Phase transition behavior and high piezoelectric properties in lead-free BaTiO3–CaTiO3–BaHfO3 ceramics

The transition behavior, structural changes, and electric properties of lead-free (1?x)Ba(Hf_0.16Ti_0.84)O₃ –x(Ba_0.70Ca_0.30)TiO₃ (BCHT) ceramics fabricated by the conventional solid-state reaction method are investigated in this study. A complete phase diagram of BCHT system has been proposed based on their dielectric behavior. It is found that BHCT ceramics undergo a complicated phase evolution, driven by Ca and Hf contents. The results clearly demonstrate that high electric properties are achieved in the ferroelectric orthorhombic–tetragonal phase boundary near the composition with x = 0.48, which could be adjusted by the contents of Ca and Hf in the composition. The optimum composition shows enhanced properties with dielectric constant ε _r = 2889 (at room temperature, 1 kHz), high piezoelectric coefficient d ₃₃ = 410 pC/N, and electromechanical coupling factor k _p = 0.47, and a relative high Curie temperature of 106 °C. This investigation yields a sight to understand different phase transition mechanisms of enhanced piezoelectricity for the system.     

Phase transition,ferroelectric and piezoelectric properties of Bi(Mg0.5Zr0.5)O3-modified BiFeO3–BaTiO3 lead-free ceramics

(0.725 ? x)BiFeO₃–0.275BaTiO₃–xBi(Mg_0.5Zr_0.5)O₃ + 1 mol% MnO₂ lead-free ceramics (x = 0–0.08) were synthesized by a conventional solid state reaction method and the effects of Bi(Mg_0.5Zr_0.5)O₃ on phase transition, piezoelectric and ferroelectric properties of the ceramics were investigated. After the addition of Bi(Mg_0.5Zr_0.5)O₃, the crystal structure of the ceramics is transformed from rhombohedral to tetragonal phase and the morphotropic phase boundary (MPB) of rhombohedral and tetragonal phase is formed at x = 0.01. The grain size of the ceramics increases with x increasing from 0 to 0.02 and then decreases with x further increasing. The dielectric peak of the ceramics becomes diffusive with x increasing after the addition of Bi(Mg_0.5Zr_0.5)O₃. The ceramics with x = 0–0.08 exhibit much better electric insulation with the resistivity of 1.0 × 10⁹–5.0 × 10⁹ Ω·cm than pure BiFeO₃ ceramic with the resistivity of ~5 × 10⁷ Ω·cm. Due to the formation of the MPB, the ceramics with x = 0–0.02 possess good densification with the relative densities ρ _r of 94.9–96.3 %, strong piezoelectricity with the d ₃₃ of 129–135 pC/N and very high Curie temperature with the T _C of 559–610 °C.     

Structural, ferroelectric and piezoelectric properties of Mn-modified BiFeO3–BaTiO3 high-temperature ceramics

Mn modified BiFeO₃–BaTiO₃ (abbreviated as BFBT-Mnx%, x = 0.1, 0.3, 0.6, 0.9, 1.2) high-temperature lead-free ceramics were prepared by conventional oxide-mixed method and the effect of Mn doping on microstructure and electrical properties was investigated. The solid solutions show a single phase perovskite structure, and the content of Mn has a significant effect on the microstructure of ceramics. The addition of Mn can induce combinatory “hard” and “soft” piezoelectric characteristics due to aliovalent substitutions. In particular, x = 0.6 BFBT-Mnx% ceramic, with a Curie temperature, T _c, of ~463 °C, shows optimum piezoelectric properties of d ₃₃ = 131pC/N, k _p = 0.298. The simultaneous existence of good piezoelectric properties and high T _c makes these ceramics suitable for elevated temperature piezoelectric devices.     

