Coexisting surface phases and coherent one-dimensional interfaces on BaTiO₃(001)

Coexistence of surface reconstructions is important due to the diversity in kinetic and thermodynamic processes involved. We identify the coexistence of kinetically accessible phases that are chemically identical and form coherent interfaces. Here, we establish the coexistence of two phases, c(2 × 2) and c(4 × 4), in BaTiO₃(001) with atomically resolved Scanning Tunneling Microscopy (STM). First-principles thermodynamic calculations determine that TiO adunits and clusters compose the surfaces. We show that TiO diffusion results in a kinetically accessible c(2 × 2) phase, while TiO clustering results in a kinetically and thermodynamically stable c(4 × 4) phase. We explain the formation of domains based on the diffusion of TiO units. The diffusion direction determines the observed 1D coherent interfaces between c(2 × 2) and c(4 × 4) reconstructions. We propose atomic models for the c(2 × 2), c(4 × 4), and 1D interfaces.