Impedance spectroscopy measurement was performed on Nbdoped
CCTOs. It was found that the conductive response at high
frequency (1MHz to 1 GHz) might have originated from domain
elements inside the grains. The domain boundary resistance
obtained from the high frequency fitting curve are approximately
the same as the grain resistance itself. The grain resistance of
CCTO is much lower compared to its grain boundary resistance.
In this work, the existence of both domain and grain resistance
are believed to strongly influence the dielectric constant of CCTO.
These findings can be explained by the proposed model, where the
large grains of CCTO consist of smaller cubic-shaped grains called
domains. The domains are separated from each other by flat domain
boundaries to form domain arrays inside the grain. As a grouped
domain, the grains are also separated by flat grain boundary. This
proposed model was supported by microstructure images which
show a large grain and thick grain boundary with smaller grains
(domains) distributed inside the grain.