Amorphous Intermediates Mediate van der Waals Nanosheets Formation via Anion-Exchange-Driven Symmetry Breaking.

Fe3GeTe2 has attracted considerable attention as a two-dimensional (2D) van der Waals (vdW) magnetic material owing to its exceptional electromagnetic properties and potential for spintronic applications. However, complex thermodynamic competition among multiple metal species, together with severe kinetic barriers associated with the transformation from dense non-vdW frameworks to vdW layered structures, has thus far prevented the solution phase synthesis, thereby severely limiting in-depth property research and mechanistic understanding. Here we report a colloidal anion exchange strategy that enables the solution phase synthesis of Fe3GeTe2. By combining experiments with density functional theory (DFT) calculations, we identify an amorphous intermediate that kinetically decouples compositional evolution from structural reconstruction, thereby lowering the energy barrier and enabling a crystalline-amorphism-recrystalline phase transition. In this process, anion exchange induces symmetry breaking of the initial lattice and subsequent structural reorganization, ultimately driving the transformation from a non-vdW framework to vdW layered structure. Moreover, this strategy is readily extended to other 2D material systems, leading to the successful synthesis of paramagnetic CuFeTe2 and NiTe2 as well as topological layered Bi2Te3, thereby establishing a general methodological pathway for accessing complex 2D vdW layered magnetic materials.