Abstract
The effect of oxygen vacancies on the charge ordered structure at room temperature (RT) in YFe2O4-δ was investigated by transmission electron microscopy (TEM) and it was found that the charge ordered structure is sensitive to the amount of oxygen vacancies. Real-space images of the three-dimensional charge ordered structure revealed that the average size of charge ordered domains can be estimated to be 20 nm. These nanosized charge ordered domains are responsible for the dielectric properties of YFe2O4-δ. The charge ordering processes were also examined by in-situ TEM.