TiO3 Lead-free Ceramics Research Articles

Energy storage properties of (Bi0.5Na0.5)0.93Ba0.07TiO3 lead-free ceramics modified by La and Zr co-doping

Lead-free [(Bi0.5Na0.5)0.93Ba0.07]1-xLaxTi1-yZryO3 (BNBLTZ) ceramics were investigated for energy storage applications. In order to adjust its energy storage properties, the La and Zr co-doping contents varied at 0.01 ≤ x, y ≤ 0.04. BNBLTZ ceramics show a single phase perovskite structure without phase transition after La and Zr co-doping. The compact and uniform microstructure with similar grain morphology and different grain sizes is obtained. The remnant polarization and coercive field decrease with the increase of La and Zr additions, and the energy storage density increases drastically. The maximum energy storage density of 1.21 J/cm3 is obtained when x = 0.04 and y = 0.01. There are two dielectric anomalies at Tp and Tm due to the phase transformation. The results suggest that lead-free BNBLTZ ceramics should be good candidates for energy storage applications.

Effect of texturing on polarization switching dynamics in ferroelectric ceramics

Highly (100),(001)-oriented (Ba0.85Ca0.15)TiO3 (BCT) lead-free piezoelectric ceramics were fabricated by the reactive templated grain growth method using a mixture of plate-like CaTiO3 and BaTiO3 particles. Piezoelectric properties of the ceramics with a high degree of texture were found to be considerably enhanced compared with the BCT ceramics with a low degree of texture. With increasing the Lotgering factor from 26% up to 94%, the piezoelectric properties develop towards the properties of a single crystal. The dynamics of polarization switching was studied over a broad time domain of 8 orders of magnitude and was found to strongly depend on the degree of orientation of the ceramics. Samples with a high degree of texture exhibited 2–3 orders of magnitude faster polarization switching, as compared with the ones with a low degree of texture. This was rationalized by means of the Inhomogeneous Field Mechanism model as a result of the narrower statistical distribution of the local electric field values in textured media, which promotes a more coherent switching process. The extracted microscopic parameters of switching revealed a decrease of the critical nucleus energy in systems with a high degree of texture providing more favorable switching conditions related to the enhanced ferroelectric properties of the textured material.

Broadband Near-Infrared Photoluminescence and Strong Visible Up-Conversion Emission in BaTiO3-(Na0.5Er0.5)TiO3 Lead-Free Piezoelectric Ceramics

For checking photoluminescence properties of BaTiO3-(Na0.5Er0.5)TiO3 lead-free piezoelectric ceramics, optical diffuse reflection spectra, visible up-conversion luminescence spectra, 1.55 μm near-infrared photoluminescence spectra, and optical temperature sensing performances under the excitation of 980 nm laser were investigated systematically. Broadband near-infrared (˜1.55 μm, FWHM˜90 nm) emission and strong visible up-conversion (˜550 nm) emission were observed under the 980 nm excitation in the ceramics at room temperature. Near-infrared emission and visible up-conversion emission became stronger with increasing (Na0.5Er0.5)TiO3 concentration below quenching point above which it will degrade. The optimal emission intensity was obtained when (Na0.5Er0.5)TiO3 content was 7 mol%. These ceramics with excellent ferro-/piezoelectric and photoluminescence properties may be useful for ultrasonic transducer, optical temperature sensor, optical amplifier, and other relative applications.

