Niobate-based Ceramics Research Articles

Effect of rare-earth doping on the dielectric property and polarization behavior of antiferroelectric sodium niobate-based ceramics

The lead-free 0.96NaNbO3-0.04CaSnO3 ceramics with rare-earth dopants (La, Sm and Lu) (NCLn100x) were prepared and characterized. It is found that a certain amount of La substitution stabilizes the antiferroelectric (AFE) phase but alleviates the lattice distortion in the fresh samples. Re-entrant-like characteristics are observed in the temperature – dielectric constant curves with the room temperature P phase gradually replaced by a possible R phase. Relaxor-like hysteresis loops with suppressed hysteresis loss and remanent polarization were obtained at high La content, achieving a relatively high Wre of 2.1 J/cm3 at a low electric field (250 kV/cm). The relaxation behaviors of the ferroelectric (FE) domain measured by piezoresponse force microscopy suggest an even long characteristic relaxation time of field-induced FE phase, which is different from the situations of other AFE perovskites. Via an explanatory defected diatomic chain model, we propose that a much larger mass of substitutive ion than the origin one helps to induce low-frequency localized mode, which is believed to be in favor of the formation of polar nano-regions and hence strengthens the dynamic stability of FE phase during electric field loading. Our research provides a further understanding of the tuning strategy for enhancing the antiferroelectricity of the NaNbO3-based system.

Phase evolution and associated high piezoelectric properties of sodium potassium niobate-based piezoelectric ceramics

Abstract (1-x)K0.5Na0.5Nb0.965Sb0.035O3-x (Bi0.9Al0.1)0.5Na0.5Zr0.42Hf0.58O3 [abbreviated as (1-x)KNNS-xBANZH] ceramics were synthesized by conventional solid reaction method to investigate combined effects of Al and Hf on electrical properties of sodium potassium niobate-based ceramics. The results showed that rhombohedral-tetragonal (R-T) phase boundary was constructed at x = 0.04–0.05 through co-doping, which was demonstrated by refined X-ray diffraction patterns, Raman spectra, transmission electron microscope analysis and temperature-dependent dielectric constants. Consequently, the ceramics with x = 0.045 exhibited significantly improved piezoelectric properties (d33∼451 pC/N, d∗33–404 p.m./V and kp∼0.46). According to calculated intrinsic piezoelectric constants (dinit) by Rayleigh law, reversible non-180° domain motion and efficient domain wall motion were of essential importance for x = 0.045, which also contributed a lot to d∗33. Together with scanning electron microscope analysis, R-T phase coexistence and fine grains accounted for the property enhancement. As a result, the addition of (Bi0.9Al0.1)0.5Na0.5Zr0.42Hf0.58O3 [abbreviated as BANZH] is an effective method to promote electrical properties of K0.5Na0.5Nb0.965Sb0.035O3 [abbreviated as KNNS] piezoceramics and the ceramics with optimized electrical properties can be treated as promising candidates for Pb-based piezoceramics in some usage fields.

Piezoelectric and electrocaloric properties of high performance potassium sodium niobate-based lead-free ceramics

