Block-layer model for intergrowth structures

Lattice match and charge transfer between distinct block layers (BLs) play an important role in the formation of an intergrowth structure. Herein we propose a simple BL model addressing the different roles of the lattice match and the charge transfer. Inter-BL charge transfer lowers the internal energy, while lattice match minimizes the elastic energy, both of which together make the intergrowth structure stabilized. The model is able to reproduce the lattice parameters precisely for complex iron-based superconductors with intergrowth structures. The elastic energy and the charge-transfer energy are evaluated with assistance of the first-principles calculations. This work rationalizes the basic principles of BL design for intergrowth structures, which can be utilized not only for finding new superconducting materials but also for investigating other layered materials with various functionalities.