Structure,ferroelectric and piezoelectric properties of Bi0.5(Na0.8K0.2)0.5TiO3 modified BiFeO3–BaTiO3 lead-free piezoelectric ceramics

A new lead-free solid solution of (0.75 ? x)BiFeO₃–0.25BaTiO₃–xBi_0.5(Na_0.8K_0.2)_0.5TiO₃ + 1 mol% MnO₂ has been prepared by a conventional ceramic technique and the effects of Bi_0.5(Na_0.8K_0.2)_0.5TiO₃ and sintering temperature on the structure, ferroelectric and piezoelectric properties of the material have been studied. The ceramics sintered at 960 °C for 2 h possess a pure perovskite structure and no second phases can be detected. After the addition of Bi_0.5(Na_0.8K_0.2)_0.5TiO₃, a morphotropic phase boundary of rhombohedral and orthorhombic phases is formed at x = 0.01. The addition of a small amount of Bi_0.5(Na_0.8K_0.2)_0.5TiO₃ can promote the grain growth, while excess Bi_0.5(Na_0.8K_0.2)_0.5TiO₃ causes an inhibition of grain growth. Sintering temperature has an important influence on the structure and electrical properties of the ceramics. The sintering temperature of 960 °C is a critical temperature to obtain the ceramics with good piezoelectric properties. For the ceramic with x = 0.01 sintered at/above 960 °C located at the morphotropic phase boundary, large grains, good densification, high resistivity and enhanced electrical properties are obtained.     

Microstructure,ferroelectric, piezoelectric and ferromagnetic properties of BiFeO3–BaTiO3–Bi(Zn0.5Ti0.5)O3 lead-free multiferroic ceramics

Multiferroic ceramics of (0.70?x)BiFeO₃–0.30BaTiO₃–xBi(Zn_0.5Ti_0.5)O₃ + 1 mol% MnO₂ with perovskite structure were prepared by a conventional ceramic technique and the effects of Bi(Zn_0.5Ti_0.5)O₃ doping and sintering temperature on the microstructure, multiferroic and piezoelectric properties of the ceramics were studied. All the ceramics possess a pure perovskite structure and no second phases can be detected. After the addition of a small amount of Bi(Zn_0.5Ti_0.5)O₃ (x ≤ 0.05), the ferroelectric and piezoelectric properties of the ceramics are improved and the grain growth is promoted. However, excess Bi(Zn_0.5Ti_0.5)O₃ (x ≥ 0.10) retards the grain growth, degrades the ferroelectricity and piezoelectricity, and induces two dielectric anomalies at high temperature. The ceramics can be well sintered at the very wide range of low sintering temperatures (880–980 °C) and exhibit good densification (relative density: 96.2–98.4 %) and strong electric insulation. The increase in the sintering temperature promotes the grain growth and improves the ferroelectricity of the ceramics. The ceramic with x = 0.05 sintered at 880–980 °C possesses improved ferroelectric and piezoelectric properties with remanent polarizations P _r of 21.9–28.1 μm/cm², piezoelectric constants d ₃₃ of 125–139 pC/N and planar electromechanical coupling factors k _p of 30.1–32.4 %, and high Curie temperatures T _C of 523–565 °C. A weak ferromagnetism with remanent magnetizations M _r of 0.0411–0.0422 emu/g and coercive fields H _c of 1.70–1.99 kOe were observed in the ceramics with x = 0–0.025.     

The electrostrictive effect and dielectric properties of lead-free 0.5Ba(ZrxTi1−x)O3–0.5(Ba0.75Ca0.25)TiO3 ceramics

Lead-free 0.5Ba(Zr_xTi_1?x)O₃–0.5(Ba_0.75Ca_0.25)TiO₃ (x = 0.25, 0.30, 0.35, 0.40) ceramics have been synthesized by a conventional solid state sintering method. The room temperature ferroelectric and electrostrictive properties of these ceramics were studied. Based on the measured properties, these ceramics showed a typical relaxor behavior. The Curie temperature of BZT–BCT ceramics decreases with increasing the Zr content. The largest electrostrictive strain and electrostrictive coefficient are founded in BZT–BCT ceramic with x = 0.25, the value is 0.16 % and 0.079 m⁴ C^?2, respectively. The polarization, electrostrictive strain and electrostrictive coefficient (Q ₁₁) decrease with increase in Zr concentration. For samples with low Curie temperature, which have large room temperature dielectric constant (ε), electrostrictive coefficient increases (Q ₁₁) is smaller. Because doping can disrupt the long range cation order, and electrostrictive (Q ₁₁) coefficient increases with cation order from disordered, through partially-ordered, simple relaxor and then ordered perovskites, ferroelectrics with a disordered structure have a huge permittivity, but a small electrostrictive coefficient (Q ₁₁).     

