Niobate-based Ceramics Research Articles

Phase structure and piezoelectric properties of Li-modified NKLN lead-free piezoelectric ceramics

Through the low-temperature sintering method, a sintered body with excellent characteristics was produced in an eco-friendly niobate-based piezoelectric ceramic, whose application was low in expectation due to poor sinterability. Li2CO3 was added in excess to (Na0.49K0.45Li0.06)NbO3, and ceramics were manufactured using a commercial sintering method. Then, the sinterability and the piezoelectric properties of the specimens containing varying amounts of Li2CO3 were investigated. The microstructure demonstrated the typical abnormal grain growth tendencies with the addition of Li2CO3, and this was explained through changes in the critical driving force in the interface reaction-controlled nucleation and growth theory. When the specimen had been sintered at 1000 °C for 4 hours in air after the addition of 1.5 mol% Li2CO3, the sintered body showed outstanding characteristics with a piezoelectric coefficient of 180 pC/N, an electromechanical coupling coefficient of 0.32, and a dielectric constant of 975. These results showed that eco-friendly niobate-based ceramics, whose use in applications was expected to be difficult in spite of their excellent properties, could be used to produce piezoelectric materials with outstanding properties through a commercial low-temperature sintering method using additives.

Fabrication and Electrical Properties of Mn-Doped KNbO3 Ceramics Synthesized from KHCO3 as a Starting Material

Potassium niobate-based ceramics with 0.1 wt % MnCO3, K(1+x)NbO3+MnCO3 0.1 wt % (KN10000x+Mn, x = 0.0000–0.0010), were fabricated using KHCO3 powder as a starting material. The KN10000x+Mn ceramics were basically fabricated using a conventional ceramic fabrication process and MnCO3 powders were added at the milling stage after the calcination. High density ratios above 95% were prepared for the wide compositional range of excess K amount for KN10000x+Mn ceramics. From these results, Mn ions are thought to act as a sintering aid for KN ceramics. Mn-doped KN10000x ceramics also showed high resisitivities of approximately 1012 Ω cm for the wide variety of x (10000x=0–9). Moreover, the electromechanical coupling factors k33 for KN10000x+Mn had constant values of higher than 0.50.

Gigantic Electrostrain in Duplex Structured Alkaline Niobates

We demonstrate that an exceptionally large strain can be induced in CaZrO3-modified alkaline-niobates by electric fields. The maximum induced strain of our niobate-based ceramics could reach more than 1,000 pm/V, which is a much higher value than that of commercial soft PZT ceramics. Atomic-scale annular bright-field (ABF) and annular dark-field (ADF) scanning transmission electron microscopy (STEM) directly revealed that individual single grains were composed of an electrically duplex core–shell structure; relaxor-like cores and paraelectric shells. Based on this ABF STEM analysis along with electrical measurements, a plausible mechanism explaining the high strain effect in the present work was suggested. This new material offers an unprecedented opportunity to produce efficient Pb-free piezoelectrics for applications that require large electrostrictive motion.

Enhanced Performance of Alkaline Niobate-Based Ceramics Manufactured by Two-Step Sintering

In this paper, a typical Li- and Ta/Sb- modified alkaline niobate-based ceramics are prepared by conventional sintering and two-step sintering respectively. The ceramics sintered by two-step sintering exhibit better electrical properties than the samples prepared by conventional sintering. The related mechanisms are also discussed in terms of phase-structures and microstructures. Results show that two-step sintering can restrain the volatilization of alkali elements and compositional segregation during the process of sintering dense alkaline niobate-based ceramics, and enhance the electrical properties accordingly. Therefore, two-step sintering is a promising approach to achieve high performance alkaline niobate-based ceramics.

Influence of sintering temperature on microstructure and electric properties of CuO doped alkaline niobate-based lead-free ceramics

In this work, microstructure characteristics, dielectric, piezoelectric and ferroelectric properties of lead-free (K0.4425Na0.52Li0.0375)(Nb0.87Ta0.06Sb0.07)O3 (KNLNST) doped with 1 mol% copper oxide (CuO) piezoelectric ceramics prepared by a conventional solid-state reaction route are investigated with an emphasis on the influence of sintering temperature. The introduction of CuO could significantly improve the sinterability of KNLNST ceramics. It is found that the tetragonality of the ceramics increases with raising sintering temperature. A dense microstructure with increased grains is developed, probably due to liquid-phase sintering. Both the piezoelectric constant d33 and planar electromechanical coupling kp increase with increasing relative density and grain size. The Curie temperature TC values increase slightly when the sintering temperature is increased. In addition, the KNLNST ceramics doped with 1 mol% CuO show obvious dielectric relaxor characteristics, and the relaxor behavior of ceramics is strengthened by increasing the sintering temperature. The improved piezoelectric and dielectric properties of d33 = 241 pC/N, kp = 0.437, dielectric loss tanδ = 0.0087, mechanical quality factor Qm = 138, dielectric constant er = 1,304 can be obtained for specimens sintered at 1,080 °C for 3 h.