The Influence of Firing Temperatures on the Crystal Structure, Microstructure and Dielectric Properties of 0.68Bi0.5Na0.5TiO3-0.22Bi0.5K0.5TiO3-0.10Bi0.5Li0.5TiO3 Ceramics Prepared Via the Combustion Technique

The 0.68Bi0.5Na0.5TiO3–0.22Bi0.5K0.5TiO3–0.10Bi0.5Li0.5TiO3 (BNKLT) lead-free ferroelectric ceramics were prepared by the combustion technique. The BNKLT was calcined from 600°C to 850°C for 2 h and sintered from 900°C to 1050°C for 2 h. The XRD diffraction pattern was indexed on the basis of rhombohedral perovskite structure. The secondary phases K4Ti3O8 and K2Ti6O3 were detected in the powders calcined below 750° C. The highest perovskite percentage was observed in the powders calcined above 750°C. The sintered pellets showed single-phase perovskite structure for all samples, which indicated that K+, Bi+ and Li+ ions substituted onto the A-site in the BNKLT lattice to form a solid solution. The increase in sintering temperature up to 1025°C significantly promoted grain growth and microstructure densification. The depolarization temperature (Td) of the sample shifted to higher temperatures whereas the temperature of maximum permittivity (Tmaxε) shifted to lower temperatures with an increase in sintering temperature. The optimum dielectric properties were obtained from the sample sintered at 1025°C with ϵr = 4,340 (at Tmaxε), density (ρ = 5.79 g/cm−3) and shrinkage (∼18.4%).

Antiferroelectricity in tantalum doped (Bi0.5Na0.5)0.94Ba0.06TiO3 lead-free ceramics

(Bi0.5Na0.5)0.94Ba0.06(Ti1−xTax)O3 (x=0.00–0.04) lead-free polycrystalline ceramics were synthesized using the solid state reaction route, and their crystal structures and electrical properties were systematically studied. With the introduction of Ta substitution, the relaxor antiferroelectric phase with tetragonal P4bm symmetry is stabilized. The representative double polarization hysteresis loops and sprout shaped strain curves for antiferroelectric ceramics are observed at higher Ta contents with x=0.01–0.02 at room temperature. x=0.01 shows the largest strain of 3.81‰ under 60kV/cm, indicating a good candidate for actuator applications. The polarization and strain hysteresis loops are also evaluated to verify the temperature-induced normal ferroelectric phase to relaxor antiferroelectric phase transition at temperature up to 120°C. The energy storage density and efficiency at various temperatures are calculated and analyzed in the compositions of x=0.00–0.02. The results indicate that the energy storage density becomes more temperature independent with the increase of Ta concentration, which are promising for applications in high-temperature capacitors.

Large strain and relaxation behavior in CeO2 doped Bi0.487Na0.427K0.06Ba0.026TiO3 piezoceramics

xCeO2-doped Bi0.487Na0.427K0.06Ba0.026TiO3 lead-free piezoelectric ceramics (BNTC1000x, x=0, 0.3, 0.6, 0.8, 1.0, 1.2, 1.4wt%), were synthesized by the solid-state reaction method. XRD patterns showed that all BNTC1000x ceramics exhibit pure single perovskite phase. At the critical composition BNTC12, a large electric-field-induced strain of 0.39% with normalized strain (Smax/Emax) of 561pm/V was obtained under an electric field of 65kV/cm. The ferroelectric phase was fully poled with electric field, and depoled once the applied electric field was removed. During that cycle, the non-180°-domains repeated switching and back-switching and the large strain was induced. The relaxation behavior was involved in BNTC1000x ceramics and induced by oxygen vacancy migration. Besides, this behavior was more predominant in BNTC12 than in BNTC0.

Large electrocaloric effect in (Bi0.5Na0.5)0.94Ba0.06TiO3 lead-free ferroelectric ceramics by La2O3 addition

Large electrocaloric effect is observed in La doped (Bi0.5Na0.5)0.94Ba0.06TiO3 lead-free ferroelectric ceramics synthesized by conventional solid state reaction. The dielectric permittivity and ferroelectric hysteresis loops are measured. The indirect method is used to calculate electrocaloric temperature change of BNBT6 doped by La. The introduction of La2O3 can enhance the electrocaloric effect of BNBT6. The largest temperature change |ΔT62|=2.61K and electrocaloric coefficient |ξmax|=0.052Kcm/kV is achieved in the 0.5wt% La doped BNBT6, which is significantly higher than that of BNT-based and lead-containing ferroelectric materials reported so far. For 1wt% ones, the |ΔT30|=1.954K and |ξmax|=0.039Kcm/kV is obtained in the room-temperature, which promises the environmental-friendly La doped BNBT6 is candidate for applications of solid state cooling devices.

