Dimensionality-driven phase engineering in 2D noble metal chalcogenides: new phase via confined chemical transformation†

This study successfully synthesized a novel two-dimensional (2D) metal chalcogenide (Ag_4.53Te₃) through the chemical transformation of 2D tellurene. We employed an anion exchange chemical transformation technique to convert tellurene films into 2D Ag_4.53Te₃ with a non-centrosymmetric structure at room temperature, inheriting the thickness and lateral dimensions from the tellurene films. The crystal structure of Ag_4.53Te₃ was characterized, revealing a superstructure of tellurium with non-stoichiometric silver penetration into the 2D tellurium matrix. The transformation mechanism was explored, considering thermodynamic parameters, kinetics of transformation, and the effect of mechanical stress on shape retention. It was found that 2D Ag_4.53Te₃ has a different Ag/Te ratio and different bonding characteristics compared to 1D Ag₂Te, leading to a unique structure and properties. The non-symmetric structure of 2D Ag_4.53Te₃ was evidenced by second-harmonic generation imaging and angle-dependent Raman spectroscopy. Additionally, the material exhibited strong out-of-plane piezoelectric properties, with a vertical piezoelectric constant (d_eff) of approximately 28.2 pm V⁻¹. We also fabricated a nanogenerator based on 2D Ag_4.53Te₃, further confirming its non-symmetric structure and potential for future nanoelectronic applications.