Sintering and piezoelectric properties of lead-free (K_0.38Na_0.58Li_0.04)(Nb_0.86Ta_0.10Sb_0.04)O₃ceramics doped with Fe₂O₃

Abstract

Abstract. Lead-free (K 0.38 Na 0.58 Li 0.04 )(Nb 0.86 Ta 0.10 Sb 0.04 )O 3 (KNLNTS) + x mol% Fe 2 O 3 (x = 0 ~ 1) ceramics were prepared by conventional solid state reaction technique. The effect of Fe 2 O 3 doping on the phase structure, microstructure and electrical properties of KNLNTS ceramics were studied. The addition of Fe 2 O 3 was found to be effective in enhancing densification of KNLNTS ceramics. When x = 0.3, the piezoelectric constant d 33 and planar piezoelectric coupling coefficient k p reached highest while maintaining a relatively high Curie point of 318 o C; d 33 =257 pC/N and k p =52 %, which suggests that the ceramics are promising for electromechanical transducer and actuator applications.

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.…”

“…In addition, the electrical properties of KNN materials could be improved by doping with two sintering aids, − such as K 4 CuNb 8 O 23 and La 2 O 3 , MnO 2 and K 5.4 Cu 1.3 Ta 10 O 29 , K 5.4 Cu 1.3 Ta 10 O 29 and CuO, ZnO and SnO 2 , CuO and SnO 2 , etc. Table shows the density and electrical properties of KNN ceramics with doping oxides. ,,,,,, − In particular, the ceramic matrixes used mainly involve a pure KNN ,,,,,,− not those doped with other components. , As shown in Table , a higher d 33 is attained in the ceramics because of the improved density induced by the addition of oxides, ,,,,,, and a higher Q m was also shown. ,,,,,,,− In addition, the atmosphere during sintering is an important factor to determine the electrical properties of KNN materials by changing the microstructure (e.g., grain morphology and density − ). Among sintering atmospheres, an oxygen atmosphere during sintering usually has a large effect on the electrical properties of KNN ceramics due to microstructure evolution. − …”

“…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...…”