ZrO3 Lead-free Ceramics Research Articles

Enhancement of Density and Piezoelectric Properties of 0.96(K0.456Na0.536)Nb0.95Sb0.05-0.04Bi0.5(Na0.82K0.18)0.5ZrO3 Lead-Free Piezoelectric Ceramics through Two-Step Sintering Method

Enhancement of Density and Piezoelectric Properties of 0.96(K0.456Na0.536)Nb0.95Sb0.05-0.04Bi0.5(Na0.82K0.18)0.5ZrO3 Lead-Free Piezoelectric Ceramics through Two-Step Sintering Method

Electrical Performance and Conduction Mechanism of Potassium Sodium Niobate-Based Lead-Free Piezoceramics via Two-Step Sintering Route

(1-x)(Li0.02Na0.48K0.48Ag0.02)(Nb0.95Sb0.05)O3-x(Ba0.4Bi0.3Na0.3)ZrO3 (LNKANbS-xBBiNZ, x = 0.04, 0.045, 0.05, 0.055 and 0.06) lead-free piezoelectric ceramics were prepared by the conventional solid-state reaction method via the two-step sintering route. The effects of the content of BBiNZ on electrical properties and microstructural morphology of the LNKANbS-xBBiNZ ceramics were studied systematically. The designing of forming rhombohedral-tetragonal phase boundary in the LNKANbS-xBBiNZ system is confirmed by XRD Rietveld refinement and Raman spectroscopy, whose phase proportion is affected greatly by the BBiNZ amount. The LNKANbS-xBBiNZ ceramics exhibit complicated dielectric behavior, whose dielectric response characteristic can be fitted by the quadratic law and the Curie-Weiss law, and both having some deviation. The high-temperature conductivity of the LNKANbS-0.045BBiNZ ceramics is controlled by oxygen vacancies detected by both conductive activation energy and relaxation activation energy fitting. The LNKANbS-0.045BBiNZ ceramics exhibit excellent electrical properties, correlating with appropriate R-T phase composition proportion and improved densification and microstructural homogeneity obtained by adjusting the BBiNZ content and using the two-step sintering method.

Grain Growth Behavior and Electrical Properties of 0.96(K0.46-xNa0.54-x)Nb0.95Sb0.05O3-0.04Bi0.5(Na0.82K0.18)0.5ZrO3 Ceramics.

This study investigated the causes of microstructural changes and the resultant electrical properties according to the sintering temperature of 0.96(K0.46−xNa0.54−x)Nb0.95Sb0.05O3-0.04Bi0.5(Na0.82K0.18)0.5ZrO3 lead-free ceramics by analyzing the correlation between vacancy concentrations and 2D nucleation. When sintered for 4 h, no grain growth occurred for the x = 0.000 composition over a wide temperature range, demonstrating that the existence of initial vacancies is essential for grain growth. As x increased, that is, as the vacancy concentration increased, the critical driving force (ΔGC) for 2D nucleation decreased, and abnormal grain growth was promoted. The number and size of these abnormal grains increased as the sintering temperature increased, but at sintering temperatures above 1100 °C, they decreased again owing to a large drop in ΔGC. The x = 0.005 specimen sintered at 1085 °C exhibited excellent piezoelectric properties of d33 = 498 pC/N and kp = 0.45 due to the large number of large abnormal grains with an 83% tetragonal phase fraction. The x = 0.000 specimen sintered at 1130 °C with suppressed grain growth exhibited good energy storage properties because of its very high relative density and small grain size of 300 to 400 nm.

Polymorphic Phase Transition and Domain Configurations of (K, Na)NbO3-Based Lead-Free Ceramics Modified by (Ba0.6Ca0.4)ZrO3

In this work, (1−x)(K0.5Na0.5)(Nb0.96Sb0.04)−x(Ba0.6Ca0.4)ZrO3 lead-free piezoelectric ceramics were prepared by a conventional solid-state sintering method. The relationship between the composition, structure and performance of the system was analyzed specifically. A polymorphic phase transition with rhombohedral-tetragonal (R-T) was formed in the sample with x = 0.3 at the room temperature (∼27 °C), which was tested by X-ray diffraction (XRD) and the temperature-dependent dielectric behavior. The high-density polar nanodomain regions were observed through Transmission Electron Microscope (TEM) in the sample with x = 0.3. Thanks to the rotation of the domain and the movement of the domain wall, the piezoelectric performance was improved, the ceramics with x = 0.3 possess enhanced piezoelectric properties of d 33 ∼ 325 pC/N together with a high Curie temperature of T c ∼ 335 °C. Furthermore, the thermal stability in the sample with x = 0.3 can be enhanced to (Δd 33/Δd 33(25 °C) ∼ 12.54%), exhibiting good temperature stability, which guarantees the ceramics could be used in a wide temperature rage.

