Mitigation of thermal and fatigue behavior in K0.5Na0.5NbO3-based lead free piezoceramics

Abstract

K 0.5 Na 0.5 NbO 3 -͑KNN͒ based lead free materials have been found to exhibit good piezoelectric properties ͑d 33 ϳ 250 pC/ N͒ due to the orthorhombic-tetragonal polymorphic phase transition ͑PPT͒ temperature compositionally shifted downward to near room temperature. However, associated with the PPT are issues of temperature and domain instability, making them impractical for applications. In this work, CaTiO 3 ͑CT͒ was used to effectively shift the PPT downward in effort to mitigate these issues. As expected, CT modified KNN based materials exhibited nearly temperature independent properties ͑−50ϳ 200°C͒ and fatigue-free behavior, together with its relatively high d 33 [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19] However, the enhanced properties are the result of compositionally shifting the orthorhombic to tetragonal polymorphic phase transition ͑PPT͒ downward from ϳ200°C to near room temperature. [6][7][8]19 Associated with a PPT are strong temperature dependent properties and degradation associated with domain instability during thermal cycling between the two distinct different ferroelectric domain states, making them impractical for various applications. 6 Based on the above, it is desirable to shift the PPT out of the application temperature range ͑usually −50ϳ 200°C͒, in order to improve thermal stability and mitigate property degradation, while maintaining high piezoelectric properties. It was reported that the addition of LN, LT, or LS in KNN effectively increased the piezoelectric properties owing to the shift of the PPT to near room temperature, but further shifts downward to below room temperature could not be achieved owing to solubility limitations ͑ϳ6% -8%͒, where excess addition͑s͒ lead to undesirable second phase͑s͒, thus deteriorating the properties. 2 Following the work on modified BaTiO 3 , 20,21 the first lead free piezoelectric ceramic, the addition of CaTiO 3 ͑CT͒ was proposed to modify the KNN-based systems, as such to further shift the orthorhombic to tetragonal PPT downward to below room temperature, achieving a more temperature stable piezoelectric material. 17 The conventional solid-state reaction method was used to prepare the KNN-based materials with and without CT modifications. High purity oxides and/or carbonates K 2 CO 3 , Na 2 CO 3 , Li 2 CO 3 , Nb 2 O 5 , Sb 2 O 5 , and CT were used as the starting materials and weighed according to the nominal compositions. After vibratory milling in anhydrous ethanol, the mixed powders were calcined at 880°C for 2 h, and then the synthesized materials were milled again and followed by the addition of binder. The granulated powders were pressed into pellets with 12 mm in diameter prior to the removal of the binder. The pellets were sintered at 1120-1180°C in sealed alumina crucibles for 2 h. X-ray powder diffraction ͑XRD͒ analysis was performed on ground sintered samples using Cu K␣ radiation ͑PANalytical X'Pert PRO͒. Narrow region slow scanning was employed using Si as a standard and the test condition was 0.01/step ...

Improved electrical properties for Mn-doped lead-free piezoelectric potassium sodium niobate ceramics

“…[3][4][5] Since Saito et al 6 have demonstrated that the KNN ceramics modified with Li, Ta, or Sb exhibit sufficient piezoelectric properties comparable to commercially available PZT-based ceramics, considerable interests have been devoted to improve the piezoelectric properties of KNN ceramics. [7][8][9][10][11] Doping is a mandatory solution to tailor the properties of KNN for specific applications. For Mn-doped KNN and KNN based ceramics, the improved electrical properties were observed.…”

Fatigue-free unipolar strain behavior in CaZrO3 and MnO2 co-modified (K,Na)NbO3-based lead-free piezoceramics

“…18,19 Therefore, it is necessary to carefully investigate the fatigue characteristics of promising lead-free compositions. Especially, only a few fatigue studies have been published so far for KNN-based materials, [20][21][22][23] and a detailed understanding of the unipolar fatigue mechanism, which is crucial for further improving the unipolar fatigue resistance, is still missing.…”

Investigation on transition behavior and electrical properties of (K0.5Na0.5)1-xLixNb0.84Ta0.1Sb0.06O3 around polymorphic phase transition region

“…Recently, potassium sodium niobate (KNN)-based ceramics are expected to have excellent piezoelectric, [9][10][11][12][13][14][15][16][17] ferroelectric and dielectric properties near orthorhombic-tetragonal polymorphic phase transition (PPT) temperature. [18][19][20] Saito et al have reported Li, Ta, Sb doped KNN ceramics with high piezoelectric constant of 416 pC/N by templated grain growth (TGG) method. 9 When Na/K ratio is near 0.5/0.5, KNN system possesses a PPT similar to that of PZT system.…”

“…It will lead to the distortion of structure and make it shifts to PPT region at room temperature. [18][19][20] In Li, Sb and Ta co-doped KNN ceramics, the introduction a To whom correspondence should be addressed. : +86-10-62517887; Tel: +86-10-82501673.…”