Piezoelectric and ferroelectric properties of Ga modified BiFeO3–BaTiO3 lead-free ceramics with high Curie temperature

High-temperature 0.71 Bi(Fe_1?x Ga _x )O₃–0.29 BaTiO₃ (x = 0, 0.01, 0.015, 0.02, and 0.025) piezoelectric ceramics have been synthesized and their structure and electric properties have been investigated systemically. The Ga addition caused insignificant change of crystal structure. However, the addition of a small amount of Ga was quite effective to increase the grain size, densification, and piezoelectric properties. For the ceramics with x = 0.015, the maximum of piezoelectric constant (d ₃₃), and electromechanical coupling factor (k _p) are d ₃₃ = 157 pC/N, k _p = 0.326, respectively. Meanwhile, the increasing Curie temperature (T _c), 467 °C, was obtained with x = 0.02 ceramics. Both remanent polarization P _r and coercive field E _c were reduced with increasing x.     

Structure and piezoelectric properties of lead-free (Na0.52K0.44−x )(Nb0.95−x Sb0.05)O3-xLiTaO3 ceramics

Lead-free (Na_0.52K_0.48?x )(Nb_0.95?x Sb_0.05)O₃-xLiTaO₃ (x = 0.025–0.05) piezoelectric ceramics in which the Sb content is kept constant, have been specially designed and successfully fabricated by a conventional solid state reaction method. The (Na_0.52K_0.48)(Nb_0.95Sb_0.05)O₃ ceramics can be well sintered after A-site and B-site cations are replaced by Li⁺ and Ta⁵⁺, respectively. A single-phase perovskite structure remains within the studied substitution concentration. An orthorhombic-tetragonal phase transition occurs with gradually increasing the content of Li⁺ and Ta⁵⁺, and was identified in the composition range of 0.0375 < x < 0.0425 where two kinds of ferroelectric phases may coexist and simultaneously a strong compositional dependence of electrical properties was found out. An appropriate content of Sb effectively enhanced the piezoelectric properties of the materials. The optimum overall properties with a piezoelectric constant d ₃₃ of 321 pC/N, a dielectric constant $ \varepsilon_{33}^{T} $ of 1,780, a planar electromechanical coupling coefficient k _p of 0.52 and a Curie temperature T _c of 315 °C were obtained in the composition with x = 0.0425, indicating the ceramics studied have potentials for replacing lead-containing ceramics for device applications.     

Phase transitions in the (BaTiO3)x/(BiFeO3)1−x composite ceramics: Dielectric studies

Dielectric studies were carried out for composite ceramics (BaTiO₃)_x/(BiFeO₃)_1−x (0 < x < 1) within a temperature range 23–450 °C. Linear permittivity studies at various frequencies showed the emergence of peaks near the temperatures of the ferroelectric phase transition in the BaTiO₃ grains and of the antiferromagnetic phase transition in the BiFeO₃ grains. The positions of the peaks did not depend visibly on frequency. The permittivity peaks near the antiferromagnetic phase transition shifted to low temperature with increasing the barium titanate fraction which suggests the reduction of the Neel temperature. The decrease in the Neel temperature in the composite ceramics was confirmed by measurements of the temperature dependence of the third harmonic generation.     

Synthesis,phase confirmation and electrical properties of (1 − x)KNNS−xBNZSH lead-free ceramics

Journal of Materials Science: Materials in Electronics - In the present work, lead-free piezoelectric ceramics (Rx)(K0.5Na0.5)(Nb0.96Sb0.04O3)?x(Bi0.5Na0.5)(Zr0.8Sn0.1Hf0.1)O3 [abb. as...     

