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- Title
Phase Structures, Electromechanical Responses, and Electrocaloric Effects in K 0.5 Na 0.5 NbO 3 Epitaxial Film Controlled by Non-Isometric Misfit Strain.
- Authors
Wu, Yingying; Ou, Yun; Peng, Jinlin; Lei, Chihou
- Abstract
Environmentally friendly lead-free K1-xNaxNbO3 (KNN) ceramics possess electromechanical properties comparable to lead-based ferroelectric materials but cannot meet the needs of device miniaturization, and the corresponding thin films lack theoretical and experimental studies. To this end, we developed the nonlinear phenomenological theory for ferroelectric materials to study the effects of non-equiaxed misfit strain on the phase structure, electromechanical properties, and electrical response of K0.5Na0.5NbO3 epitaxial films. We constructed in-plane misfit strain ( u 1 − u 2 ) phase diagrams. The results show that K0.5Na0.5NbO3 epitaxial film under non-equiaxed in-plane strain can exhibit abundant phase structures, including orthorhombic a 1 c , a 2 c , and a 1 a 2 phases, tetragonal a 1 , a 2 , and c phases, and monoclinic r 12 phases. Moreover, in the vicinity of a 2 c − r 12 , a 1 c − c , and a 1 a 2 − a 2 phase boundaries, K0.5Na0.5NbO3 epitaxial films exhibit excellent dielectric constant ε 11 , while at a 2 c − r 12 and a 1 c − c phase boundaries, a significant piezoelectric coefficient d 15 is observed. It was also found that high permittivity ε 33 and piezoelectric coefficients d 33 exist near the a 2 c − a 2 , a 1 a 2 − r 12 , and a 1 c − a 1 phase boundaries due to the existence of polymorphic phase boundary (PPB) in the KNN system, which makes it easy to polarize near the phase boundaries, and the polarizability changes suddenly, leading to electromechanical enhancement. In addition, the results show that the K0.5Na0.5NbO3 thin films possess a large electrocaloric response at the phase boundary at the a 1 a 2 − r 12 and a 1 c − a 1 phase boundaries. The maximum adiabatic temperature change Δ T is about 3.62 K when the electric field change is 30 MV/m at room temperature, which is significantly enhanced compared with equiaxed strain. This study provides theoretical guidance for obtaining K1−xNaxNbO3 epitaxial thin films with excellent properties.
- Subjects
DEVON (England); PYROELECTRICITY; FERROELECTRIC thin films; FERROELECTRIC materials; PERMITTIVITY; THIN films; ADIABATIC temperature
- Publication
Crystals (2073-4352), 2023, Vol 13, Issue 9, p1321
- ISSN
2073-4352
- Publication type
Article
- DOI
10.3390/cryst13091321