Potassium Sodium Niobate-based Ceramics Research Articles

Effect of Sintering Conditions on the Electrical Properties of Lead-Free Piezoelectric Potassium Sodium Niobate-Based Ceramics

Lead-free piezoelectric 0.92(K0.445Na0.5Li0.05)NbO3-0.08BaZrO3 (KNLN-BZ) ceramics were prepared via conventional sintering. Single-step, 2-step and 3-step temperature-controlled conditions were designed. The structure and electrical properties of ceramics obtained using different temperature-controlled procedures were systematically studied. It was found that ceramic prepared using the 3-step method with a holding time of 20 h showed the highest electrical properties. The Curie temperature was approximately 286 °C, and the dielectric constant and dielectric loss at room temperature were 1350 and 4.5% at the frequency of 1 kHz, respectively. The highest remanent polarization, piezoelectric strain and piezoelectric coefficient, d33*, were obtained 60 °C, indicating a phase transition between ferroelectric phases. Although the ceramics did not show excellent piezoelectric properties, the 3-step sintering method can be considered an effective method to optimize the electrical performances of KNN-based ceramics. Combined with an appropriate composition, ceramics with excellent electrical properties could be obtained. This study provides a path to enhance the density and electrical properties for KNN-based ceramics with simple composition and potential for industry application.

Electric-Field-Insensitive Temperature Stability of Strain in KNN Multilayer Composite Ceramics.

The prominent advances in both piezoelectricity and temperature stability of potassium sodium niobate-based ceramics make this material system the most potential alternative to toxic lead-based families. However, previous studies have shown that the excellent temperature stability of the electrostrain can be obtained only under a high electric field. This issue can be well solved by our new proposed strategy of constructing multilayer composite ceramics, where an extremely low electric-field-dependent temperature stability of the strain can be achieved, far outperforming the results reported so far. The synergistic contributions from stacking components with different strain responses under different temperatures and electric field strengths realize the dynamic balance of electrostrain of the multilayer composite ceramics, which is also revealed by phase-field simulation. This work provides new ideas for the artificial structural design for the development of stable and reliable high-performance piezo/ferroelectric ceramics.

Optical and electrical properties of Li0.5La0.5TiO3 modified potassium sodium niobate-based ceramics

(1-x)(0.94K0.51Na0.5NbO3-0.06SrZrO3)-xLi0.5La0.5TiO3 ceramics were prepared using a conventional solid-state reaction method. The doping of LLTO can improve the density of ceramics and broaden the sintering temperature range from 20 °C to 50 °C. The average grain size is not dependent on the doping content of LLTO, but high doping content (x ≥ 0.04) leads to inhomogeneous distribution of grain size. With the sintering temperature increasing, the density of ceramics first increases and then decreases, but the grain size increases monotonously. For the sample x = 0.02, the transmittance of the ceramic sintered at 1190 °C reaches 58.5% in the visible range (the thickness of the sample is 0.3 mm), and the maximum transmittance reaches 73% in the near-infrared range. Besides, a behavior of photosensitive resistance is achieved at room temperature in the sample x = 0.02, which suggests that this system has great application prospect as a transparent ceramic.

Significant increase in comprehensive energy storage performance of potassium sodium niobate-based ceramics via synergistic optimization strategy

K0.5Na0.5NbO3 (KNN)-based ceramics are considered as one of the most promising lead-free dielectric ceramics owing to relatively high dielectric breakdown strength (DBS) resulted from their unique submicron grains. Unfortunately, it has been difficult to increase recoverable energy-storage density (Wrec) and energy-storage efficiency (η) simultaneously at present. Herein, we propose a synergistic optimization strategy, namely, simultaneously enhancing DBS by tailoring grain size to submicron scale and inducing the temperature range between the maximum dielectric permittivity temperature (Tmax) and the Burns temperature (TB) to room temperature, for solving the bottleneck. (1-x)K0.5Na0.5NbO3-xBi(Ni0.5Zr0.5)O3 (KNN-BNZ) ceramics were chosen as an example to illustrate the validity of this strategy. An ultrahigh Wrec of 8.09 J·cm−3 was obtained at the optimum composition of x = 0.15 under the electric field of 870 kV·cm−1, which is much higher than those of other reported KNN-based ceramics. Most importantly, this high Wrec was accompanied by a high η of 88.46%, which is superior to those of other KNN-based ceramics and very important for practical applications. The excellent comprehensive energy storage performance was resulted from the polar nanoregions, which is confirmed by high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM), piezo-force microscopy (PFM) and first-order reversal curve (FORC) distributions. The work not only finds out novel KNN-based ceramics with excellent comprehensive energy storage properties, but also provides a remarkable designing strategy for exploring a series of novel lead-free dielectric ceramics with high energy storage properties for practical applications in the future.

