The Hydration Structure at Yttria-Stabilized Cubic Zirconia (110)-Water Interface with Sub-Ångström Resolution.

Binyang Hou,Taeho Kim,Jongjin Kim,Changyong Park,Ji Hyun Kim,Seungbum Hong,Seunghyun Kim,Chi Bum Bahn

doi:10.1038/srep27916

Abstract

The interfacial hydration structure of yttria-stabilized cubic zirconia (110) surface in contact with water was determined with ~0.5 Å resolution by high-resolution X-ray reflectivity measurement. The terminal layer shows a reduced electron density compared to the following substrate lattice layers, which indicates there are additional defects generated by metal depletion as well as intrinsic oxygen vacancies, both of which are apparently filled by water species. Above this top surface layer, two additional adsorbed layers are observed forming a characteristic interfacial hydration structure. The first adsorbed layer shows abnormally high density as pure water and likely includes metal species, whereas the second layer consists of pure water. The observed interfacial hydration structure seems responsible for local equilibration of the defective surface in water and eventually regulating the long-term degradation processes. The multitude of water interactions with the zirconia surface results in the complex but highly ordered interfacial structure constituting the reaction front.

Highlights

For many decades, researchers have studied the degradation of zirconia in relation to the phase transformation
Degradation during aging of transformation-toughened yttria-stabilized zirconia (YSZ) at 250 °C was reported, caused by depletion of dopant metal when exposed to water vapor[23]
The results can be summarized into two main opinions: firstly, the degradation process under humid conditions starts from the water chemisorption on the surface Zr sites, which creates point defects; secondly, the degradation process involves the leach of the dopant metal ions, which makes the crystal structure unstable and undergoes phase transformation

Summary

Introduction

Researchers have studied the degradation of zirconia in relation to the phase transformation. There has been a great deal of effort to the study of interfacial structures of zirconia in contact with water, attempting to reveal the oxide degradation mechanism from the molecular insight. Costa et al studied the energetics of water adsorption on YSZ surfaces to reveal the reduction of anhydrous surface energy by adsorbing water on the surface[24] These studies of zirconia-water interfaces have brought into great knowledge about the initiation mechanism of the degradation and corrosion processes. The results can be summarized into two main opinions: firstly, the degradation process under humid conditions starts from the water chemisorption on the surface Zr sites, which creates point defects; secondly, the degradation process involves the leach of the dopant metal ions, which makes the crystal structure unstable and undergoes phase transformation. These two opinions hardly found their consensus[25], suggesting the lack of knowledge on the experimentally determined structure of the zirconia-water interface at the molecular scale

Methods

Results

Conclusion