  Metal-oxide interfaces with poor coherency have unique properties comparing
to the bulk materials and offer broad applications in the fields of
heterogeneous catalysis, battery, and electronics. However, current
understanding of the three-dimensional (3D) atomic metal-oxide interfaces
remains limited because of their inherent structural complexity and limitations
of conventional two-dimensional imaging techniques. Here, we determine the 3D
atomic structure of metal-oxide interfaces in zirconium-zirconia nanoparticles
using atomic-resolution electron tomography. We quantitatively analyze the
atomic concentration and the degree of oxidation, and find the coherency and
translational symmetry of the interfaces are broken. Moreover, we observe
porous structures such as Zr vacancies and nano-pores and investigate their
distribution. Our findings provide a clear 3D atomic picture of metal-oxide
interface with direct experimental evidence. We anticipate this work could
encourage future studies on fundamental problems of oxides such as interfacial
structures in semiconductor and atomic motion during oxidation process.