Emerging new phase boundary in potassium sodium-niobate based ceramics.

Developing eco-friendly high-performance piezoceramics without lead has become one of the most advanced frontiers in interdisciplinary research. Although potassium sodium-niobate {(K,Na)NbO3, KNN} based ceramics are believed to be one of the most promising lead-free candidates, the relatively inferior piezoelectric properties and strong temperature dependency have hindered their development for more than 50 years since being discovered in the 1950s. It was not until 2014 that our group initially proposed a new phase boundary (NPB) that simultaneously improved the piezoelectric properties and temperature stability of non-textured KNN-based ceramics to the level of partly lead-based ceramics. The NPB has been then proved by some researchers and believed to pave the way for "lead-free at last" proposed by E. Cross (Nature, 2004, 432, 24). However, the understanding of the NPB is still in its infancy, leaving many controversies, including the phase structure and physical mechanisms at the NPB as well as the essential difference when compared with other phase boundaries. In this context, we systematically summarized the origin and development of the NPB, focusing on the construction, structure and intrinsic trait of the NPB, the effects of the NPB on the performance, and the validity and related incipient devices of the NPB. Particularly, we concluded the phase structure and domain structure locating at the NPB, analyzed the physical mechanisms in depth, proposed the possible methods to further improve the performance at the NPB, and demonstrated the validity and scope of the NPB as well as the device application. Finally, we gave out our perspective on the challenges and future research of KNN-based ceramics with NPB. Therefore, we believe that this review could promote the understanding of the NPB and guide the future work of KNN-based ceramics.

Effects of MnO2 addition on the electrical properties of lead-free textured potassium sodium niobate-based ceramics

In our previous work, we developed lead-free potassium sodium niobate-based textured ceramics with a piezoelectric response (d33*) of 505 pm/V and superior thermal stabilities. However, the dielectric loss of the ceramics is 3.5% at 1 kHz which is higher than the PZT-based ceramics. To solve this problem, MnO2 was introduced into the KNLN-BZ-BNT ceramics in this work. It is found that the introduction of MnO2 does not affect the crystalline phase nor grain size. In addition, the effect of MnO2 of less than 2.0% on the texture degree is insignificant. The 0.5% and 1.0% MnO2 modified samples show similar electrical properties and thermal stability as the one without MnO2. The addition of MnO2 can reduce the dielectric loss. Compared to the ceramic with 0.5% MnO2 addition, the 1.0% MnO2-added KNLN-BZ-BNT ceramic possesses a better performance.

Decoding the Role of Diffused Multiphase Coexistence in Potassium Sodium Niobate-Based Ceramics with Nanodomains for Enhanced Piezoelectric Devices

Although multiphase coexistence endows potassium sodium niobate (KNN)-based ceramics with enhanced piezoelectric properties and promising potential in electronic devices, the physical mechanisms ar...

Thermally-induced phase transformations in KNNS-BNKZ lead-free piezoceramics

Promising piezoelectric properties have been reported in potassium sodium niobate-based ceramics by introducing Bi0.5(Na0.82K0.18)0.5ZrO3 (BNKZ) into K0.48Na0.52Nb0.95Sb0.05O3 (KNNS) solid solutions in order to control the polymorphic phase transformation temperatures. In the present study, synchrotron x-ray powder diffraction (SXPD) was employed in combination with dielectric and ferroelectric measurements in order to clarify the influence of BNKZ on the phase transition temperatures of (1-x)KNNS-(x)BNKZ ceramics (with x = 0 to 0.05). The results, presented in terms of temperature-dependent SXPD patterns, dielectric permittivity and thermal depolarisation characteristics, confirmed that polymorphic phase transformation temperatures all shifted in a systematic manner with increasing BNKZ content. Broadening of the phase transition regions was also observed with increasing BNKZ content, leading to improvements in thermal stability of the ferroelectric properties. Microstructural examination of the KNNS-BNKZ ceramics revealed the presence of core-shell microstructures; this was correlated with the presence of weak shoulders on the diffraction peaks.

