Synthesis, atomic structure and electronic properties of ferroelectric AgBiP2Se6 ultrathin flakes

Layered transition metal thiophosphate ABP2X6(A = Ag or Cu, B = V, Cr, In or Bi, X = S or Se) as a promising 2D ferroelectric material, has attracted great attention nowadays. In this work, ultrathin AgBiP2Se6 sheets down to 6 nm were synthesized for the first time. Atomic force microscopy, double spherical aberration scanning TEM and Raman spectra were performed to investigate the morphology, atomic structure and vibration modes of the samples. The first-principles calculations utilizing density-functional theory(DFT) were also used to analyze the electronic properties, band structures and projected density of states (PDOS) for both ferroelectric (FE) and paraelectric(PE) states of AgBiP2Se6 monolayer.