, 0.66, 0.68, 0.70, 0.72, and 0.74) ceramics with the compositions in tetragonal antiferroelectric (AFE) region, near the morphotropic phase boundary, were prepared by using the conventional solid‐state reaction process. Their electric field‐induced phase transitional behaviors, composition‐ and temperature‐dependent dielectric, depolarization, and pyroelectric properties were investigated systematically. The AFE to ferroelectric phase switching field E_A‐F decreased with increasing x, while depolarization temperature T_d increased with a linear relationship of T_d = 842x‐483. Enhanced pyroelectric coefficient with a value of 12.1 μC/cm²/K was obtained at 88°C for the ceramics with x = 0.68, which was four times larger than the reported values. Composition‐dependent pyroelectric response over 24°C–140°C was realized by changing x from 0.60 to 0.74. The results also suggested that the enhanced pyroelectric response near T_d was accompanied by a release of large P_r, caused by an induced ferroelectric to AFE phase transition.     

Electrocaloric Effect in Ba(Zr,Ti)O3–(Ba,Ca)TiO3 Ceramics Measured Directly

In this paper, we report on studies of the electrocaloric (EC) effect in lead‐free (1?x)Ba(Zr_0.2Ti_0.8)O₃–x(Ba_0.7Ca_0.3)TiO₃ ceramics with compositions range between 0.32 ≤ x ≤ 0.45. The EC effect was measured directly using a modified differential scanning calorimeter. The maximum EC temperature change, ΔT_direct = 0.33 K under an electric field of 2 kV/mm, was observed for the composition with x = 0.32 at ~63°C. We found that the EC effect peaks not only around the Curie temperature but also at the transition between the ferroelectric phases with different symmetries. A strong discrepancy observed between the results of the direct measurements and indirect estimations points out that using Maxwell's equations is invalid for the thermodynamic nonequilibrium conditions that accompany only partial (incomplete) poling of ceramics. We also observe a nonlinearity of the EC effect above the Curie temperature and in the temperature range corresponding to the tetragonal ferroelectric phase.     

Electrical Properties and Relaxor Phase Evolution of Li‐Modified BNT‐BKT‐BT Lead‐Free Ceramics

By conventional ceramics sintering technique, the lead‐free 0.85Bi_0.5Na_0.5(1?x)Li_0.5xTiO₃‐0.11Bi_0.5K_0.5TiO₃‐0.04BaTiO₃ (x =0–0.15) piezoelectric ceramics were obtained and the effects of Li dopant on the piezoelectric, dielectric, and ferroelectric properties were studied. With increasing Li addition, the temperature‐dependent permittivity exhibited the normal ferroelectric‐to‐ergodic relaxor (FE‐to‐ER) transition temperature (T_FE‐ER, abbreviated as T_F‐R) decreasing down to room temperature. The increasing Li content also enhanced the diffuseness of the FE‐to‐ER transition behavior. For composition with x = 0.15, a large unipolar strain of 0.37% ( = S_max/E_max = 570 pm/V) was achieved under 6.5 kV/mm applied electric field at room temperature. Both unipolar and bipolar strain curves related to the temperature closely, and when the temperature reached the T_F‐R, the normalized strain achieved a maximum value (e.g., for x = 0.10, = 755 pm/V) owing to the electric‐field‐induced ER‐to‐FE state transition.     

CaTiO3 induced ferroelectric phase coexistence and low temperature dielectric relaxation in BaTiO3–BaZrO3 ceramics

The series of 0.86BaTiO₃–(0.14?x)BaZrO₃–xCaTiO₃ (abbreviated as BT–BZ–xCT) ceramics with 0.03 ≤ x ≤ 0.11 were studied to obtain high piezoelectric properties. Rietveld refinement analysis indicated that the BT–BZ–CT compositions follow a gradual rhombohedral (R) → orthorhombic (O) + R → O + tetragonal (T) → T phase transformation with increasing x. Clear evidence of the series of ferroelectric phase transitions was also found in the dielectric results. The R‐O and O‐T transition temperature shifted close to ambient temperature, while the Curie temperature slightly increased with increasing x. In addition to the dielectric loss peaks associated with the structural phase transitions, a broad low‐temperature dielectric loss peak was detected in the R phase at T = 90‐150 K. This dielectric relaxation was attributed to the domain wall freezing and fits well to the Vogel‐Fulcher model with activation energy E_a ≈ 60‐300 meV and freezing temperature T_VF ≈ 75‐140 K. High piezoelectric strain coefficient (d₃₃*) of about 1030 pm/V at 10 kV was achieved at x = 0.07, and a high Curie temperature (T_C) was maintained at about 375 K.     

