Dielectric properties and diffuse phase transition behavior of CuO-doped lead-free Ba(ZrxTi1−x)O3 ceramics

CuO-doped lead-free Ba(Zr_0.2Ti_0.8)O₃ (BZT20) ceramics were prepared through a solid state processing technique, and the effects of CuO on microstructure, dielectric properties and diffuse phase transition behavior were investigated. The average grain sizes were increased by CuO doping. The temperature and frequency dependences of the dielectric constant revealed that CuO-doped BZT20 ceramics exhibited broad diffuse phase transition behavior. The dielectric constant increased with increasing CuO concentration. The value of T_m and degree of diffusion (γ) changed regularly in the studied compositional ranges. The BZT20 samples with 1.0 mol% CuO doping, sintered at 1310 °C, showed excellent dielectric property and lower diffusivity with ε_m=21,371 and γ=1.87. These results can be explained by the disordered distribution of Cu ions in the B sites and the weakened bonding force with oxygen ions in Cu substituted BZT20 structure.     

Enhanced temperature stability in the O–T phase boundary of (K,Na)NbO3-based ceramics

In order to obtain excellent electrical properties and its temperature stability of KNN-based ceramics to meet the practical applications, a new lead-free material system of (1−x)K_0.5Na_0.5Nb_0.96Sb_0.04O₃-xBi_0.5Na_0.5Zr_0.8Sn_0.2O₃ (KNNS-xBNZS, 0 ≤ x ≤ 0.060) was designed, and the enhanced electrical properties (eg, d₃₃ ~ 465 pC/N, ε_r ~ 3318, S_uni ~ 0.133%) is obtained in the ceramics with x = 0.04. The physical origin of enhanced electric properties should be ascribed to the phase instability of R-T, resulting in a low-energy barrier, which can greatly facilitate the polarization switching. Moreover, the temperature stable of piezoelectric constant (d₃₃ or d₃₃*) is measured by three distinctive methods in different phase boundaries (O, O-T, R-T) at the temperature range 20°C-180°C, revealing that the O-T phase boundary has a relatively good temperature stability. A mode is used to show how to effectively modified the piezoelectric constant (d₃₃ or d₃₃*) and its temperature stability, we believe that such a strategy may further improve the temperature stability of d₃₃ or d₃₃* value in KNN-based ceramics.     

Enhanced piezoelectric strain of BiFeO3–Ba(Zr0.02Ti0.98)O3 lead-free ceramics near the phase boundary

The xBiFeO₃-(1-x)Ba(Zr_0.02Ti_0.98)O₃ + 1.0 mol% MnO₂ (xBF-BZT) lead-free piezoelectric ceramics were prepared by conventional solid-state reaction method. The structure, dielectric, and piezoelectric properties were studied. X-ray diffraction (XRD) analysis showed that xBF-BZT ceramics exhibited pure perovskite structure with the coexistence of tetragonal and rhombohedral phases (0.66 ≤ x ≤ 0.74). The Curie temperature T_c, the dielectric constant ε_r (1 kHz), dielectric loss tanδ (1 kHz), piezoelectric constant d₃₃, coercive field E_c (80 kV/cm), and remnant polarization P_r (80 kV/cm) of 0.7BF-0.3BZT-Mn ceramics were 491°C, 633, 0.044, 165 pC/N, 35.6 kV/cm, and 22.6 μC/cm², respectively. The unipolar strain of 0.7BF-0.3BZT reached up to 0.20% under the electric field of 60 kV/cm, which is larger than that (0.15%) of BiFeO₃–BaTiO₃ ceramics. These results indicated that the xBF-BZT ceramics were promising candidates for high-temperature piezoelectric materials.     

Structures and microwave dielectric properties of Ca(1−x)Nd2x/3TiO3 ceramics

Ca_(1?x)Nd_2x/3TiO₃ microwave dielectric ceramics were prepared by the mixed oxide route; powders were calcined at 1100 °C and sintered at 1450–1500 °C. High density, single phase products were obtained for all compositions. Grain sizes ranged from 1 μm to 100 μm. There was evidence of significant discontinuous grain growth in mid range compositions; all ceramics were characterised by complex domain structures. With increasing Nd content there was a evidence of a transition from an orthorhombic Pbnm structure to a monoclinic C2/m structure. This was accompanied by a decrease in relative permittivity (?_r) from 180 to 78, and decrease in the temperature coefficient of resonant frequency (τ_f) from +770 ppm K^?1 to +200 ppm K^?1. The product of dielectric Q value and resonant frequency (Q × f) varied in a grossly non-systematic way, exhibiting a peak at 13,000 GHz in Ca_0.7Nd_0.2TiO₃.     