Rare earth element boosting temperature stability of (K,Na)NbO3-based ceramics

It is difficult to realize the balanced development of piezoelectric response {piezoelectric constant (d33) and strain} and temperature stability of potassium-sodium niobate ceramics. Here, we constructed one kind of lead-free piezoceramic system of 0.965K0.45Na0.55Nb0.96Sb0.04O3-0.035(Bi1-xHox)0.5Na0.5HfO3, and rhombohedral & tetragonal (R-T) multiphase coexistence maintains in a wide compositional range of x = 0.05–0.55. Greatly improved temperature stability of piezoelectric response is realized by doping rare earth Ho. Excellent temperature stability of both strain and d33 mainly originates from the weak temperature dependence of domain structure as well as the increased R-T phase transition temperature. As a result, the addition of rare earth Ho can boost temperature stability of potassium-sodium niobate-based ceramics.

Understanding the piezoelectricity of high-performance potassium sodium niobate ceramics from diffused multi-phase coexistence and domain feature

Unveiling the physical mechanisms of high performance in potassium sodium niobate-based ceramics from diffused multi-phase coexistence and a single domain feature.

Electric field-induced phase transitions and composition-driven nanodomains in rhombohedral-tetragonal potassium-sodium niobate-based ceramics

The mechanisms behind the high piezoelectricity of (K,Na)NbO3-based lead-free ceramics were investigated, including electric field-induced phase transitions and composition-driven nanodomains. The construction of a rhombohedral-tetragonal (R-T) phase boundary, confirmed using several advanced techniques, allowed a large piezoelectric constant (d33) of 450 ± 5 pC/N to be obtained in (1-x)K0.4Na0.6Nb0.945Sb0.055O3-xBi0.5Na0.5(Hf1-ySny)O3 (0 ≤ x ≤ 0.06 and 0 ≤ y ≤ 0.5) ceramics possessing an ultralow ΔUT-R of 7.4 meV. More importantly, the existence of an intermediate phase, i.e., the electric-induced phase (EIP), bridging the rhombohedral R [Ps//(111)] and tetragonal T [Ps//(001)] phases during the polarization rotation was demonstrated. Striped nanodomains (∼40 nm) that easily responded to external stimulation were also observed in the ceramics with an R-T phase. Thus, the enhanced piezoelectric properties originated from EIP and the striped nanodomains.

Understanding the piezoelectric properties in potassium-sodium niobate-based lead-free piezoceramics: Interrelationship between intrinsic and extrinsic factors

Lead zirconate titanate (PZT) based ceramics are currently enjoying a wide use in piezoelectric devices despite lead toxicity. Due to growing environmental concerns, the attention on piezoelectric ceramics has been moving to lead-free materials, in particular to (K,Na)NbO3-based ceramics. Here we report a systematic evaluation of the effects of the compositional modifications on [(K0.44Na0.52Li0.04)[(Nb0.86Ta0.10Sb0.04)1-xZr5x/4]O3 lead–free piezoceramics. We show that an interrelationship between the intrinsic and extrinsic factors is the linchpin for the development of good piezoelectric properties. Hence, the stabilization of the tetragonal symmetry on the orthorhombic-tetragonal polymorphic phase boundary facilities the poling process of the system, thereby enhancing the piezoelectric response. Additionally, the microstructure appears to be related to the piezoelectric properties; i.e., the improved piezoelectric properties correlate to the increase in grain size. The results of this work could help to understand the origin of piezoelectricity in potassium–sodium niobate-based ceramics.

