Ferroelectric Polarization Rotation in Order-Disorder-Type LiNbO3 Thin Films

Tae Sup Yoo; Sang A Lee; Changjae Roh; Seunghun Kang; Daehee Seol; Xinwei Guan; Jong-Seong Bae; Jiwoong Kim; Young-Min Kim; Hu Young Jeong; Seunggyo Jeong; Ahmed Yousef Mohamed; Deok-Yong Cho; Ji Young Jo; Sungkyun Park; Tom Wu; Yunseok Kim; Jongseok Lee; Woo Seok Choi

doi:10.1021/acsami.8b12900

Ferroelectric Polarization Rotation in Order-Disorder-Type LiNbO₃ Thin Films

ACS Appl Mater Interfaces. 2018 Dec 5;10(48):41471-41478. doi: 10.1021/acsami.8b12900. Epub 2018 Nov 20.

Authors

Affiliations

¹ Department of Physics and Photon Science , Gwangju Institute of Science and Technology (GIST) , Gwangju 61005 , Korea.
² Materials Science and Engineering , King Abdullah University of Science and Technology , Thuwal 23955-6900 , Saudi Arabia.
³ Busan Center , Korea Basic Science Institute , Busan 46742 , Korea.
⁴ Department of Physics , Pusan National University , Busan 46241 , Korea.
⁵ UNIST Central Research Facilities , Ulsan National Institute of Science and Technology , Ulsan 44919 , Korea.
⁶ IPIT & Department of Physics , Chonbuk National University , Jeonju 54896 , Korea.
⁷ School of Materials Science and Engineering , Gwangju Institute of Science and Technology (GIST) , Gwangju 61005 , Korea.
⁸ School of Materials Science and Engineering , University of New South Wales , Sydney , NSW 2052 , Australia.

PMID: 30406659
DOI: 10.1021/acsami.8b12900

Abstract

The direction of ferroelectric polarization is prescribed by the symmetry of the crystal structure. Therefore, rotation of the polarization direction is largely limited, despite the opportunity it offers in understanding important dielectric phenomena such as piezoelectric response near the morphotropic phase boundaries and practical applications such as ferroelectric memory. In this study, we report the observation of continuous rotation of ferroelectric polarization in order-disorder-type LiNbO₃ thin films. The spontaneous polarization could be tilted from an out-of-plane to an in-plane direction in the thin film by controlling the Li vacancy concentration within the hexagonal lattice framework. Partial inclusion of monoclinic-like phase is attributed to the breaking of macroscopic inversion symmetry along different directions and the emergence of ferroelectric polarization along the in-plane direction.

Keywords: LiNbO3 thin films; ferroelectric polarization rotation; second harmonic generation; spatial inversion symmetry breaking; vacancy engineering.