title: Domain Evolution and Piezoelectric Response across Thermotropic Phase Boundary in (K,Na)NbO3-Based Epitaxial Thin Films.
abstract: Recent research progress in (K,Na)NbO3(KNN)-based lead-free piezoelectric ceramics has attracted increasing attention for their applications to microsystems or microelectromechanical systems (MEMS) in the form of thin films. This work demonstrates that high-quality KNN-based epitaxial films can be synthesized by a conventional sol-gel method, whose phase structure and domain characteristics have been investigated with emphasis on the temperature effect. A monoclinic MCstructure is observed at room temperature in KNN-based epitaxial films, which is close to but different from the orthorhombic phase in bulk counterparts. Piezoresponse force microscopy (PFM) at elevated temperatures reveals continuous changes of ferroelectric domains in KNN films during heating and cooling cycles between room temperature and 190 °C. A distinct change in domain morphology is observed upon heating to 110 °C, accompanied by a clear variation of dielectric permittivity suggesting a thermotropic phase transition, which is revealed to belong to a MC-MAphase transition on the basis of structural and PFM analysis on local ferroelectric and piezoelectric behaviors. Enhanced piezoelectric response at the thermotropic phase boundary is observed, which is attributed to active domains and/or nanodomains formed across the boundary. Domain engineering by utilizing the phase transition should be important and effective in KNN-based films not only for property enhancement but also for its textured ceramics.
authors.affiliation: State Key Laboratory of New Ceramics and Fine Processing, School of Materials Science and Engineering, Tsinghua University , Beijing 100084, China.
authors.forename: Jin
authors.initials: J
authors.lastname: Luo
authors.affiliation: State Key Laboratory of New Ceramics and Fine Processing, School of Materials Science and Engineering, Tsinghua University , Beijing 100084, China.
authors.forename: Wei
authors.initials: W
authors.lastname: Sun
authors.affiliation: State Key Laboratory of New Ceramics and Fine Processing, School of Materials Science and Engineering, Tsinghua University , Beijing 100084, China.
authors.forename: Zhen
authors.initials: Z
authors.lastname: Zhou
authors.affiliation: Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences , Shenyang 110016, China.
authors.forename: Yu
authors.initials: Y
authors.lastname: Bai
authors.affiliation: Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences , Shenyang 110016, China.
authors.forename: Zhan Jie
authors.identifier: http://orcid.org/0000-0002-9288-4928
authors.initials: ZJ
authors.lastname: Wang
authors.affiliation: Institute for Advanced Materials and Guangdong Provincial Key Laboratory of Quantum Engineering and Quantum Materials, South China Normal University , Guangzhou 510006, China.
authors.forename: Guo
authors.initials: G
authors.lastname: Tian
authors.affiliation: Institute for Advanced Materials and Guangdong Provincial Key Laboratory of Quantum Engineering and Quantum Materials, South China Normal University , Guangzhou 510006, China.
authors.forename: Deyang
authors.identifier: http://orcid.org/0000-0002-8370-6409
authors.initials: D
authors.lastname: Chen
authors.affiliation: Institute for Advanced Materials and Guangdong Provincial Key Laboratory of Quantum Engineering and Quantum Materials, South China Normal University , Guangzhou 510006, China.
authors.forename: Xingsen
authors.identifier: http://orcid.org/0000-0002-2725-0785
authors.initials: X
authors.lastname: Gao
authors.affiliation: Shanghai Institute of Applied Physics, Chinese Academy of Sciences , No. 239 Zhangheng Road, Pu-dong District, Shanghai 201204, China.
authors.forename: Fangyuan
authors.initials: F
authors.lastname: Zhu
authors.affiliation: State Key Laboratory of New Ceramics and Fine Processing, School of Materials Science and Engineering, Tsinghua University , Beijing 100084, China.
authors.forename: Jing-Feng
authors.identifier: http://orcid.org/0000-0002-0185-0512
authors.initials: JF
authors.lastname: Li
keywords: domain evolution; lead-free; phase transition; piezoelectric; thermotropic phase boundary