Polarization-dependent H2O adsorption on polar surfaces of BiAlO3 (0001)

Abstract

The effect of ferroelectric polarization on adsorption characteristics of a water (H2O) sub-monolayer (Θ ≤ 1 ML) on thermodynamically preferred positive (Z + ) and negative (Z − ) BiAlO3 (0001) polar surfaces was investigated. The study is based on first-principles density functional theory calculations. Both adsorption configurations and electronic properties were determined as a function of surface coverage. Results indicate that the adsorption is different for both surfaces, non-dissociative for Z + surface and dissociative for Z − surface, depending on surface coverage. The different water affinity of two surfaces can be explained by electrostatic interactions and different adsorption energies between surfaces and polar molecules. For the Z + surface, the H2O molecule is adsorbed at the edge of the surface, while it forms a periodic chain structure for Θ = 2/3 ML. The chain structure is destroyed and H2O is dissociative for 1 ML. For the Z − surface, the structure of the H2O molecule is dissociative. The interactions among H2O molecules decrease the disassembly of H2O structure, and H2O shows non-dissociative behavior. Until Θ = 1 ML, the dissociative H2O contains many hydrogen bonds. Overall, different physical and chemical properties of Z + and Z − surfaces, and the chemical environment affect the adsorption behavior of H2O molecules.