Phase evolution and associated electrical properties of Al-doped KNN–Bi0.5Na0.5ZrO3 lead-free piezoelectric ceramics

Samples of Al-doped (1–x)K0.5Na0.5Nb0.965Sb0.035O3–x(Bi0.82Al0.18)0.5Na0.5ZrO3 [((1–x)KNNS–xBANZ)] (x = 0.02, 0.03, 0.04, and 0.05) have been prepared by a conventional solid-state method. The results of XRD analysis suggest that the ceramics underwent a typical phase transition from orthorhombic (O) to tetragonal (T) as x was increased. According to the Raman shifts of key vibrational modes, lattice deformation and associated phase transition have been qualitatively deduced. Moreover, the ceramic with x = 0.05 exhibits enhanced piezoelectric properties compared with K0.5Na0.5NbO3 due to an O-T phase boundary (d33 ≈ 258 pC/N and kp ≈ 0.40). More importantly, the mechanism through which small ions function in a KNN lattice, as well as the phase transition, is addressed herein.

Enhanced piezoelectric properties in 0.96(K0.48Na0.52)(Nb1−xTax)O3–0.04(Bi0.5Ag0.5)ZrO3 lead-free ceramics

0.96(K0.48Na0.52)(Nb1−xTax)O3–0.04(Bi0.5Ag0.5)ZrO3 lead-free ceramics were fabricated by solid-state reaction method. Because of the sensitive energy state in the coexisting phase structure, the addition of Ta5+ caused a palpable phase transformation from orthorhombic to tetragonal. At the same time, doping with (Bi0.5Ag0.5)ZrO3 could have effectively promoted densification and continued to enhance the piezoelectric and dielectric properties. Enhanced dielectric/ferroelectric properties were achieved for the ceramics which has a composition of (x = 0.15), and the ceramics expressed a high d33 of ∼ 373 pC/N with a TC of ∼ 255 °C. We believe that to design a binary phase system is a valid method to attain both large d33 and high TC in (K,Na)NbO3 (KNN)-based lead-free ceramics.

Phase structure regulation and enhanced piezoelectric properties of Li-doped KNN-based ceramics

0.96(K0.48Na0.52-xLix)NbO3-0.04Bi0.5Na0.5ZrO3 (KNLxN-BNZ) lead-free ceramics have been synthesized by traditional solid-state reaction. Here, the relationship between phase composition and piezoelectric performance of ceramics is explored systematically. Analysis of XRD and Raman spectroscopy confirmed that the orthogonal (O) phase and the tetragonal (T) phase coexisted in each sample at room temperature. By studying the function curve of temperature and dielectric constant εr, it is found that the introduction of Li+ in ceramics can have a lower O-T phase transition temperature (TO-T) and a higher Curie temperature (TC), with the TO-T closest to room temperature and the highest coexistence volume proportion of O-T phase in the ceramic when x = 0.03, which had the optimum values for d33 = 252 pC/N and TC = 382 °C. Due to the excellent piezoelectric properties and high TC, it is believed that KNLxN-BNZ piezoceramics can have great application prospects at high temperatures.