Enhanced dielectric energy storage performance of A-site Ca2+-doped Na0.5Bi0.5TiO3–BaTiO3–BiFeO3 Pb-free ceramics

(1-x) (0.98Na_0.5Bi_0.5TiO₃–0.01BaTiO₃–0.01BiFeO₃)–xCaTiO₃ (NBB-xCT) ceramics were produced using traditional solid-state synthesis methods. The surface morphology, domain structure, and electrical properties of the ceramic samples were systematically studied. In addition, the temperature and frequency stabilities of the NBB-15CT sample at 200 kV/cm were tested. Generally, NBB-xCT ceramics exhibit a typical single perovskite phase structure. The results indicate that the NBB-15CT ceramics showed a high energy density of 3.14 J/cm³ at 250 kV/cm. The piezoresponse force microscopy (PFM) results showed that the addition of CT broke the macrodomains of the 0.98Na_0.5Bi_0.5TiO₃-0.01BaTiO₃-0.01BiFeO₃ ceramic and helped to form nanodomains, leading to an improved energy storage performance. The above performance indicates that the specimens possess very good temperature-and frequency-dependent energy storage performances at 30–150 °C and 1–100 Hz. Moreover, the electric energy storage and release in the NBB-15CT ceramic indicated that the power density could reach 55.30 MV/cm³ at 180 kV/cm. Therefore, the NBB-15CT ceramic is a promising material for electrical capacitors.     

DC field effect on dielectric property of Ba(ZrxTi1−x)O3 ceramics

Barium zirconate titanate Ba(Zr_xTi_1?x)O₃ (BZT) ceramics have been fabricated by conventional solid state route. The dielectric properties and ferroelectric relaxor behavior were investigated as a function of Zr content and DC bias field. It was found that the relaxor behavior of BZT is enhanced with the increase in Zr content. The temperature of maximum dielectric peak (T_m) of BZT ceramic is greatly increased with DC bias field (E) up to a certain threshold field E_t, below which T_m starts to increase gradually. This behavior could be associated with the size of domain. The relationship between temperature and dielectric tunability is also discussed in details.     

Microwave-assisted sintering and improved dielectric,ferroelectric properties of 0.5[(Ba0.7Ca0.3)TiO3]–0.5[Ba(Zr0.2Ti0.8)O3] lead-free ceramics

0.5[(Ba_0.7Ca_0.3)TiO₃]–0.5[Ba(Zr_0.2Ti_0.8)O₃] lead-free ceramics were synthesised by coprecipitation method and sintered by fast microwave sintering (MWS) and by conventional sintering (CS) at 1200°C. After being sintered with the two different methods, the materials were characterised for structural, microstructural, frequency and temperature-dependent dielectric properties, Raman spectroscopy, and ferroelectric measurements. Results are compared and discussed in the present paper. X-ray diffraction confirms the presence of the tetragonal and rhombohedral phases in the composites sintered by both methods. The ferroelectric to paraelectric transition temperature (Tc) is increased in microwave-sintered composite. Diffuse constant (γ) values show BCT–BZT ceramics to be neither normal ferroelectrics nor relaxor ferroelectrics. Raman spectra confirm phase transition in the ceramic samples. Saturation polarisation (Ps) values are 7.62 and 4.28?µC?cm^?2 and nearly equal remanant polarisation (Pr) values were observed for BCT–BZT composite sintered with MWS and CS, respectively.     

Temperature stability and phase transition of Li0.02(KxNa1−x)0.98NbO3 ceramics

Li_0.02(K_xNa_1?x)_0.98NbO₃(x = 0.35–0.55) ceramics were prepared using the conventional solid state sintering method. The thermal behaviors of Li-modified (K_xNa_1?x)NbO₃ ceramics were investigated from ?30 to 150 °C, and the effect of Na/K ratio in (K_xNa_1?x)NbO₃ ceramics on thermal behavior and electrical properties was also studied. In the case of Li_0.02(K_xNa_1?x)_0.98NbO₃ ceramics with 0.5 wt.% ZnO, the transition temperature was sharply decreased because of a phase transition as the composition range of x was 0.425–0.475. From the results of the temperature dependence of piezoelectric properties, it is assumed that the Na-rich phase is less stable than the K-rich phase for temperature change.     