Effect of bismuth titanate on the properties of potassium sodium niobate-based ceramics

The effect of modifying the properties of KNN-based ceramics with Bi2Ti2O7 (BiT) been investigated in this work. The density measurements show that additions of BiT to the samples slightly increase the density values. Scanning electron microscope images of the samples indicate that the average sizes of the grains decrease with BiT addition while the volume of pores increase. X-ray diffraction results show that for (K0.5Na0.5)NbO3 based samples, a transformation from orthorhombic to pseudo-cubic phase is observed. For both K0.48Na0.48Li0.04)(Nb0.9Ta0.1)O3 and K0.48Na0.48Li0.04)(Nb0.86Ta0.1Sb0.04)O3-based compositions, the phase transition is from an orthorhombic-tetragonal coexistence to a tetragonal structure dominated phase coexistence.

Large recoverable energy storage density and low sintering temperature in potassium‐sodium niobate‐based ceramics for multilayer pulsed power capacitors

AbstractMultilayer pulsed power ceramic capacitors require that dielectric ceramics possess not only large recoverable energy storage density (Wrec) but also low sintering temperature (<950°C) for using the inexpensive metals as the electrodes. However, lead‐free bulk ceramics usually show low Wrec (<2 J/cm3) and high sintering temperature (>1150°C), limiting their applications in multilayer pulsed power ceramic capacitors. In this work, large Wrec (~4.02 J/cm3 at 400 kV/cm) and low sintering temperature (940°C) are simultaneously achieved in 0.9(K0.5Na0.5)NbO3–0.1Bi(Mg2/3Nb1/3)O3–1.0 mol% CuO ceramics prepared using transition liquid phase sintering. Wrec of 4.02 J/cm3 is 2‐3 times as large as the reported value of other (Bi0.5Na0.5)TiO3 and BaTiO3‐based lead‐free bulk ceramics. The results reveal that 0.9(K0.5Na0.5)NbO3–0.1Bi(Mg2/3Nb1/3)O3–1.0 mol% CuO ceramics are promising candidates for fabricating multilayer pulsed power ceramic capacitors.

Superior Piezoelectric Properties in Potassium-Sodium Niobate Lead-Free Ceramics.

A superior piezoelectric coefficient (d33 = 570 ± 10 pC N"1 ), the highest value reported to date in potassium-sodium niobate-based ceramics, is obtained in (1-x-y)K1-w Naw Nb1-z Sbz O3-y BaZrO3-x - Bi0.5 K0.5 HfO3 ceramics. This high d33 value can be ascribed to the co-existence of "nano-scale strain domains" (1-2 nm) and a high density of ferroelectric domain boundaries. Therefore, ternary KNN-based ceramics demonstrate the potential for applications.

Identification of Phase Boundaries and Electrical Properties in Ternary Potassium-Sodium Niobate-Based Ceramics

A large piezoelectric constant (d33) of ∼480 pC/N was attained in new ternary (1-x-y)K0.5Na0.5Nb0.96Sb0.04O3-xBaSnO3-yBi0.5Na0.5ZrO3 ceramics by forming rhombohedral-orthorhombic-tetragonal (R-O-T) phase boundary using the variations of x and y, and such a phase boundary was successfully confirmed by the convergent beam electron diffraction (CBED) patterns. For (1-x)K0.5Na0.5Nb0.96Sb0.04O3-xBaSnO3, the orthorhombic (O) phase is well-maintained for 0 ≤ x ≤ 0.015, and both the R and T phases can be introduced to (0.99-y)K0.5Na0.5Nb0.96Sb0.04O3-0.01BaSnO3-yBi0.5Na0.5ZrO3 with y = 0.025-0.04 by simultaneously tailoring their compositions (x and y); then, R-O-T multiphases can be well-established. The CBED patterns strongly support the existence of R-O-T multiphases in the ceramics with y = 0.035. When the phase transitions endure from O to R-O-T, their piezoelectric activity endures a leapfrog development from ∼165 to ∼480 pC/N. In the region of the R-O-T phase boundary, a large d33 of ∼480 pC/N was attained in the ceramics with x = 0.01 and y = 0.035. In addition, the ceramics with x = 0.01 and y = 0.04 possess a high strain of ∼0.274% due to the multiphases coexistence. According to the variations of dielectric and ferroelectric properties, the enhancement in εr and Pr plays a part in the improved d33 except for the R-O-T phase boundary. We believe that the (K, Na)NbO3 ternary systems can be used to promote piezoelectric activity by forming new phase boundaries.