Electrical Properties of La-Doped Ba0.7Ca0.3TiO3 Lead-Free Ceramics

(Ba0.7Ca0.3)1-1.5xLaxTiO3 ceramics with x = 0 – 0.03 were prepared using a solid state sintering method. Upon La3+ increasing content, tetragonality of doped ceramics decreased. The intrinsic contribution affected piezoelectric coefficient decrement. The changes in dielectric loss, remanent polarization, coercive field, planar electromechanical coupling coefficient and mechanical quality factor seemed to be correlated with the extrinsic contribution from domain wall mobility. La3+ addition caused both grain size reduction and dielectric constant enhancement. The results here suggested that BCT electrical properties' dependence on La3+ substitution may be useful for ferroeletric devices.

Enhanced energy-storage properties of BaZrO3-modified 0.80Bi0.5Na0.5TiO3–0.20Bi0.5K0.5TiO3 lead-free ferroelectric ceramics

Large energy-storage density is observed in BaZrO3 (BZ)-modified 0.80Bi0.5Na0.5TiO3-0.20Bi0.5K0.5TiO3 (BNBK) lead-free ferroelectric (FE) ceramics synthesized by conventional solid-state reaction. The energy-storage property of (1 − x)BNBK–xBZ has been investigated. Certain content of BZ can enhance the energy-storage property of BNBK by enhancing the breakdown strength. The largest energy-storage density W1 = 0.73 J/cm3 and efficiency of energy storage η = 0.75 at E = 70 kV/cm are achieved in the 0.96BNBK–0.04BZ, which is significantly higher than that of BNT-based and lead-containing FE materials reported. Its energy-storage density exhibits the superior thermal stability with temperature range of 30–100 °C. Those properties promise that the environmental friendly (1 − x)BNBK–xBZ ceramics are candidate for applications of energy-storage devices.

Full set of material constants of (Na0.5K0.5)NbO3–BaZrO3–(Bi0.5Li0.5)TiO3 lead-free piezoelectric ceramics at the morphotropic phase boundary

The perovskite solid solution system of (1−x−y)(Na0.5K0.5)NbO3–xBaZrO3–y(Bi0.5Li0.5)TiO3 (BZ/BLT/NKN) is a new family of lead-free piezoelectric material. Compositions near the morphotropic phase boundary (MPB) (x = 0.06, y = 0.02) have been reported to have good piezoelectric coefficients with the moderate Curie temperature. In this work, the full set of material constants for the MPB composition of BZ/BLT/NKN solid solution was characterized using the resonance method. ε33T, tanδ, d31, d33, d15, Qm and TC are 2496, 0.025, −159 pC/N, 321 pC/N, 602 pC/N, 44 and 256 °C, respectively. The piezoelectric properties are not only superior to those of other (Na,K)NbO3-based ceramics at room temperature, but also relatively stable against temperature up to 200 °C. These results show that BZ/BLT/NKN solid solution is a promising candidate for practical piezoelectric applications in actuating and sensing fields.

Enhancement of energy-storage properties of K0.5Na0.5NbO3 modified Na0.5Bi0.5TiO3–K0.5Bi0.5TiO3 lead-free ceramics