Piezoelectric ceramics, as a kind of functional material, can realize the mutual transformation between mechanical energy and electrical energy, and has been widely used in civil and military fields. With the improvement of people's awareness of environment protection and self-health care, the study of lead-free piezoelectric ceramics with excellent performance and environmental friendliness has become an urgent task. Among several kinds of lead-free piezoelectric materials, potassium sodium niobate [(K, Na)NbO<sub>3</sub>, KNN]-based ceramics has attracted much attention due to its good comprehensive properties, but there have been carried out few studies focusing on the utilization of phase boundary to regulate the properties of high piezoelectric and electrocaloric effect simultaneously. In this work, lead-free 0.944K<sub>0.48</sub>Na<sub>0.52</sub>Nb<sub>0.95</sub>Sb<sub>0.05</sub>O<sub>3 </sub>-0.04Bi<sub>0.5</sub>(Na<sub>0.82</sub>K<sub>0.18</sub>)<sub>0.5</sub>ZrO<sub>3</sub>-1.6%(Ag<i><sub>x</sub></i>Na<sub>1–</sub><i><sub>x</sub></i>)SbO<sub>3</sub>-0.4%Fe<sub>2</sub>O<sub>3</sub> ceramics is prepared via the conventional solid-state method, and the effect of AS/NS ratio on phase structure, electrical properties, and electrocaloric effect are studied. The obtained results show that the ceramics has a multiphase coexistence with “rhombohedral-orthorhombic-tetragonal” (R-O-T) in all compositions. With the increase of AS content, the piezoelectric and ferroelectric properties of the ceramics fluctuate (<i>d</i><sub>33</sub> = 518–563 pC/N, <i>k</i><sub>p</sub> = 0.45–0.56; <i>P</i><sub>max</sub> = 21–23 μC/cm<sup>2</sup>, <i>P</i><sub>r</sub> = 14–17 μC/cm<sup>2</sup>). In addition, the electrocaloric effect (ECE) for each of the samples is studied by the indirect method. Broadening temperature span (～90 K) of electrocaloric effect is obtained in the vicinity of O-T phase transition region, while a low ECE value is observed. A stronger ECE peak (Δ<i>T</i><sub>max</sub> > 0.6 K) can be observed when the measurement temperature reaches near the Curie temperature. Consequently, both large piezoelectric property and high electrocaloric performance can be realized in KNN-based ceramics by new phase boundary construction.

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.

Dielectric and ferroelectric properties of CuO-doped lead magnesium niobate-based relaxor ferroelectric ceramics

In this work, we report the dielectric and ferroelectric properties of CuO-doped ([Formula: see text])[0.5573Pb(Mg[Formula: see text]Nb[Formula: see text])O3-0.4427PbTiO3]-[Formula: see text]Ba(Zn[Formula: see text]Nb[Formula: see text]O3 (PMNT-[Formula: see text]BZN) relaxor ferrielectric ceramic samples with [Formula: see text], 0.1925, 02125 and 0.2325, which were fabricated by a conventional solid-state reaction method. By introducing the CuO into PMNT-[Formula: see text]BZN, the sintering temperature of this system is drastically lowered from 1280∘C to 1120∘C. The second pyrochlore phase, which is often generated during sintering at high temperature, is also inhibited. Meanwhile, broad dielectric peaks with strong dielectric relaxation characteristics are observed from [Formula: see text]C to 100∘C. Slim and slanted [Formula: see text]-[Formula: see text] hysteresis loops and purely electrostrictive strains with V-shape are obtained simultaneously in studied compositions from 30∘C to 150∘C. These results suggest that CuO could effectively lower the sintering temperature while maintaining the dielectric and ferroelectric properties of PMNT-[Formula: see text]BZN relaxor ferroelectric ceramics.

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.

Excellent optical transparency of potassium-sodium niobate-based lead-free relaxor ceramics induced by fine grains

Here we report a lead-free multifunctional material (1-x)(K0.5Na0.5)NbO3-xBa(Mg1/3Nb2/3)O3 prepared by pressure-less sintering procedure. X-ray diffraction indicates a gradual crystal structure transformation with increasing x. Microstructural observation demonstrates that the addition of Ba(Mg1/3Nb2/3)O3 additive reduces the size of grains with clear grain boundary, which is favorable for a high optical transmittance. The relaxor characteristics of the ceramics could lead to further enhancement of the transparency, owing to the low defects and weak light scattering. Notably, the ceramics with 0.04 ≤ x ≤ 0.06 all show good transparency over 70% in visible region and 80% in infrared region.

Oxygen octahedron tilting, electrical properties and mechanical behaviors in alkali niobate-based lead-free piezoelectric ceramics

In this work, we present a new piezoelectric solid solution consisting of two typical alkali niobate-based materials, K0.5Na0.5NbO3 (KNN) and Li0.15Na0.85NbO3 (LNN). Although KNN and LNN have the same perovskite structure, they exhibit extremely different electrical properties and mechanical behaviors. The phase structures, electrical and mechanical evolutions of the new lead-free piezoelectric materials with different ratios of KNN and LNN are comprehensively and theoretically investigated. According to the X-ray diffraction patterns and curves of permittivity versus temperature, a series of complicated phase transitions can be found with varied LNN content. Rietveld refinement results based on XRD patterns reveal an oxygen octahedron tilting in the LNN-rich crystal structure, and simultaneously the reasons for octahedron tilting are discussed. The distorted crystal structure is accompanied by extremely decreased electric properties but increased mechanical properties, which reveals electrical and mechanical properties of alkali niobate-based piezoelectric ceramics strongly depend on their inner structures, and the enhancement of intrinsic hardness results in the deterioration of piezoelectric properties. Our work exhibits the detailed evolutions of structure, electrical and mechanical properties from KNN to LNN, which provides experimental and theoretical basis for development of new alkali niobate-based piezoelectric materials.

