Effect of tetragonal perovskite phase addition on the electrical properties of KNN thick films fabricated by aerosol deposition Guifang Han, Cheol-Woo Ahn, Jungho Ryu ⁎, Woon-Ha Yoon, Jong-Jin Choi, Byung-Dong Hahn, Jong-Woo Kim, Joon-Hwan Choi, Dong-Soo Park Functional Ceramics Group, Korea Institute of Materials Science (KIMS), 66 Sangnam-Dong, Changwon, Gyeongnam 641–831, Republic of Korea abstract article info Article history: Received 9 March 2011 Accepted 4 June 2011 Available online 13 June 2011 Keywords: KNN Complex-perovskite-materials Thick film Ferroelectric Aerosol deposition The effect of complex-perovskite-materials (CPs) doping on phase transition and dielectric/ferroelectric properties was investigated in lead-free 0.985[0.92(Na 0.535 K 0.48 )NbO 3 –0.08LiNbO 3 ]–0.015CPs (KNN–Li–CPs) films. Three CPs were selected: Ba(Cu 1/3 Nb 2/3 )O 3 (BCN), Ca(Cu 1/3 Nb 2/3 )O 3 (CCN), and Sr(Cu 1/3 Nb 2/3 )O 3 (SCN). The films were fabricated by aerosol deposition (AD) method. In the KNN–Li–BCN film annealed at 700 °C for 1 h in air, the ferroelectric and dielectric properties (75% P r at 400 kV/cm and 40% ε r ) were increased compared to those of the KNN-Li film, which was attributed to the variation of phase, secondary phases, and the softening effect of the dopants. © 2011 Elsevier B.V. All rights reserved. 1. Introduction (K,Na)NbO 3 (KNN)-based lead-free ceramics have attracted attention as alternative materials to Pb(Zr,Ti)O 3 (PZT) ceramics owing to their high Curie temperature, ferroelectricity and piezoelec- tricity [1]. In recent studies, the piezoelectric and dielectric properties of KNN-based materials were improved by dopant addition and modifications to the fabrication process [2–4]. However, compared to the material study, thin/thick films have not been actively studied, especially the development of new compositions, in KNN-based films. This may be because of the phase decomposition, due to the evaporation of Na and K ions, that occurs during the fabrication of KNN-based films [5]. In our previous studies, KNN-based thin/thick films were well-formed by aerosol-deposition (AD) without serious phase decomposition [6,7]. In the AD process, the evaporation of those elements from the films can be minimized since they are deposited on the substrates at room temperature. Hence, the AD method was chosen in the present study to form the films of complex-perovskite- materials (CPs)-doped 0.92(Na 0.535 K 0.48 )NbO 3 –0.08LiNbO 3 (KNN–Li) ceramics. KNN–Li ceramics have been reported to show not only high piezoelectric and ferroelectric properties but also dense microstruc- tures at low sintering temperature [8]. Thus, KNN–Li was chosen as a base material in this study. In addition, a solid solution with other perovskite or ilmenite compositions reduces the phase transition point (from orthorhombic phase to tetragonal phase, T O–T ) down to room temperature and the coexistence of two phases (orthorhombic and tetragonal phases) offers high piezoelectric and ferroelectric properties at room temperature in KNN-based ceramics [9,10]. Hence, many solid solutions have been studied in attempts to maximize the piezoelectric and ferroelectric properties by reduction of T O–T to room temperature in KNN-based ceramics. However, tetragonal structured CPs such as Ba(Cu 1/3 Nb 2/3 )O 3 (BCN), Sr(Cu 1/3 Nb 2/3 )O 3 (SCN), and Ca (Cu 1/3 Nb 2/3 )O 3 (CCN) have not been used to form solid solutions with KNN-based ceramics. Moreover, the A-site ions (such as Ba 2+ , Sr 2+ , and Ca 2+ ) of CPs can show a softening effect in KNN-based ceramics (A site: Na 1+ ,K 1+ , and Li 1+ ). Therefore, in this study, CPs-doped KNN–Li (KNN–Li–CPs) ceramics were selected and the effect of CPs doping on the phase transition and dielectric/ferroelectric properties was investigated in KNN–Li–CPs films. 2. Experimental procedure Reagent-grade raw materials [K 2 CO 3 (99%), Na 2 CO 3 (99.5%), Nb 2 O 5 (99.9%), LiCO 3 (99+%), Cu 2 O (99%), BaCO 3 (99+%), SrCO 3 (99.9%) from Aldrich Co., Milwaukee, WI and CaCO 3 (99%) from Wako Pure Chemical Industries Ltd., Japan were used to fabricate KNN–Li–CPs- based powder. The powder composition was 0.985[0.92(Na 0.535 K 0.48 ) NbO 3 –0.08LiNbO 3 ]–0.015CPs (KNN–Li–CPs, CPs: BCN, CCN, and SCN). In order to compare the effect of CPs doping, 0.92(Na 0.535 K 0.48 )NbO 3 – 0.08LiNbO 3 (KNN–Li) was also prepared. All the raw materials were mixed, ball milled for 24 h, and calcined at 900 °C for 5 h. Around 10 μm-thick films were deposited on sapphire substrates coated with Materials Letters 65 (2011) 2762–2764 ⁎ Corresponding author. Tel.: + 82 55 280 3378; fax: + 82 55 280 3392. E-mail address: jhryu@kims.re.kr (J. Ryu). 0167-577X/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.matlet.2011.06.010 Contents lists available at ScienceDirect Materials Letters journal homepage: www.elsevier.com/locate/matlet