Dielectric and Piezoelectric Properties of Lead-free (Li,Na,K)(Nb,Ta,Sb)O3 System Ceramics as a Function of Calcination Temperature

The alkaline niobate-based perovskite ceramics (Li,Na,K)(Nb,Ta,Sb)O3 has been regarded as a new candidate of lead-free piezoelectric materials due to its excellent piezoelectric properties. In this study, Li0.02(Na0.55K0.45)0.98(Nb0.77Ta0.18Sb0.05)O3 (abbreviated as LNKNTS) piezoelectric ceramics were fabricated by a conventional solid-state reaction method at various calcinations temperature and then, their dielectric and piezoelectric properties were investigated. At the calcinations temperature of 870°C and sintering temperature of 1140°C, the optimum values of density = 4.736g/cm3, kp = 0.423, Qm = 65, ϵr = 1545 and d33 = 256 pC/N, were obtained, respectively. Taking into consideration above physical properties, it is considered that this composition is applicable to lead-free haptic piezoelectric actuators.

Phase and Electrical Properties of [Li<sub>0.065</sub>(Na<sub>0.535</sub>K<sub>0.48</sub>)<sub>0.95</sub>]NbO<sub>3</sub> Lead-Free Piezoelectric Ceramics Sintered at Low Temperature

Li-doped (Na, K)NbO3lead-free piezoelectric ceramics with nominal composition of [Li0.065(Na0.535K0.48)0.95]NbO3were prepared by normal sintering method, and its phase structure, microstructure and electric properties were studied with a special emphasis on the influence of sintering temperature in the range of 950-1020 oC. The result of XRD analysis indicates that a polymorphic phase transition (PPT) separating orthorhombic and tetragonal phases was found at the temperature of 950 oC, whereby enhanced piezoelectric properties of d33=255 pC/N and kp= 44.5% were obtained although the density was low. Our study indicates that the importance of PPT for enhancing electric properties in niobate-based ceramics at low temperature.

(K, Na)NbO3-based lead-free piezoelectric ceramics manufactured by two-step sintering

Two-step sintering was applied to manufacture a typical Li- and Ta/Sb-modified alkaline niobate-based lead-free piezoelectric ceramics. The sintering condition dependences of dielectric constants and piezoelectric properties were investigated. Under the optimal condition, dense specimens have an average grain size of approximately 5μm, and show good dielectric and piezoelectric properties. Significantly, the (K0.4425Na0.52Li0.0375) (Nb0.8925Sb0.07Ta0.0375)O3 ceramics sintered under the condition “1130/10/1020/15” show the peak values of the piezoelectric coefficient (d33), electromechanical coupling coefficient (kp), and dielectric constant (ɛ), which are 281pC/N, 50% and 1500, respectively, owing to the densest microstructure of typical bimodal grain size distributions. Furthermore, the KNLNST ceramics maintain relatively low dielectric loss over wide temperature ranges. The result indicates that the KNLNST ceramics sintered by two-step sintering exhibit good temperature stability.

Knudsen effusion mass spectrometric approach to the thermodynamics of Na 2O–Nb 2O 5 system

Knudsen effusion mass spectrometry (KEMS) was used to determine the equilibrium vapour pressures of sodium over five selected compositions in different solid two-phase regions of the Na 2O–Nb 2O 5 system at 1100–1470 K. The results were then used to determine the standard thermodynamic functions ( Δ f G T ° , Δ f H 298 K ° , S T ° ) of five solid compounds: Na 3NbO 4, NaNbO 3, Na 2Nb 4O 11, NaNb 3O 8 and NaNb 13O 33. These data were then incorporated into the IVTANTHERMO database to perform equilibrium calculations under real conditions relevant to the high temperature stability of sodium niobate, which is an important end member of the alkali niobate-based lead-free piezoelectric ceramics.