Significantly enhanced room temperature electrocaloric response with superior thermal stability in sodium niobate-based bulk ceramics

This work simultaneously achieved a large temperature change (ΔT, ∼0.70 K) at room temperature and ultra-stable ΔT(±1.4% variation between 300 K with 380 K) in 0.78NaNbO3–0.22BaTiO3bulk ceramic.

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.

Enhanced piezoelectric performance and thermal stability of alkali niobate-based ceramics

In this study, 0.5 wt% MnO2 doped (0.99-x)(K0.5Na0.5)(Nb0.965Sb0.035)O3–0.01CaZrO3-x(Bi0.5K0.5)(Hf0.98Ti0.02)O3 [abbreviated as (0.99-x)KNNS-0.01CZ-xBKHT, x = 0.01, 0.02, 0.03, 0.04, 0.05, 0.06] lead-free piezoelectric ceramics were fabricated by traditional solid-state reaction method. The microstructure, phase transformation, electromechanical properties and the thermal stability of the ceramics were systematically studied. Resulting from the R-T phase coexisting, a large piezoelectric coefficient (d33 ~ 425 pC/N), planar electromechanical coupling factor (kp ~ 49%) were achieved in the ceramics with x = 0.04. Furthermore, the specimens with x = 0.04 also exhibit excellent temperature stability for d33 which was manifested by the less than 10% variation of d33 values when the annealing temperature increase from 25 °C to 100 °C. The good comprehensive properties indicate that MnO2 doped (0.99-x)KNNS-0.01CZ-xBKHT ceramics are promising candidates for practical application to eliminate the Pb-based piezoelectric ceramics from the market.

High-Performance 0-3 Type Niobate-Based Lead-Free Piezoelectric Composite Ceramics with ZnO Inclusions.

Because of their high toxicity, lead-based materials in electronic devices must be replaced by lead-free piezoelectric materials. However, some issues remain that hinder the industrial applications of these alternative ceramics. Here, we report the construction of a 0-3-type ceramic composite (KNNS-BNKZ: xZnO), where the Sb-doped ZnO submicronic particles were randomly distributed throughout the potassium-sodium niobate-based ceramic matrix. In this (K,Na)NbO3 (KNN)-based ceramic composite, superior temperature stability, excellent piezoelectric properties, and a high Curie temperature were simultaneously achieved. The unipolar strain varied from +20 to -16% when the temperature was increased from 23 to 200 °C in KNNS-BNKZ: xZnO with x = 0.75. By increasing the ZnO content from x = 0 to x = 5.0, the Curie temperature was increased from 227 to 294 °C. More importantly, the piezoelectric coefficient remained high ( d33 = 480-510 pC/N) for a wide range of compositions, x = 0.25-1.0. Transmission electron microscopy (TEM) experiments showed that the compensatory electric fields generated by the Sb-doped ZnO submicronic particles were responsible for the improved temperature stability. The high piezoelectricity was due to the existence of nanodomains, which were clearly observed in the TEM experiments. The results presented in this work clarify some of the physical mechanisms in this KNN-based ceramic composite, thus advancing the development of lead-free ceramics.

Large Piezoelectric Strain with Superior Thermal Stability and Excellent Fatigue Resistance of Lead-Free Potassium Sodium Niobate-Based Grain Orientation-Controlled Ceramics.