Electrical properties and luminescence properties of 0.96(K0.48Na0.52)(Nb0.95Sb0.05)\u20130.04Bi0.5(Na0.82K0.18)0.5ZrO3-xSm lead-free ceramics

In this paper, Sm-doped 0.96(K0.48Na0.52)(Nb0.95Sb0.05)–0.04Bi0.5(Na0.82K0.18)0.5ZrO3 (abbreviated as KNSN–0.04BNKZ) lead-free piezoelectric ceramics were prepared by conventional solid-state sintering method and the effects of Sm2O3 on the phase structure, microstructure, electrical and luminescent properties of KNSN–0.04BNKZ potteries were studied. Results revealed that a single solid solution phase with pseudo-cubic perovskite structure was formed between KNSN–0.04BNKZ and Sm2O3. Existence of weak dielectric/ferroelectric properties with a diffuse dielectric anomaly and slim P–E hysteresis loops of the Sm-doped KNSN–0.04BNKZ demonstrated the ferroelectric relaxor behavior of the KNNS–0.04BNKZ–xSm ceramics. Accordingly, the temperature stability and fatigue behavior of the modified ceramics were significantly improved. It was found that the KNSN–0.04BNKZ ceramics with 0.002 mol Sm addition exhibited nearly temperature independent properties and fatigue-free behavior. Moreover, Sm-modified KNSN–0.04BNKZ exhibits a bright photoluminescence with a strong orange emission under visible light irradiation. As a material with both electrical and luminescent properties, it has good application prospect in future optoelectronic components by integrating its luminescent and electrical properties.

Phase structure, electrical properties, and component stability in (1 − x)K0.40Na0.60Nb0.96Sb0.04O3–x(Bi0.92Nd0.08)0.5Na0.5ZrO3 lead-free ceramics

(1 − x)K0.40Na0.60Nb0.96Sb0.04O3–x(Bi0.92Nd0.08)0.5Na0.5ZrO3 (KNNS–xBNNZ) lead-free piezoceramics have been synthesized by a conventional solid state sintering method, and the effects of BNNZ content on their phase structure and electrical properties were investigated. The phase boundary of rhombohedral–orthorhombic–tetragonal (R–O–T) has been formed in the composition range of 0.030 ≤ x ≤ 0.040. An optimal comprehensive performance (e.g., d33 ~ 470 ± 10 pC/N, kp ~ 0.50 ± 0.02, TC ~ 283 °C, er ~ 1950, tanδ ~ 0.043, Strain ~ 0.135%, and d33* ~ 450 pm/V) is obtained in the ceramics with x = 0.035. Moreover, a relatively good component stability of piezoelectric properties (d33 ~ 402–470 pC/N, kp ~ 0.485–0.524, Strain ~ 0.133–0.135%, and d33* ~ 443–450 pm/V) is gained in a broad component range from 0.030 to 0.045, which is benefited from the contribution of multiphase boundary (R–O–T, R–T). Therefore, we believe that KNNS–xBNNZ ceramics opens a window for the practical applications in piezoelectric material markets.

Improving densification and electrical properties of KNN-based lead-free piezoceramics via two-step sintering method

ABSTRACTThe 0.95(Li0.03Na0.5K0.47)(Nb0.92Sb0.05Ta0.03)O3-0.05(Ba0.5Ca0.5)ZrO3 (LNKNST-BCZ) lead-free piezoelectric ceramics were prepared by the conventional ceramic processing via the two-step sintering method. The phase structure purity and electrical properties of the LNKNST-BCZ ceramics can be improved further by tailoring the sintering temperature and sintering time. Rather pure perovskite structure with the coexistence of ferroelectric rhombohedral (R) and tetragonal (T) phases can be obtained in the LNKNST-BCZ ceramics via the two-step sintering method confirmed by the X-ray diffraction (XRD) analysis. Sintered at optimized conditions the LNKNST-BCZ ceramics present high densification and rather homogeneous microstructure morphology. The Curie-Weiss law and the quadratic law fitting prove that the dielectric behavior of the LNKNST-BCZ ceramics approaches closer to the normal ferroelectrics with slight diffused phase transition characteristic. The LNKNST-BCZ ceramics sintered at 1180°C for 0.5 h exhibit the optimum dielectric, ferroelectric and piezoelectric properties. The improvement of the densification and piezoelectric properties of the LNKNST-BCZ ceramics can be attributed to the polymorphic R-T phase boundary and densified microstructure morphology induced by (Ba0.5Ca0.5)ZrO3 (BCZ) doping and two-step sintering method.

