Phase transition and electrical properties of LiNbO 3 -modified K 0.49 Na 0.51 NbO 3 lead-free piezoceramics Zong-Yang Shen • Yue-Ming Li • Liang Jiang • Run-Run Li • Zhu-Mei Wang • Yan Hong • Run-Hua Liao Received: 9 October 2010 / Accepted: 20 November 2010 / Published online: 3 December 2010 Ó Springer Science+Business Media, LLC 2010 Abstract Lead-free (1-x)K 0.49 Na 0.51 NbO 3 -xLiNbO 3 (KNN- LN, x = 0 * 0.08) piezoelectric ceramics were prepared by the conventional solid-state sintering method. The effects of LiNbO 3 doping amount x on the phase transition behavior and the electrical properties of KNN-LN ceramics were investigated. By increasing LiNbO 3 doping amount x, the orthorhombic-tetragonal polymorphic phase transition (PPT) temperature (T o–t ) of KNN-LN ceramics shifted downwards, however, the Curie temperature (T c ) slightly moved upwards. The room temperature phase structure thus changed from orthorhombic to tetragonal across the compositions with 0.05 B x B 0.06, named as PPT region. The composition with x = 0.06 in the tetragonal side of PPT region exhibited optimized electrical properties of d 33 = 246pC/N, k p = 41.6%, e r = 679, tgd = 0.028, and Q m = 52. In addition to its very high T c = 467 °C, this ceramic can be an excellent candidate for replacing the lead-based piezoceramics in high temperature applications. 1 Introduction In recent years, (K,Na)NbO 3 (KNN)-based lead-free pie- zoelectric ceramics have been extensively studied as one promising candidate for replacing the lead-containing materials in many applications owing to their good electrical properties and relatively high Curie temperatures [1–7]. As is known, pure KNN ceramic had a polymorphic phase transition (PPT) temperature separating the orthorhombic phase and the tetragonal one at *220 °C[8]. Meanwhile, this PPT can be shifted downwards to near room temperature by doping a couple of different compounds, such as AETiO 3 (AE = Ba, Sr, Ca or Mg), LiNbO 3 , LiTaO 3 , and LiSbO 3 , which generates new lead-free solid solutions with enhanced electromechanical response and improved sinterability [3, 9–11]. Especially, Li-, Ta-, and Sb-modified KNN ceramics showed most significant enhancement in the pie- zoelectric properties [1, 3, 7, 9, 10]. However, due to the expensive price of Ta 2 O 5 and the toxicity of Sb element, LiNbO 3 was regarded as the most promising dopant among them. Furthermore, Ta and/or Sb entering into B-site of KNN lattice will induce the T c shifting to lower temperature, which suggested that the materials were not suitable for high temperature applications. Nevertheless, by doping LiNbO 3 with super high T c * 1210 °C[12], the T c of KNN ceramics will be increased correspondingly. Piezoelectric ceramics with high T c can be made into devices such as small-signal sensors, high-signal acoustic transducers, and actuators for temperatures higher than 400 °C. These devices may find applications in space exploration, electric aircraft, oil and geothermal well drilling tools, and automotive smart brakes. On the other hand, for the pure KNN ceramics, most works focused on an equal molar ratio of K/Na, i.e. K:Na = 0.5:0.5, which was identified as the morphotropic phase boundary (MPB) of KNN discovered by Egerton and Dillon in 1959 [8]. However, recent investigations on pure KNN ceramics showed that optimizing K/Na ratio around the MPB composition can enhance the piezoelectric prop- erties effectively [13, 14]. Our recent work also revealed that optimal piezoelectric properties can be obtained for the composition of K 0.49 Na 0.51 NbO 3 , whose piezoelectric constant d 33 was enhanced to 146 pC/N [15]. On the base of this result, LiNbO 3 was introduced to further enhance the piezoelectric properties of K 0.49 Na 0.51 NbO 3 ceramics in Z.-Y. Shen Á Y.-M. Li (&) Á L. Jiang Á R.-R. Li Á Z.-M. Wang Á Y. Hong Á R.-H. Liao School of Materials Science and Engineering, Jingdezhen Ceramic Institute, Jingdezhen 333403, China e-mail: lym6329@yahoo.com.cn 123 J Mater Sci: Mater Electron (2011) 22:1071–1075 DOI 10.1007/s10854-010-0261-1