Environment-friendly lead-free piezoelectric materials with high piezoelectric response and high stability in a wide temperature range are urgently needed for various applications. In this work, grain orientation-controlled (with a 90% ⟨001⟩c-oriented texture) (K,Na)NbO3-based ceramics with a large piezoelectric response ( d33*) = 505 pm V-1 and a high Curie temperature ( TC) of 247 °C have been developed. Such a high d33* value varies by less than 5% from 30 to 180 °C, showing a superior thermal stability. Furthermore, the high piezoelectricity exhibits an excellent fatigue resistance with the d33* value decreasing within only by 6% at a field of 20 kV cm-1 up to 107 cycles. These exceptional properties can be attributed to the vertical morphotropic phase boundary and the highly ⟨001⟩c-oriented textured ceramic microstructure. These results open a pathway to promote lead-free piezoelectric ceramics as a viable alternative to lead-based piezoceramics for various practical applications, such as actuators, transducers, sensors, and acoustic devices, in a wide temperature range.

Non-equivalent ionic dopants and their impacts on properties of potassium sodium niobate-based lead-free ceramics

In the work, (1-x) (K0.48Na0.52) (Nb0.96Sb0.04)O3-x(Bi0.5K0.5)0.7Ca0.3ZrO3 [(1-x)KNNS–xBKCZ] lead-free piezoceramics are prepared to investigate location and associated impacts of non-equivalent ionic dopants on phase transition and property enhancement. Results of XRD refinement and analysis of transmission electron microscopes (TEM) strongly prove that Rhombohedral-Tetragonal (R-O-T) phase coexistence for 0 ≤ x ≤ 0.04. According to lattice parameters, R phase should be ascribed to lattice deformation subjected to shear stress owing to the cooperation of multiple ionic dopants in A sites and B sites. Based on the variation of temperature-dependent capacitances with the frequencies and atomic-resolution HR-O-TEM image, much more oxygen vacancies are investigated because of major substitution of Ca2+ in B site, which leads to an obvious decrease of TC in (1-x)KNNS–xBKCZ besides c/a of O phase. Additionally, domain wall motion is demonstrated to become easier through calculating intrinsic piezoelectric response using Rayleigh law and consequently, piezoelectric properties of (1-x)KNNS–xBKCZ are greatly enhanced (d33∼440 pC/N and d*33–500 pm/V) in R-O-T phase coexistence region.

Balanced development in piezoelectricity and Curie temperature of the alkaline niobate-based ceramics

Large piezoelectricity (d33) and high Curie temeprature (TC) are highly expected to attain in alkaline niobate-based piezoceramics, which is of high significance in the practical applications. For the compositionally optimized composition, we achieved both large d33 (~ 395 pC/N) and high TC (~ 342 °C) in (0.995-x)K0.485Na0.485Li0.03NbO3–xBi0.5(Na0.8K0.2)0.5ZrO3–0.005BiScO3 (0 ≤ x ≤ 0.06) (KNNL–xBNKZ–BS) lead-free ceramics through the construction of rhombohedral–orthorhombic–tetragonal (R–O–T) phase boundary. A systematic study of the effect of phase boundary on resulting piezoelectric, ferroelectric, and strain properties in the ceramics was investigated. The KNNL–xBNKZ–BS ceramics with x = 0.04 exhibited an enhanced unipolar strain properties (strain ~ 0.161%, d33*~402 pm/V) and thermal stability of d33 (Ta ≤310 °C, normalized d33 ≥ 84.6%), which was mainly ascribed to the R–O–T phase boundary and high TC respectively. Therefore, a balanced development of the parameters (e.g., d33, TC) can be well realized in KNNL–xBNKZ–BS ceramics, we believe that such a material system opens a window for the practical applications.

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.

Large improvement on energy storage and charge-discharge properties of Gd2O3-doped BaO-K2O-Nb2O5-SiO2 glass-ceramic dielectrics

Potassium barium niobate-based glass ceramics doped with different proportion of Gd2O3 were fabricated by conventional melts and controllable crystallization. The influence of Gd2O3 content was further investigated on the phase compositional change, energy storage performance and charge-discharge properties of the optimized glass ceramics (crystallization temperature 900°C). The microstructure has been remarkably transformed through the addition of Gd2O3. On the basis of the results, the doping of 1.0% Gd2O3 achieved a remarkable improvement on the energy storage density that reached 12.14J/cm3 with a dielectric breakdown strength (BDS) of 1818kV/cm and dielectric constant of 83. The discharge efficiency of 80% and discharge time of 25ns were obtained in the glass ceramics with 1.0% Gd2O3, which illustrated the excellent charge-discharge properties of Gd2O3-doped glass ceramics.