Dielectric properties of (K0.5Na0.5)NbO3–(Bi0.5Li0.5)ZrO3 lead-free ceramics as high-temperature ceramic capacitors

(1 − x)K0.5Na0.5NbO3–x(Bi0.5Li0.5)ZrO3 (labeled as (1 − x)KNN–xBLZ) lead-free ceramics were fabricated by a solid-state reaction method. A research was conducted on the effects of BLZ content on structure, dielectric properties and relaxation behavior of KNN ceramics. By combining the X-ray diffraction patterns with the temperature dependence of dielectric properties, an orthorhombic–tetragonal phase coexistence was identified for x = 0.03, a tetragonal phase was determined for x = 0.05, and a single rhombohedral structure occurred at x = 0.08. The 0.92KNN–0.08BLZ ceramic exhibits a high and stable permittivity (~ 1317, ± 15% variation) from 55 to 445 °C and low dielectric loss (≤ 6%) from 120 to 400 °C, which is hugely attractive for high-temperature capacitors. Activation energies of both high-temperature dielectric relaxation and dc conductivity first increase and then decline with the increase of BLZ, which might be attributed to the lattice distortion and concentration of oxygen vacancies.

Multi-phase structure and electrical properties of Bi0.5Li0.5ZrO3 doping K0.48Na0.56NbO3 lead-free piezoelectric ceramics

(1–x)K0.48Na0.56NbO3–xBi0.5Li0.5ZrO3 (KNN–xBLZ, x = 0–0.06) lead-free piezoelectric ceramics were prepared by the conventional solid-state sintering method, and their phase structures and electric properties as well as TC were systematically investigated. The orthorhombic–tetragonal (O–T) two phases were detected in all (1–x)K0.48Na0.56NbO3–xBi0.5Li0.5ZrO3 ceramics at 0.01 ≤ x ≤ 0.05. Due to the appropriate ratio between O phase and T phase (CO/CT= 45/55), high piezoelectric properties of d33 = 239 pC/N, kp = 34%, and Pr = 25.23 μC/cm2 were obtained at x = 0.04. Moreover, a high TC = 348°C was also achieved in KNN–xBLZ ceramic at x = 0.04. These results indicate that (1–x)K0.48Na0.56NbO3–xBi0.5Li0.5ZrO3 system is a promising candidate for high-temperature piezoelectric devices.

Balanced development of piezoelectricity and Curie temperature in (1 − x)K0.44Na0.52Li0.04Nb0.96Sb0.04O3–xBi0.25Na0.25Ba0.5ZrO3 lead-free piezoelectric ceramics

(1 − x)K0.44Na0.52Li0.04Nb0.96Sb0.04O3–xBi0.25Na0.25Ba0.5ZrO3 [(1 − x)KNLNS-xBNBZ] (0 ≤ x ≤ 0.05) lead-free piezoelectric ceramics were prepared by using the conventional solid-state reaction method. The relationships among the composition, phase structure, phase volume fraction, microstructure, dielectric, ferroelectric, and piezoelectric properties as well as the phase diagram are established. Rietveld refinements of X-ray diffraction patterns show that with increasing doping level the volume fractions of the orthorhombic and tetragonal phases evolve from 58.7 and 41.3% for x = 0 to 1.7 and 98.3% for x = 0.05, which has strong impacts on the piezoelectric coefficient d 33 and Curie temperature T C. Upon the doping of BNBZ an orthorhombic-tetragonal (O–T) phase boundary forms near room temperature, resulting in an optimum d 33 ~ 288 pC/N, T C ~ 305 °C, a converse piezoelectric coefficient d 33 * ~ 391 pm/V, and a field-induced strain S ~ 0.156% for the x = 0.035 ceramics. These results demonstrate that a balanced development of d 33 and T C can be realized by choosing suitable doping materials and content.

Enhanced electrical properties, phase structure, and temperature-stable dielectric of (K0.48Na0.52)NbO3-Bi0.5Li0.5ZrO3 ceramics

(1-x)(K0.48Na0.52)NbO3-xBi0.5Li0.5ZrO3 (KNN-xBLZ, 0 ≤ x ≤ 0.05) lead-free ceramics were prepared by the conventional solid-state technique. The evolution of their phase structure and electrical properties was systematically investigated as a function of the amount of BLZ. An orthorhombic-tetragonal (O-T) phase was found in the composition range of 0.02 ≤ x ≤ 0.05, and obtained an enhanced electrical property (e.g., d33 ~ 265 pC/N, kp ~ 36.5%, TC ~ 364°C, εr ~ 1210, tan δ ~ 0.032, and Pr ~ 27.5μC/cm2) in the ceramics with x = 0.03. Notably, a good temperature-stable dielectric [εr(300°C) / εr(20°C) ≈ 1.07%] was observed in a broad temperature range from 20°C to 300°C at x =0.03, which was benefited from the contributions of TO-T closing to the room temperature and high TC to avoid the sudden change in dielectric properties at the temperature range of 20–300°C, indicating that such a material may have great potential for high temperature applications.