A lead-free ceramics (1 − x)(0.84Na0.5Bi0.5TiO3–0.16K0.5Bi0.5TiO3)–xK0.5Na0.5NbO3 (x = 0, 0.03, 0.06, 0.09, 0.12, 0.15) for energy-storage application have been fabricated by conventional solid state method. All compositions were crystallized into perovskite solid solution structure ascertained by XRD. SEM micrograph revealed that homogeneous grain could be obtained by addition of appropriate K0.5Na0.5NbO3 (KNN). The depolarization temperature (Td) decreased significantly from 140 to 70 °C, while the maximum dielectric constant temperature (Tm) reduced slightly with increasing KNN. And the addition of KNN improved the energy-storage properties significantly by weakening the ferroelectricity of Na0.5Bi0.5TiO3–K0.5Bi0.5TiO3 (NBT–KBT) ceramics. When x = 0.09, the highest energy-storage density (W = 1.51 J/cm3) and energy efficiency (η = 65.0 %) were obtained at room temperature. Besides, the temperature stability of energy-storage density could satisfy ΔW/W100°C ≤ ±20 % when the addition of KNN was over 0.09 from 20 to 150 °C.

The Study on the Phase Transition and Piezoelectric Properties of Bi<sub>0.5</sub>(Na<sub>0.78</sub>K<sub>0.22</sub>)<sub>0.5</sub>TiO<sub>3</sub>-LaMnO<sub>3</sub> Lead-free Piezoelectric Ceramics

Bi 0.5 (Na 0.78 K 0.22 ) 0.5 TiO₃ (BNKT) lead-free piezoelectric ceramics modified by LaMnO₃ (LM) were fabricated by conventional solidstate method. The crystal structure and the morphology of the lead free ceramics were analyzed by XRD (X-ray diffraction) and FE-SEM (Field Emission Scanning Electron Microscopy). The LM modified BNKT ceramics have a phase transition from ferroelectric tetragonal to non-polar pseudo-cubic. Despite decreases in the remnant polarization (P r ) and coercive field (E c ) in the P-E hysteresis loops, the electric-field induced strain properties were significantly enhanced by the LM modification. The highest value of S max /E max = 412 pm/V at an applied electric field of 5 ㎸/㎜ was found in BNKT-0.01LM ceramic.

(Na,K)NbO3–(Bi,Na)TiO3 piezoelectric ceramics for energy-harvesting applications

A wide variety of energy harvesting materials have been investigated for renewable energy applications. Piezoelectric energy harvesters have attracted attention because of their versatility and reliability. In this work, we prepared (1−x)(Na0.5K0.5)NbO3–x(Bi0.5Na0.5)TiO3 piezoelectric ceramics through conventional mixed oxide fabrication methods with different amounts of (Bi0.5Na0.5)TiO3 and various sintering temperatures. We then analyzed the electrical and structural properties of the resulting materials in an attempt to determine the optimal fabrication conditions for enhanced piezoelectric properties. The crystalline properties and surface morphology of (1−x)(Na0.5K0.5)NbO3–x(Bi0.5Na0.5)TiO3 lead-free piezoelectric ceramics were examined via X-ray diffraction and field emission scanning electron microscopy, respectively. We systematically investigated the effect of the sintering temperature on the microstructure, piezoelectric properties, and ferroelectric properties of the materials. The output voltage generated by the (1−x)(Na0.5K0.5)NbO3–x(Bi0.5Na0.5)TiO3 ceramics was measured by a mechanical force system. Optimizing the sintering temperature improved the piezoelectric and ferroelectric properties of (1−x)(Na0.5K0.5)NbO3–x(Bi0.5Na0.5)TiO3 ceramics, increasing their viability for use in energy-harvesting applications.

The effect of CuO and NiO doping on dielectric and ferroelectric properties of Na0.5Bi0.5TiO3 lead-free ceramics

