Structural phase transitions and dielectric anomaly in YFe ₂O_4-δ

We examined structural changes related to charge ordering (CO) in the temperature window between 100 K and room temperature (RT) in YFe ₂O_4-δ by transmission electron microscopy. Characteristic diffuse scattering elongated along the [001] direction through the (1/3 1/3 0)-type reciprocal positions was found at RT, which is related to the microdomains due to the CO with a size of 10 - 20 nm. In addition, it was also found that the superlattice structures characterized by the (1/3 - n1/3 + n 0)-type modulation vector, which should be due to the vacancy ordering, coexist with the microdomains due to the CO. On the other hand, in stoichimetric YFe₂O₄, we found temperature variations of the superlattice structures on warming from 100 K, which should be strongly related to the dielectric anomalies in YFe₂O₄.