Layer control of Sr1.8Bi0.2Nan-3NbnO3n+1 (n = 3–5) perovskite nanosheets: dielectric to ferroelectric transition of film deposited by Langmuir Blodgett method

• Published in: NPJ 2D materials and applications Vol. 7; no. 1; pp. 53 - 7
• Main Authors: Yoo, So-Yeon, Yim, Haena, Ryu, Ahrom, Yoon, Chansoo, Park, Bae Ho, Nahm, Sahn, Choi, Ji-Won
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 11-08-2023; Nature Publishing Group; Nature Portfolio
• Subjects: 639/301/357/1018; 639/925/357/995; Cation exchanging; Chemistry and Materials Science; Coercivity; Electric fields; Ferroelectric materials; Ferroelectricity; Langmuir-Blodgett films; Materials Science; Nanoelectronics; Nanosheets; Nanotechnology; Perovskites; Polarization; Surfaces and Interfaces; Synthesis; Thickness; Thin Films; Two dimensional materials
• ISSN: 2397-7132; 2397-7132
• DOI: 10.1038/s41699-023-00418-9

Solution-based processable high-k 2-dimensional (2D) ferroelectrics have attracted significant interest for use in next-generation nanoelectronics. Although few studies on potential 2D ferroelectric nanosheets in local areas have been conducted, reports on the thin-film characteristics applicable to the device are insufficient. In this study, we successfully synthesize high-k 2D Sr
1.8
Bi
0.2
Na
n-3
Nb
n
O
3n+1
(octahedral units,
n
 = 3–5) nanosheets by the engineering of the
n
of NbO
6
octahedral layers with A-site modification, and realized ferroelectric characteristics in ultrathin films (below 10 nm). The nanosheets are synthesized by a solution-based cation exchange process and deposited using the Langmuir-Blodgett (LB) method. As increasing the NbO
6
octahedral layer, the thickness of the nanosheets increased and the band gaps are tuned to 3.80 eV (
n
 = 3), 3.76 eV (
n
 = 4), and 3.70 eV (
n
 = 5). In addition, the dielectric permittivity of the 5-layer stacked nanofilm increase to 26 (
n
 = 3), 33 (
n
 = 4), and 62 (
n
 = 5). In particular, the increased perovskite layer exhibits large distortions due to the size mismatch of Sr/Bi/Na ions at the A-site and promotes local ferroelectric instability due to its spontaneous polarization along the c-axis caused by an odd
n
number. We investigate the stable ferroelectricity in Pt/ 5-layer Sr
1.8
Bi
0.2
Na
2
Nb
5
O
16
/ Nb:STO capacitor by polarization-electric field (P-E) hysteresis; the coercive electric field (E
c
) was 338 kV cm
−1
and the remnant polarization (P
r
) 2.36 μC cm
−2
. The ferroelectric properties of ultrathin 2D materials could drive interesting innovations in next-generation electronics.