Modification of microstructure and electrical properties in (K,Na)NbO3-(Ba,Ca)ZrO3 ceramics by changing K/Na ratio

ABSTRACT0.94(KxNa1-x)NbO3-0.06Ba0.8Ca0.2ZrO3 lead-free ceramics were prepared by the conventional solid-state method, and the effects of K/Na ratio on their piezoelectric properties were investigated in detail. Their grain sizes gradually decrease as the K/Na contents reach 60/40. By optimizing the K/Na ratio, an optimum piezoelectric behavior of d33∼270 pC/N and kp∼45% can be observed in the ceramics with x = 0.48. In addition, its piezoelectric activity was also strongly sensitive to the sintering temperatures and poling conditions, that is, d33 increases from 120 pC/N to 270 pC/N by a sintering temperature of 1160 °C and an optimum poling condition of >120 °C and 3 kV/mm. As a result, the modification of K/Na ratio is an effective way to further improve piezoelectric properties of KNN ceramics.

Composition dependence of phase boundary and electrical properties in lead-free (K0.5Na0.5)(Nb0.96Sb0.04)O3–Bi0.5Na0.5ZrO3–Bi0.5Li0.5ZrO3 ceramics

In this work, (K0.5Na0.5)(Nb0.96Sb0.04)O3–Bi0.5Na0.5ZrO3–Bi0.5Li0.5ZrO3 lead-free ceramics were fabricated by the conventional solid-state method, and effects of Bi0.5Li0.5ZrO3 on their phase structure and electrical properties were studied. Their piezoelectric properties are sensitive to the addition of Bi0.5Li0.5ZrO3 as well as its contents. The addition of Bi0.5Li0.5ZrO3 simultaneously increased their Curie temperature and decreased rhombohedral and tetragonal phase transition temperature. Their dielectric, ferroelectric, and piezoelectric properties were strongly dependent on Bi0.5Li0.5ZrO3 contents. With increasing Bi0.5Li0.5ZrO3 contents, their dielectric loss can be decreased, and their k p and P r values can be further optimized. However, their e r and d 33 slightly decreased with the increase of Bi0.5Li0.5ZrO3 contents due to the deviation of rhombohedral and tetragonal phase boundary, and the ceramics with x ≤ 0.2 exhibited a high d 33 of >410 pC/N. As a result, this work could further understand the role of Bi0.5Li0.5ZrO3 in electrical properties of high-performance alkali niobate ceramics.

Phase structure and enhanced piezoelectric properties in (1-x)(K0.48Na0.52)(Nb0.95Sb0.05)O3-x(Bi0.5Na0.42Li0.08)0.9Sr0.1ZrO3 lead-free piezoelectric ceramics

The piezoelectric properties of KNN lead-free piezoelectric ceramics could be greatly enhanced by forming multiphase coexistence. In this work, binary system (1-x)(K0.48Na0.52)(Nb0.95Sb0.05)O3-x(Bi0.5Na0.42Li0.08)0.9Sr0.1ZrO3 [(abbreviated as (1-x)KNNS-xBNLSZ] ceramics with rhombohedral-tetragonal (r-T) phase boundary was designed and synthesized using the conventional solid-state sintering method, and effects of BNLSZ contents on their micrograph, phase structure and electrical properties were also investigated. According to phase diagram from the results of temperature-dependent capacitance and dielectric constant, the ceramics exhibit the R-T phase coexistence in the composition range of 3.5%≤x<4.5%, and an enhanced dielectric, ferroelectric, and piezoelectric behavior was obtained at such a phase boundary zone. As a result, the ceramics with x=0.04 exhibit optimum electrical properties of d33~461pC/N, kp~46%, tan δ~0.03, Pr~16.9μC/cm2, and Ec ~9kV/cm, together with a Curie temperature (TC) of ~228°C. Such a good comprehensive performance obtained in this present work is due to the R-T phase transition and enhanced ɛrPr. It was believed that this ceramic system would promote the development of KNN-based lead-free ceramics.

