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

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 Sr1.8Bi0.2Nan-3NbnO3n+1 (octahedral units, n = 3-5) nanosheets by the engineering of the n of NbO6 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 NbO6 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 Sr1.8Bi0.2Na2Nb5O16 / 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 & mu;C cm(-2). The ferroelectric properties of ultrathin 2D materials could drive interesting innovations in next-generation electronics.

Automated summary

Solution-based processable high-k 2D ferroelectrics were synthesized by engineering the n value of NbO6 octahedral layers, which demonstrated ferroelectric characteristics in ultrathin films. The increase in NbO6 octahedral layer led to thicker nanosheets and tuned band gaps. The dielectric permittivity of the 5-layer stacked nanofilm also increased. The stable ferroelectricity of the synthesized material was investigated, and its ferroelectric properties have the potential to drive interesting innovations in next-generation electronics.