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https://doi.org/10.1007/s11664-020-08436-9  2020 The Minerals, Metals & Materials Society

Large Electric Field-Induced Strain Response Under a Low Electric Field in Lead-Free Bi1/2Na1/2TiO3-SrTiO3-BiAlO3 Ternary Piezoelectric Ceramics HOANG THIEN KHOI NGUYEN,1 TRANG AN DUONG,1 FARRUKH ERKINOV,1 CHANG WON AHN,2 BYEONG WOO KIM,3 HYOUNG-SU HAN,1 and JAE-SHIN LEE 1,4 1.—School of Materials Science and Engineering, University of Ulsan, 12, Techno saneopro, 55 beon-gil, Nam-gu, Ulsan, Republic of Korea. 2.—Department of Physics and EHSRC, University of Ulsan, 93, Daehak-ro, Nam-gu, Ulsan, Republic of Korea. 3.—Department of Electrical Engineering, University of Ulsan, 93, Daehak-ro, Nam-gu, Ulsan, Republic of Korea. 4.—e-mail: [email protected]

Bismuth-based lead-free ceramics are some of the most promising candidates for actuator applications due to their large strain response. Despite the large strains in bismuth-based piezoelectric ceramics, there still remain challenges regarding their utilization in practical applications. For instance, a relatively high operating field is required to obtain the large strain properties. In this work, lead-free Bi1/2Na1/2TiO3-SrTiO3-BiAlO3 (BNT-ST-BA) ternary piezoelectric ceramics are proposed as materials that could enhance the electromechanical strain performance under low driving field. We found that the highest normalized strain d*33 value of 707 pm/V was achieved at a relatively low electric field of 3 kV/mm from 2 mol.% BA-modified BNT-ST ceramics. We suggest that the naturally induced nonergodicities in the ergodic relaxor generate internal stress. This induced internal stress is responsible for the excellent strain properties of this material. We believe that the materials synthesized in this study are promising candidates for actuator applications. Key words: Lead-free, relaxor, ternary system, electromechanical strain

INTRODUCTION Lead-based piezoelectric materials, such as lead zirconate titanate (PZT), are widely used in electrical devices such as piezoelectric actuators, sensors, and transducers due to the excellent electromechanical properties of these materials.1 However, it is well known that lead (Pb) is toxic and can damage the human body and the environment.2 Accordingly, many countries have encouraged academic and industrial researchers to replace these materials with lead-free piezoelectric materials.3 Recently, (K0.5Na0.5)NbO3 (KNN)- and Bi1/2Na1/2TiO3 (BNT)based lead-free piezoelectric materials have

(Received May 26, 2020; accepted August 20, 2020)

attracted wide-spread attention as promising candidates to replace PZT ceramics.4–14 (Bi1/2Na1/ 2)TiO3 (BNT)-based ceramics are of particular interest for actuator applications because of their excellent electromechanical strain properties.15–21 It is understood that the large electromechanical strain (referred to as incipient piezoelectricity) in BNTbased ceramics originates from a reversible electric field-induced phase transition from an ergodic relaxor (ER) phase to a ferroelectric via application of an e