Effect of oxide dopants on the structure and electrical properties of (Na 0.5K 0.5)NbO 3-LiSbO 3 lead-free piezoelectric ceramics

The alkaline niobate-based perovskite ceramics (K,Na,Li)(Nb,Sb)O 3 has been regarded as a new candidate of lead-free piezoelectric materials due to its excellent piezoelectric properties. In this study, 0.948(Na 0.5K 0.5)NbO 3-0.052LiSbO 3 (KNN-LS) based ceramics were prepared by a conventional solid-state reaction method. The effects of ZnO, CuO and MnO 2 on the structure, dielectric and piezoelectric properties of KNN-LS were investigated in this study. When 1 mol% oxide dopants were added, respectively, KNN-LS piezoelectric ceramics became “hard”. Mechanical quality factor Q value increased significantly with unobvious change of d 33 (93–119 pC/N). KNN-LS ceramics kept high Curie temperature Tc around 350 °C. Dielectric loss at 1 KHz decreased a lot to below 5%. The results show that the oxide-doped KNN-LS ceramics are promising lead-free piezoelectric materials for electromechanical transducer applications.

Thermal Reliability of Alkaline Niobate-Based Lead-Free Piezoelectric Ceramics

Alkaline niobate-based (K,Na,Li,Ba,Sr)(Nb,Ta,Zr)O3 (ANSZ) ceramics were prepared by conventional sintering process, and their piezoelectric properties were measured. The Curie temperature (TC) of the ANSZ ceramic was 278 °C. The electromechanical coupling factor (kp) and the piezoelectric constant (d33) were 45.5% and 295 pC/N, respectively, and the dielectric permittivity (ε33T/ε0) was 1610 at room temperature. The thermal reliability was tested by 1000 cycles of thermal shock with temperatures ranging from -55 to 125 °C. The change in d33 of ANSZ was compared with that of commercial Pb(Zr,Ti)O3 after 1000 cycles of thermal shock. The phase transition behavior of ANSZ was investigated by X-ray diffraction (XRD) and differential scanning calorimetry (DSC) simultaneous measurement. No appreciable endothermic peak accompanied by a polymorphic phase transition was observed on the DSC curve. The crystalline structure was investigated in detail by XRD measurement with high-energy synchrotron radiation. The coexistence of two ferroelectric phases in a wide temperature range (from -175 to 150 °C) was observed.

Effect of BiScO3 and LiNbO3 on the Piezoelectric Properties of (Na0.5K0.5)NbO3 Ceramics

Lead‐free potassium sodium niobate‐based piezoelectric ceramics (1−y)(Na0.5−0.5xK0.5−0.5xLix)NbO3−yBiScO3 ( y=0.01, x=0–0.06) have been prepared by an ordinary sintering process. The XRD analysis showed that the structure changes from orthorhombic to tetragonal with the increase of x (at y=0.01, abbreviated as KNNBSL100x). At room temperature, the polymorphic phase transition from the orthorhombic to the tetragonal phase was identified at approximately 0.02≤x≤0.04. The piezoelectric and ferroelectric properties were significantly enhanced. The temperature dependences of the relative permittivity revealed that the Curie temperature was increased with the addition of LiNbO3. These solid solution ceramics are promising as potential lead‐free candidate materials.

Transition Temperature of Lead-Free Piezoelectric Ceramics by Electrochemical Impedance Spectroscopy

Piezoelectric ceramics with perovskite structure based on lead zirconate titanate (PZT) show excellent electrical properties near the morphotropic phase boundary (MPB) and thus are widely used for actuators, sensors as well as microelectronic devices. However, because of the high toxicity of lead oxide and its high vapour pressure during sintering, the use of lead-based ceramics has caused serious lead pollution and environmental problems; for this reason, the development of lead-free piezoelectric ceramics has been demanded to replace lead-based ceramics. Therefore, it is necessary to develop lead-free piezoelectric ceramics with good properties. Among the lead-free piezoelectric materials, the alkaline niobate-based perovskite compounds and Bi-containing materials, have attracted a large amount of attention because of their superior characteristics. The alkaline niobates (K,Na)NbO 3 (KNN)-based material exhibits especially good piezoelectric properties and have been studied as substitutes for PZT piezoelectrics. In this work, alkaline niobate-based piezoelectric ceramics were sintetized, system (K 0.5 Na 0.5 )xLi (1-x) Nb yTa (1-y) O3, and were characterized by X-ray diffraction (DRX) and scanning electron microscopy (SEM). In order to determine their transition temperature, electrochemical impedance spectroscopy (EIS) was used, and it was found the transition temperature was about 420 oC, which is a desirable value in this kind of materials.

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).

