Dielectric and conductive spectra of the composite of barium titanate and LiClO4-doped polyethylene oxide

Dielectric and conductive frequency spectra in a 10 mHz-10 GHz range have been measured for a composite consisting of barium titanate (BaTiO3) inclusions dispersed in a LiClO4-doped polyethylene oxide (Li-PEO) matrix with volume fraction Phi = 0-40%. Pure Li-PEO behaves as a dielectric showing a segmental-mode dielectric relaxation at high frequencies (dielectric regime) and transfers to an ionic conductor below 10 MHz (conductive regime). BaTiO3 is a ferroelectric having a very large dielectric permittivity and spontaneous polarization. The introduction of BaTiO3 into Li-PEO caused a rapid increase in permittivity in the dielectric regime. In the conductive regime, the composite exhibited an additional relaxation at a frequency related to the ratio of dc conductivity of Li-PEO and the permittivity of BaTiO3. This relaxation was attributed to accumulation of dissociated Li+ and ClO4- ions at the inclusion/matrix interface which resulted in an increase of effective permittivity and a decrease of effective conductivity. Quantitative analyses based on mixing laws for the two-phase spherical dispersion system have shown that the Bruggeman equation accurately predicted the Phi-dependence of the effective permittivity over the entire frequency range. Regarding the effective conductivity, it predicted values lower than the observed. We attributed this discrepancy to the spontaneous polarization of BaTiO3 which induced ion trapping to reduce the dc conductivity of Li-PEO matrix.