Potassium Sodium Niobate Ceramics Research Articles

Preperation of Lead-Free Potassium Sodium Niobate Based Piezoelectrics and their Electromechanical Characteristics

In this study, %7 Li modified and 0.67 % copper oxide added potassium sodium niobate (KNN) ceramics were investigated. Copper oxide was used as a sintering aid. The ceramics were prepared with conventional solid state calcination technique. All samples were crystallized in pure perovskite phase with no additional peak. The density of the samples increased with copper addition and lithium modification. The Curie temperature of KNN ceramics was found to shift to lower temperatures by CuO addition. The Curie temperature was measured as 414°C and 504°C for copper oxide added and lithium modified KNN samples, respectively. The maximum strain of copper oxide added sample was 0.12%, whereas Li modified KL ceramics yielded up to 0.10 %.

Influence of Sintering Atmosphere on Abnormal Grain Growth Behaviour in Potassium Sodium Niobate Ceramics Sintered at Low Temperature

The present study aims to identify the effect of sintering atmosphere [O 2 , 75N 2 -25 H 2 (mol%) and H 2 ] on microstructural evolution at the relatively low sintering temperature of 1040℃. Samples sintered in O 2 showed a bimodal microstructure consisting of fine matrix grains and large abnormal grains. Sintering in 75 N 2 - 25 H 2 (mol %) and H 2 caused the extent of abnormal grain growth to increase. These changes in grain growth behaviour are explained by the effect of the change in step free energy with sintering atmosphere on the critical driving force necessary for rapid grain growth. The results show the possibility of fabricating (K 0.5 Na 0.5 )NbO 3 at low temperature with various microstructures via proper control of sintering atmosphere.

Properties of Ultrafine-Grained Na0.5K0.5NbO3 Ceramics Prepared From Nanopowder

In this paper, highly pure Na0.5K0.5NbO3 nanopowder was prepared from an economical sol–gel method. Using the nanopowder, dense Na0.5K0.5NbO3 ceramics with ultrafine grain sizes in the range of 200–600 nm were fabricated successfully by low-temperature solid-state sintering at 1085°C for 4 h. The ultrafine-grained ceramics exhibited fine ferroelectric, piezoelectric, and dielectric characteristics. Its room temperature d33, Kp, ɛ33T/ɛ0 at 1 kHz, tan δ and relative density are 154 pC/N, 30.5%, 407%, 0.0155%, and 96.8%, respectively. The results indicate that it is considerably potential to synthesize ultrafine-grained doped potassium-sodium niobate ceramics with excellent properties by using of nanopowder prepared from the sol–gel method.

Piezoelectric properties of Li–Ta co-doped potassium–sodium niobate ceramics prepared by spark plasma and conventional sintering

Lead-free piezoelectric ceramics with (K0.48Na0.52)0.96Li0.04Nb0.85Ta0.15O3 composition were sintered by conventional pressureless (PLS) and spark plasma sintering (SPS) techniques. A comparative analysis of the sintering effect on the piezoelectric and dielectric properties was conducted. The SPS treated specimen revealed an enhancement in the piezoelectric properties as compared to the PLS counterpart. The piezoelectric and dielectric parameters of PLS sintered sample were k′p=0.41, s′11E=11.80×10−12 m2/N, d′31=−55.7 (pC/N), ε′33T=464.5 and tanδ=0.010 at 10kHz, whereas these parameters for the SPS sintered sample were k′p=0.50, s′11E=12.20×10−12 m2/N, d′31=−66.17 (pC/N), ε′33T=557.4 and tanδ=0.024 at 10kHz. The piezoelectric properties enhancement of the SPS treated sample is attributed to, both the lower sintering temperature and the higher density achieved over the PLS sintered sample.

Lead-free piezoelectric ceramics and thin films

Recent progress in lead-free piezoelectric ceramics and thin films with special emphasis on alkaline niobatebased and bismuth sodium titanate-based systems is reviewed concisely. Modifications of potassium sodium niobate (KNN) ceramics are presented and subsequent improvements in the electrical properties are summarized. Special attention is devoted to the phase diagram of the KNN system when a solid solution is formed with other perovskite niobates and titanates. Impact of A-site and B-site dopants on the electromechanical properties of KNN ceramics are distinguished in view of transition temperatures. It is shown that the addition of most A-site and B-site dopants reduces the transition temperatures and improves the piezoactivity at room temperature. This is attributed to the shift of polymorphic transition from tetragonal to orthorhombic phase in the vicinity of room temperature. In contrast, formation of a solid solution of KNN with 18 mol% AgNbO₃ revealed a significant enhancement of properties without a notable change in the transition temperatures. Also, a bismuth sodium titanate (BNT) composition is introduced with particular emphasis on its binary and ternary derivatives. Moderate piezoelectric properties reported at the morphotropic phase boundaries, formed in BNT-based solid solutions are also represented. Advances on thin films based on these two compositions are evaluated and challenges involved with development of stoichiometric thin films with low leakage current are discussed.