Microwave dielectric properties of high dielectric tunable - low permittivity Ba0.5Sr0.5TiO3–Mg2(Ti0.95Sn0.05)O4 composite ceramics

Ba_0.5Sr_0.5TiO₃–Mg₂(Ti_0.95Sn_0.05)O₄ composite ceramics have been synthesized by the solid-state reaction. Phase structure, microstructure and microwave dielectric properties have been systematically characterized. The permittivity is tailored to a certain extent with the addition of Mg₂(Ti_0.95Sn_0.05)O₄. Both X-ray diffraction (XRD) and back electric image (BEI) analysis show the co-existence of two-phase structures of ABO₃ perovskite and A₂BO₄ spinel structure. A high dielectric tunablity can be obtained and a high Q value can be achieved at microwave frequency. The composition 30 wt.%Ba_0.5Sr_0.5TiO₃–70 wt.%Mg₂(Ti_0.95Sn_0.05)O₄ exhibits good dielectric properties with ? of 79, Q of 152 (at 2.997 GHz) and T of 15.8% (30 kV/cm & 10 kHz) at room temperature, which make it a promising candidate for tunable microwave device applications in the wireless communication system.     

Characterization of acceptor-doped (Ba,Ca)TiO3 “hard” piezoelectric ceramics for high-power applications

Acceptor Mn or Co-doped Ba_0.925Ca_0.075TiO₃ (abbreviated as BCT-Mn and BCT-Co) lead-free piezoelectric ceramics with high density and fine grains were synthesized by conventional solid-state reaction method. The phase structure and electrical properties of the ceramics were investigated. The acceptor-doped BCT ceramics were found to exhibit asymmetrical polarization-electric field hysteresis loops corresponding to the presence of an internal bias field E_i, indicating that the domain walls were pinned by preferentially oriented defect dipoles formed by the acceptors and oxygen vacancies. High mechanical quality factor Q_m and low dielectric loss tanδ were obtained for the ceramics due to the strong internal bias field (E_i =4–5kV/cm). In particular, BCT-Mn ceramics exhibited the best properties, with mechanical quality factor Q_m =1020, dielectric loss tanδ=0.2% and piezoelectric coefficient d₃₃ =190 pC/N. Furthermore, the planar electromechanical coupling factor k_p for BCT-Mn ceramics was found to be larger than 0.4 in the temperature range of 25 °C to 75 °C. These results indicate that the Mn-doped BCT lead-free ceramics material is a promising candidate for high-power piezoelectric applications.     

Low temperature sintering and dielectric properties of (Ba0.85Ca0.15)(Ti0.9Zr0.1)O3−xCu2+ ceramics obtained by the sol-gel technique

Lead-free Cu²⁺-modified (Ba_0.85Ca_0.15)(Ti_0.9Zr_0.1)O₃ (BCZT−xCu²⁺) piezoelectric ceramics was synthesized by sol-gel method. The effects of Cu²⁺ additions on sintering characteristics, the phase structure, microstructure, electrical properties and complex impedance characteristic were investigated systematically. The XRD patterns exhibited a pure perovskite structure without impurity phase in all samples. SEM micrographs, temperature dependence of dielectric constant and polarization-electric field (P-E) hysteresis loops indicated that a small amount of Cu²⁺ addition affected the properties obviously. The results revealed that the addition of Cu²⁺ significantly improved the sinterability of BCZT ceramics which resulted in a reduction of sintering temperature from 1440 °C to 1230 °C. The TG-DSC was analyzed to verify the reaction process of BCZT−Cu²⁺ materials. (Ba_0.85Ca_0.15)(Ti_0.9Zr_0.1)O₃ ceramics with x=0.020 Cu²⁺ exhibited good electrical properties: ε_m=12,112, T_c=360 K, ε_r=2614, tan δ=0.026, K_p=0.47 and d₃₃=382 pC/N. The results indicated that Cu²⁺-modified BCZT ceramics could be a promising candidate for commercial purposes.     

Origin of superior dielectric and piezoelectric properties in 0.4Ba(Zr0.2Ti0.8)O3–0.6(Ba0.7Ca0.3)TiO3 at intermediate grain sizes

Grain size effect is one of the most important issues to develop next-generation multilayer microdevices. In this work, the tetragonal 0.4Ba(Zr_0.2Ti_0.8)O₃–0.6(Ba_0.7Ca_0.3)TiO₃ (BZT–60BCT) ceramics with a wide grain size from 2.1 to 24 μm were successfully prepared by using ultrafine nano powder and two-step sintering. The results demonstrate that critical/intermediate grain size of dielectric constant ε_r and piezoelectric constant d₃₃ appears at ∼12.9 μm. It was found that the presence of large lattice tetragonality, and enhanced domain wall motion induced by domain coexistence between submicron and nano size in sample with a grain size of ∼12.9 μm, resulting in the superior dielectric and piezoelectric properties. These findings and analyses of the origin of superior dielectric and piezoelectric properties at intermediate grain size have important practical implications in the design of high-performance piezoelectric ceramics.     

