Study On The Adsorption Mechanism Of Pt And H₂O On The Polar Surface Of BiAlO₃ (0001)

BiAlO₃(BAO)is a novel ferroelectric perovskite and belongs to the R3c structure.In the four-index Bravais-Miller representation,the direction of polarization is along the direction of[0001],which is equivalent to the direction of[111]in the pseudo cube representation.Similar to BiFeO₃,the ferroelectric polarization is mainly due to the off-center displacement of Bications with respect to the O octahedra,which can be ascribed to the stereochemical activity of the Bi6s² lone pair electrons.Therefore,BAO has high ferroelectric/piezoelectric properties and may be an attractive lead-free piezoelectric material.In addition,the recent reports show that there are differences in physical and chemical properties of different ferroelectric oxides polar surfaces,and these differences affect the adsorbate behaviors on the surface,and the latest new catalytic theory makes the potential application of iron electrode surfaces in catalysis.Therefore,the study of iron electrode surface has gradually become an important research direction.In this paper,the first principle calculation which is based on density functional theory is used to study the adsorption mechanism of Pt and H₂O on BiAlO₃(0001)Z±polar surfaces.The adsorption mechanism of Pt sub-monolayer with the coverage(?=1/4?1/2?3/4?1)on both positive and negative polar surfaces was studied.The adsorption configuration,charge transfer and electronic structure of different Pt atoms were calculated.The results show that there are obvious orbital hybridization and charge transfer behaviors between Pt atoms and the surface,and the electronic properties of the surface are changed due to Pt adsorbed.Pt sub-monolayer exhibit similar adsorption behavior on the both surfaces,but the specific action is different.When??1/2 ML,Pt atoms are deposited in the polar surface.There is a strong interaction and a significant charge transfer behavior with Biand O on the surface.When?=3/4ML,the Pt atoms extend outward under the interaction.1 ML form a good epitaxial film structure on the surface.However,the adsorption energy of the negative surface is larger than that of the positive surface,the charge transfer behavior and interaction of the whole surface are stronger than that of the positive surface.For the adsorption behavior of H₂O on the Z±polar surface,the mechanism of H₂O adsorption on both surfaces and the effects of different coverage of H₂O monolayer(?=1/3?2/3?1)on H₂O adsorption were studied.The adsorption configuration,charge transfer and electronic structure were studied by the first principle.The results show that there is interaction and a little charge transfer between H₂O and the surface,the electronic properties of the surface are also affected by H₂O.In all structures,H in H₂O closes to O on the surface and O closes to Bion the surface.However,the adsorption behavior of H₂O on the positive and negative surfaces is completely different.On the Z+surface,the H₂O monomers(?=1/3 ML)is nondissociation adsorption,two H₂O(?=2/3 ML)form chain on the surface,and three H₂O(?=1 ML)destroies the chain and dispersed to form a new spatial structure.For Z-surface,the structure of H₂O is dissociation adsorption,and increasing the amount of H₂O,the interaction between H₂O will weaken the destruction of H₂O structure,until?=1 ML,a new structure appears.It can be understood that the polarization direction of the positive and negative surfaces and the chemical environment have a great impact on the adsorption behavior of H₂O.The innovation of this paper lies in:(1)the adsorption behavior of different coverage of Pt atoms on the positive and negative polar surfaces has been studied systematically.The results show that there is a similar adsorption behavior of Pt atoms on the positive and negative surfaces.When the coverage of Pt atoms reaches 1,the positive and negative polar surfaces all form a good epitaxial structure.(2)The adsorption behavior of H₂O on the positive and negative surfaces was studied.The results show that H₂O is seriously affected by different ferroelectric polarized surfaces and shows completely different adsorption behaviors.The distribution of H₂O on Z+surface is regular,while the structure of H₂O on Z+surface changes greatly.The systematic study of two types of adsorbates provides theoretical basis for the deposition of adsorbates on the surface in the future experiments.