In the present work, lead-free piezoelectric ceramics (Na0.5Bi0.5)TiO3 –xCuO–yNiO (for x = 0.0, 0.02, 0.04 and 0.06) have been prepared by a conventional solid-state reaction method. An investigation of CuO and NiO doping in bismuth sodium titanate (BNT) and a study of the structure, morphology, and dielectric and ferroelectric properties of the NBT–CuNi system have been conducted. Phase and microstructural analysis of the (Na0.5Bi0.5)TiO3 (NBT) based ceramics has been carried out using X-ray diffraction and scanning electron microscopy (SEM) techniques. Field emission scanning electron microscopy (FE-SEM) images showed that inhibition of grain growth takes place with increasing Cu and Ni concentration. The results indicate that the co-doping of NiO and CuO is effective in improving the dielectric and ferroelectric properties of NBT ceramics. Temperature-dependent dielectric studies have also been carried out at room temperature to 400 °C at different frequencies. The NBT ceramics co-doped with x = 0.06 and y = 0.06 exhibited an excellent dielectric constant ϵr = 1514. The study suggests that there is enormous scope of application of such materials in the future for actuators, ultrasonic transducers and high-frequency piezoelectric devices.

Dielectric and impedance spectroscopic studies of 0.8BaTiO3–0.2Bi0.5K0.5TiO3lead-free ceramics

0.8 BaTiO3–0.2 Bi0.5K0.5TiO3(BT–BKT20) lead-free ceramics were prepared by conventional solid state reaction method followed by high energy ball milling. The formation of a single phase tetragonal structure in the material was confirmed by X-ray diffraction. Frequency and temperature-dependent dielectric studies show relaxor behavior in the BT–BKT20 which was found to obey modified Curie–Weiss law with degree of diffuseness 1.573. Complex impedance and electric modulus spectroscopy studies reveal temperature-dependent relaxation process in the material. The Cole–Cole plots were measured at high temperatures at which grain effect was observed. Impedance and electric modulus spectroscopy studies show non-Debye kind of conductivity relaxation process in the present material. Activation energies were calculated from impedance and electric modulus spectroscopy and the values of activation energy indicated that the conduction is ionic in nature. AC and DC conductivity have been measured and studied at different temperatures.

Large electric-field-induced strain in SrZrO3 modified Bi0.5(Na0.80K0.20)0.5TiO3 lead-free electromechanical ceramics with fatigue-resistant behavior

The effect of SrZrO3 (SZ) addition on the ferroelectric behavior and piezoelectric properties of Bi0.5(Na0.80K0.20)0.5TiO3 (BNKT20) lead-free piezoceramics were investigated. Results showed that BNKT20–xSZ samples underwent a phase transition from ferroelectric rhombohedral and tetragonal phases to relaxor pseudocubic phase with increasing SZ content, and such transition are accompanied with the significant disruption of ferroelectric order and the shift of the ferroelectric–relaxor transition temperature TF−R down to room temperature. Accordingly, it induced an enhancement of the field-induced strain with a peak at a value of ∼0.39% (at 80 kV/cm, corresponding to a large signal d33∗ of ∼488 pm/V) obtained in 1.5 mol%SZ-modified samples. Temperature dependent measurements of both polarization and strain suggest that the origin of the large strain is due to a reversible field-induced ergodic relaxor to ferroelectric phase transformation. Moreover, an attractive property for application as actuators was obtained in this system, as BNKT20 modified with 1.5 mol%SZ exhibits fatigue-free behavior up to 106 cycles. This exceptionally good fatigue resistance is identified due to the presence of an ergodic relaxor state.

Relaxor behavior and piezoelectric properties of Bi(Mg0.5Ti0.5)O3-modified Bi0.5Na0.5TiO3 lead-free ceramics

Lead-free (1−x)Bi0.5Na0.5TiO3−xBi(Mg0.5Ti0.5)O3 (BNT–BMT) (x=0.00−0.06) solid solutions were synthesized via a solid state processing technique, and the effects of BMT on the structural, microstructural, dielectric, ferroelectric, and piezoelectric properties were investigated. The XRD analysis demonstrated that BMT has no pronounced effect on the crystal structure of BNT in the composition range studied, where all samples consisted of a pure perovskite phase with rhombohedral symmetry. The temperature and frequency dependences of the dielectric constant revealed that the studied compositions exhibited dielectric diffuse-to-relaxor type phase transformation. The degree of deviation from the Curie–Weiss law increased with increasing BMT concentration. The addition of BMT significantly decreased the coercive field of BNT and resulted in enhanced remnant polarization and piezoelectric constant of 38µC/cm2 and 108pC/N, respectively at x=0.04. Polarization hysteresis was also measured at increased temperatures. These findings, along with the thermal hysteresis in the dielectric maximum, provide evidence for the observed diffuse-to-relaxor type phase transformation of these ceramics.