Dielectric tunable properties of high dielectric breakdown Ba0.5Sr0.5TiO3–Zn2P2O7 composite ceramics

Dielectric properties of Ba_0.5Sr_0.5TiO₃–xZn₂P₂O₇ (x = 1, 3, 5, 10, 15 wt%) composite ceramics, which were prepared by solid-state reaction process, were intensively investigated. The results showed that the Curie temperature (T_c) of composites gradually shifted to lower temperature (?140 °C) with increasing the content of Zn₂P₂O₇, and the dielectric constant were tuned effectively from 2020 to 107, while maintaining a relatively high tunability. Zn₂P₂O₇ additions remarkably inhibited the grain growth of Ba_0.5Sr_0.5TiO₃ phases, and improved the breakdown strength of samples up to 385 kV/cm. The sample with x = 10 wt% exhibited good dielectric properties (?_r = 290, tg δ = 0.0006, T = 20.5%, BDS = 297 kV/cm). Meanwhile Zn₂P₂O₇ addition also made the T_c far away from the room temperature, which reduced the sensitivity of the dielectric constant to temperature change and simultaneously improved the stability of materials.     

Ba/Sr比对Ba_xSr_(1-x)Zr_(0.18)Ti_(0.82)O_3陶瓷结构及性能的影响

本文采用溶胶-凝胶法制备Ba_xSr_(1-x)Zr_(0.18)Ti_(0.82)O_3(x=0.3,0.4,0.5)陶瓷粉末,通过传统的陶瓷制备方法制备陶瓷样品,研究了不同Ba/Sr比对陶瓷结构及充放电性能的影响。研究结果显示,随着Ba/Sr的增加,陶瓷的介电常数变大,居里温度向高温方向移动,介电性由线性向非线性演变;室温下,Ba_(0.5)Sr_(0.5)Zr_(0.18)Ti_(0.82)O_3陶瓷有最大的介电常数(~2250,0.004,1 k Hz),最大的饱和极化(~10.8μC/cm~2,110 k V/cm),最大的能量密度(~0.42 J/cm~3,110 k V/cm),其放电效率也达到93%。     

Structural,dielectric and ferroelectric properties of Ba1−x(Bi0.5Na0.5)xTiO3 ceramics

Lead free Ba_1?x(Bi_0.5Na_0.5)_xTiO₃ (x=0, 0.02, 0.04, 0.06, 0.08, 0.1) ferroelectric ceramics were synthesized by conventional solid state reaction technique. Sintering was done at 1200 °C for 2 h in air atmosphere. The final products have tetragonal symmetry with decreasing c/a ratio confirmed by X-ray diffraction analysis. The grain size varies between 300 nm to 1000 nm for x=0 to 0.1. With increase in Bi_0.5Na_0.5TiO₃ [BNT] content, the room temperature permittivity decreases whereas the Curie temperature (T_c) increases and its highest value was found to be 155 °C for 10 mol% of BNT addition. The ceramics show stable and low dielectric loss characteristics. The remnant polarization (P_r) and the coercive field (E_c) increases monotonously with increase in BNT content. The highest value of 2P_r (=17 μC/cm²) and 2E_c (=22 Kv/cm) was obtained for x=10 mol% BNT addition.     

Enhanced energy-storage properties and dielectric temperature stability of (Bi0·5Na0.5)0.84Sr0·16Ti1-x(Y0·5Nb0.5)xO3 lead-free ceramics

A series of lead-free (Bi_0·5Na_0.5)_0.84Sr_0·16Ti_1-x(Y_0·5Nb_0.5)_xO₃ (abbreviated as BNST-100xYN) relaxor ferroelectric ceramics were prepared by solid state reaction sintering. The micro morphology, dielectric properties, and energy storage properties of the ceramics with increasing doping content were systematically studied, and their conductive mechanism was also studied. The perovskite structure was not significantly changed with the addition of (Y_0·5Nb_0.5)⁴⁺ complex ions, but it led to a certain amount of flake grains appear and element precipitation with increasing composition. And the larger dielectric breakdown strength (DBS) and lower remanent polarization (P_r) were attained with the recoverable energy storage density (W_rec) of ~1.0433 J/cm³ for x = 0.04 composition. In addition, it showed outstanding dielectric temperature stability and cycle stability. These results indicated that BNST-4YN ceramics are an excellent candidate for energy storage device and temperature-stable dielectric equipment.     

