Then, the selective etching of A ions from 2D-AZnSb has been performed to create the 2D-ZnSb via two different processes: (i) chemical reaction in deionized (DI) water–incorporated solutions and (ii) electrochemical ion etching reaction in alkali-based electrolyte.
S1 for A = Na and K) that can have a layered structure of ZnSb from the transformation of 3D-ZnSb by A alloying, although each 3D-ZnSb and 2D-AZnSb phase can be synthesized independently ( 21, 22). First, we aimed to synthesize layered AZnSb (2D-AZnSb) ternary compounds (A refers to alkali metal, and here, we present 2D-LiZnSb as a representative form see also fig. Our methodological strategy to create the 2D-ZnSb Zintl phase is schematically illustrated in Fig. As a proof-of-concept material, we have selected a 3D orthorhombic ZnSb (3D-ZnSb) Zintl phase and created the unprecedented 2D layered structure of ZnSb (2D-ZnSb). By considering the sp 2 hybrid orbital bonding of honeycomb-structured 2D atomic crystals such as graphene and hexagonal boron nitride, one may expect that 3D structured Zintl phases with sp 3 hybrid orbital bonding transform to the sp 2 honeycomb-structured 2D layered materials via electron transfer ( 19, 20). Here, we establish the bidimensional polymorphism through the discovery of a 2D layered structure in Zintl phases that have a vast number of chemical compositions with p-block metals satisfying the valence electron count rule ( 19). Reaching an ultimate crystal engineering that can alter the structural dimensionality of multicomponent compounds is promising to be a next frontier in material science beyond the allotropes of carbon. However, these polymorphic transitions only occurred between different layered structures in the same two dimensions and have not yet been realized between different dimensionalities of a crystal structure at ambient pressure. This transition also leads to promising applications such as electronic homojunction and photonic memory devices, as well as catalytic energy materials ( 16– 18). In particular, most transition metal dichalcogenides exhibit the polymorphic phase transition that opens up access to diverse properties, including superconducting and topological states ( 15). The temperature-, pressure-, and electrostatic doping–induced structural phase transitions have been a core subject for exploring a novel crystal structure and switching material properties of 2D materials ( 12– 14).
In the context of a new material discovery, the transformation of a crystal structure has been widely recognized as a key factor ( 10, 11).
This dimensional manipulation of a crystal structure thus provides a rational design strategy to search for new 2D layered materials in various compounds, enabling unlimited expansion of 2D libraries and corresponding physical properties. The bidimensional polymorphism is a previously unobserved phenomenon at ambient pressure in Zintl families and can be a common feature of transition metal pnictides.
Using structural analysis combined with theoretical calculation, it is found that the 2D-ZnSb has a stable and robust layered structure. Here, through the dimensional manipulation of a crystal structure from sp 3-hybridized 3D-ZnSb, we create an unprecedented layered structure of Zintl phase, which is constructed by the staking of sp 2-hybridized honeycomb ZnSb layers. However, it has been challenging to artificially develop layered materials with honeycomb atomic lattice structure composed of multicomponents such as hexagonal boron nitride. The discovery of new families, beyond graphene, of two-dimensional (2D) layered materials has always attracted great attention.