Lattice Dynamics,Dielectric Constants,and Phase Diagram of Bismuth Layered Ferroelectric Bi3Ti1−xWxNbO9+δ Ceramics

Lattice dynamics and phase transitions of Aurivillius ferroelectric Bi₃Ti_1?xW_xNbO_9+δ (BTWN100x, 0 ≤ x ≤ 15%) ceramics have been investigated by temperature‐dependent Raman spectra (80–800 K) and far‐infrared (FIR) reflectance spectra (6–300 K). The frequency, intensity, and line width of phonon modes as well as complex dielectric functions of BTWN100x ceramics have been extracted by fitting Raman and FIR reflectance spectra with the multi‐Lorentzian oscillator model. It was found that the dielectric constants at a certain frequency region become lower with increasing W compositions at room temperature due to the compressive stress on W–O bands. Moreover, the temperature‐dependent behavior of optical phonon modes in BTWN100x ceramics indicates that there are two intermediate phases during the phase transition from paraelectric I4/mmm to ferroelectric A2₁am phase on cooling. The phase diagram of BTWN100x ceramics as a function of W composition has been improved.     

Ferroelectric and magnetic properties in (1−x)BiFeO3–x(0.5CaTiO3–0.5SmFeO3) ceramics

Multiferroic ceramics were prepared and characterized in (1?x)BiFeO₃–x(0.5CaTiO₃–0.5SmFeO₃) system by a standard solid‐state reaction process. The structure evolution was investigated by X‐ray diffraction and Raman spectrum analyses. The refinement results confirmed the different phase assemblages with varying amounts of polar rhombohedral R3c and nonpolar orthorhombic Pbnm as a function of the substitution content. In the compositions range of 0.2≤x≤0.5, polar R3c and nonpolar Pbnm coexisted, which was referred to polar‐to‐nonpolar morphotropic phase boundary (MPB). According to the dielectric and DSC analysis results, the ceramics with x≤0.2 changed to diffused ferroelectric, and the ferroelectric properties were enhanced significantly. Two dielectric relaxations were detected in the temperature range of 200‐300 K and 500‐700 K, respectively. The high‐temperature dielectric relaxation was attributed to the grain‐boundary effects. While the low temperature dielectric relaxation obtained in the samples with x=0.3‐0.5 was related to the charge transfer between Fe²⁺ and Fe³⁺. The magnetic hysteresis loops measured at different temperature indicated the enhanced magnetic properties in the present ceramics, which could be attributed to the suppressed cycloidal spin magnetic structure by Ti ions. In addition, the rare‐earth Sm spin moments might also affect the magnetic properties at relatively lower temperature.     

High permittivity (1−x)Bi1/2Na1/2TiO3‐xPbMg1/3Nb2/3O3 ceramics for high‐temperature‐stable capacitors

(1?x)Bi_1/2Na_1/2TiO₃‐xPbMg_1/3Nb_2/3O₃[(1?x)BNT‐xPMN] ceramics have been fabricated via a conventional solid‐state method for compositions x ≤ 0.3. The microstructure, phase structure, ferroelectric, and dielectric properties of ceramics were systematically studied as high‐temperature capacitor materials. XRD pattern certified perovskite phase with no secondary phase in all compositions. As PMN concentration increased, the phase of (1?x)BNT‐xPMN ceramics transformed from ferroelectric to relaxor gradually at room temperature, with prominent enhancement of dielectric temperature stability. For the composition x = 0.2, the temperature coefficient of capacitance (TCC) was <15% in a wide temperature range from 56 to 350°C with high relative permittivity (>3300) and low dielectric loss (<0.02) at 150°C, which indicated promising future for (1?x)BNT‐xPMN system as high‐temperature stable capacitor materials.     

Metastable Ferroelectric Phase Induced by Electric Field in xPb(Zn1/3Nb2/3)O3–(1–x)Pb(Zr0.95Ti0.05)O3 Ceramics

A xPb(Zn_1/3Nb_2/3)O₃–(1–x)Pb(Zr_0.95Ti_0.05)O₃ (xPZN–(1–x) PZT) system close to antiferroelectric–ferroelectric (AFE–FE) morphotropic phase boundary has been prepared and investigated. The XRD results reveal PZN addition induces a phase transition from the orthorhombic (AFE) to rhombohedral (FE) phase through a phase coexistence region (AFE+FE). The polarization–electric field (P–E) measurements indicate that the AFE phase can be induced into a metastable FE (FE_m) phase. And the FE_m can recover to AFE around a critical temperature indicated by temperature‐dependent P–E loops. A composition‐temperature phase diagram was generalized within a certain range of PZN content in which an AFE–FE phase boundary connecting orthorhombic antiferroelectric to rhombohedral ferroelectric phase zones is formed near room temperature.     

