Chemical Vapor Deposition Synthesis of Intrinsic High‐Temperature Ferroelectric 2D CuCrSe₂

Abstract

Ultrathin 2D ferroelectrics with high Curie temperature are critical for multifunctional ferroelectric devices. However, the ferroelectric spontaneous polarization is consistently broken by the strong thermal fluctuations at high temperature, resulting in the rare discovery of high‐temperature ferroelectricity in 2D materials. Here, a chemical vapor deposition method is reported to synthesize 2D CuCrSe2 nanosheets. The crystal structure is confirmed by scanning transmission electron microscopy characterization. The measured ferroelectric phase transition temperature of ultrathin CuCrSe2 is about ≈800 K. Significantly, the switchable ferroelectric polarization is observed in ≈5.2 nm nanosheet. Moreover, the in‐plane and out‐of‐plane ferroelectric response are modulated by different maximum bias voltage. This work provides a new insight into the construction of 2D ferroelectrics with high Curie temperature.

Facile Coordination Transitions in AgCrX2 (X = S, Se): Unprecedented Electrostrain, Negative Piezoelectricity and Thermal Expansion

“…In 2019, we proposed that some intercalant metal ions like Cu ions may form into tetra-coordinate configurations in 2D Cu x MoS 2 , Cu x Bi 2 Se 3 , 2 and CuCrX 2 (X = S, Se), 3 which break the symmetry and give rise to ferroelectricity coupled with magnetism. In later studies, the robust intercorrelated inplane and out-of-plane ferroelectricity of 2D CuCrX 2 has been experimentally confirmed, 4,5 which is also a proof of unconventional ferroelectricity violating Neumann's principle considering its C 3v symmetry, and the high Curie temperature around 700 K 4 can be attributed to the high switching barrier over 0.23 eV/f.u.. Similar ferroelectricity is likely to emerge in the same group of compounds AgCrX 2 (X = S, Se) with similar structures.…”