Negative and low positive thermal expansion behaviour of niobate-based ceramics and solid solutions

Negative and low positive thermal expansion behaviour of niobate-based ceramics and solid solutions

Enhancing piezoelectric d33 coefficient in Li∕Ta-codoped lead-free (Na,K)NbO3 ceramics by compensating Na and K at a fixed ratio

Lead-free alkali niobate piezoelectric ceramics with nominal compositions [(Na0.535K0.480)0.942+xLi0.058](Nb0.90Ta0.10)O3 compensated with Na and K at a fixed and optimized ratio of 0.535:0.480 were prepared by normal sintering. The electrical properties were investigated with a special emphasis on the influence of compensating amount x of Na0.535K0.480. A phase transition from tetragonal to orthorhombic was observed as x was increased from 0 to 0.024, resulting in enhanced piezoelectric coefficient and planar electromechanical coupling coefficient from 216 and 38.1% to 268pC∕N and 46.2%, respectively. Our results indicate the importance of elaborate compositional control for enhancing piezoelectric properties in niobate-based ceramics.

Effect of Small Amount CuO Doping on Microstructure and Properties of the Alkaline Niobate-Based Lead-Free Ceramics

Recently, it was reported that the alkaline niobate-based (K,Na,Li)(Nb,Ta,Sb)O3 (LF4) perovskite ceramics showed excellent piezoelectric properties and has been regarded as a new candidate of lead-free piezoelectric materials. However, the effects of additives on the piezoelectric property of LF4 have not been studied intensively so far. In this study, the effect of CuO addition to the LF4 was investigated. The sample showed a tetragonal phase at room temperature and also a second phase with low melt point. The Cu2 + can replace both A-site and B-site because of its radii. The mechanical quality factor (Q m ) increased from 26 to 137 as the CuO increased.

Investigation of Electroplating-Induced Degradation of PMZNT Relaxor Ferroelectrics

Resistance degradation of lead magnesium niobate-based (PMZNT) ceramics during nickel electroplating was investigated using resistivity measurement and auger electron spectroscopy (AES) analysis. It was found that the resistivity of the ceramics remained nearly unchanged at the initial stage of the electroplating, and, as electroplating time increased, the resistivity decreased rapidly. An AES depth profile analysis of a degraded specimen showed oxygen content in the surface to be lower than the theoretical value, and the relationship of oxygen content and detection depth was obtained. The results indicated that Pb 2+ and Nb 5+ were reduced to lower valence states and oxygen in the lattice was lost, thereby leading to a generation of oxygen vacancies. Hence, the conductivity of the dielectrics was enhanced. The results also indicated that only the outermost surface had suffered the reducing effect induced by hydrogen generated during nickel electroplating, whereas the bulk material remained impervious.

Reliability improvement of PMZNT relaxor ferroelectrics through surface modification by MnO2 doping against electroplating-induced degradation

Electroplating treatment, scanning electron microscopy (SEM) observation, X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) analyses were conducted to investigate the reliability improvement of lead magnesium niobate-based ceramics (PMZNT) through MnO2 vaporous doping against hydrogen reduction during electroplating. The results showed that manganese dopant was reduced to be +3 oxidation state during the sintering and Mn3+ was incorporated into the perovskite lattice; however, only the outermost ceramics surface was doped while 50μm beneath kept unchanged. This technique proved to enhance the reliability of PMZNT against electroplating significantly without changing the dielectric properties of ceramics body. Based on the above results, the modification mechanism of MnO2 vaporous doping was analyzed from the viewpoint of defect chemistry.

Postsintering annealing induced extrinsic dielectric and piezoelectric responses in lead–zinc–niobate-based ferroelectric ceramics

The effect of postsintering annealing on the dielectric and piezoelectric responses in lead–zinc–niobate (PZN)-based ferroelectric ceramics was systematically studied in this work. Sintered PZN ceramics with the same composition were annealed at temperatures from 700 to 900 °C from 30 min to 24 h in various atmospheres. As a result, significant improvements in the dielectric and piezoelectric responses were observed in this system. After annealing, there was a huge increase of up to 130% in the dielectric constants, especially near the temperature of maximum dielectric constant. While the dielectric peaks became sharper and less diffuse, there was almost no change in frequency dispersion. Similar large improvements in the piezoelectric properties such as the coupling factor and piezoelectric constant were also observed. Optimized parameters, such as d33=642 pC/N, d31=−256 pC/N, kp=48% and εm=28 000, were achieved by annealing at 850 °C in an O2-rich atmosphere for 4–8 h. The observed improvement in the electrical properties can be attributed to an extrinsic contribution induced by domain wall motion. After annealing, the pinning effects caused by oxygen vacancies and internal stress on domain wall motion were largely reduced or eliminated, therefore a significantly reduced coercive field, an increased polarization level, and a greatly increased dielectric constant were observed in the PZN-based ferroelectric ceramics.