Microstructure and electrical properties of (Ba0.85Ca0.15)1−xLix(Ti0.90Zr0.10)1−xNbxO3 ceramics with a low dielectric loss and a low sintering temperature

A low sintering temperature is demonstrated for (Ba_0.85Ca_0.15)_1?xLi_x(Ti_0.90Zr_0.10)_1?xNb_xO₃ (BCLTZN-x) piezoelectric ceramics, where BCLTZN-x lead-free piezoelectric ceramics were prepared by the normal sintering. Effects of Li and Nb on the microstructure and electrical properties of these ceramics were investigated. The sintering temperature of BCLTZN-x ceramics was decreased greatly by introducing Li and Nb, and the grain size of these ceramics decreases with increasing x. These ceramics with a small amount of Li and Nb maintain good piezoelectric properties, together with a low sintering temperature and a lower dielectric loss. These ceramics with x = 0.01 demonstrate optimum electrical properties: d₃₃ ～ 353 pC/N, k_p ～ 41.1%, T_c ～ 86 °C, ?_r ～ 4236, and tan δ ～ 0.75%.     

Bond characteristics,sintering behavior and microwave dielectric properties of Ce2[Zr1−x(Ca1/3Sb2/3)x]3(MoO4)9 ceramics

Ce₂[Zr_1?x(Ca_1/3Sb_2/3)_x]₃(MoO₄)₉ (CZ_1?x(CS)_xM) (x = 0.02–0.10) ceramics were prepared by the conventional solid-state reaction method. The correlations between the chemical bond parameters and microwave dielectric properties were calculated and analyzed by using the Phillips–Van Vechten–Levine (P–V–L) theory. Phase composition and microstructures were evaluated by scanning electron microscopy and X-ray diffraction patterns. Lattice parameters were obtained by Rietveld refinements based on XRD data. Excellent properties for Ce₂[Zr_0.96(Ca_1/3Sb_2/3)_0.04]₃(MoO₄)₉ ceramic sintered at 775 °C: ε_r = 10.68, Q×f = 85,336 GHz and τ_f = ?7.58 ppm/°C were achieved.     

Aging effect in Er3+-doped 0.5Ba(Zr0.2Ti0.8)O3–0.5(Ba0.7Ca0.3)TiO3 ceramics

Usually, aging in poled ferroelectrics leads to degradation of certain physical properties. In this study, we found a remarkable aging effect in tetragonal Er³⁺-doped 0.5Ba(Zr_0.2Ti_0.8)O₃–0.5(Ba_0.7Ca_0.3)TiO₃ (BZT-BCT) ceramics after poling. It is observed that the domains can spontaneously rotate to keep their spontaneous polarization direction similar to that of the poling electric field during aging for the poled ceramics. Furthermore, compared with freshly poled ceramics, the thermally stimulated current (TSC) peak of the aged ones shifts toward a higher temperature (10°C). And the temperature of the TSC peak in the aged ceramics is exactly equal to their Curie temperature. Such features indicate that aging for the poled ceramics could stabilize the alignment of ordered ferroelectric domains. Additionally, a downward TSC peak above Curie temperature is obtained in both poled and aged ceramics, demonstrating that poling and aging can lead to ordered alignment of defect dipoles. The aging mechanism of poled Er³⁺-doped BZT-BCT ceramics has proposed and discussed in this article.     

Processing mediated enhancement of ferroelectric and electrocaloric properties in Ba(Ti0.8Zr0.2)O3–(Ba0.7Ca0.3)TiO3 lead-free piezoelectrics

High-performance Ba(Ti_0.8Zr_0.2)O₃–(Ba_0.7Ca_0.3)TiO₃ (BCZT) fiber crystals were grown using laser-heated pedestal growth (LHPG) for a systematic investigation of processing effects on structure and physical properties. By changing the growth rate (200−5 mm/h), fiber crystals with varying stoichiometry were realized: controlled composition, Ba_0.872Ca_0.128Ti_0.925Zr_0.075O_3-δ, for the optimized crystal (5 mm/h), relative to the ceramic sample (SS) synthesized by the ceramic method. SS and optimized fibers exhibited larger energy storage densities of 700 and 868 mJ/cm³, respectively. Electrocaloric (EC) measurements by direct and indirect methods yielded ΔT of 1.3 K & 0.95 K and EC responsivity (ΔT/ΔE) of 0.3 and 0.43 K mm/kV for SS and 5 mm/h respectively, at 30 kV/cm, at least two-folds higher compared to 200 mm/h fiber. The EC responsivity of our samples is comparable to that of Pb(Mg,Nb)O₃ crystals. These results demonstrate that BCZT has potential application as EC elements when the composition is controlled by fine-tuning of growth parameters.