Enhanced dielectric and piezoelectric properties of Ta-doped 0.50(Na0.5Bi0.5)TiO3–0.50(K0.5Bi0.5)TiO3 lead-free ferroelectric ceramics

Ta-doped 0.50(Na0.5Bi0.5)TiO3–0.50(K0.5Bi0.5)TiO3 piezoelectric ceramics were synthesized by solid state reaction and the effect of doping concentration on dielectric, ferroelectric and electrical properties were investigated. Ta-doping showed an increase in depolarization (Td) and phase transition (Tm) temperatures; thus increasing its usable temperature range. Ferroelectric properties were also enhanced in terms of increased remnant polarization and better squareness of P–E loop. In conductivity studies, activation energy was calculated and the contribution of grains to polarization mechanism was confirmed through Nyquist plots.

Enhancement of relaxor properties by Nb doping in Ba0.8Sr0.12Ca0.08TiO3 lead-free ferroelectric ceramics

Niobium-doped barium strontium calcium titanate (BSCTN) ceramics were prepared using a conventional solid-state reaction method. The effects of Nb contents on crystal structure, microstructure, dielectric properties and ferroelectric relaxor behavior of the BSCTN ceramics were investigated. The BSCTN ceramics showed dense microstructures with uniform crystal grains with Nb doping. It was demonstrated that Nb5+ entered the B-site of the perovskite BSCTN ceramic and substituted for Ti4+, which caused the expansion and distortion of crystal lattice of the tetragonal BSCTN ceramic. Doping of Nb resulted in more diffused phase transition and lower Curie temperature of the BSCTN ceramics. The diffuseness degree indicator γ increased until the addition of Nb dopant exceeded 1.5mol% where a maximum γ of 1.98 was achieved. Among the compositions assayed in this work, the BSCTN ceramics with Nb contents of approximately 1.0–1.5mol% yielded promising relaxor properties that made them alternative sources for development of environmental friendly lead-free relaxor ferroelectric materials.

Structural, microstructure and electrical properties of La2O3-doped Bi0.5(Na0.68K0.22Li0.1)0.5TiO3 lead-free piezoelectric ceramics synthesized by the combustion technique

The effect of firing temperatures on phase formation, microstructure and physical properties of [Bi0.5(Na0.68K0.22Li0.1)0.5TiO3] doped with La2O3 at 0.1wt% (BNKLLT) ceramics prepared by the combustion method was studied. Glycine was used as fuel and the ratio of raw material (corresponding oxidant metal nitrate) with fuel was about 1:0.56. The samples were calcined at 600–900°C for 2h and sintered at 1075–1150°C for 2h. The single rhombohedral peroveskite phase of BNKLLT powders was observed from the sample calcined at 750°C for 2h. The BNKLLT ceramics exhibited a pure peroveskite phase in all samples. The microstructures of the BNKLLT powders exhibited an agglomerated form while the grain ceramics exhibited a square shape. The average particle size and average grain size increased with increasing firing temperatures. The density, dielectric constant (εr and εm), Pr and d33 tended to increase with increasing sintering temperatures up to 1100°C and then decreased. The maximum density (5.73g/cm2), maximum dielectric constant (εr~2572 and εm~5536), good ferroelectric properties (Pr~35.78µC/cm2 and Ec~22.42kV/cm) and highest d33 (210 pC/N) were obtained by the sample sintered at 1100°C for 2h.