Sintering behavior,structural phase transition,and microwave dielectric properties of La1‐xZnxTiNbO6‐x/2 ceramics

La_1‐xZn_xTiNbO_6‐x/2 (LZTN‐x) ceramics were prepared via a conventional solid‐state reaction route. The phase, microstructure, sintering behavior, and microwave dielectric properties have been systematically studied. The substitution of a small amount of Zn²⁺ for La³⁺ was found to effectively promote the sintering process of LTN ceramics. The corresponding sintering mechanism was believed to result from the formation of the lattice distortion and oxygen vacancies by means of comparative studies on La‐deficient LTN ceramics and 0.5 mol% ZnO added LTN ceramics (LTN+0.005ZnO). The resultant microwave dielectric properties of LTN ceramics were closely correlated with the sample density, compositions, and especially with the phase structure at room temperature which depended on the orthorhombic‐monoclinic phase transition temperature and the sintering temperature. A single orthorhombic LZTN‐0.03 ceramic sintered at 1200°C was achieved with good microwave dielectric properties of ε_r~63, Q×f~9600 GHz (@4.77 GHz) and τ_f ~105 ppm/°C. By comparison, a relatively high Q × f~80995 GHz (@7.40 GHz) together with ε_r~23, and τ_f ~?56 ppm/°C was obtained in monoclinic LTN+0.005ZnO ceramics sintered at 1350°C.     

Dielectric relaxation spectra of chemically treated woods

The changes in the dielectric properties of absolutely dried Sitka spruce (Picea sitchensis Carr.) wood caused by chemical treatments were investigated. Eight kinds of chemical treatments with various levels of weight percentage gain (WPG) were performed. Through the application of the Cole–Cole circular arc law to the results of the dielectric measurements in the frequency range of 1 kHz to 1 MHz at ?60°C, the relaxation spectrum was calculated. The relaxation magnitude (ε₀ ? ε_∞) was reduced by formalization, acetylation, propylene oxide, and phenol–formaldehyde resin treatments, in which chemical reactions occurred between the OH groups in the cell wall and the added reagents. On the other hand, the generalized relaxation time (τ_m) decreased with increasing WPG, except for acetylation, for which τ_m decreased up to a WPG level of 20% and then increased. In poly(ethylene glycol) impregnation, (ε₀ ? ε_∞) decreased with increasing WPG up to about 50% and then increased, whereas τ_m linearly decreased with increasing WPG. No significant changes in these parameters were recognized for the wood methyl methacrylate composite and heat treatment. With the steam treatment, τ_m increased. The distribution of the relaxation times was broad in acetylation and narrow in propylene oxide treatment and poly(ethylene glycol) impregnation. However, it remained almost unchanged in the other treatments. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 37–43, 2005     

Dielectric relaxation and thermodynamic properties of polyvinylpyrrolidone using time domain reflectometry

Temperature‐dependent values of dielectric permittivity ε′ and dielectric loss ε″ of polyvinylpyrrolidone (PVP, commercialized as PVP K‐60) solution of average molecular weight 160 000 g mol^?1 were measured. The measurements were carried out in the frequency range 10 MHz to 20 GHz using time domain reflectometry at temperatures from 25 to 0 °C. The dielectric spectra can be described by the Davidson‐Cole model. Dielectric parameters such as the static dielectric constant ε₀, the high frequency limiting dielectric constant ε_∞, the relaxation time τ₀ and the distribution parameter β and thermodynamic parameters such as the free energy of activation ΔF_τ, the enthalpy of activation ΔH_τ and the entropy of activation ΔS_τ were determined. The average free energy of activation was found to be in the range 12.55–14.65 KJ mol^?1 and the enthalpy of activation was found to be 6.86 KJ mol^?1. Entropies of activation were found to be positive at all the measured temperature values and these large positive values of entropies reveal a less ordered structure of the PVP solution. The Kirkwood correlation factor g and the dipole moment µ were also determined for PVP solution. The results were compared with the results of the PVP‐water system studied previously. Copyright © 2011 Society of Chemical Industry