Dielectric and multiferroic properties of 0.75BiFeO3–0.25BaTiO3 solid solution

Solid solution 0.75BiFeO₃–0.25BaTiO₃ (BFO–25 % BT) was prepared by solid state reaction method. Powder X-ray diffraction showed the morphotropic phase boundary (MPB) with the coexistence of both rhombohedral and cubic phases due to splitting in the line at 2θ = 39.7°. Scanning electron micrographs indicated that the ceramic has compact and uniform microstructure with average grain size <3 μm. The polarization vs applied electric field analysis showed an unsaturated hysteresis loop with the remnant polarization 12.95 μC/cm² at 22 kV/cm for 0.75BiFeO₃–0.25BaTiO₃ ceramic. The calculations of diffuse parameter i.e. slope γ = 1.63 suggested a high degree of diffusion in BFO–BT lattice. The room temperature magnetic measurements confirmed the weak ferromagnetism of magnetization ~0.1 emu/gm at an applied magnetic field of H = 5 kOe for 0.75BiFeO₃–0.25BaTiO₃ ceramic. The high temperature magnetic and dielectric analysis suggested a coupling between ferroelectric and magnetic parameters near the antiferromagnetic–paramagnetic transition T_c ~ 310 °C, which was responsible for the broad frequency dependent dielectric maxima. The impedance spectroscopy and complex modulus analysis confirmed the conventional relaxor, NTCR (negative temperature coefficient of resistance), giant ferroelectricity and polydispersive non-Debye type dielectric relaxation behaviour for 0.75BiFeO₃–0.25BaTiO₃ ceramic at 170 °C on 1 kHz with activation energy 2.33 eV. The modulus analysis also confirmed the possibility of hopping mechanism for electrical transport process in material.     

Structure,ferroelectric, piezoelectric and ferromagnetic properties of BiFeO3–Ba0.6(Bi0.5K0.5)0.4TiO3 lead-free multiferroic ceramics

(1?x)BiFeO₃–xBa_0.6(Bi_0.5K_0.5)_0.4TiO₃ + 1 mol% MnO₂ lead-free multiferroic ceramics were fabricated by a conventional ceramic technique and the effects of Ba_0.6(Bi_0.5K_0.5)_0.4TiO₃ doping and sintering temperature on the microstructure, ferroelectric, piezoelectric and ferromagnetic properties of the ceramics were studied. All the ceramics show good electric insulation with the resistivity values of 1.97 × 10⁹–1.20 × 10¹⁰ Ω cm. After the addition of Ba_0.6(Bi_0.5K_0.5)_0.4TiO₃, two dielectric anomalies are observed at high temperatures (T ₁ ~ 453–710 °C and T ₂ ~ 716–755 °C, respectively). The ceramic with x = 0.275 exhibits the optimum piezoelectricity (d ₃₃ = 48 pC/N and k _p = 13.6 %, respectively). The Ba_0.6(Bi_0.5K_0.5)_0.4TiO₃ doping and the increasing in sintering temperature improve significantly the ferromagnetic properties of the ceramics. The ceramic with x = 0.25 sintered at 1,040 °C gives the optimum remnant magnetization M _r of 0.13 emu/g.     

Effects of Co doping on microstructure and properties of (K0.5Na0.5)NbO3–LiSbO3–BiFe(1−x)Co x O3 lead-free piezoelectric ceramics

0.998 [(0.95(K_0.5Na_0.5)NbO₃–0.05LiSbO₃]–0.002BiFe_(1?x)Co _x O₃ (KNN–LS–BF_(1?x)C _x ) lead-free piezoelectric ceramics were prepared by conventional solid-state reaction method. The influences of Co content on the phase structure, microstructure, density and related electrical properties were investigated. The results reveal that the substitution of Co significantly improves the sinterability and the electrical properties of KNN–LS–BF_(1?x)C _x ceramics, sintered at a lower temperature of 1,030 °C, compared with that of KNN–LS–BF ceramics. With increasing x from 0 to 0.8, all samples show a pure perovskite structure, but the grain size increases continuously,and the porosity level reaches it’s lowest value at x = 0.2. The density ρ, piezoelectric constant d ₃₃, coupling factor k _p and dielectric constant ε _r increase with x up to 0.2, and then decrease with further increase in x value, but the variation of dielectric loss tan δ is opposite. The density and electrical properties achieve optimal value of ρ = 4.287 g/cm³, d ₃₃ = 276 pC/N, k _p  = 48 %, ε _r  = 1,284 and tan δ = 1.95 %, when x = 0.2. And Tc ≈ 340 °C at all the variation range of Co content.     