Examination of selectivity of templates for the textured potassium sodium niobate ceramics

To achieve the surface-orientation-controlled microstructure of K 0.5Na 0.5NbO 3, not only the template must exhibit the high anisotropy like a plate-shape but the reactive stability as well as the crystallographic coherency between the template and the K 0.5Na 0.5NbO 3 must be carefully considered. In this work, we focused on what kinds of ceramics are suitable for the fabrication of the surface-orientation-controlled K 0.5Na 0.5NbO 3. First of all, BaTiO 3, SrTiO 3, Ba(Zr 0.1Ti 0.9)O 3, KNbO 3, NaNbO 3, KTaO 3 and NaTaO 3 were chosen as the candidates in the regard of the crystallographic coherency. To verify the chemical stability between candidate ceramics and K 0.5Na 0.5NbO 3, the prepared candidate ceramic bulks were embedded by the K 0.5Na 0.5NbO 3 powder, they were annealed at 1100 °C, and then the interface regions between candidate ceramics and K 0.5Na 0.5NbO 3 were investigated using Secondary Electron Microscopy (SEM) equipped with Energy Dispersive Spectrometer (EDS). From these experimental results, BaTiO 3, SrTiO 3, Ba(Zr 0.1Ti 0.9)O 3, KNbO 3 and NaTaO 3 were found to be not appropriate for the templates for the tailoring of K 0.5Na 0.5NbO 3, while the NaNbO 3 and KTaO 3 showed a good crystallographic coherency and a chemical stability with K 0.5Na 0.5NbO 3.

Microstructural features and electrical properties of copper oxide added potassium sodium niobate ceramics

In this study, effects of 0.5, 1.0 and 1.5 mole% CuO addition on the properties of potassium sodium niobate (K 0.5Na 0.5)NbO 3-KNN ceramics were investigated. Pure KNN and CuO-added KNN pellet samples were sintered at 1100 and 1090 °C for 4 h, respectively. Phase analysis showed that all samples crystallized in pure orthorhombic perovskite phase. Addition of 1.0 and 1.5 mole% CuO caused grain growth, densification and formation of a liquid phase at the grain boundaries. Curie temperature has shifted from 480 to 435 °C with increasing CuO ratio. The most remarkable characteristic of the hysteresis loops were the constricted nature of the 0.5 mole% CuO-added KNN's curve and the antiferroelectric-like appearance of the 1.5 mole% CuO-added KNN's curve. Piezeoelectric properties of d 33 = 120 pC/N, k p = 0.27 and Q m = 772 were obtained from the 1.5 mole% CuO-added KNN.

Enhanced Ferroelectric Properties of Potassium Sodium Niobate Ceramics Modified by Small Amount of K3Li2Nb5O15

(1−x)K0.5Na0.5NbO3–xK3Li2Nb5O15 (KNN–100xKLN) ceramics were prepared by the solid‐state reaction method. The results showed that small amount of KLN (x≤0.02) incorporated into the lattice and formed a single phase perovskite structure. The KLN modification lowered the phase transition temperature of orthorhombic–tetragonal (TO−T) and increased the Curie temperature (Tc), but the transition temperatures remained almost unchanged in the range of x from 0.02 to 0.03. Small amount of KLN decreased the amount of defects, thus the remnant polarization increased and the coercive field decreased markedly, and the piezoelectric properties of KNN ceramics modified by small amount of KLN also enhanced markedly.

Sintering and Piezoelectric Properties of Potassium Sodium Niobate Ceramics with Newly Developed Sintering Aid

As a candidate for lead-free piezoelectric materials, (K0.5Na0.5)NbO3 (KNN)-based ceramics have been successfully synthesized via a solid state reaction. In this study, KNN-based ceramics were sintered under atmospheric pressure by adding the newly developed sintering aid (K5.4Cu1.3Ta10O29, KCT). The effects of KCT addition on the sinterability and electrical properties of the KNN ceramics were examined. The KCT addition to KNN at more than 0.38 mol% was effective to improve the sinterability of the KNN ceramics. The phase transition temperature of the KNN ceramics prepared indicated that part of KCT reacted with the KNN matrix during the sintering process. The εr, kp, Np and Qm values of prepared KNN ceramics strongly depended upon the KCT content. The KCT addition to KNN greatly improved the Qm values (>1000) of the KNN ceramics. The Qm and kp of 0.38 mol% KCT added KNN ceramics were 1200 and 0.42, respectively. In addition, the KNN ceramics with 0.38 mol% KCT showed large field induced strain of 0.09% at 40 kV/cm, and d33 of approximately 190 pm/V under a unipolar field from 30 to 40 kV/cm.