Phase structure and piezoelectric properties of (1−x)K0.48Na0.52Nb0.95Sb0.05O3-x(Bi0.5Na0.5)0.9(Li0.5Ce0.5)0.1ZrO3 lead-free piezoelectric ceramics

(1−x)K0.48Na0.52Nb0.95Sb0.05O3-x(Bi0.5Na0.5)0.9(Li0.5Ce0.5)0.1ZrO3 [(1−x)KNNS-xBNLCZ] lead-free piezoceramics were prepared by the conventional solid state sintering method. The effects of BNLCZ contents on their phase structure, microstructure, and piezoelectric properties were investigated. All the samples show a pure perovskite structure, and no secondary phases were formed in the detected range. The rhombohedral and tetragonal phases of (1−x)KNNS-xBNLCZ coexist in the composition range of 0.0325 ≤ x ≤ 0.0425 at room temperature. A remarkably strong piezoelectricity was obtained by the addition of appropriate BNLCZ contents. The excellent piezoelectric properties of the ceramics with x = 0.04 were obtained: d33 ∼ 485 pC/N, kp ∼ 48%, and TC ∼ 227 °C. All the results show that the introduction of (Bi0.5Na0.5)0.9(Li0.5Ce0.5)0.1ZrO3 is a very effective way to form the rhombohedral and tetragonal phase coexistence of potassium-sodium niobate-based ceramics, which can improve its piezoelectric properties.

Enhanced piezoelectricity over a wide sintering temperature (400–1050 °C) range in potassium sodium niobate-based ceramics by two step sintering

In this study, we achieved an enhanced d33 of 350–400 pC N−1 in the dense 0.96(K0.4Na0.6)(Nb0.96Sb0.04)O3–0.04Bi0.5K0.5Zr0.9Sn0.1O3 ceramics over a wide sintering temperature range of 400–1050 °C by two-step sintering.

A Shear-Mode Ultrasonic Motor Using Potassium Sodium Niobate-Based Ceramics with High Mechanical Quality Factor

(K,Na)NbO3–LiNbO3–CuO lead-free piezoelectric ceramics that show a high mechanical quality factor Qm were synthesized and used as a drive element of an ultrasonic motor. The Qm of the (K,Na)NbO3 ceramic could be enhanced by chemical modification using Li and Cu as well as microstructure control to obtain ceramics with fine grains. The grain size dependence of the Qm was consistent with a model based on the formation of internal bias field to stabilize the domain structure. A shear mode was used to drive the ultrasonic motor because the piezoelectric d31 and d33 constants of the ceramics were not sufficient for the motor applications. A shear-mode motor driven with four piezoelectric ceramic plates was developed using the lead-free ceramics with a high Qm of 1400, a high d15 of 207 pC/N, and a high k15 of 0.72. The highest revolution speed of 486 rpm was achieved at 34.5 kHz with the input voltage of approximately 180 Vp–p (peak to peak).

Crack detection in silicon nitride by acoustic microscopy : Lawrence, C.W.; Scruby, C.B.; Briggs, G.A.D.; Dunhill, A. United Kingdom Atomic Energy Authority, Harwell, AERE-R-13196, 22 pp. (Dec. 1988)

Lead zirconate titanate (PZT) based ceramics are currently enjoying a wide use in piezoelectric devices despite lead toxicity. Due to growing environmental concerns, the attention on piezoelectric ceramics has been moving to lead-free materials, in particular to (K,Na)NbO3-based ceramics. Here we report a systematic evaluation of the effects of the compositional modifications on [(K0.44Na0.52Li0.04)[(Nb0.86Ta0.10Sb0.04)1-xZr5x/4]O3 lead–free piezoceramics. We show that an interrelationship between the intrinsic and extrinsic factors is the linchpin for the development of good piezoelectric properties. Hence, the stabilization of the tetragonal symmetry on the orthorhombic-tetragonal polymorphic phase boundary facilities the poling process of the system, thereby enhancing the piezoelectric response. Additionally, the microstructure appears to be related to the piezoelectric properties; i.e., the improved piezoelectric properties correlate to the increase in grain size. The results of this work could help to understand the origin of piezoelectricity in potassium–sodium niobate-based ceramics.