Three types of BaTiO3 core - amorphous nano-shell composite ceramics were
processed from the same core-shell powder by standard sintering, spark-plasma
sintering and two-step sintering techniques and characterized by XRD, HRSEM and
broad-band dielectric spectroscopy in the frequency range 10^3 - 10^13 Hz
including the THz and IR range. The samples differed by porosity and by the
amount of interdiffusion from the cores to shells, in correlation with their
increasing porosity. The dielectric spectra were also calculated using suitable
models based on effective medium approximation. The measurements revealed a
strong dielectric dispersion below the THz range, which cannot be explained by
the modeling, and whose strength was in correlation with the degree of
interdiffusion. We assigned it to an effect of the interdiffusion layers,
giving rise to a strong interfacial polarization. It appears that the
high-frequency dielectric spectroscopy is an extremely sensitive tool for
detection of any gradient layers and sample inhomogeneities even in dielectric
materials with negligible conductivity
