Electrical and Mechanical Properties of Fine‐Grained Li/Ta‐Modified (Na,K)NbO₃‐Based Piezoceramics Prepared by Spark Plasma Sintering

Abstract

Dense and fine-grained (Na 0.535 K 0.485 ) 1Àx Li x (Nb 0.8 Ta 0.2 )O 3 (x 5 0.02-0.07) (abbreviated as NKL x NT) lead-free piezoceramics were fabricated by spark plasma sintering (SPS), followed by postannealing in air. All the NKL x NT ceramics showed single perovskite structures with a phase transition from an orthorhombic symmetry to a tetragonal one across a composition region of 0.04oxo0.05. The sample with a composition of x 5 0.05 had the maximum values of piezoelectric coefficient (d 33 5 243 pC/N) and planar electromechanical coupling coefficient (k p 5 46.1%), and other good properties such as Q m 5 85, e r 5 1240, and tg d 5 0.023. Because of the enhanced densification and refined microstructure, the SPSprocessed NKL x NT ceramics also had better fracture strength than that prepared by normal sintering.

Piezoelectric properties of (K0.5Na0.5)NbO3-BaTiO3lead-free ceramics prepared by spark plasma sintering

“…[21][22][23] SPS has the advantages of short soaking time and lower sintering temperature, yielding higher mechanical properties and restraining the volatilization of alkaline elements in KNN-based ceramics, compared with the conventional sintering approaches. Park 26 but it has no significant positive effect on more complex compositions, e.g., 0.95(Na 0:49 K 0:49 Li 0:02 Þ-(Nb 0:8 Ta 0:2 ÞO 3 -0.05CaZrO 3 (CZ5), 27 is possibly attributed to the severe compositional segregation. As is shown, a simple composition is preferred for SPS-sintered KNN-based ceramics.…”

Low Temperature Sintering of the Alkali-Niobate Ceramics

“…Therefore, it is necessary to develop a method to decrease the sintering temperature of the NKNCs to below 1,000 C in order to obtain stable piezoelectric properties. [27][28][29] In addition, sintering of the NKN-based ceramics at low temperatures also facilitates their use in multilayers. The addition of CuO reduced the sintering temperatures of the NKN-based ceramics to approximately 950 C. The Cu 2+ ions transformed the NKNCs to good, hard piezoelectric materials.…”

“…4.16c. In particular, The NKL x NT ceramic with x ¼ 0.05 exhibited good piezoelectric properties: d 33 ¼ 243 pC/N, k p ¼ 46.1%, and Q m ¼ 85 [29]. In addition, the NKL x NT ceramics prepared by SPS had a better fracture strength than of that prepared by normal sintering, due to the enhanced densification and refined microstructure.…”

Lead-Free Ferroelectric Ceramics with Perovskite Structure

“…Very recently it was applied for sintering KNN (K. , and related compositions (Abe et al, 2007;Shen et al, 2010). The advantage of the SPS over CS or HP is that it requires lower temperatures and shorter times for producing ceramics with densities close to the theoretical values.…”