Microstructure and piezoelectric properties of lead-free 0.95(Na0.5K0.5)NbO3–0.05(Bi0.5K0.5)Zr1−x Ti x O3 ceramics

0.95(Na_0.5K_0.5)NbO₃–0.05(Bi_0.5K_0.5)Zr_1?x Ti _x O₃ (abbreviated as KNN–BKZT _x ) ceramics were prepared by the conventional solid state method, and the effect of the Ti content on the surface morphology, crystalline structure, and electrical properties of KNN–BKZT _x ceramics were mainly investigated. With the increase of Ti content, the temperature of the orthorhombic–tetragonal (O–T) phases transitions shifted to lower temperatures, and the O–T phase boundary of KNN–BKZT _x ceramics was identified in the composition with 0 ≤ x ≤ 0.3 at room temperature. It was considered that the piezoelectric properties of the ceramics were enhanced significantly owing to the more possible polarization states resulting from the coexistence of two phases. The ceramic with x = 0.2 exhibited optimum properties: d ₃₃ = 260 pC/N, k _p = 0.38, and T _C = 323 °C.     

Phase transition, dielectric and piezoelectric properties of K0.5Na0.5NbO3–CaTi0.9Zr0.1O3 lead-free ceramics

Lead-free (1 − x)K_0.5Na_0.5NbO₃–xCaTi_0.9Zr_0.1O₃ + 0.75 mol%MnO₂ piezoelectric ceramics have been prepared by an ordinary sintering technique and their phase transition, dielectric and piezoelectric properties have been studied. The results of X-ray diffraction show that CaTi_0.9Zr_0.1O₃ diffuse into K_0.5Na_0.5NbO₃ lattices to form a solid solution with a perovskite structure. After the addition of CaTi_0.9Zr_0.1O₃, both the cubic–tetragonal and tetragonal–orthorhombic phase transition temperatures decrease, and a relaxor behavior is induced. Coexistence of the orthorhombic and tetragonal phases is formed in the ceramics with 0.03 < x < 0.07 at room temperature. Owing to the higher number of possible polarization states resulting from the coexistence of the two phases, the piezoelectric properties of the ceramics are enhanced significantly. The ceramic with x = 0.05 exhibits the following optimum properties: d ₃₃ = 203 pC/N, k _p = 45.0%, and T _C = 342 °C.     

Phase transition and piezoelectric properties of (1−x)(K0.42Na0.58)(Nb0.96Sb0.04)O3–x(Bi0.5Na0.5)0.90Mg0.10ZrO3 lead-free ceramics

(1?x)(K_0.42Na_0.58)(Nb_0.96Sb_0.04)O₃–x(Bi_0.5Na_0.5)_0.90Mg_0.10ZrO₃ [(1?x)KNNS–xBNMZ] lead-free ceramics have been prepared by the normal sintering, and effects of BNMZ content on their phase structure, microstructure, and electrical properties have been systematically investigated. These ceramics with 0.045 ≤ x ≤ 0.05 possess a rhombohedral–tetragonal (R–T) phase boundary, as confirmed by the temperature dependence of dielectric properties and X-ray diffraction patterns. The grain size of the ceramics first increases and then decreases as the BNMZ content increases, and the ceramic with x = 0.06 possesses much smaller grains (<1 μm), resulting in the abnormal electrical and phase transition behavior. In addition, the Mg²⁺ was homogenously distributed in the ceramic matrixes. These ceramics with R–T phase boundary show enhanced dielectric, ferroelectric, and piezoelectric properties as compared with a pure KNN, and optimum electrical properties (e.g., P _r ~ 16.23 μC/cm², E _C ~ 7.58 kV/cm, ε _r ~ 2,663, tan δ ~ 0.034, d ₃₃ ~ 434 pC/N, k _p ~ 0.47, and T _C ~ 244 °C) were found in the ceramic with x = 0.0475. We believe that the (1?x)KNNS–xBNMZ ceramic is a promising candidate for lead-free piezoelectric devices.