Phase structure and electrical properties of (1 − x)K0.48Na0.52NbO3–xBi0.46La0.04(Na0.82K0.18)0.5ZrO3 lead-free piezoceramics

In this work, (1 − x)K0.48Na0.52NbO3–xBi0.46La0.04(Na0.82K0.18)0.5ZrO3 (abbreviated as KNN–xBLNKZ) lead-free piezoelectric ceramics were fabricated by using the conventional solid-state method. The phase structure, microstructure, and electrical properties of KNN–xBLNKZ ceramics have been investigated. Both large piezoelectric coefficient (d33 ~368 pC/N) and high Curie temperature (TC ~323 °C) can be achieved for the composition of x = 0.050 with rhombohedral–orthorhombic–tetragonal (R–O–T) multi ferroelectric phases coexistence near room temperature. In addition, a good thermal stability of piezoelectricity can also be observed in this composition (e.g., d33 ≥ 308 pC/N, Ta ≤ 300 °C). Therefore, we believe that this material system is a promising lead-free piezoelectric candidate for the high-temperature piezoelectric applications.

Effect of (Co1/3Sb2/3) complex doping on the structure and electrical properties of 0.96(K0.49Na0.51)(Nb0.97Ta0.03)O3–0.04Bi0.5Na0.5ZrO3 lead-free piezoelectric ceramics

0.96(K0.49Na0.51)(Nb0.97−x (Co1/3Sb2/3) x Ta0.03)O3–0.04Bi0.5Na0.5ZrO3 (abbreviated as 0.96KNNT-CS x –0.04BNZ, x = 0.000, 0.002, 0.004, 0.006, 0.008, 0.010) lead-free piezoelectric ceramics were prepared via a solid state reaction method. The effect of (Co1/3Sb2/3) doping amount x on the structure and electrical properties of the ceramics was investigated. The XRD patterns showed the formation of a pure perovskite structure with the coexistence of orthorhombic and tetragonal phases over the whole compositions. However, the vibrational modes slightly shift towards lower frequencies with the increase of x value in the Raman scattering spectra, indicating that the (Co1/3Sb2/3) should be incorporated into the perovskite lattice. The optimal electrical properties obtained in the ceramics with x = 0.008 were as follows: piezoelectric coefficient d 33 = 347 pC/N, planar electromechanical coupling coefficient k p = 42.9 %, mechanical quality factor Q m = 47, dielectric permittivity \( \varepsilon_{33}^{T} /\varepsilon_{0} \) = 1435, dielectric loss tanδ = 2.7 %, and Curie temperature T c = 303 °C.

Phase Structures and Piezoelectric Properties of (K,Na,Li)(Nb,Sb)O3-(Bi,Ag)ZrO3 Lead-Free Ceramics

Samples in the pseudoternary lead-free piezoelectric ceramic system 0.94KNN-(0.06 − x)LiSbO3-x(Bi0.5Ag0.5)ZrO3 were prepared using a solid-state reaction technique and their phase transition behavior and electrical properties studied. Results showed that BAZ diffuses into KNN-LS to form a new solid solution, and induces a phase transition from tetragonal to rhombohedral phase with increase of x. At 0.02 ≤ x ≤ 0.03, coexistence of tetragonal and rhombohedral phases is observed, and enhanced piezoelectric properties are achieved in this composition range due to the polymorphic phase transition near room temperature. Doping with (Bi0.5Ag0.5)ZrO3 effectively promotes densification and further enhances the piezoelectric and dielectric properties of of the ceramics. Moreover, the ceramic with x = 0.025 possesses excellent electrical properties of kp = 42.3%, \({d_{33}^{*}}\) = 320 pm/V and d33 = 235 pC/N, tan δ = 0.039, and Tc = 326°C. This result indicates that 0.94KNN-0.035LS-0.025BAZ ceramic is a promising lead-free material for practical applications.