Influence of Monoxides Addition on Sintering of Sodium-Potassium Niobates Solid Solution

Abstract

In this paper the preparation, structure and dielectric parameters of ceramics from different powders of pure potassium sodium niobate (KNN) and KNN doped with 1.0 wt% of Li 2 O, CdO, Bi 2 O 3 , MnO 2 , V 2 O 5 and WO 3 have been studied. The dopping of sintering aids did not affect the crystallographic structure of the ceramics significantly; all ceramic samples had a single-phase perovskite structure. Added elements Li 2 O, CdO, MnO 2 , V 2 O 5 effectively decreased the sintering temperature of KNN (50 • -80 • C). All sintering aids influenced sinterability, microstructure and dielectric properties of ceramics. Dielectric constant for doped samples increased from 6000 up to 8000.

Potassium–Sodium Niobate Lead-Free Piezoelectric Materials: Past, Present, and Future of Phase Boundaries

“…Sintering aids can improve the electrical properties of KNN materials by the improvement in the densification and microstructure. ,,,,− In recent decades, many aids have been used to sinter KNN ceramics (refs , , , , − , , , and ), including K 4 CuNb 8 O 23 (KCN), K 5.4 CuTa 10 O 29 (KCT), ,, K 1.94 ­Zn 1.06 ­Ta 5.19 O 15 (KZT), CuNb 2 O 6 , CuO, ,− , Mn 3 O 4 , MnO 2 , , MoO 3 , ZnO, − La 2 O 3 , Bi 2 O 3 , ,, Fe 2 O 3 , , V 2 O 5 , and ZrO 2 . Sintering aids have two main advantages for KNN materials: (i) improving the density, such as KZT, KCN, etc.…”

“…It is clear that a pure KNN ceramic sintered in air has a lower density than one sintered by SPS or hot press methods; ,,, thus, higher d 33 values are shown by SPS or hot-pressed samples due to the improved density. , In the past decade, some methods (e.g., sintering temperature, ,,,− , rapid sintering technique, ,,, the use of sintering aids (refs , , , , − , and ), and sintering atmosphere − ) have been used to improve the density of KNN ceramics. Among these methods, the main goal is to suppress the loss of alkali metals ,,,,− ,,,, or the formation of liquid phases ,,,,− …”

“…It is usually accepted that the microstructure (e.g., grain morphology) of KNN-based materials can be modulated by a sintering aid, ,,,,− the use of new preparation techniques, ,,,, various sintering atmospheres, and others. Many researchers have improved the sinterability of KNN-based materials using different sintering aids ,,,,,,, (e.g., CuO, ,, NiO, ZnO, , MnO, and MnO 2 ), and the existence of A-site vacancies can offset the formation of the hygroscopic secondary phases because these chemical elements substitute the B site in ABO 3 .…”

“…Many researchers have improved the sinterability of KNN-based materials using different sintering aids ,,,,,,, (e.g., CuO, ,, NiO, ZnO, , MnO, and MnO 2 ), and the existence of A-site vacancies can offset the formation of the hygroscopic secondary phases because these chemical elements substitute the B site in ABO 3 . In addition, sintering aids are often used to densify KNN ceramics by introducing a liquid phase ,,,,,− or a “transient” liquid phase, ,, and the grain morphologies can be also controlled by changing the concentration of sintering aids. ,, In particular, bimodal grain size distributions were often observed in KNN-based ceramics doped by oxides. , It was proposed that the general grain growths observed in oxide-doped samples should be attributed to enhanced atomic mobility, , dramatic grain growth can be induced by the difference in surface free energies between large grains and small grains, and then bimodal grain sizes can be facilitated and accelerated due to the presence of a liquid phase. However, piezoelectric activity will usually be degraded by the addition of sintering aids because a material’s phase transition temperature deviates to room temperature. ,,,, In addition, the piezoelectric activity of KNN-based ceramics is closely related to their average grain sizes. , Also, the grain growth behavior of a pure KNN ceramic can be controlled by different sintering atmospheres because of the critical driving force for 2D nucleation-controlled grain growth caused by their different edg...…”

Sintering Aid‐Assisted Growth of 0.95(K0.5Na0.5)NbO3–0.05(Bi0.5Na0.5)(Zr0.85Sn0.15)O3 Single Crystals by the Solid‐State Crystal Growth Method and Their Characterization

“…Abnormal grain growth, reduction in the mean grain size, and development of bimodal grain size distributions resulting from the continuous addition of Li 2 CO 3 and Bi 2 O 3 are in reasonable agreement with a continuous decrease in Δ μ C . [ 66–68 ] On the other hand, very small grains in the sample with excess sintering aid (0.3 mol% Li 2 CO 3 + 0.3 mol% Bi 2 O 3 ) are due to a very slow grain growth rate, suggesting that the driving forces for many grains are higher than the critical driving force, causing grain growth behavior to change to pseudonormal, which also slows down single‐crystal growth [ 35,58 ] [Figure 1e”]. Segregation of excess Bi at the grain boundaries may also be a reason for the slow grain growth rate due to an increase in the thickness of the solid/liquid interface across which atoms must diffuse.…”